Peighambardoust2010 PDF

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 9 3 4 9 e9 3 8 4
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Review of the proton exchange membranes for fuel

cell applications
S.J. Peighambardoust a, S. Rowshanzamir a,b,*, M. Amjadi a

a
School of Chemical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran
b
Fuel Cell Laboratory, Green Research Centre, Iran University of Science and Technology, Tehran, Iran
article info abstract
Article history: Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising tech-
Received 27 July 2009 nology for clean and efficient power generation in the twenty-first century. Proton
Received in revised form exchange membranes (PEMs) are the key components in fuel cell system. The researchers
26 April 2010 have focused to reach the proton exchange membrane with high proton conductivity, low
Accepted 4 May 2010 electronic conductivity, low permeability to fuel, low electroosmotic drag coefficient, good
Available online 19 June 2010 chemical/thermal stability, good mechanical properties and low cost. These are classified
into the “iron triangle” of performance, durability, and cost. Current PEMFC technology is
Keywords: based on expensive perflourinated proton-exchange membranes (PEMs) that operate
Polymeric electrolyte effectively only under fully hydrated conditions. There is considerable application-driven
Proton exchange membrane interest in lowering the membrane cost and extending the operating window of PEMs.
Fuel cell PEMFC system complexity could be reduced by the development of ‘water-free’ electrolytes
Nafion that do not require hydration. It also enables the PEMFC to be operated under ‘warm’
Composite membranes conditions (i.e. above 100 C) thus further improving its efficiency. Capital cost could also
be further reduced because at warmer conditions less Pt could be used. This paper presents
an overview of the key requirements for the proton exchange membranes (PEM) used in
fuel cell applications, along with a description of the membrane materials currently being
used and their ability to meet these requirements. A number of possible alternative
candidates are reviewed and presented in this paper. Also discussed are some of the new
materials, technologies, and research directions being pursued to try to meet the
demanding performance and durability needs of the PEM fuel cell industry. The alternative
PEMs are classified into three categories: (1) modified Nafion composite membranes; (2)
functionalized non-fluorinated membranes and composite membranes therein; and (3)
acidebase composite membranes. Several commonly used inorganic additives are
reviewed in the context of composite membranes. Finally, the general methods of the
measuring and evaluating of proton exchange membrane properties have been investi-
gated such as proton conductivity, ion exchange capacity, water uptake, gas permeability,
methanol permeability, durability, thermal stability and fuel cell performance test.
ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Green Research Centre, Iran University of Science and Technology, Tehran, Iran. Tel.: þ98 2177491223; fax: þ98
217491242.
E-mail address: rowshanzamir@iust.ac.ir (S. Rowshanzamir).
0360-3199/$ e see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijhydene.2010.05.017
9350 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 9 3 4 9 e9 3 8 4
1. Introduction
Fuel cells due to their particular properties are on the verge of

creating a vast revolutionary change in the field of electricity.
By definition, fuel cell is an electrochemical apparatus that the
chemical energy of fuel without fuel combustion turned to
electrical energy. Therefore, in a fuel cell system, the chemical
energy related to electrochemical reaction of the fuel with
oxidant directly change into the water, electricity and heat.
Fuels such as H2, methanol, ethanol, and etc have been
usually used in fuel cells. In summary, the reactions have
been done in a fuel cell can be explained in following:
Hydrogen in Anode electrode change into a hydrogen ion and
electrons is released. These electrons move through foreign
circuit towards the cathode and produce the electrical current.
Anodic and cathodic reactions have been done in the PEM fuel
cell with H2 gas in anode in following: Fig. 1 e Schematic design of the PEM fuel cell.
Anode electrode: H2 / 2Hþ þ 2e

cells (AFC) with the alkaline solution electrolyte (such as
þ potassium hydroxide KOH), (2) phosphoric acid fuel cells
Cathode electrode: O2 þ 4H þ 4e / 2H2O
(PAFC) with acidic solution electrolyte (such as phosphoric
the two above reactions will be change the following general acid), (3) solid proton exchange membrane (PEMFC) which
reaction after the combination: are known to polymer electrolyte membrane fuel cells and
their electrolyte consist of the proton exchange membrane,
General Reaction of cell: 2H2 þ O2 / 2H2O (4) molten carbonate fuel cells (MCFC) with molten
carbonate salt electrolyte, (5) solid oxide fuel cells (SOFC)
The most important part and in the other words the central with ceramic ion conducting electrolyte in solid oxide form.
core of the fuel cell is the membrane electrode assembly (MEA) Table 1 summarizes the operating and applicable properties
which is consist of two part namely electrocatalyst and of five main types of fuel cells [2].
membrane. In this part, the production of the electrical Ion-exchange membranes have been used in various
current process (electrochemical reaction) will be done. The industrial processes, e.g., in the electrodialytic concentration
role of membrane between electrodes is the conduction of of seawater to produce edible salt, as a separator for elec-
produced protons from anode to cathode [1]. The existing ions trolysis, in the desalination of saline water by electrodialysis,
move towards the cathode through the electrolyte membrane in the separation of ionic materials from non-ionic materials
and on that place produce water and heat with free electrons. by electrodialysis, in the recovery of acid and alkali from
The primary compartments of the PEM fuel cell have been waste acid and alkali solution by diffusion dialysis, in the
shown in the Fig. 1. Advantages of fuel cells in comparison dehydration of water-miscible organic solvent by pervapora-
with other types of equipments which are producing energy tion, etc [3]. As mentioned at above section, in PEM fuel cells
are as follows: higher efficiency, no existence of the mobile will be used from solid polymeric electrolytes which have the
parts and as a result lack of sonic pollution, no emissions of ability of proton transferring. These ionic polymer electrolytes
environmental polluting gases such as SOx, NOx, CO2, CO, and are including the gel-like polymeric structures that were
etc. In contrary of benefits, only disadvantage of fuel cells is severely swollen and carrying fixed positive and negative
their higher cost that this problem will be solved by applying charges. These polymers don’t have the ability of proton
the new technologies and also mass production of these fuel transferring in dry conditions and only have this property in
cells. the moist state and will be increase the ionic conductivity
Fuel cells may be classified based on the used criteria to with increasing the water inside them. In 1970s, a chemically
different methods which typically depend on the different stable cation-exchange membrane based on sulfonated poly-
parameters related to operating conditions and fuel cell tetrafluoro-ethylene was first developed by Dupont as
structure. Fuel cell systems have different variables such as Nafion, leading to a large scale use of this membrane in the
type of the electrolyte used in fuel cell, type of the chlor-alkali production industry and energy storage or
exchanged ion through the electrolyte, type of the reactants conversion system (fuel cell) [4]. This fluorinated sulfonic acid
(e.g. primary fuels and oxidants), operating temperature and Nafion membrane developed by DuPont Co. was selected as
pressure, direct and indirect usage of the primary fuels in a standard membrane for polymeric electrolyte fuel cells.
fuel cell system, And finally the primary and regenerative Fig. 2 shows the types of ion exchange membranes and time of
systems. Generally, it is common that fuel cells are classi- their development from the beginning of appearance.
fied and nominated based on the nature of used electrolyte Traditionally, ion exchange membranes are classified into
in the fuel cell. Therefore, based on this classification, fuel anion exchange membranes and cation-exchange membranes
cells include the following different types: (1) alkaline fuel depending on the type of ionic groups attached to the
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 9 3 4 9 e9 3 8 4 9351
Table 1 e Operating and applicable properties of five main types of fuel cells.
Type of Operating Power Density Fuel Efficiency Lifetime Capital Cost Area of
Fuel Cell Temp. ( C) (mW/cm2) (Chem. to Elec.) (hr) ($/kW) Application
AFC [2] 60e90 100e200 40e60 >10,000 >200 Space, Mobile

PAFC 160e220 200 55 >40,000 3000 Distributed Power
PEMFC 50e80 350 45e60 >40,000 >200 Portable, Mobile,
Stationary
MCFC 600e700 100 60e65 >40,000 1000 Distributed Power
Generation
SOFC 800e1000 240 55e65 >40,000 1500 Baseload Power
Generation
membrane matrix. Cation exchange membranes contain studies have been done on reducing the cost of fuel cell
negatively charged groups, such as eSO3, eCOO, ePO2 3 , membranes. Much of the research on new materials for
ePO3H, eC6H4O, etc., fixed to the membrane backbone and PEMFC membranes, while promising, may be too far away
allow the passage of cations but reject anions. While anion from commercialization to meet this timeframe, and could
exchange membranes contains positively charged groups, such be the next generation technology. Today’s research is
as eNHþ þ þ þ þ þ
3 , eNRH2 , eNR2H , eNR3 , ePR3 , eSR2 , etc., fixed to the based on materials that can accelerate commercialization of
membrane backbone and allow the passage of anions but reject fuel cell. This paper is a review of past and present research
cations [5,6]. in the field of development of proton exchange membranes
According to the connection way of charge groups to the for fuel cell to achieve better performance, higher durability
matrix or their chemical structure, ion exchange membranes and lower cost.
can be further classified into homogenous and heterogeneous
membranes, in which the charged groups are chemically
bonded to or physically mixed with the membrane matrix, 2. Proton exchange membranes for fuel cell
respectively. Homogenous ion exchange membranes have applications
good electrochemical properties but don’t have any required
mechanical strength, while, the heterogeneous ion exchange As mentioned above, in general Membrane is the core
membranes have a good mechanical strength but the elec- component of the PEM fuel cell. Triple roles of the polymeric
trochemical Performance of these membranes are weak [7]. membrane in the PEM fuel cells are as follows: charge carrier
The other difference between homogenous and heteroge- for protons, to separate of the reactant gases, and electronic
neous ion exchange membranes is related to their dimen- insulator for not passing of electrons through the membrane
sional stability that the heterogeneous ion exchange (due to have a negative charge from SO 3 and electron repel-
membranes have a good dimensional stability compared with ling). In 1970s, DuPont developed a perfluorosulfonic acid
homogenous ion exchange membranes [8]. called “Nafion” that not only showed a two-fold increase in
During the past few years, many advances have been the specific conductivity of the membrane but also extended
made but there are still technical and economic obstacles in the lifetime by four orders of magnitude (104e105 h). This
the commercialization of fuel cell. In this regard, many soon became a standard for PEMFC and remains so till today.
efforts have been made to develop membranes for PEMFC’s The Dow Chemical Company and Asahi Chemical Company
with improved performance and durability. Also, other synthesized advanced perfluorosulfonic acid membranes
Fig. 2 e Types of the ion exchange membranes based on their development time (reprinted with permission from [8]).
with shorter side chains and a higher ratio of SO3H to CF2

groups [9]. Table 2 provides a comparison of some commercial
cation-exchange membranes [10].
This Nafion membrane, has a structure of copolymer from
flouoro 3,6-dioxo 4,6-octane sulfonic acid with polytetra-flu-
orethylene (PTFE) that Teflon backbone of this structure gives
the hydrophobic nature for membrane and hydrophilic
sulfonic acid groups (HSO 3 ) have been grafted chemically into
backbone. These ionic groups have caused the absorption of
the large amount of water by polymer and therefore, lead to
hydration of polymer. Thus, the factors affecting the perfor-
mance of the suitable proton exchange membrane are the Fig. 3 e Chemical structures of perflourinated polymer
level of hydration and thickness of the membrane which is electrolyte membranes (reprinted with permission
playing an important role in deciding their suitability for from [12]).
application in fuel cell [11]. The proton exchange membrane
performance related to the extent of its proton conductivity
and the proton conductivity also related to the extent of the structures of Nafion and other famous perfluorinated elec-
humidity of the membrane. Higher proton conductivity ach- trolyte membranes [12].
ieve by the higher extent of the humidity. One of the ways to
avoid water drag or water crossover is to reduce the
membrane thickness thereby enabling an improvement in the 3. Proton conduction mechanisms in proton
fuel cell performance. Other advantages of reduced thickness exchange membranes
include lower membrane resistance (and therefore an
enhancement in membrane conductivity), lower cost and Proton conduction is fundamental for proton exchange
rapid hydration. However, there is a limit to the extent to membrane fuel cells and is usually the first characteristic
which membrane thickness can be reduced because of diffi- considered when evaluating membranes for potential fuel cell
culties with durability and fuel by-pass. To achieve high effi- use. Resistive loss is proportional to the ionic resistance of the
ciency in fuel cell applications, the polymer electrolyte as membrane and high conductivity is essential for the required
membrane must possess the following desirable properties: performance especially at high current density. At a molecular
high proton conductivity to support high currents with level, the proton transport in hydrated polymeric matrices is
minimal resistive losses, zero electronic conductivity, in general described on the basis of either of the two principal
adequate mechanical strength and stability, chemical and mechanisms: (1) “proton hopping” or “Grotthus mechanism”
electrochemical stability under operating conditions, mois- and “diffusion mechanism” which water is as vehicle or
ture control in stack, extremely low fuel or oxygen by-pass to “vehicular mechanism” [13e15].
maximize columbic efficiency and production costs compat- In proton hopping mechanism protons hop from one
ible with intended application [10]. Fig. 3 shows the chemical hydrolyzed ionic site (SO þ
3 H3O ) to another across the
Table 2 e Properties of commercial cation-exchange membranes.

Membrane Membrane Type IEC Thickness Gel water Conductivity
(mequiv./gr) (mm) (%) (S/cm) at 30 C and
100% R.H.
Asahi Chemical Industry Company Ltd., Chiyoda-ku, Tokyo, Japan [10]

K 101 Sulfonated polyarylene 1.4 0.24 24 0.0114
Asahi Glass Company Ltd., Chiyoda-ku, Tokyo, Japan
CMV Sulfonated polyarylene 2.4 0.15 25 0.0051
DMV Sulfonated polyarylene e 0.15 e 0.0071
Flemion Perflourinated e 0.15 e e
Ionac Chemical Company, Sybron Corporation, USA
MC 3470 e 1.5 0.6 35 0.0075
MC 3142 e 1.1 0.8 e 0.0114
Ionics Inc., Watertown, MA 02172, USA
61AZL386 e 2.3 0.5 46 0.0081
61AZL389 e 2.6 1.2 48 e
61CZL386 e 2.7 0.6 40 0.0067
DuPont Company, Wilmington, DE 19898, USA
N 117 Perflourinated 0.9 0.2 16 0.0133
N 901 Perflourinated 1.1 0.4 5 0.01053
Pall RAI Inc., Hauppauge, NY 11788, USA
R-1010 Perflourinated 1.2 0.1 20 0.0333
exchange membrane which allow the transferring of the

hydrated protons through the membrane. The schematic
design of the vehicular mechanism in proton conduction in
pristine and nanocomposite membranes has been shown in
the Fig. 5(a,b). Water also has two suggested transport
mechanisms: electroosmotic drag and concentration
Fig. 4 e The simple scheme of the hopping mechanism gradient driven diffusion (this probably occurs as self-
(reprinted with permission from [16]). associated clusters: (H2O)y). The hydrophobic nature of
Teflon backbone facilitates the water transfer through the
membrane because the surfaces of the hydrophobic holes
membrane. The produced proton by oxidation of hydrogen in tend to repel the water molecules [16].
anode adheres to water molecule than the provisional The prevalence of one or the other mechanism depends on
hydronium ion is formed and one different proton from same the hydration level of the membrane. On the other hand, the
hydronium ion hops on the other water molecule. In this mechanism of proton transport within nanocomposite and
mechanism, ionic clusters were swelled in presence of water hybrid systems based on the aforementioned membranes is
and formed the percolation mechanism for proton trans- a much more complex process as it involves both the surface
ferring. The simple scheme of the hopping mechanism has and chemical properties of the inorganic and organic phases.
been shown in Fig. 4 [16]. The hopping mechanism has little Although the exact role of inorganic components in stabilizing
contribution to conductivity of perflourinated sulfonic acid the proton transport properties of nanocomposites based on
membranes such as Nafion. Nafion and other polymers is still under discussion, it may be
The second mechanism is a vehicular mechanism. In this presumed that the primary function of the nanoparticles is to
mechanism hydrated proton (H3Oþ) diffuses through the stabilize the polymer morphology with increasing tempera-
aqueous medium in response to the electrochemical differ- ture. If the inorganic additive happens to be an alternative
ence. In vehicular mechanism, the water connected protons proton transporter like heteropolyacids, their contribution to
(Hþ(H2O)x) in the result of the electroosmotic drag carry the the transport processes has also to be analyzed. Proton
one or more molecules of water through the membrane and conductivity improvements would, however, depend upon
itself are transferred with them. The major function of the whether the fraction of bulk water and the bulk proton
formation of the vehicular mechanism is the existence of concentrations are increased as a result of the inorganic
the free volumes within polymeric chains in proton additives or not.
Fig. 5 e The Schematic design of the Vehicular Mechanism as proton conduction in (a) pristine membranes and (b) polymer/
nano-particle composite membranes (reprinted with permission from [13,17]).
Fig. 6 e Classification of membranes based on materials (perfluorinated, partially fluorinated and non-fluorinated) and
preparation method (acid-base blends and others) (modified with permission from [10]).
benzene ring structures in the polymeric backbone of

4. Classification of the materials used in membrane or in the bulky pendant groups from this
proton exchange membranes synthesis membrane polymeric backbone. Presently, one of the most
promising routes to high-performance proton conducting
In general, the materials used in synthesis of the polymer elec- polymer electrolyte membranes is the use of hydrocarbon
trolyte membranes can be classified into three vast groups: polymers for polymer backbones [12]. Hydrocarbon
perflourinated ionomers (or partially perflourinated), non- membranes provide some definite advantages over per-
flourinated hydrocarbons (including aliphatic or aromatic flourinated membranes. They are less expensive, commer-
structures), and acidebase complexes. In Fig. 6, the classifica- cially available and their structure permits the introduction of
tion of membranes based on materials (perfluorinated, partially polar sites as pendant groups [10]. Hydrocarbon polymers
fluorinated and non-fluorinated) and preparation method containing polar groups have high water uptakes over a wide
(acidebase blends and others) has been shown [10]. temperature range, and the absorbed water is restricted to the
polar groups of polymer chains. Decomposition of hydro-
4.1. Perflourinated ionomeric membranes carbon polymers can be depressed to some extent by proper
molecular design. Hydrocarbon polymers are easily recycled
The Perflourinated polymers due to the small size and the by conventional methods. These chemical structures of the
high electronegativity of the fluorine atom have a strong CeF hydrocarbon membranes are illustrated in Fig. 8 [12].
bond and a low polarizability. These polymers due to their In order to enhance stability at elevated temperatures,
thermostability, chemical inertness and the enhanced acidity aromatic hydrocarbons can be (a) incorporated directly into
of sulfonic acid group in eCF2SO3H, have been utilized in the backbone of a hydrocarbon polymer or (b) polymers
chlor-alkali process and as proton exchange membranes for modified with bulky groups in the backbone to render them
fuel cell applications [19]. These membranes are prepared by suitable for conduction of protons [10,21]. Polyaromatic
the polymerization of monomers, which contain a moiety that membranes are high temperature rigid polymers with
can be made either cationic or anionic by further treatment. Tg > 200 C owing to the presence of inflexible and bulky
These membranes are the fluorocarbon-based ion-exchange aromatic groups [22]. The aromatic rings offer the possibility
membranes (Nafion) with good chemical and thermal stability of electrophilic as well as nucleophilic substitution. Polyether
have been developed by DuPont. The four-step synthesis sulfones (PESF) [23e25], polyether ketones (PEK) with varying
procedure of these membranes such as Nafion which intro- number of ether and ketone functionalities (such as PEEK,
duced by DuPont in 1966 has been shown in Fig. 7. These are PEKK, PEKEKK, etc.), poly(arylene ethers), polyesters and pol-
high equivalent weight (EW) perflourinated membranes and yimides (PI) are some of the relevant examples of main chain
have limited their use in fuel cells because they consume high polyaromatics [26]. Poly (2,6-dimethyl-1,4-phenylene oxide)
power density [3]. Similar polymers are Flemion produced by (PPO) can meet most of the requirements for application in
Asahi Glass and Aciplex-S produced by Asahi Chemical. PEMFCs because it is a hydrophobic polymer with high glass
Among the three major types, the DuPont product is consid- transition temperature (Tg ¼ 210 C), high mechanical
ered to be superior because of its high proton conductivity, strength, and excellent hydrolytic stability. Although the
good chemical stability and mechanical strength [20]. structure of PPO is simple as compared to other aromatic
polymers, it allows many modifications in both aryl and
4.2. Non-fluorinated hydrocarbon membranes benzyl positions: (1) electrophilic substitution on the benzene
ring, (2) radical substitution of the hydrogen from the methyl
The other type of materials used in proton exchange groups, (3) nucleophilic substitution of the bromomethylated
membrane synthesis, are non-fluorinated hydrocarbon poly- PPO, (4) capping and coupling of the terminal hydroxyl groups
mers which can be aliphatic or aromatic polymers having in PPO chains, and (5) metalation of PPO with organometallic
Fig. 7 e Nafion membrane and its preparation scheme (reprinted with permission from [3]).
compounds [27]. Polyaromatics are often preferred for fuel cell considered for fuel cell membranes involve incorporation of
application due to their thermal stability. Also, the poly- an acid component into an alkaline polymer base to promote
aromatics from oxidant point of view are stable in the acidic proton conduction [10].
medium. The structures of prominent acidic and basic polymers and
their complexes are given in Fig. 9.
4.3. Acidebase complexes The phosphoric acid-doped polybenzimidazole (PBI/H3PO4)
membrane seems so far the most successful system for high
Acidebase complexes have been considered as a viable temperature PEMFC preferably under ambient pressure. It has in
alternative for membranes that can maintain high conduc- recent years motivated extensive research activities covering
tivity at elevated temperatures without suffering from dehy- polymer synthesis, membrane casting, physicochemical char-
dration effects. In general, the acidebase complexes acterizations and fuel cell technologies. Acid-doped PBI
Fig. 8 e Chemical structure of polymer electrolyte membranes based on hydrocarbon polymers (reprinted with permission
from [16]).
Fig. 9 e Structure of basic polymers (aed) and acidic polymers (e, f) (reprinted with permission from [10]).
membranes have been extensively characterized. Related fuel For example, at 450% doping and a temperature of 165 C,
cell technologies have been developed and high temperature the conductivity of PBI membrane was about 4.6 102 S/cm.
PEMFC has been successfully demonstrated at temperatures of It was also observed that at very high levels of doping (around
up to 200 C under ambient pressure. No gas humidification is 1600%), the conductivity could reach 0.13 S/cm. A fuel cell was
mandatory, which enables the elimination of the complicated operated with a doped PBI/H3PO4 membrane at 190 C and
humidification system, compared with Nafion cells. Other atmospheric pressure yielding a power density of 0.55 W/cm2
operating features of the PBI cell include easy control of air flow and a current density of 1.2 A/cm2 [32].
rate and cell temperature (in a wider range) [28]. Kerres et al. made sPEEK/PBI membranes were composed
To date, many studies have been carried out to develop of sulfonated poly(etheretherketone) sPEEK as the acidic
alternative membranes with good fuel cell performance and compound and poly (benzimidazole) PBI as the basic
low cost. Among those alternatives, acidebase polymer blends compound. The membranes showed good proton conductiv-
are promising materials. The interactions between acid and ities at ion-exchange capacities IEC of 1, and they showed
base polymers, such as ionic crosslinking (electrostatic forces) excellent thermal stabilities (decomposition temperatures
and hydrogen bonding bridges, contribute markedly to the >270 C). Also, the membranes were tested in a H2 membrane
control of membrane swelling without a decrease in flexibility. fuel cell and showed good performance [146].
Therefore, these membranes have low water uptake, reduced Vargas MA et al. have synthesized a new protonic
crossover, high proton conductivity, good thermal stability, conductor gel (PVAL/H3PO2/H2O) using PVAL (polyvinyl
and high mechanical flexibility and strength [29]. alcohol) and H3PO2 (hypophosphorous acid) as prime chem-
For application in fuel cells, a series of hybrid acidebase icals; the common solvent was water. The gels are transparent
polymer membranes were prepared by blending sulfonated and have good mechanical properties. With this system they
poly (2,6-dimethyl-1,4-phenylene oxide) (sPPO) with 3-ami- have reached the highest electrical conductivity at ambient
nopropyl) triethoxysilane (A1100) through a solegel process. and subambient temperatures in this type of material repor-
Experiments have shown that, the acidebase interaction ted up to now in the literature (in the order of 101 S cm1).
improves not only the membrane homogeneity and thermal The variation of the electrical conductivity with temperature
stability but also the mechanical strength and flexibility [29]. and acid concentration was studied. The highest open fuel cell
The novel acidebase membranes composed of acidic voltage, measured at 23 C was 435 mV. The performance of
sulfonated polymers (sPPENK, sPPESK and sPBEK) and basic the fuel cell improved when it was fed with humidified
polyetherimide (PEI), prepared and showed excellent resis- hydrogen [94].
tance to swelling, thermostability, hydrolysis resistance and The most important blends in the preparation of acidebase
oxidative resistance with highly proton conductivity. complex are presented in Table 3. The main advantage of
Accordingly, they are expected promising fuel cell proton using high temperature specialty polymers is related not only
exchange membrane materials in the future [30]. to the thermal stability, but more to the expected stability in
The conductivity of acidebase complex membrane does oxidative, reducing and acidic environments.
not depend on humidity in contrast to Nafion but it is
strongly sensitive to the doping level of complex. In general,
the conductivity of the acidebase complexes is sensitive to 5. Fabrication and preparation methods of
the doping level and temperature. The extent of doping of the proton exchange membranes
alkaline polymer is defined as a phosphoric acid mole percent
per any repeating unit of polymer. As the doping increases, The development of cost-effective and functional materials
the distance between the clusters of acid sites decreases and and components for the polymer electrolyte fuel cell (PEFC) is
the anion moieties support the proton hopping between an important stepping stone towards the commercialization
imidazole sites. Data reported by Bouchet et al. also supports and market introduction of this technology. In addition to the
a Grotthus mechanism for PBI membrane doped with phos- noble metal catalyst, the proton exchange membrane (PEM)
phoric acid as acidebase complex (PBI/H3PO4) [31]. material is a major contributor to the cost of the membrane
Table 3 e The most important blends in the preparation of acidebase complex.

S. No. Membrane Blend Physical Observations In situ
Materials Ration Properties Performance
1 sPEEK/PBI [10] 90/10 High temperature Short-term tests (300hr) Higher voltages of
tolerance at 350 C; yield comparable 650 mV obtainable at
thermally stable; performance to High current densities of
good miscibility Nafion 112 1000 mA/cm2 for Hydrogen
fuel cell
2 PVA/H3PO4 Highly doped Good mechanical With decreasing acid Low open cell voltage
Strength concentration, grotthus (a max. of 436 mV With
transport mechanism very low current Density of
decreases Mechanism 1 mA/cm2) Maximum
likely at low temperatures conductivity of 101 S/cm at
100 MV
3 PBI/H3PO4 500% doping Good mechanical Doped PBI shows greater Conductivity of 6 102 S/cm
Strength; potential for fuel cell achievable
thermally stable operating at moderate
temperatures
electrode assembly (MEA). The state-of-the-art technology is 50e100 US $m2 [38]. The process for the preparation of the
mostly based on perfluorinated membrane materials, such as new polymer electrolyte membrane by irradiation grafting as
Nafion (DuPont, USA), Flemion (Asahi Glass, Japan) and shown in Fig. 10, in which three steps are as follows: In first
Aciplex (Asahi Kasei, Japan), and composites. These mate- step the polyethylene tetrafluoro ethylene (ETFE) films were
rials are expensive due to the complex fluorine chemistry pre-irradiated in argon gas at room temperature. In this step,
involved in the fabrication [33]. Therefore, the development of the ETFE films were activated in a pre-irradiation step and
the membranes with low cost and higher performance is then grafted with monomers in a subsequent step (second
necessary. Today, the new membranes as a substitute for the step) which is named substitution stage. Finally, the grafted
Nafion membranes that are including the membranes with ETFE films were sulfonated in a chlorosulfonic acid solution to
hydrocarbon polymer matrixes, inorganic e organic hybrid introduce the sulfonic acid groups into the membranes which
membranes, acidebase complexes and grafting membranes is followed by hydrolysis in distilled water. Characterization of
by irradiation. The radiation grafting method is of interest and the new polymer electrolyte membranes was carried out by
suitable method for the preparation of proton exchange means of the Fourier transform infra-red (FT-IR) and ther-
membranes for fuel cell and other electrochemical applica- mogravimetric analysis (TG-DTA) [38]. The dimensional unit
tions. Generally, there are four methods for fabrication and of the irradiation in the preparation of the polymer electrolyte
preparation of the proton exchange membranes are as membranes by grafting method is kGy that is defined as an
follows: (1) grafting polymerization method with using of the extent of absorbed energy by polymeric membrane in terms of
g-ray irradiation, (2) grafting polymerization method with kJ per gram of polymer is grafting (1 kGy ¼ 1 kJ/gr membrane).
using of the plasma, (3) the Crosslinking method, (4) solegel The irradiation rate is defined by kGy in hour or kGy/hr.
method and (5) direct polymerization of monomers. In follow, Radiation-induced graft polymerization is a well-known
the above methods are explained in detail [34e35]. method for the modification of the physicochemical proper-
ties of materials, and is of particular interest for achieving
5.1. Irradiation grafting polymerization method specifically desired properties as well as excellent mechanical
properties [39]. The mass-based degree of grafting DGm is
Graft polymerization, by means of electron-beam, g-ray, and defined as percent of the weight difference between polymeric
ultraviolet (UV) light irradiation or by plasma, is a convenient films before and after of the grafting action which is calculated
method for the preparation of ion exchange membranes according to:
because a rapid formation of active sites on an appropriate
Wg W0
polymer matrix can be achieved [36]. The radiation-grafted DGm ¼ 100 (1)
W0
membranes have been reviewed by Nasef and Jegzey [37]. The
advantages of radiation-grafted membranes include the lack where W0 and Wg are the weights of the film before and after
of need for chemical initiators or catalysts, the easy prepara- grafting, respectively [35].
tion from the already prefabricated base film, and the easy
control of the degree of grafting and ion exchange capacity of 5.2. Crosslinking method
the membranes. The grafting can be initiated by high-energy
irradiation such as g-ray, electron-beam and swift heavy ions. As in previous sections mentioned, perfluorosulfonic acid
The base film in the polymer electrolyte membrane is a func- membranes such as Nafion are used as a proton exchange
tion as hydrophobic host that constrains the membrane membranes for fuel cell applications [40]. Nafion has excellent
swelling in water and provides the mechanical strength and proton conductivity, but it has been found that over 40% of
dimensional stability. In addition, the price of commercial methanol can be lost in direct methanol fuel cell (DMFC) across
radiation-grafted membranes is said to be in the range of the membrane due to excessive swelling [41]. To improve the
Fig. 10 e Preparation of the new polymer electrolyte membranes by irradiation grafting method (reprinted with permission
from [38]).
performance of a DMFC, it is necessary to reduce the loss of fuel 5.3. Plasma grafting polymerization method
and methanol crossover across the polymer electrolyte
membrane in the fuel cell [42e43]. It is lead to increase of the The grafting polymerization by plasma is one of the methods
proton conductivity of the proton conductive polymer for preparation of proton exchange membranes for applica-
membranes and as a result the produced voltage per consumed tions in miniaturized fuel cells. Plasma polymerized films
current density increase in the unit fuel cell. Therefore, from exhibit a high degree of crosslinkage and are pinhole free even
the crosslinking method can be used to obtain three dimen- for films of only a few hundred nanometer in thickness, in
sional networks in membrane structures in order to reduce the contrast to conventionally polymerized films. Hence, a sharp
methanol crossover through membrane [44]. In the cross- reduction of the methanol permeability and a decrease in the
linking method for preparation of the proton exchange resistance of a fuel cell electrolyte membrane is achieved by
membranes, the membranes without charged sites are using plasma polymerized electrolytes. The overall
changed into proton exchange membranes by crosslinking in membrane resistance also will be reducing by plasma poly-
presence of the organic charged groups. The creation of merization method due to the lower thickness of the ion
crosslinking caused to improve the chemical and thermal exchange membrane (in about 1 mm) [46]. By increasing the
stability of ion exchange membrane. Fig. 11 shows the plasma energy in this polymerization, ionic conductivity of
proposed reaction mechanism of PVA and PSSA MA for prep- membrane will be reduce due to the higher degree of cross-
aration of the crosslinked proton exchange membranes [45]. linking, because the transferring of water molecules is so
hard. The plasma polymerized electrolyte membranes have
been developed by using tetrafluoro ethylene to generate the
polymeric backbone of an ion-conductive membrane and
vinylphosphonic acid to incorporate acid groups, which are
responsible for the proton conductivity [47]. In Fig. 12 has been
shown the major differences between a monomer, a conven-
tional polymer and the polymer prepared by plasma poly-
merization. The structure of the prepared polymer in plasma
polymerization is a quietly dense which this matter caused to
severely reduction of the methanol crossover in the usage of
this polymer as a membrane in direct methanol fuel cells.
5.4. Solegel method
The solegel method provides the easier introduction of pure

inorganic phase into polymeric matrix (mostly in composite
membranes). In solegel chemistry, molecular pre-materials
will change into particles with nano sizes. This colloidal
suspension form or sol, leads to formation of the gel networks.
Fig. 11 e Possible reaction mechanism of PVA and PSSA Gel will change into different materials with the different
MA (reprinted with permission from [45]). properties by the various drying techniques. The sols have
Fig. 12 e Differences between a monomer, a conventional polymer and the polymer prepared by plasma polymerization.
been formed from dispersing colloidal particles (with the size proton exchange membranes. The membranes are prepared
about 1e100 nm) in liquid and gel from rigid and continuous directly from the polymerization of possible monomers such
network with pores under micrometer size and polymer chains as styrene and di-vinyl benzene, followed by sulfonation. The
which have the average length greater than micron too. The polymerization mostly takes place in an inert matrix through
sols are usually prepared by using of the metallic alkoxides. monomer soaking or pore can filling. It has been noted that
With regard to this, the metallic organics are insoluble in the sometimes, the polymerization is directly conducted from
water, but these alkoxides solved in the alcoholic solution. The sulfonated monomers without the post-sulfonation step [49].
polymerization reaction begins by adding of water in sol. This
process will be done by two main reactions as hydrolysis and
condensation. These reactions are as follows:
6. Modification of the proton exchange
Hydrolysis reaction: M e O e R þ H2O / M e OH þ R e OH membranes in fuel cell applications
Condensation reactions: M e OH þ HO e M / M e O e Recently, the modification of the fluorinated membranes such

M þ H2O as Nafion and non-fluorinated membranes such as sulfonated
polyether ether ketones, sulfonated polyether sulfones,
M e O e R þ HO e M / M e O e M þ R e OH sulfonated polyether imides and other types of proton
exchange membranes have been studied and investigated in
In this above reactions, R is the alkyl groups such as methyl, fuel cell applications. It is clear that Nafion and related
ethyl, propyl, etc [48]. Fig. 13 shows the general scheme of the polymers are still being intensely examined in view of the
hydrolysis and condensation processes. complex cell requirements of high proton conductivity and
outstanding chemical stability combined with longevity of
5.5. Direct polymerization of monomers method 60,000 h at 80 C. The major disadvantages of these PFSA
materials are: the high cost of membrane amounting to US$
Direct polymerization of monomers is a new and traditional 700 per square meter [49], requirement of supporting equip-
method of preparing proton exchange membranes and can be ment [50e51], and temperature related limitations. Degrada-
also used to prepare fuel cell membranes, a special category of tion of PFSA membrane properties at elevated temperatures is
Fig. 13 e General scheme of the hydrolysis and condensation processes (reprinted with permission from [49]).
another serious drawback. Conductivity at higher tempera- strength and also creation of the self-humidity of the
tures (up to 100 C) is reduced than lower temperatures [12]. membranes in elevated temperatures.
Also, the phenomena related to membrane dehydration, As mentioned in above, Nafion, the conventional proton
reduction of ionic conductivity, decreased affinity for water, conducting polymer electrolyte membrane is expensive,
loss of mechanical strength due to softening of polymer mechanically unstable at temperatures above 100 C, and
backbone and increased parasitic losses through high fuel conductive only when soaked in water, which limits fuel cell
permeation are observed at temperatures above 80 C. With operating temperatures to 80 C, which in turn results in lower
regard to the application in direct methanol fuel cells (DMFC), fuel cell performance due to slower electrode kinetics and low
Nafion exhibits a high methanol permeability greater 80,000 CO tolerance [71]. Thus, the development of membranes
Barrers at 80 C, which drastically reduces the DMFC perfor- which are mechanically and chemically stable at higher
mance and renders it unsuitable for DMFCs [52]. Efforts are temperatures (above 100 C) is an active area of research for
directed to eliminate the disadvantages such as crossover producing economical fuel cells. A wide range of the fillers
problems and loss of hydration above 100 C. Despite its such as SiO2, zirconium phosphate, phosphotungestic acid
shortcomings, Nafion is still the polymer of choice for most [72e73], molibdophosphoric acid, suspending SiO2, organi-
PEFC and DMFC applications. However, it is likely that Nafion cally modified silicates, silane based fillers and zeolites are
will be replaced by an alternative membrane in the future [53]. used for the preparation of the Nafion-based composite
In order to overcome few of the disadvantages of the PFSA proton exchange membranes. Composite membranes are
membranes enumerated above, the authors are also carrying shown the promising characteristics such as lower H2, O2 and
out research work to identify promising alternatives [54e55]. methanol crossover, good thermal stability, increased proton
Basically, there are two ways to enhance the properties of conductivity, and higher water uptake. In the following
proton exchange membrane: Polymeric blend membranes sections, the types of the modified proton exchange
and polymer/inorganic composite membranes. The latter is membranes in the PEM fuel cells are investigated.
easier to fabricate. This type of composite can be configured in
a number of ways: 6.1. Modified Nafion membrane with inorganic oxides
MO2 (M ¼ TieSieZr)
- Both polymer and inorganic components can be ionically
conductive; An increase of the cell temperature produces enhanced CO
- Ionic polymer with inorganic filler for mechanical support; tolerance in PH-PEFC, faster reaction kinetics and reduced
- Ionic polymer with water-retaining inorganic filler; heat-exchanger requirement. The main problem for PEFC
- Ionically conductive inorganic additive with supporting operation above 100 C is the loss of proton conductivity of the
polymer [56]. perfluorosulphonic electrolyte due to the lower-water content
with a consequent decrease of the cell performance. For all
This partial list only covers a few of the possible combi- these reasons, great interest has been focused on the devel-
nations. Polymer inorganic composite membranes are inter- opment of alternative membranes able to work above 100 C.
esting because many of the inorganic additives used are able Several approaches have been used to overcome this problem,
to operate at much higher temperatures than the pure such as the use of thermally resistant polymers or the intro-
polymers. Some of the possible advantages of incorporating duction of a hygroscope and/or proton conductor material as
inorganic compounds into composite membranes include, filler in the polymeric perfluorosulphonic matrix. In the latter
enhanced proton conductivity, water retention at high case, the inclusion of inorganic fillers improves the mechanical
temperatures, and mechanical support [57]. Rikukawa and properties, the membrane water management and also
Sanui [12] suggest that in order to produce materials that are contributes to inhibiting the direct permeation of reaction
less expensive than Nafion, some sacrifice in material life- gases by increasing the transport pathway tortuousness
time and mechanical properties may be acceptable, provided [48,74]. Modified Nafion membranes containing inorganic
the cost factors are commercially realistic. Hence the use of fillers such as SiO2, TiO2, ZrO2 [60,75e80 and other compounds
hydrocarbon polymers, even though they had been previ- characterized by water retention capacity or by proton
ously abandoned due to low thermal and chemical stability, conduction as hetero-poly-acids (PWA, PMoA, SiWA) or layered
has attracted renewed interest. Therefore, the efforts to zirconium phosphate [58,81e85] are valid materials to use as
develop these higher temperature membranes include polymer electrolytes in a medium temperature PEFC. There-
modification of the conventional host polymers, e.g., via fore, in general, the so-called ‘high-temperature membranes’
incorporation of various hygroscopic inorganic nanosized can be developed via modification of the polymer host
particles or by developing alternate new polymer systems membranes with (1) hygroscopic oxides such as SiO2 and TiO2
[58e70]. The most important goals of modification of the to increase water uptake; (2) inorganic solid acids such as ZrO2/
proton exchange membranes in PEM fuel cells can be SO24 to increase the water uptake as well as the concentration
mentioned such as preparation of the proton exchange of acid sites; and (3) inorganic proton conductors such as
membranes with lower cost compared to the fluorinated hetero-poly-acids to enhance further proton conductivity
membranes, the desirable water uptake and retain in the using inorganic-assisted proton transport together with high
elevated temperatures, desirable proton conductivity in the water uptake and high acid concentration in the membrane
higher temperatures, the lower extent of the reactant [86e89]. The method of preparation of the ZrO2, SiO2 and TiO2
gaseous and methanol crossover through the membrane, composite proton exchange membranes was based on the in
improved thermal stability, higher mechanical and chemical situ solegel synthesis methods [67]. In this procedure, the host
Fig. 14 e Water uptake vs. activity of water vapor for nanocomposite of Nafion - MO2 and Nafion membrane at
temperatures a) 90 C and b) 120 C (reprinted with permission from [90]).
proton exchange membrane serves as a template that directs activity. The increase in the conductivity of Nafion - ZrO2
the morphology, particle growth, and size of the oxide in the solegel nanocomposites is the combined result of higher water
PEM matrix, resulting in nanosized particles. Fig. 14 shows the uptake as well as acidity. Hence, from water uptake, ion
water uptake measurements for the nanocomposite exchange capacity and conductivity results, it is evident that
membranes at 90 and 120 C, respectively. At both tempera- higher water uptake does not inevitably result into higher
tures, all Nafion-MO2 nanocomposite exhibited better water conductivity. It is not only the total water uptake, but also the
uptake at a given relative humidity (RH) than unmodified distribution of water between surface and bulk that deter-
Nafion membrane. The enhanced water uptake can be mines conductivity [88]. Bulk water is much more effective in
attributed to the hydrophilic nature of the acidic inorganic proton conduction. The fuel cell performance of a single cell
additives within the pores of Nafion membrane and the with all four types of membranes under fully humidified and
increased acidity and surface areas of nanoparticles. The basic dry conditions is shown in Fig. 16. Since sulfated zirconia is
sorption trend at both temperatures was similar, with water acidic, it causes higher water sorption in the nanocomposites
uptake increasing from silica to Titania to Zirconia nano- [90]. Composite membranes have a lower resistivity than
composites. This is in order of increasing acid strength. Higher Nafion under fully humidified conditions and give better I-V
water uptake and enhanced acidity result in greater proton performance in fuel cells. Also, water sorption into Nafion-
conductivity, which would presumably result into better fuel based membranes increases with increased temperature [91].
cell performance under hot and dry conditions [90].
Fig. 15 shows the conductivity measurements for the 6.2. Modified Nafion membrane with types of clays
nanocomposite membranes at 90 and 120 C, respectively, as
compared to Nafion membrane. At both temperatures, Among the inorganic compounds suitable for the organic
Nafion ZrO2 solegel nanocomposite showed higher conduc- matrix, the clay family is a promising candidate. Indeed,
tivity than Nafion for over the complete range of water layered silicate, like smectite clays, show attractive
Fig. 15 e Conductivity vs. activity of water vapor for nanocomposite Nafion - MO2 and Nafion membrane at temperatures
a) 90 C and b) 120 C (reprinted with permission from [90]).
Fig. 16 e The cell performance of Nafion-112 vs. Nafion - MO2 solegel, composite membrane. Oxygen and Hydrogen at 2.0
and 1.3 times stoichiometric flows, respectively, P [ 1.0 atm, THumidifier [ 80 C, under a) fully humidified condition at 80 C
and b) dry condition at 110 C (reprinted with permission from [90]).
hydrophilic properties and good thermal stability at high higher with composite membranes (87 and 70%) than with the
temperature [92,93]. The layered silicates commonly used for perflourinated membranes (50% for recasted Nafion and 30%
PEM fuel cell applications are Laponite (Lp) or Montmorillonite for Nafion-117) while the thickness expansion stays compa-
(MMT) made of silica tetrahedral and alumina octahedral rable (18 2%). This relevant difference in water uptake is due
sheets which have advantageous hygroscopic properties to the high water adsorption capacity of this kind of Laponite
[95e99]. Indeed, the monovalent ions located between the clay [100].
layers allow the absorption of polar solvent, like water, with This observation suggests that the water retention of the
good retention capacity. The smectite clays are so usually inorganic phase is responsible for the improved water reten-
named “swelling” clays. These synthetic (Lp) or natural (MMT) tion of the hybrid membranes. Because proton conduction is
inorganic materials incorporated into a polymer membrane directly related to the water content, it is important to deter-
help to prevent the loss of the hydration water at high mine, for membranes presenting some interesting water
temperature but also under low relative humidity environ- retention capacities, the dependence of their proton conduc-
ment. Nevertheless, the addition of clay, which is a poor tivity with the environment conditions, like temperature and
proton conductor, inside Nafion, which is highly proton humidity level. Fig. 17 shows the results of conductivity
conductive, can lead to a reduction of the global proton measurements for different relative humidity conditions
conductivity of the membrane [100]. If a comparison is made (from 50 to 100% RH) at 25 C for Nafion-115 and for hybrid
with commercially available Nafion membranes, the addi- membranes. From Fig. 17, it can be noted that the proton
tion of a small amount of montmorillonite salts to per- conductivity of the Nafion/Lp-g membrane is higher than the
fluorosulfonic acid (PFSA) membranes leads to the reduction one of the Nafion-115 whatever the relative humidity
of the methanol crossover and, concurrently, a decrease of conditions, and is higher than the one of the Nafion/Lp
conductivity [98]. Organic modification was done with the between 70 and 98% RH. The decrease of the proton conduc-
following objectives: (1) to have a better compatibility with the tion with relative humidity is faster for commercial
polymer, i.e., to have a good interface bonding between membrane than for hybrid ones [107]. The improvement of the
polymer and silicates/Aerosils; [101] (2) to decrease methanol composite membrane behavior has been previously evi-
permeability; (3) to aid the proton conductivity of the whole denced by ex situ analysis and has to be evidenced now in fuel
composite membrane system [102]. Table 4 reports the water cell. Then, Nafion/Lp-g hybrid membranes are tested in a fuel
uptake, and the thickness of the dry (Td) and fully hydrated cell test station at different operation conditions, changing for
(Tw) states of hybrid membranes filled with Laponite type of example, the cell temperatures (80e120 C), the reactant gases
the clay. As shown clearly in Table 4, the water uptake is (H2/O2 and H2/air), and the gas pressures (3e4 bar) in order to
Table 4 e Thickness in dry and wet states (Td and Tw) and corresponding thickness expansion and water uptake (Wut) for
Nafion and for hybrid membranes at room temperature.
Sample Dry State, Fully hydrated state Thickness
Td (mm) Expansion (%)
Tw (mm) Wut (wt.%)
Nafion 117 [100] 185 205 30 11

Recasted Nafion 102 120 50 18
Nafion/Lp (90/10, w/w) 121 140 87 16
Nafion/Lp-g (90/10, w/w) 117 140 70 20
the composite one (Nafion/Lp-g) can reach 500 mA cm2, as

seen in Fig. 18. Then, composite Nafion presents a better
behavior than the commercial Nafion, whatever the opera-
tion conditions. Nevertheless, the gain in power density is
always more significant under difficult humidification condi-
tions. This improvement in fuel cell work has to be related to
the good water retention of the inorganic filler while the
sulfonic acid groups grafted to the particles surface enhance
the global proton conductivity of the material [100].
Fig. 19 presents the methanol permeability and proton
conductivity of membranes fabricated with various propor-
tions (0e6 wt.%) of montmorillonite clay modified with the
Fig. 17 e Variation of proton conduction at 25 C with POPD400-PS in Nafion membrane. The methanol perme-
relative humidity for Nafion-115 (B) and hybrid Nafion ability decreased rapidly as the amount of MMT-POPD400-PS
containing 10 wt.% of unmodified Laponite (Nafion/Lp added to Nafion increased. Indeed, several studies have
(,)) and containing 10 wt.% of grafted Laponite (Nafion/ demonstrated that adding montmorillonite nanofiller can
Lp-g (-))(reprinted with permission from [100]). improve the barrier properties of Nafion membrane towards
methanol, because the length-to-width ratio of the additive is
high [98,103e106]. The methanol permeability of the
determine the benefit brought by the particular formulation of composite membranes that contained 6 wt.% MMT-POPD400-
the material. The comparison of the two membranes perfor- PS was 1.2 106 cm2 S1, 60% of that of pristine Nafion. The
mances is made directly on the corresponding polarization proton conductivity of the composite membranes increased
curves. with added MMT-POPD400-PS. The proton conductivity of the
The corresponding polarization curves are represented in composite membranes generally declined from that of pris-
Fig. 18 for Nafion and for composite membrane of Nafion for tine Nafion membrane as the inorganic filler content
the two working conditions. In the optimal operation condi- increased [61,98,103e107]. However, the cause may involve
tions, the humidity level in the cell is good. As seen in Fig. 18, various mechanisms of proton transportation. We suggest
the use of Nafion enables to reach about 600 mA cm2 of two mechanisms that improve proton transportation in the
electronic current produced at 0.6 V, while the use of composite membrane: (1) hopping mechanism is promoted by
a Nafion/Lp-g membrane leads to the production of about the intercalating agent (POPD400-PS) with a long chain and (2)
720 mA cm2 at the same voltage. This difference corresponds the vehicle mechanism is accelerated on the surface of the
to a 20% improvement in power density (430 mW cm2 versus introduced clay network oxide [108]. Three to five weight
360 mW cm2) [100]. The improvement of the power density percent MMT-POPD400-PS is tentatively concluded to be the
produced in the cell with the hybrid Nafion is then inter- optimum level of inorganic filler in the composite electrolyte
esting even for the optimal operation conditions of Nafion. membrane for DMFCs [109].
The difficult operation conditions, corresponding to higher Fig. 20 plots cell potential versus current density and power
temperature (120 C instead of 80 C), dilute cathode gas (air density versus current density of the DMFC membrane elec-
instead of O2) and lower gas pressure (3 bar instead of 4 bar), trode assembly (MEA) with an MMT-POPD400-PS and pristine
induce a drastic dehydration effect in the cell. Then, the Nafion composite membrane. Indeed, the suppression of the
sensitivity of the membrane to humidity can easily be methanol crossover results in higher OCV at lower current
observed with this procedure. In those conditions, a Nafion
membrane can deliver 390 mA cm2 of current at 0.6V while
Fig. 18 e Polarization curves for Nafion-115 (B) and

hybrid membranes (Nafion/Lp-g (90/10, w/w)dsymbol Fig. 19 e The proton conductivity (B) and methanol
(-)) under good operation conditions (80 C, H2/O2, 4 bar) permeability (-) of the pristine Nafion and composite
and hard operation conditions (120 C, H2/air, 3 bar) membranes fabricated with different amounts of MMT-
(reprinted with permission from [100]). POPD400-PS (reprinted with permission from [109]).
As a result, The Nafion/MMT-POPD400- PS composite

membranes exhibit a higher selectivity than pristine Nafion,
perhaps because of the increased proton conductivity and
decreased methanol permeability of the composite
membranes. The high selectivity reveals that the composite
membrane is suited to DMFC applications. The combination of
these effects substantially improved the properties of
Nafion/MMT-POPD400-PS composite membranes, which are
appropriate for DMFC applications [109].
6.3. Modified Nafion membrane with types of zeolites
Zeolites are a class of crystalline aluminosilicates, which form

a framework of SiO2 and AlO4 tetrahedra and contain
exchangeable cations on the extra-framework to maintain the
electrical neutrality. The ion exchange of cations often
Fig. 20 e Polarization curves for the MEA made with changes the chemical and physical properties of zeolites, such
pristine Nafion membrane and composite membranes as a thermostability, adsorption capacity, amount and
operated at 313 K (reprinted with permission from [109]). strength of acid site [111]. Therefore, zeolites can potentially
be a candidate for novel ion-conducting materials, since the
cation is mobile in the framework structure, which has been
densities [110]. The composite membrane with 5 wt.% MMT- materialized as ion exchangers in an aqueous phase [112].
POPD400-PS outperformed pristine Nafion. The current However, membranes made of pure zeolites are plagued by
densities measured with composite membranes that con- defects, such as cracks or gaps and exhibit poor mechanical
tained 0, 3, 5 and 6 wt.% MMT-POPD400-PS, were 51 and 64, 95 properties, such as brittleness and fragility [113]. Moreover,
and 88 mA cm2, respectively, at a potential of 0.2V. Mean- these membranes are expensive to manufacture [114].
while, the membrane with 6 wt.% inorganic loading does not A zeoliteepolymer composite membrane represents
outperform that with 5 wt.%, perhaps because the proton a compromise between the nonselective polymeric films and
conductivity at 6 wt.% inorganic loading is reduced, as plotted the brittle zeolite film. The composite combines the highly
in Fig. 19. However, all of the composite membranes that selective solid state proton conductor with the flexibility of
contain MMT-POPD400-PS outperform pristine Nafion at a polymer matrix [115]. For zeolites at 100% relative humidity,
high current densities [109]. the higher temperature of the higher ion conductivity is up to
Fig. 21 e SEM micrographs of the surface zeolite powders: (a) NaA zeolite, (b) Mordenite, (c) ETS-10 and (d) Umbite (reprinted
with permission from [119]).
Fig. 22 e Proton conductivity versus temperature curves for

all of the samples are plotted for R.H. 100% up to 150 C
(reprinted with permission from [119]).
100 C [116]. Above this value, conductivity in zeolites is

strongly influenced by the amount of adsorbed water
[117e118]. SEM micrographs of the zeolite powder used in the Fig. 23 e HD and methanol ions passing way in the
preparation of the polymer - zeolite composite membranes polymer matrix of the filled membranes with zeolite
are presented in Fig. 21. It can be seen that umbite shows (reprinted with permission from [115]).
a different morphology compared with the other ones. The
spherical geometry can be a drawback because the higher
inter-grain void volume and the lower contact surface than through both the dispersed phase and the polymer matrix. If
the other three zeolites that are prism in shape [119]. the dispersed material is impermeable to methanol, protons
In Fig. 22, conductivity versus temperature for all the will have a more direct and shorter path compared to meth-
samples are plotted for RH 100% up to 150 C. Although lower anol. This membrane could enhance the proton selectivity,
values than Nafion were measured, zeoliteepolymer while reducing methanol crossover. Choice of zeolites as the
composites show a more stable performance at high dispersed membrane phase because their regular pore size
temperatures. Ionic conductivity in solids, zeolites included, promises selective separations based on molecular size and
increases with temperature mainly due to higher ion mobility shape (Coronas and Santamaria, 1999). For example in the
and the bigger quantity of adsorbed water. From 100 C, Nafion case of including a mordenite as the zeolite phase and poly-
drops sharply due to the dehydration process. However, NaA vinyl alcohol (PVA) [120] as the polymer, the hydrophilic
zeolite continues increasing conductivity up to 120 C and nature of both PVA and mordenite prevents the formation of
ETS-10 up to 150 C. Moreover, ETS-10 was subjected at several nonselective voids at the polymer-zeolite interface, while also
warningecooling cycles and did not present hysteresis. exploiting the selectivity of the mordenite. Mordenite is one of
Umbite and Mordenite presented the worst results. Umbite the most stable zeolites in existence (Breck, 1974), and is one
behavior can be due to the morphology as it was seen in SEM of the most highly conducting (103 s/cm) and widely studied
micrographics. Mordenite conductivity was 1.86 105 S cm1 (Knudsen et al., 1988). In the best case, a PVA membrane
at room temperature and 100% R.H. after 24 h in the cell. This containing 60% mordenite by volume demonstrates a mere
value is similar to that obtained by Hibino et al. [111], two-fold increase in selectivity over Nafion. The substantial
1.07 105 S cm1, for the same conditions [119]. decrease in methanol permeability is not offset by the
Electrochemical selectivity (b), defined in Eq. (2) as the decrease in proton conductivity, yielding better selectivity.
proton conductivity divided by the methanol permeability, The most successful result by far is a PVA membrane con-
allows a comparison of the new membranes with each other taining 50% mordenite by volume. Compared to Nafion, this
and with the Nafion benchmark. membrane demonstrates a 200-fold decrease in methanol
s permeability, with only an order of magnitude decrease in
b¼ (2) proton conductivity, which results in w20-fold increase in
P
selectivity [115].
In the past, this goal was taken to imply high proton
conductivity. However, while the current standard fuel cell
membrane Nafion 117 has a very high conductivity, its selec- 6.4. Modified Nafion membrane with conductive
tivity is compromised due to high methanol permeability. If polymers such as polyaniline
another membrane had higher selectivity, but lower conduc-
tivity, the membrane conductance could be kept large by Several research groups have used various methods and
making the membrane thin [115]. As shown in Fig. 23, the strategies to decrease methanol crossover, e.g., operating
components are chosen so that protons are transported a cell with relatively low methanol concentrations <2 M [121]
condensation of TEOS as described elsewhere [134e136] to

yield a silica content of 3.8 wt.%. In this technique, silica
nanoparticles were embedded into the hydrophilic clusters of
the perflourinated membrane by means of a solegel process.
Nafion 117 and the Nafion/silica composite membranes were
modified with polyaniline by a redox polymerization process
[137]. The membranes are hereinafter identified as Nafion/
PAni-X or Nafion/silica/PAni-X, where PAni stands for poly-
aniline and X represents the aniline solution immersion
times. Polyaniline modification was evident because of the
dark-green colouration of the Emeraldine salt due to the
protonation of polyaniline by the sulfonic groups of Nafion
[138].
The results obtained from methanol/water uptake experi-
ments are given in Fig. 24. All the uptake results indicate that
Fig. 24 e Solvent uptake of Nafion and Nafion/PANi the polyaniline layer on the Nafion surface reduces water
composite membranes (reprinted with permission from absorption (less hydrophilic), which prevents the methanol
[139]). from diffusing into the bulk of the Nafion structure. For Nafion/
silica membranes, the data suggest that the silica nano-
particles provide structural stability to Nafion, but no further
and limiting temperatures below 70 C. Another strategy is to benefits. The XRD patterns of Nafion measured dry and after
carry out structural modifications of Nafion membranes. immersion in methanol/water solutions of different methanol
These includes: (1) grafting of styrene monomer [122]; (2) pore- concentrations are presented in Fig. 25. These show that the
filling type PEM using Teflon as a substrate and acrylic acid- crystallinity of the Nafion Teflon backbone drops dramatically
vinyl sulfonic acid copolymer as the proton conductive matrix when immersed in methanol solution, and the backbone
[123]; (3) modification with polyvinyl alcohol [124] or poly- character peak almost disappears in 50 vol. % methanol solu-
pyrrole [125]; (4) silicon dioxideeNafion composites [126]. All tions. The XRD data give strong evidence to suggest that the low
these studies have achieved a considerable reduction of hydrophilic polyaniline layer provides a barrier on the Nafion
methanol permeation, but at the same time an undesirable and therefore prevents to large degree methanol diffusion
decrease in proton conductivity. Tan and Belenger [127e128], through the membrane whilst maintaining the integrity and
carried out extensive characterization of composite Nafion/ crystalline structure of the Nafion. These results suggest that
polyaniline films for proton conduction. The results showed the polyaniline modification layer restrains Nafion swelling,
that protonic transport is dependent on the amount of poly- and thus reduces methanol uptake [139].
aniline disrupting the ionic pathways with potential applica- The influence of temperature on proton conductivity for all
tion in fuel cell technology. Polyaniline is a well-known membranes tested in a fully hydrated condition is given in
intrinsically conductive polymer. It can be easily obtained by Fig. 26. Both polyaniline modified membranes show conduc-
chemical or electrochemical oxidation of the monomer tivities 3e5 folds below that of Nafion. The low the proton
aniline [129e131]. The electrical conduction in polyaniline conductivity values are probably the result of two effects.
may be ionic (charge carriers are ions), electronic (charge First, the polyaniline molecules have a strong interaction
carriers are electrons) or mixed [132e133]. The Nafion/silica (chemical bond) with Nafion, via the positive charged imine/
and sPEEK/silica membranes were synthesized by in situ amine groups and the negatively charged sulfonic groups
Fig. 25 e X-ray diffraction patterns (XRD) of (a) Nafion and (b) Nafion/PANi-5 composite membranes measured after
immersion in different methanol concentrations (reprinted with permission from [139]).
proton transport via the Grotthus mechanism and the global

proton conductivity of composite membrane comes down.
Membrane modification with polyaniline caused to decrease
the proton conductivity of the composite membrane about
3e5 fold lower than that of Nafion. The polyaniline modifica-
tion also allows the membrane to become less hydrophilic,
which explains the lower proton conductivity. On a positive
note, methanol crossover is reduced by over two orders of
magnitude, as verified by crossover limiting current analysis.
Thus, in general, modification of the Nafion membranes
caused to improve the selectivity and performance of the
direct methanol fuel cells [139].
6.5. Modified Nafion blend membrane with sPEEK and

polyacrylonitrile (PAN)
Fig. 26 e Proton conductivity of Nafion and Nafion/PANi
composite membranes measured at different temperatures
Poly (ether ether ketone) (ICI: Vitrex PEEK) is a semi-crystal-
(reprinted with permission from [139]).
line polymer possessing excellent thermal stability, chemical
resistance, and mechanical properties. The electroosmotic
[140e142], thus interfering with essential elements of the drag coefficient and solvent (water and methanol) crossover of
proton transport mechanisms. The second cause for the sulfonated PEEK (sPEEK) are lower than that of Nafion.
reduction of proton conductivity of Nafion is the lower However, the general problem of sPEEK membranes is that
hydrophilic properties of the polyaniline layer. The polyani- they begin to swell too easily in operating temperatures
line layers therefore restrict not only methanol diffusion but between 60 and 80 C and thus lose their mechanical stability.
also water permeability into the membrane and thereby result Different strategies is considered for swelling reduction that
in low conductivities [139]. the most important cases can be mentioned blending of
The polarization curves in 2 M methanol solution and air sPEEKs with basic N-containing polymers such as PBI to
operation mode are shown in Fig. 27. The results of the curves generate ionic crosslinking via acidebase interaction [40]. On
show that polyaniline modified membranes have higher the other hand, there are several promising investigations
open-circuit voltage (OCV) values but lower polarization using blended membranes involving polyacrylonitrile (PAN)
curves compared with Nafion-117. The results strongly for fuel cells. Carter et al. reported that the addition of linear
suggest that the large interfacial resistance value in polyani- PAN into sulfonated polyphosphazene has several advantages
line modified Nafion membranes provides the possible reason including: (1) improved mechanical properties of the blended
for low performance output. These observations clearly justify membrane, (2) easier membrane electrode assembly (MEA)
the findings discussed above in that polyaniline adds lower fabrication during hot-pressing of the electrodes, and (3) a low
hydrophilic properties to the composite membrane whilst methanol crossover due to the very low permeability of PAN to
also having a strong interaction with the sulfonic groups. As water and methanol [143]. The PAN addition allows the
a result, the interaction of aniline with the sulfonic groups of fabrication of polymeric blend membranes with superior
Nafion causes a restriction of protonic pathways. In addition, mechanical properties as well as low methanol permeability
the polyaniline hydrophilicity is low, and further impedes [144]. Table 5 showed the effect of PAN content on membrane
swelling ratios. The incorporation of thermally treated PAN
reduces the swelling of membranes in water, as the swelling
Table 5 e IEC and swell ratios of composite membranes

from sPEEK and commercial PAN (MW [ 150,000).
Membranesa IEC Swell ratio (%)
(m mol/gr)
sPEEK without 2.10 Dissolved in

heat treatment [145] water
100:0 1.78 8.1
99:1 1.76 4.4
98:2 1.74 3.8
95:5 1.67 2.5
90:10 1.58 2.1
80:20 1.37 0.0
Fig. 27 e Polarization curves of DMFCS with Nafion or 70:30 1.22 0.0
Nafion/PANi composite membranes at 20 C (reprinted
a Weight ratio of sPEEK against PAN.
with permission from [139]).
Table 6 e Methanol permeability of Nafion L117 and

composite membranes from sPEEK and commercial PAN
(MW [ 150,000).
Membranesa Properties
Thickness Slope Methanol permeability

(cm) (105 (107 cm2 s1)
s1)
Nafion 117 0.022 1.444 27.4

[145]
100:0 0.0027 4.554 10.6
95:5 0.0035 1.802 5.4
80:20 0.0047 1.117 4.5
70:30 0.0047 0.419 1.7
Fig. 28 e Proton conductivity versus PAN (MW [ 150,000) a Weight ratio of sPEEK against PAN.
in composite membranes (reprinted with permission
from [145]).
SEM images in Fig. 29 showed the microstructure change of
these blended membranes. The size of the PAN regions
ratio decreased with increasing of PAN content in blended increased with the content of PAN below 10%. At 20e30%, the
membranes [145]. phase inversion was clearly observed through the elemental
In Fig. 28, proton conductivity of blended membranes first distribution maps. In the maps, the bright white region cor-
increased with the addition of PAN. As shown in Fig. 28, above 5%, responded to the sulfur/oxygen rich phase, i.e. sPEEK. At 20
the conductivities decreased quickly. This could be due to larger and 30%, the bright white region was isolated by the darker
PAN regions in the blended membranes blocking the proton PAN phase. Methanol permeability of these membranes are
transport. When PAN was 20 or 30%, there was a phase inversion listed in Table 6 and compared to Nafion-117. The sPEEK
between PAN and sPEEK, and PAN became the continuous phase. membrane without PAN displayed methanol permeability of
Therefore, proton conductivity would be further reduced. The 39% of Nafion-117. The blended membranes with thermally
dilution of sPEEK in blended membranes might be another reason treated PAN resulted in lower methanol permeability because
for the drop of proton conductivities [145]. the microsized dispersion of rigid ladder PAN chains
Fig. 29 e (a) SEM of composite membranes with 1, 2 and 5% PAN (MW [ 150,000). (b) Elemental distribution maps through
SEM of composite membranes with 10, 20 and 30% PAN (MW [ 150,000) (reprinted with permission from [145]).
Table 7 e Methanol permeability of composite membranes from sPEEK and PAN with different MW (sPEEK:PAN [ 80:20).
Membranesa Properties
Thickness Slope Methanol permeability

(cm) (105 s1) (107 cm2 s1)
3500 [145] 0.0068 0.114 0.67

7500 0.01 0.109 0.94
35,000 0.0075 0.195 1.26
150,000 0.0047 1.117 4.5
a MW of PAN.
prevented methanol from transferring through the of the cross-section of Cs2.5H0.5PW12O40 -SiO2/Nafion
membrane. At 5 wt.% PAN, the methanol permeability was membrane. It can be seen that the Si and Cs elements were
only 20% of that of Nafion-117 while the proton conductivity dispersed homogeneously along the cross-section of the
was similar. Hence, methanol permeability and hot water membrane (Fig. 30). It means that the Cs2.5H0.5PW12O40/SiO2
swelling of blended membranes were significantly reduced particles were uniformly dispersed in the membrane [156].
while proton conductivity was increased to be competitive to Fig. 31 shows the polarization curves of cells with
Nafion-117. These properties would make it a candidate as Cs2.5H0.5PW12O40-SiO2/Nafion e proton exchange membrane
a possible low cost alternative to Nafion-117. and Nafion NRE-212 membrane operated under fully
As shown in Table 7 we found that the methanol perme- humidified condition with the cell temperature at 60 and
ability increased with PAN molecular weight (MW). The 80 C, respectively. The cell performance with the
possible reason is that there are more molecular chains in Cs2.5H0.5PW12O40-SiO2/Nafion was better than that with the
PAN with lower MW than in PAN with higher MW at the same NRE-212. Fig. 31 shows the effect of Cs2.5H0.5PW12O40/SiO2
weight. Thus, the amount of ladder chains formed during heat particles addition into Nafion matrix in composite membrane
treatment is greater and occupies larger space, which results than the pristine Nafion. From the Tafel slope of the polari-
in a stronger effect of blocking methanol [145]. zation curves, the conductivity of the composite membrane
was greatly improved by the addition of the Cs2.5H0.5PW12O40/
6.6. Modified Nafion membrane with proton conductive SiO2 particles [156]. Fig. 32 shows the polarization curves of H2/
materials (heteropolyacids) O2 fuel cells with Cs2.5H0.5PW12O40-SiO2/Nafion and Nafion
NRE-212 membrane operated under fully humidified and un-
The proton exchange membranes (PEMs) currently used in humidified conditions at 60 C. The fuel cell performance were
fuel cells, such as Nafion membranes, are highly proton decreased when the fuel cell were operated with dry gas
conductive and chemically and physically stable at moderate compared to that operated with fully humidified gas. The
temperatures [40,147]. However, these preferable properties decrease of the cell performance with Cs2.5H0.5PW12O40-SiO2/
are deteriorated above their glass transition temperature (Tg) Nafion is slighter than that with NRE-212 membrane. The cell
ca. 110 C. Additionally, they require adding water to humidify performance under dry gas conditions was obviously
the fuel and oxygen in order to maintain the membrane’s improved which is because of the addition of
proton conductivity. The humidifier will make the whole Cs2.5H0.5PW12O40/SiO2 as hygroscopic material dramatically
system complex and large. Therefore these needs promote the increased the water content in the membrane, and increase
research and development self-humidifying membranes for the proton conductivity as well. Meanwhile, the SiO2 particles
PEMFC [3]. Up to now, many materials such as Pt, metal play an important role in maintenance the water produced in
oxides, Pt/SiO2, hetero-poly-acid, and ZrHSO4 were highly the self-humidifying membrane in situ at high temperature
dispersed into Nafion or sulfonated poly (ether ether ketone) due to their hygroscopic property and to release the water
(sPEEK) resin to fabricate self-humidifying membranes once the proton exchange membrane needs it. The new self-
[75,148e152]. Heteropolyacids (HPA) with Keggin anion struc- humidifying membrane was considered to be a very prom-
tures have received the most attention due to their simple ising membrane for PEM fuel cells [156].
preparation and strong acidity in development of composite
membranes for PEMFCs [153,81,58]. But the major factor limit 6.7. Modified Nafion membrane with polymeric
the performance of Nafion/HPA composite membranes is the acidebase complexes
extremely high solubility of the HPA additive in aqueous
media [81,155]. Cs2.5H0.5PW12O40 is insoluble in water and The typical membranes (DuPont’s Nafion series or other per-
organic solvents and has micro and mesopores with a high fluorosulfonic acid membranes) only perform properly below
surface area. The Cs2.5H0.5PW12O40/SiO2 particles which were 100 C because that the membranes dehydrate at higher
expected to increase the proton conductivity of the membrane temperature and the proton conductivity decays sharply
and catalyze the recombination of H2 and O2. The single cell [157e158]. Therefore, many different approaches have been
(electrode area ¼ 5 cm2) with these proton exchange carried out to develop novel PEM membranes for high
membranes exhibited better performance than that with the temperature operation. The novel composite membrane was
commercial Nafion (NRE-212) membrane under fully synthesized according to the acidebase polymer complexes
humidified and dry conditions. Fig. 30 shows the EDX results concept developed by Kerres et al. [157], which consists of
Fig. 30 e EDX analysis result of Cs2.5H0.5PW12O40-SiO2/Nafion membrane: Si element (top left); S element (top right); Cs
element (bottom left); the region used for the EDX analysis (bottom right) (modified with permission from [156]).
mixing polymeric acid with polymer bearing basic sites. study was shown in Fig. 33. The sulfonic acid groups of Nafion
Phosphoric acid-doped polybenzimidazole (H3PO4/PBI) and interact with the N-base of PBI either by formation of hydrogen
H3PO4/PBI/silica nanocomposite membranes have been bridges or by protonation of the basic N-sites. In the polymer
investigated intensively and used more successfully [160e161] complex, Nafion not only plays as a crosslinking agent but also
in high temperature PEMFC because of the excellent thermo- improves the chemical stability of the polymer matrix. The
chemical stability, lower gas permeability [162] and mechan- transformation of Nafion resin from Hþ form to Naþ form was
ical property of PBI, and good proton conductivity after doped the most important step for the composite membrane fabri-
with H3PO4 at elevated temperature (200 C) [163,164]. The cation. NafioneNa in the NafionePBI composite membrane
formation of acidebase polymer complex presented in this was protonated and then interacted with PBI component
Fig. 31 e Fuel cell performance of the Cs2.5H0.5PW12O40- Fig. 32 e Fuel cell performance of the Cs2.5H0.5PW12O40-
SiO2/Nafion self-humidifying membrane and NRE-212 at 60 SiO2/Nafion self-humidifying membrane and NRE-212 at
and 80 C under fully humidified conditions (modified with 60 C under fully humidified and un-humidified conditions
permission from [156]). (modified with permission from [156]).
conductivity, which was a result of the increase in perme-

ability of membrane [166].
The performance at constant current (700 mA cm2) and
the open current voltage (OCV) of the H2/O2 single cell with the
composite membrane were shown in Fig. 35(a), as a contrast,
those of the H2/O2 single cell with the H3PO4/PBI membrane
were shown in Fig. 35(b). Comparing the steady performance
curves of the two single cells, it is definite that the stability and
durability of the H3PO4/NafionePBI composite membrane is
much higher than that of the H3PO4/PBI membrane in high
temperature PEMFCs. The results of proton conductivity
investigations of H3PO4/NafionePBI composite membranes
indicated that the introduction of Nafion had not reduced the
proton conductivity of the H3PO4/PBI membrane. The results
of the mechanical tensile properties (Not shown in here) can
Fig. 33 e Acidebase complex formation mechanism
be seen that even after the 760 h durability test, the composite
between the sulfonic acid group of Nafion and the
membrane hold still better mechanical strength than the
imidazole nitrogen of PBI (reprinted with permission
500 h-tested H3PO4/PBI membrane. All above results implied
from [165]).
the H3PO4/NafionePBI composite membrane also had more
mechanically robust than the H3PO4/PBI membrane and
therefore the novel H3PO4/NafionePBI composite membrane
formed NafionePBI crosslinked complex. In this step, the
is a better candidate in high temperature PEMFC for achieving
composite membrane was also doped with H3PO4 [165].
longer cell lifetime [165].
The acid doping level of H3PO4/NafionePBI composite
As mentioned in the previous sections, Nafion as a fluo-
membrane was lower about 8% than that of the H3PO4/PBI
rinated proton exchange membrane, the conventional proton
membrane, which accorded with the molar ratio (about 7%) of
conducting polymer electrolyte membrane is expensive,
eSO3H to PBI repeat unit. This result indicated that the reac-
mechanically unstable at temperatures above 100 C, and
tion, as shown in Fig. 33, occurred certainly between the
conductive only when soaked in water, which limits fuel cell
sulfonic acid group of Nafion and the imidazole nitrogen of
operating temperatures to 80 C, which in turn results in lower
PBI. The polarization curves of the H2/O2 single cell with the
fuel cell performance due to slower electrode kinetics and low
composite membrane were shown in Fig. 34. It is obvious that
CO tolerance [71]. Thus, the development of membranes
the performance of the single cell reached its maximum at
which are mechanically and chemically stable at higher
60 h, and then degraded a lot during the following test, for
temperatures (above 100 C) is an active area of research for
example, the voltage of the single cell at 1000 mA cm2 fell
producing economical fuel cells. Similarly, the non-fluori-
from 0.55 V at 60 h to 0.45 V, at 540 h, but it increased a little
nated proton exchange membranes such as aliphatic or
again at 720 h. After about 60 h, the single cell reached its
aromatic structures as polymeric backbone in membranes
maximum performance. The degradation in the single cell
(e.g. sPEEK, sPES, sPEI,.) has been studied and investigated.
performance during the test was results of the degradation of
The modification of these polymers with wide range of the
the electrocatalyst and membrane [165]. The little increase at
fillers such as MO2 (e.g. SiO2, TiO2, ZrO2, .) [167e174], zirco-
720 h was due to the increase in the membrane proton
nium phosphate [175e177,155,66], phosphotungestic acid
[178], boron phosphate [179], phenolic resins [180e181],
organically modified silicates (clays) [73,182e183], silane
based fillers [184] and zeolites [1] have been done for the
preparation of the non-fluorinated based composite proton
exchange membranes in fuel cell applications. Composite
membranes are shown the promising characteristics such as
lower H2, O2 and methanol crossover, good thermal stability,
increased proton conductivity, and higher water uptake. In
this section, the types of the modified non-fluorinated proton
exchange membranes in the PEM fuel cells are investigated.
7. Measurement and investigation methods

of the proton exchange membranes properties
In this section, methods of evaluation and characterization of

Fig. 34 e The polarization curves of the H3PO4/NafionePBI proton exchange membrane includes proton conductivity
composite membrane single cell at different test time measurement, ion exchange capacity (IEC), water uptake, ion
(reprinted with permission from [166]). exchange capacity, methanol permeability, gas permeability,
Fig. 35 e The steady state performance and open current voltage (OCV) variations of single cell with H3PO4/NafionePBI
composite membrane (a) and H3PO4/PBI membrane (b) during life test (reprinted with permission from [165]).
durability, thermal stability and fuel cell performance of the

A Ea
membrane were presented. s¼ exp (4)
T RT
A is a constant proportional to the number of charge carriers,

7.1. Membrane proton conductivity measurement with Ea is the activation energy and R is the ideal gas constant.
electrochemical impedance spectroscopy (EIS) Above glass transition temperature (Tg), the conductivity
usually follows the VTF formula [18,187]:

Proton conductivity of the proton exchange membranes A B
s ¼ pffiffiffiexp (5)
measure by the electrochemical impedance spectroscopy T T T0
method over the frequency range of 10 Hze10 MHz with
B is a pseudo activation energy related to the segmental
50e500 mV oscillating voltage in the particular conductivity
motions of the polymer and T0 is called equilibrium glass
cell. The proton conductivity of the membrane was measured
transition temperature. The VTF behavior describes conduc-
by AC impedance technique using a Solartron impedance-
tivity in polymers where the segmental motions contribute to
gain phase analyzer. Membrane sample was equilibrated in
the proton transport. As a consequence, amorphous polymers
deionized water for 24 h at room temperature prior to testing.
exhibit a higher conductivity above glass transition tempera-
Then, the surface water was removed, and the swollen
ture than below. Typically, three distinct conductivity
membrane was rapidly placed between two stainless-steel
behaviors can be observed in polymer electrolytes:
electrodes in a conductivity cell (this cell is used to host the
sample). The water content of the membrane was assumed to
1. VTF behavior is observed above glass transition tempera-
remain constant during the short period of time required for
ture (Tg) of the polymers.
the measurement. All impedance measurements were per-
2. Arrhenius-type behavior at low temperatures and VTF at
formed at room temperature and relative humidity 100%. The
high temperatures.
membrane resistance (R) was obtained from the intercept of
3. Arrhenius-type behavior throughout the whole tempera-
the impedance curve with the real-axis at the high-frequency
ture range with a clear decrease of the activation energy
end (obtained from a Niquyist plot). Then, proton conductivity
around Tg. This is the behavior of polymers with an
of membrane, s (Siemens per centimeter (S/cm)), was calcu-
extremely rigid structure; thus, the contribution of
lated according to Eq. (3), where s is defined as the reciprocal
segmental motions is low [18].
of R and L and S are the thickness and area of the membrane,
respectively [185]. 7.2. Water uptake measurement of the proton exchange
L membranes
s¼ (3)
R$S
High temperature conductivity measurements were con- The performance of a membrane is dependent on proton
ducted in water vapor. The conductivity cell was placed above conductivity, which in turn often depends on its water content.
liquid water in the head space of a sealed vessel. This exper- High proton conductivity is supported by high level of water
imental setup allowed the membrane to equilibrate with uptake; at the same time, it is also a sign of low-dimensional
saturated water vapor at the desired temperature. The stability as water influences the polymer microstructure and
temperature was controlled by a wrap-around resistance mechanical properties. Since water is also known to assist the
heater and feedback temperature controller [185]. mass transport of methanol and oxygen through the
Ionic conduction in a solid material is due to a thermally membrane, the water uptake measurements could serve as
activated process. Proton conductivity obeys either a simple a quantitative measure of membrane performance for DMFC
Arrhenius law or a Vogel-Tamman-Fulcher (VTF) equation. At application as well. Gravimetric technique has been widely
temperatures below the glass transition temperature, Tg, the used for this purpose. Water uptake measurements due to
conductivity obeys generally an Arrhenius-type law [186]: gravimetric techniques are generally done by double weighing.
‘Wet’ weights (Wwet) of the membranes are first measured after conductivity and water uptake both rely heavily on the
equilibrating with water at different temperatures or upon concentration of ion conducting units (most commonly
exposure to water vapor at various pressures. The membrane sulfonic acid) in the polymer membrane. The ion content is
samples are then dried at a temperature above the boiling point characterized by the mass of dry membrane per molar equiv-
of water for a particular period of time and their ‘Dry’ weights alents of ion conductor and is expressed as EW with units of
(Wdry) measured. The total water content (Wuptake%) is deter- grams of polymer per equivalent or as IEC with units of milli-
mined from the difference between the wet and the dry mass of equivalents per gram (mequiv. g1 or mmol g1) of polymer.
the membranes as follows [1]: Varying the ion content of the membrane can control both its
water uptake and conductivity. While it is desirable to maxi-
Wwet Wdry
Water Uptake ¼ 100 (6) mize the conductivity of the membrane by increasing its ion
Wdry
content (decreasing equivalent weight), other physical prop-
If tw and td are the thicknesses of wet and dry membranes, erties must be considered. Too many ionic groups will cause
respectively, the membrane swelling ratio may be calculated as: the membrane to swell excessively with water, which
tw td compromises mechanical integrity and durability.
Swelling Ratio ¼ 100 (7)
td IEC of membranes is determined by titration at room
temperature. The membranes in the acidic forms (Hþ) are first
The membrane water content parameter, ‘l’, the number of
converted to the sodium forms by immersing the membranes
moles of water per mole of acidic group can be calculated:
in NaCl solutions to exchange the Hþ ions for Naþ ions by
NH2 O Wwet Wdry
l¼ ;l ¼ (8) following equation:
NSO3 18 IEC Wdry
R H þ Naþ /R Na þ Hþ
IEC is the ion exchange capacity of the membrane. Water
uptake curves are generally represented as number of water the exchanged Hþ ions within the solutions are titrated with
molecules per sulfonic acid group ‘l’ versus thermodynamic 0.01 N NaOH solutions. IEC values may be calculated from the
water activity or relative humidity, which is the ratio of water titration result using the formula [188]:
partial pressure and saturation partial pressure of water
Consumed ml of NaOH Molarity of NaOH
(Fig. 36). The factors that affect the extent of the water uptake IEC ¼ meguiv: g1
Weight dried membrane
of a membrane are temperature, ion-exchange capacity, and
(9)
pretreatment of membrane, the physical state of absorbing
water, whether it is in liquid or vapor phase, and the elastic
modulus of the membrane. A major objective in the nano- 7.4. Methanol permeability measurement through the
composite and hybrid membrane research is to determine proton exchange membranes
which chemical attributes of the composite membranes
improve water level at elevated temperature and thereby The study of the methanol mass transport through DMFC
improve PEMFC performance [15]. membranes is very common due to its detrimental effect on
the DMFC performance (reduced coulombic efficiency). Even if
7.3. Ion exchange capacity measurement by using of the not accounting for the anode catalytic reaction and the elec-
titration method troosmotic drag mass transfer, the methanol permeability in
the proton exchange membranes is usually evaluated by
IEC or EW is the measure of relative concentration of acid pervaporation and diffusion cell experiments [189]. For
groups within polymer electrolyte membranes. Proton methanol permeability experiments, most researchers use
Fig. 36 e (a) Equilibrium water uptake or isotherm curve for Nafion at 300 K. The shaded line corresponds to coexistence
with liquid water (l [ 22), (b) Conductivity vs. water-uptake curve at 300 K. The shaded area corresponds to coexistence
with liquid water (l [ 22) (reprinted with permission from [15]).
a side-by-side diffusion cell, where the proton exchange the membrane was dried under vacuum at appropriate
membrane is sandwiched between donor (upstream side) and temperature for more than 1 h. All the measurements were
receptor (downstream side) compartments [16]. The donor performed when the other chamber of the cell was main-
compartment is charged with methanol (w1e2 M) and the tained under vacuum and the measured gas permeability is
concentration of methanol is measured on the downstream regarded as for dry membranes [198].
side as a function of time. The permeability can be determined
from the slope of the early time data [190] where a variety of 7.6. Durability measurement of proton exchange
detection methods have been used, including gas chroma- membranes
tography [191] refractometry [192e194] and FTIR-ATR spec-
troscopy [190,195e197]. Proton exchange membrane fuel cells (PEMFCs) are very
promising as environment-friendly energy supplier.
However, their durability and cost are the key issues that
7.5. Gas permeability measurement through the proton
should be solved for practical applications. Now the research
exchange membranes
emphasis has shifted from improving the initial performance
(“beginning-of-life”) to enhancing fuel cell reliability and
The gas permeability of the membranes was measured by
lifetime and to making fuel cell cost competitive. Proton
means of a two chambers cell as shown in Fig. 37. A sample
exchange membranes (PEMs) are the key components in fuel
membrane was fixed by porous carbon plates with the
cell system, which limit the lifetime of the whole PEMFCs.
membrane edges sealed by Viton (DuPont) gaskets. During
Thus enhancement of the durability of the PEMs is critical to
the measurement, a pressure difference of up to 1 106 Pa was
the lifetime and commercial viability of the PEMFCs. In the
applied to the membrane. The gas pressure of each side of the
last decade, the membrane degradation mechanism studies
membrane was monitored via pressure sensors. The
became the focus of attention. To sum up the recent pub-
temperature was controlled with an oil bath by immersing the
lished reports, the membrane degradations are mainly clas-
cell system in it. For the measurement of the gas permeability
sified as chemical/electrochemical degradation and physical
coefficient, Ƥ, one chamber of the cell was filled with pres-
degradation. As for the former degradation, hydrogen
surized gases while the other was always kept under vacuum.
peroxide and its decomposition intermediate products HO
The gas diffused through the membrane under the driving
and HO2 with strong oxidative characteristics generated
force of pressure. The mole number of the gas, n, passed
during the fuel cell operation have been considered as one of
through the membrane can be calculated from the decreased
the important factors resulting in the membrane degrada-
pressure Pd on one side of the membrane within a certain time
tion. The formation of H2O2 has been confirmed using
(t in s) by using the equation:
a microelectrode in an operating fuel cell [199] and detected
Pd $V in the outlet stream of the cell with Nafion membrane by
n¼ ðmolÞ (10)
R$T Scherer [200].
where R is the gas constant, T the temperature in Kelvin and V Therefore, the membrane durability was evaluated by both
is the volume of the gas chamber. The gas permeability ex situ Fenton test [201] and in situ OCV accelerated test [202].
coefficient, Ƥ, can then be calculated: Membrane samples were respectively immersed in 50 ml
Fenton solution (3 wt.% hydrogen peroxide solution and
n$L 20 ppm Fe2þ). The durability tests were carried out at 80 C for
P¼ mol cm cm2 s1 Pa1 (11)
A$t$Pd
where L (in cm) is the membrane thickness, A (in cm2) the area
of the membrane for gas diffusion and Pd (in Pa) is the pressure
difference through the membrane. Before the measurement,
Fig. 37 e The Cell for gas permeability measurements Fig. 38 e Example of a polarization curve showing the
(reprinted with permission from [198]). typical losses in a polymer-electrolyte fuel cell.
Table 8 e Advantages and disadvantages of the different modifications on Nafion as the perflourinated proton exchange
membranes.
Modification Filler Type Advantages Disadvantages Suitable
Methods Application
Inorganic SiO2, TiO2, ZrO2 - Higher water uptake - Lower proton conductivity PEMFC
Oxides, MO2 [60,67,75e80,90,233] - Better fuel cell performance - Higher membrane cost
(M ¼ TieSieZr) ZrO2/SO24 [86e89] in higher temperatures
- Higher membrane retention
properties
- Lower water Swelling
Clays Laponite (Lp), - Lower methanol crossover - Lower proton conductivity DMFC
Montmorillonite - Lower membrane cost
(MMT) [95e100] - Higher thermal stability
MMT modified with - Higher membrane selectivity
POPD400-PS [109]
Zeolites NaA zeolite, ETS-10, - Higher thermal stability - Poor mechanical properties DMFC
Umbite, Mordenite [111,119] - Stable fuel cell performance in - Higher membrane cost
higher temperatures - Lower proton conductivity
- Lower methanol crossover
- Higher membrane selectivity
Conductive Polyaniline (PANi) - Lower methanol crossover - Lower proton conductivity PEMFC, DMFC
Polymers [127e133,137e138] - Higher membrane selectivity - Lower water uptake
Polypyrrole (PPy) [125] - Lower water swelling
- Higher membrane cost
Polymer sPEEK/PBI [40] - Better mechanical properties - Lower proton conductivity DMFC
Blend Polyacrylonitrile (PAN)/ - Easier MEA fabrication - Higher membrane cost
Membranes Polyphosphazene [143e144] - Lower methanol crossover
sPEEK/PAN [145] - Lower water Swelling
- Improved thermal stability
Proton Pt/SiO2, ZrHSO4 [75,148e152] - Higher proton conductivity - Higher leaching rate PEMFC
Conductive Heteropolyacid (HPA) - Self-humidifying properties - Higher membrane cost
Fillers [58,153e154,81,156] - Better fuel cell performance
in higher temperatures
AcideBase PBI/H3PO4 [159] - Better fuel cell performance - Higher membrane cost PEMFC
Complexes PBI/H3PO4/Silica [160e164] in higher temperatures
Nafion/PBI/H3PO4 [165e166] - Excellent thermo-chemical
stability
- Lower gas permeability
- Better mechanical properties
- Higher proton conductivity
150 h prior to fluorine ion characterization, the Pt wire was Effective strategies should be taken to improve the
immersed into the analyte solution to decompose the residual membrane durability. The passive approach is to improve
hydrogen peroxide, which was to assure of the accurate and polymer stability, such as synthesis of short side chain poly-
reproducible results. mers [206,207], novel hydrocarbon polymer electrolytes [208],
There are two different pathways for the H2O2 generation or composite membrane with PTFE [209]. The active approach
and the free radical species: (1) generating at the cathode due to is to suppress the free radicals attack, such as avoiding H2O2
the electrochemical two-electron reduction of oxygen [203] or formation, destroying H2O2 [210e213] or scavenging the free
the chemical combination of crossover hydrogen and oxygen radicals [214,215]. Trogadas and Ramani [211] prepared Pt/C/
at the cathode (mechanisms 1e4) and (2) generating at the MnO2 hybrid catalyst to minimize the effect of reactive oxygen
anode due to the chemical combination of crossover oxygen species at fuel cell operation condition. Though the hybrid
and hydrogen at the anode (mechanisms 4e7) [204,205]. catalyst can mitigate the generation of hydrogen peroxide, the
activity of the catalysts is poor at the same time. Zhao and
(1) O2 þ 2Hþ þ 2e / H2O2 et al. have been designed a multifunctional catalyst which can
(2) H2O2 þ M2þ / M3þ þ HO þ HO decompose H2O2 and scavenge the free radicals on the
(3) HO þ H2O2 / H2O þ HO2 (hydrogen peroxide radical surfaces of the nanoparticles. Since the scavenging catalyst is
attacks PEM) nonconductive, the cell performance may reduce with the
(4) H2 þ O2 / [O] þ H (on Pt surface) nanoparticles dispersion. Thus, the proton conductivity was
(5) H2 / 2H (via Pt catalyst) also considered. In their study, they have been investigated
(6) H þ O2 (diffused through PEM to anode) / HO2 the effects of the multifunctional catalyst composed of
(7) HO2 þ H / H2O2 (diffused into PEM) a metal oxide with variable valence, cerium nanoparticles,
Table 9 e Advantages and disadvantages of the different modifications on sPEEK as the non-fluorinated proton exchange
membranes.
Modification Methods Filler Type Advantages Disadvantages Suitable
Application
Inorganic SiO2 [225], TiO2 [174], - Higher thermal stability - Lower proton conductivity PEMFC, DMFC
Oxides, MO2 ZrO2 [229] - Lower methanol crossover - Higher membrane cost
(M ¼ TieSieZr) - Higher water uptake
- Lower water Swelling
Clays Silica-SO3H [224] - Higher chemical and - Lower proton conductivity DMFC
Modified nano-silica [225] mechanical stability
Organo modified MMT [226] - Lower methanol crossover
Lapinte, MCM-41 [227] - Lower membrane cost
Modified MMT with - Higher water retention properties
Krytox [232]
Zeolites b-zeolite [221] Modified - Lower methanol crossover - Lower proton conductivity DMFC
zeolite with ZrP [222] - Higher thermal stability - Higher membrane cost
H-type of b-zeolite [223] - Better fuel cell performance in
higher temperatures
- Lower membrane swelling -
Higher mechanical stability
Conductive Polypyrrole (PPy) [228] - Lower methanol crossover - Lower proton conductivity DMFC
Polymers - Better DMFC performance - Higher membrane cost
- Higher thermal stability
Proton Cs2.5H0.5PW12O40 [155] - Higher proton conductivity - - Higher leaching rate PEMFC
Conductive Tungstophosphoric acid [220] Better self-humidifying properties - Higher membrane cost
Fillers phosphatoantimonic acid [230] at high temperatures
Phosphotungestic acid [231] - Chemical and physical stability
- Better fuel cell performance in
higher temperatures
- Higher water uptake - Higher
IEC amounts
and a solid acid, cesium substituted 12-tungstophosphoric, in improvement in thermal degradation temperature as
PEMs [216]. compared with Nafion. A systematic investigation on the
thermal behavior of nanocomposite and hybrid membranes
7.7. Thermal stability of measurement of proton would thus give more insights into their stability at high
exchange membranes temperatures. Although informative, these thermal stability
results can hardly be used to predict the long-term durability
One of the major issues to be addressed in the development of of these membranes. Therefore, the degradation of the proton
proton-conducting nanocomposite and hybrid membranes exchange membranes mostly was investigated by Thermog-
for fuel cell applications is their high temperature stability. It ravimetric analysis (TGA). The primary degradation in degra-
arises primarily due to the fact that the sulfonic acid side dation mechanism of theses membranes is the degradation of
chains in backbone polymers such as Nafion and other polymeric backbone of membranes and the secondary
sulfonated hydrocarbon membranes undergo desulfonation degradation is the degradation of the pendant groups or
with increase in temperature. While the sulfonic acid groups inorganic compounds inside the membranes in higher
in Nafion are stable up to a temperature of 280 C in air temperatures than the primary degradation.
[215,217,218], the degradation temperature of sPEEK is repor-
ted to be in the range of 240e330 C. Desulfonation is in 7.8. MEA testing in fuel cell performance test system
general studied by means of thermogravimetric analysis
(TGA), differential thermal analysis (DTA), Fourier-transform The development of new or modified PEMs with improved
infra-red spectroscopy (FT-IR) and TGA-mass spectrometry characteristics for fuel cell applications requires a quantita-
(MS). In Nafion-based composites this decomposition tive determination of their electrochemical performance
behavior is attributed to the loosening of sulfonic acid groups under relevant fuel cell conditions. The most straightforward
present in the unmodified Nafion membrane [219]. It was also approach for this is to construct a membrane electrode
observed that the temperature at which this decomposition assembly (MEA) and measure the cell parameters in a single
occurs shifts with the nature of inorganic additive within the cell configuration. A membrane electrode assembly includes
pores of Nafion membrane. For example, sharp thermal an anode, a cathode, a membrane disposed between the
degradation of the unmodified Nafion occurs at about 325 C, anode and the cathode and an extended catalyst layer
whereas for Nafion-ZrO2, and Nafion-SiO2 solegel between the membrane and the electrodes. The conversion
membranes, degradation temperature shifts to about 360 C efficiency of MEA depends on many factors including type and
and 470 C, respectively [90]. The TiO2 incorporated thickness of both membrane and gas-diffusion material,
membranes on the other hand are reported to show not much nature of binder used in the electrodes and the binder to
catalyst ratio apart from the operation conditions (tempera- technical challenge is up-scaling single cell performance to
ture, pressure, flow rates, humidification of reactant gases). In multi-cell stacks [197].
addition, the ability to collect data from an operating elec-
trochemical system can be alluring. Single cell testing is
relatively straightforward and operation conditions can be 8. Conclusions
accurately monitored as it allows specific control over
humidity, reactant flow and temperature. Cell performance is Today energy crises and environmental pollution has turned
often described by the polarization curve, i. e., and cell voltage into a great problem for human. For solving these problems
vs. current density. A typical curve is shown in Fig. 38. In vast efforts to replace fossil fuels with other energy sources
general three main polarization losses can be identified: (a) such as its connotation clean fuel have been taken. Fuel cells
activation overpotentials, arising from charge transfer and due to their particular properties are on the verge of creating
other reaction kinetics; (b) ohmic losses, arising from the a vast revolutionary change in the field of electricity. In the
electrical resistances of the cell materials and interfaces and PEM fuel cells, from solid polymer electrolytes which have the
(c) mass transport overpotentials, arising from the limitations ability to transfer of proton, has used as membrane. Ion
of mass transport. At low current densities, the shape of the exchange membranes especially proton exchange membrane,
curve is primarily determined by activation polarization, has an important role in the proton transferring in PEM fuel
which gives it the characteristic logarithmic shape. It plays an cells electrolyte. The desirable ion exchange membrane
important role if the reaction rate on the electrode surface is should be have the higher perm selectivity, suitable proton
restricted by sluggish electrode kinetics. Similar to a chemical conductivity, good mechanical and chemical stability and the
reaction, the electrochemical reaction has to overcome an factors affecting the performance of the suitable proton
activation barrier. This barrier usually depends on the elec- exchange membrane are as follows: sufficient hydration and
trode material (electrocatalyst). When pure hydrogen is used thickness of the membrane. Cation exchange membranes
as fuel, the activation losses of the anode are negligible, were obtained from the attachment of the acidic functional
because the rate of the hydrogen oxidation reaction is orders groups and the anion exchange membranes from the attach-
of magnitude higher than the rate of the cathode reaction. ment of the alkaline functional groups into polymer backbone
Hence, the main source of activation overpotential is the of membrane. The reduction of the membrane thickness
cathode, which means the oxygen reduction. When current caused to increase of the membrane proton conductivity but
density increases, the shape of the curve becomes approxi- also leads to increase the fuel crossover through the
mately linear, reflecting the effect of ohmic losses. This is membrane. The fluorinated membranes due to their high cost,
caused by both the resistance due to the migration of ions low proton conductivity in higher temperatures and higher
within the electrolyte and the resistance due to the flow of methanol crossover caused to develop the composite
electrons. It can be expressed by the product of cell current (I ) membranes. Therefore, the most important goals of modifi-
and the overall cell resistance (R, including electronic, ionic cation of the proton exchange membranes in PEM fuel cells
and contact resistances). When current density is increased can be mentioned such as preparation of the proton exchange
further, the curve begins to bend down due to mass transport membranes with lower cost compared to the fluorinated
overpotentials, which result from limitations in the avail- membranes, the desirable water uptake and retain in the
ability of reactants at the catalyst surfaces. The main source of elevated temperatures, desirable proton conductivity in the
losses is the cathode side again, because the diffusivity of higher temperatures, the lower extent of the reactant gaseous
oxygen is significantly lower than that of hydrogen, due to the and methanol crossover through the membrane, improved
larger molecular size of oxygen. thermal stability, higher mechanical and chemical strength
Fuel cell efficiency on the other hand is directly propor- and also creation of the self-humidity of the membranes in
tional to the power density (in W cm2), which can be linked elevated temperatures. For example, the introduction of the
directly to the chemistry of the polymer membrane. Higher metallic oxides such as MO2 into polymer matrix of the proton
achievable power density directly translates to smaller, thus exchange membrane caused to increase the water uptake and
less expensive fuel cells. Thus, a swift comparison of the retention property and then increase the proton conductivity
obtained data against those obtained with unmodified of membrane in elevated temperatures which this increase in
membranes will provide useful information on the influence the water uptake is related with the acidity of these oxides.
of inorganic phase on the nanocomposite efficiency. Their The clays modified with sulfonic acid groups caused to
effectiveness as a catalyst binder may be evident from an increase the membrane IEC and then the proton conductivity
investigation on the interfacial effects of membrane on elec- and membrane performance increases in fuel cells at elevated
trodes and catalysts. In the case of Class I membranes inten- temperatures. Although the polymer-zeolite composite
ded for high temperature operations, apart from IeV membranes have the lower values of proton conductivity than
measurements, the methanol crossover flux vs. methanol Nafion, but polymer-zeolite composites show a more stable
feed concentration can be collected; the suitability of the performance at high temperatures. Also, the lower extent of
membrane for DMFC applications may be accessed from these the methanol permeability of the polymer-zeolite composite
data. The long time stability of the membranes against membranes with their lower proton conductivities caused to
different operating conditions may also be studied. In short, increase their selectivity in direct methanol fuel cell applica-
membrane electrode assembly (MEA) testing will be of great tions. The incorporation of the heteropolyacids into polymer
advantage to fine tune the hybrid membrane properties in matrix of membranes not only caused to increase the
order to give them commercial viability. However, a major composite proton conductivity, but also due to retention
properties of the heteropolyacids, the composite membranes Fundamental scientific aspects. J Power Sourc 2001;102:
have self-humidity properties in the elevated temperatures. 242e52.
Tables 8 and 9 summarize the advantages and disadvantages [10] Smitha B, Sridhar S, Khan AA. Solid polymer electrolyte
membranes for fuel cell applications - a review. J Membr Sci
of the different modifications on the perflourinated and non-
2005;259:10e26.
fluorinated proton exchange membranes respectively, which [11] Appleby AJ, Foulkes FR. Fuel cell handbook. New York: Van
have been discussed in this review paper. As a result from Nostrand Reinhold; 1989.
Tables 8 and 9, the proton exchange membranes modified [12] Rikukawa M, Sanui K. Proton-conducting polymer
with clays are suitable for DMFC applications of fuel cells and electrolyte membranes based on hydrocarbon polymers.
the fabrication cost of these composite membranes is low. Prog Polym Sci 2000;25:1463e502.
[13] Weber AZ, Breslau JBR, Miller IF. A hydrodynamic model for
However, these membranes don’t have sufficient proton
electroosmosis. Ind Eng Chem Fundam 1971;10:554e65.
conductivity for PEMFC and the PEM fuel cell performance of
[14] De Grotthuss CJT. Ann Chim (Paris) 1806;58:54.
these membranes is low. The using of the polyaromatic [15] Kreuer KD, Paddison SJ, Spohr E, Schuster M. Transport in
structures in proton exchange membranes such as sPEEK is proton conductors for fuel-cell applications: simulations,
suitable for high temperature fuel cells. The modification of elementary reactions, and phenomenology. Chem Rev 2004;
these polyaromatic membranes with acidic oxides (MO2) 104:4637e78.
cause to increasing of membrane thermal stability in elevated [16] Deluca NW, Elabd YA. Polymer electrolyte membranes for
the direct methanol fuel cell: a review. J Polym Sci Part B
temperatures. Therefore, for high temperature fuel cells the
Polym Phys 2006;44:2201e13.
use of polyaromatic structures of membranes and self-
[17] Hogarth WHJ, Diniz da Costa JC, Lu GQ. Solid acid
humidifying additive cause to the improvement of fuel cell membranes for high temperature (140 C) proton exchange
performance with dry reactant gases. For increasing of the membrane fuel cells. J Power Sourc 2005;142:223e37.
fuel cell performance in PEMFCs, the proton conductivity of [18] Bruce PG. Solid state electrochemistry. Cambridge
the membrane must be high. For reaching this goal, the using University Press; 1995.
of the proton conductor materials such as heteropolyacids is [19] Renaud S, Ameduri B. Functional fluoropolymers for fuel
cell membranes. Prog Polym Sci 2005;30:644e87.
recommended. Therefore, fuel cells with proton exchange
[20] Motupally S, Becker AJ, Weidner JW. Diffusion of water in
membranes modified with proton conductors have a higher Nafion-115 membranes. J Electrochem Soc 2000;147:3171e7.
fuel cell performances compared with membranes modified [21] Tomoya H, Kazuya M, Mitsuru U. Sulfonated aromatic
other fillers. hydrocarbon polymers as proton exchange membranes for
fuel cells. Polymer 2009;50:5341e57.
[22] Soczka-Guth T. International patent: WO99/29763; 1999.
[23] Lee JK, Li W, Manthiram A. Poly(arylene ether sulfone)s
Acknowledgments
containing pendant sulfonic acid groups as membrane
materials for direct methanol fuel cells. J Membr Sci 2009;
The authors are grateful for the financial support of the 330:73e9.
Renewable Energy Initiative Council of Iran (REIC). [24] Young TH, Chang HL, Hyung SP, Kyung AM, Hyung JK,
Sang YN, et al. Improvement of electrochemical
performances of sulfonated poly(arylene ether sulfone) via
references incorporation of sulfonated poly(arylene ether
benzimidazole). J Power Sourc 2008;175:724e31.
[25] Sheng W, Chunli G, Wen-Chin T, Yao-Chi S, Fang-Chang T.
[1] Ahmad MI, Zaidi SMJ, Rahman SU. Proton conductivity and Sulfonated poly(ether sulfone) (sPES)/boron phosphate
characterization of novel composite membranes for (BPO4) composite membranes for high-temperature proton-
medium-temperature fuel cells. Desalination 2006;193: exchange membrane fuel cells. Int Journal Hydrogen Energy
387e97. 2009;34:8982e91.
[2] Xianguo L. Principles of fuel cells. New York: Taylor & [26] Gowariker VR, Vishwanathan NV, Sridhar J. Polymer
Francis Group; 2006. science. New Delhi: New Age International; 1999.
[3] Kariduraganavar MY, Nagarale RK, Kittur AA, Kulkarni SS. [27] Tongwen X, Dan W, Liang W. Poly(2,6-dimethyl-1,4-
Ion-exchange membranes: preparative methods for phenylene oxide) (PPO)-a versatile starting polymer for
electrodialysis and fuel cell applications. Desalination 2006; proton conductive membranes (PCMs). Prog Polym Sci 2008;
197:225e46. 33:894e915.
[4] Grot WG. Laminates of support material and fluorinated [28] Qingfeng L, Jens O, Robert FS, Niels JB. High temperature
polymer containing pendant side chains containing proton exchange membranes based on polybenzimidazoles
sulfonyl groups. U.S. Patent:3,770,567; 1973. for fuel cells. Prog Polym Sci 2009;34:449e77.
[5] Hideo K, Tsuzura K, Shimizu H. Ion exchange membranes. [29] Wu D, Xu T, Wu L, Wu Y. Hybrid acidebase polymer
Ion exchangers. Berlin: Walter de Gruyter; 1991. membranes prepared for application in fuel cells. J Power
[6] Strathmann H. Electrodialysis and related processes. Sourc 2009;186:286e92.
Membrane separation technology-principles and [30] Liang YF, Pan HY, Zhu XL, Zhang YX, Jian XG. Studies on
applications. Elesevier Science; 1995. 214e278. synthesis and property of novel acidebase proton exchange
[7] Risen JW. Applications of ionomers. Ionomers- membranes. Chin Chem Lett 2007;18:609e12.
characterization, theory and applications. New Jersey: CRC [31] Bouchet R, Miller S, Deulot M, Sonquet JL. A thermodynamic
Press; 1996. approach to proton conductivity in acid-doped
[8] Tongwen X. Review - ion exchange membranes: state of their polybenzimidazole. Solid State Ionics 2001;145:69e78.
development and perspective. J Membr Sci 2005;263:1e29. [32] Steiner P, Sandor R. Polybenzimidazole prepreg: improved
[9] Costamagna P, Srinivasan S. Quantum jumps in the PEMFC elevated temperature properties with autoclave
science and technology from the 1960 to the year 2000 part I. processability. High Perform Polym 1991;3:139e50.
[33] Doyle M, Rajendran G, Vielstich W, Gasteiger HA, Lamm A. [54] Smitha B, Sridhar S, Khan AA. Synthesis and
Handbook of fuel cells-fundamentals, technology and characterization of proton conducting polymer membranes
applications. Chichester: John Wiley and Sons; 2003. for fuel cells. J Membr Sci 2003;225:63e76.
[34] Mosa J, Durán A, Aparicio M. Proton conducting sol-gel [55] Smitha B, Sridhar S, Khan AA. Polyelectrolyte complexes of
sulfonated membranes produced from 2-allylphenol, 3- chitosan and poly(acrylic acid) for fuel cell applications.
glycidoxypropyl trimethoxysilane and tetraethyl Macromolecules 2004;37:2233e9.
orthosilicate. J Power Sourc 2009;192:138e43. [56] Ramı́rez-Salgado J. Study of basic biopolymer as proton
[35] Gubler L, Prost N, Gursel SA, Scherer GG. Proton exchange membrane for fuel cell systems. Electrochimica Acta 2007;
membranes prepared by radiation grafting of styrene/ 52:3766e78.
divinylbenzene onto poly(ethylene-alt-tetrafluoroethylene) [57] Hickner MA. Transport and structure in fuel cell proton
for low temperature fuel cells. Solid State Ionics 2005;176: exchange membranes. Doctor of philosophy in chemical
2849e60. engineering. Virginia Polytechnic Institute and State
[36] Choi EY, Strathmann H, Park JM, Moon SH. Characterization University:237.
of non-uniformly charged ion-exchange membranes [58] Malhotra S, Datta R. Membrane-supported nonvolatile
prepared by plasma-induced graft polymerization. J Membr acidic electrolytes allow higher temperature operation of
Sci 2006;268:165e74. proton-exchange membrane fuel cells. J Electrochem Soc
[37] Nasef MM, Hegazy EA. Preparation and applications of ion 1997;144(2):L23e6.
exchange membranes by radiation-induced graft [59] Ramani V, Kunz HR, Fenton JM. Investigation of Nafion/HPA
copolymerization of polar monomers onto non-polar films. composite membranes for high temperature/low relative
Prog Polym Sci 2004;29:499e561. humidity PEMFC operation. J Membr Sci 2004;232(1e2):31e44.
[38] Chen J, Asano M, Yamaki T, Yoshida M. Preparation and [60] Watanabe M, Uchida H, Seki Y, Emori M, Stonehart P. Self-
characterization of chemically stable polymer electrolyte humidifying polymer electrolyte membranes for fuel cells.
membranes by radiation-induced graft copolymerization of J Electrochem Soc 1996;143(12):3847e52.
four monomers into ETFE films. J Membr Sci 2006;269:194e204. [61] Watanabe M, Uchida H, Seki Y, Emori M. Polymer
[39] Ivanov VS. Raidation chemistry of polymers. Netherlands: electrolyte membranes incorporated with nanometer-size
VSP. Utrecht; 1992. particles of Pt and/or metal-oxides: experimental analysis
[40] Kerres JA. Development of ionomer membrane for fuel of the self-humidification and suppression of gas-crossover
cells. J Membr Sci 2001;185:3e27. in fuel cells. J Phys Chem B 1998;102(17):3129e37.
[41] Tricoli V, Carretta N, Bartolozzi M. A comparative [62] Adjemian KT, Lee SJ, Srinivasan S, Benziger J, Bocarsly AB.
investigation of proton and methanol transport in Silicon oxide nafion composite membranes for proton-
fluorinated ionomeric membranes. J Electrochem Soc 2000; exchange membrane fuel cell operation at 80e140 C. J
147:1286e90. Electrochem Soc 2002;149(3):A256e61.
[42] Heinzel A, Barragan VM. A review of the state-of-the-art of [63] Miyake N, Wainright JS, Savinell RF. Evaluation of a sol-gel
the methanol crossover in direct methanol fuel cell. J Power derived nafion/silica hybrid membrane for polymer
Sourc 1999;84:70e4. electrolyte membrane fuel cell applications: ii. methanol
[43] Shuangling Z, Xuejun C, Tiezhu F, Hui N. Modification of uptake and methanol permeability. J Electrochem Soc 2001;
sulfonated poly(ether ether ketone) proton exchange 148(8):A905e9.
membrane for reducing methanol crossover. J Power Sourc [64] Apichatachutapan W, Moore RB, Mauritz KA. Asymmetric
2008;180:23e8. nafion/(zirconium oxide) hybrid membranes via in situ sol-
[44] Krumova M, Lopez D, Benavente R, Mijangos C, Perena JM. gel chemistry. J Appl Polym Sci 1996;62(2):417e26.
Effect of crosslinking on the mechanical and thermal [65] Yang C, Costamagna P, Srinivasan S, Benziger J,
properties of poly(vinyl alcohol). Polymer 2000;41:9265e72. Bocarsly AB. Approaches and technical challenges to high
[45] Kim DS, Guiver MD, Nam SY, Yun TI, Seo MY, Kim SJ, et al. temperature operation of proton exchange membrane fuel
Preparation of ion exchange membranes for fuel cell based cells. J Power Sourc 2001;103(1):1e9.
on crosslinked poly(vinyl alcohol) with poly(styrene [66] Zaidi SMJ, Mikhailenko SD, Robertson GP, Guiver MD,
sulfonic acid-co-maleic acid). J Membr Sci 2006;281:156e62. Kaliaguine S. Proton conducting composite membranes
[46] Brumlik CJ, Parthasarathy A, Chen WJ, Martin CR. Plasma from polyether ether ketone and heteropolyacids for fuel
polymerization of sulfonated fluorochlorcarbon ionomer cell applications. J Membr Sci 2000;173(1):17e34.
films. J Electrochem Soc 1994;141:2273e9. [67] Mauritz KA, Stefanithis ID, Davis SV, Scheez RW,
[47] Mex L, Sussiek M, Muller J. Plasma polymerized electrolyte Pope RK, Wilkes GL, et al. Microstructural evolution of
membranes and electrodes for miniaturized fuel cells. a silicon oxide phase in a perfluorosulfonic acid ionomer
Chem Eng Commun 2003;190:1085e95. by an in situ solegel reaction. J Appl Polym Sci 1995;55
[48] Saccá A, Carbone A, Passalacqua E, D’Epifanio A, Licoccia S, (1):181e90.
Traversa E, et al. NafioneTiO2 hybrid membranes for [68] Staiti P, Arico AS, Baglio V, Lufrano F, Passalacqua E,
medium temperature polymer electrolyte fuel cells (PEFCs). Antonucci V. Hybrid Nafion-silica membranes doped with
J Power Sourc 2005;152:16e21. heteropolyacids for application in direct methanol fuel
[49] Tongwen X, Jung-Je W, Seok-Jun S, Seung-Hyeon M. In situ cells. Solid State Ionics 2001;145(1e4):101e7.
polymerization: a novel route for thermally stable proton- [69] Savagodo OJ. New Mater Electrochem Syst 1998;1:66.
conductive membranes. J Membr Sci 2008;325:209e16. [70] Arico AS, Baglio V, Blasi AD, Antonucci V. FTIR
[50] Ion Power Homepage. Nafion material safety data sheet spectroscopic investigation of inorganic fillers for
(MSDS). Available on, http://ion-power.com/nafion/naf001. composite DMFC membranes. Electrochem Comm 2003;5
html:2001. (10):862e6.
[51] Larminie J, Dicks A. Fuel cell systems explained. West [71] Zawodzinski TA, Davey J, Valerio J, Gottesfeld S. The water
Sussex: John Wiley; 2000. content dependence of electro-osmotic drag in proton-
[52] Sakari T, Takenaka H, Wakabayashi N, Kawami Y, Tori K. conducting polymer electrolytes. Electrochim Acta 1995;40
Gas permeation properties of SPE membranes. J (3):297e320.
Electrochem Soc 1985;132:1328e32. [72] Mahrenia A, Mohamad AB, Kadhum AAH, Daud WRW,
[53] Watkins DS. Fuel cell systems. New York: Plenum Press; 1993. Iyuke SE. Nafion/silicon oxide/phosphotungestic acid
nanocomposite membrane with enhanced proton [92] Chang JH, Park JH, Park GG, Kim CS, Park OO. Proton
conductivity. J Membr Sci 2009;327:32e40. conducting composite membranes derived from sulfonated
[73] Colicchio I, Wen F, Keul H, Simon U, Moeller M. Sulfonated hydrocarbon and inorganic materials. J Power Sourc 2003;
poly(ether ether ketone)esilica membranes doped with 124:18e25.
phosphotungstic acid. Morphology and proton conductivity. [93] Greaves CR, Bond SP. Whinne WRMc. Conductivity studies
J Membr Sci 2009;326:45e57. on modified laponites. Polyhedron 1995;14:3635e9.
[74] Jones DJ, Rozière J. Handbook of fuel cells: fundamentals [94] Vargas MAMA, Vargas RA, Mellander BE. New proton
technology and applications. John Wiley; 2003. 3. conducting membranes based on PVAL/H3PO2/H2O.
[75] Watanabe M, Uchida H, Seki Y, Emori M. Analyses of self- Electrochimica Acta 1999;44:4227e32.
humidification and suppression of gas crossover in Pt- [95] Liao B, Song MK, Liang H, Pang Y. Polymer-layered silicate
dispersed polymer electrolyte membranes for fuel cells. J nanocomposites. I. A study of poly(ethylene oxide)/Naþ-
Electrochem Soc 1998;145(4):1137e41. montmorillonite nanocomposites as polyelectrolytes and
[76] Antonucci PL, Aricó AS, Cretı̀ P, Ramunni E, Antonucci V. polyethyleneblock- poly(ethylene glycol) copolymer/Naþ-
Investigation of a direct methanol fuel cell based on montmorillonite nanocomposites as fillers for
a composite Nafion-silica electrolyte for high temperature reinforcement of polyethylene. Polymer 2001;42(25):
operation. Solid State Ionics 1999;125(1e4):431e7. 10007e010011.
[77] Carotta MC, Butteri A, Martinelli G, Di Vona ML, Licoccia S, [96] Wang J, Merino J, Aranda P, Galvan JC, Hitzky-Ruiz E.
Traversa E. Electron Tecnol 2000;33:113. Reactive nanocomposites based on pillared clays. J Mater
[78] Baglio V, Blasi AD, Aric o AS, Antonucci V, Antonucci PL, Chem 1998;9:161e8.
Serraino Fiory F, et al. Influence of TiO2 nanometric filler on [97] Ruiz-Hitzky E, Galvan JC, Merino J, Casal B, Aranda P, Jimenez-
the behaviour of a composite membrane for applications in Morales A. Proton conductivity in Al-montmorillonite pillared
direct methanol fuel cells. J New Mater Electrochem Sys clays. Solid State Ionics 1996;85:313e7.
2004;7(4):275e80. [98] Jung DH, Cho SY, Peck DH, Shin DR, Kim JS. Preparation and
[79] Hague DC, Mayo MJ. Controlling crystallinity during performance of a Nafion/montmorillonite nanocomposite
processing of nanocrystalline titania. J Am Ceram Soc 1994; membrane for direct methanol fuel cell. J Power Sourc 2003;
77(7):1957e60. 118(1e2):205e11.
[80] Park KT, Jung UH, Choi DW, Chun K, Lee HM, Kim SH. ZrO2- [99] Jaafar J, Ismail AF, Matsuura T. Preparation and barrier
SiO2/Nafion composite membrane for polymer electrolyte properties of sPEEK/Cloisite 15A/TAP nanocomposite
membrane fuel cells operation at high temperature and low membrane for DMFC application. J Membr Sci 2009;345:
humidity. J Power Sourc 2008;177:247e53. 119e27.
[81] Tazi B, Savadogo O. Parameters of PEM fuel-cells based on [100] Bébin P, Caravanier M, Galiano H. Nafion/clay-SO3H
new membranes fabricated from Nafion, silicotungstic acid membrane for proton exchange membrane fuel cell
and thiophene. Electrochim Acta 2000;45(25e26):4329e39. application. J Membr Sci 2006;278:35e42.
[82] Tazi B, Savadogo O. Effect of various heteropolyacids (HPAs) [101] Peighambardoust SJ, Pourabbas B. Synthesis and
on the characteristics of Nafion- hpas membranes and characterization of conductive polypyrrole/montmorillonite
their H2/O2 polymer electrolyte fuel cell parameters. J New nanocomposites via one-pot emulsion polymerization.
Mater Electrochem Sys 2001;4(3):187e96. Macromolecular Symposia 2007;247:99e109.
[83] Staiti P, Aricó AS, Baglio V, Lufrano F, Passalacqua E, [102] Karthikeyan CS, Nunes SP, Prado LASA, Ponce ML, Silva H,
Antonucci V. Hybrid Nafion-silica membranes doped with Ruffmann B, et al. Polymer nanocomposite membranes for
heteropolyacids for application in direct methanol fuel DMFC application. J Membr Sci 2005;254(1e2):139e46.
cells. Solid State Ionics 2001;145(1e4):101e7. [103] Song MK, Park SB, Kim YT, Kim KH, Min SK, Rhee HW.
[84] Carbone A, Casciola M, Cavalaglio S, Costantino U, Characterization of polymer-layered silicate
Ornelas R, Fodale I, et al. Composite nafion membranes nanocomposite membranes for direct methanol fuel cells.
based on PWA-Zirconia for PEFCs operating at medium Electrochim Acta 2004;50(2e3):639e43.
temperature. J New Mater Electrochem Sys 2004;7(1):1e5. [104] Thomassin JM, Pagnoulle C, Bizzari D, Caldarella G,
[85] Alberti G, Casciola M. Composite membranes for medium- Germain A, J’erôme R. Improvement of the barrier
temperature PEM fuel cells. Annu Rev Mater Res 2003;33: properties of Nafion by fluoro-modified montmorillonite.
129e54. Solid State Ionics 2006;177(13e14):1137e44.
[86] Thampan TM, Jalani NH, Choi P, Datta R. Systematic [105] Rhee CH, Kim HK, Chang H, Lee JS. Nafion/sulfonated
approach to design higher temperature composite PEMs. montmorillonite composite: a new concept electrolyte
J Electrochem Soc 2005;152(2):A316e25. membrane for direct methanol fuel cells. Chem Mater 2005;
[87] Choi P, Jalani NH, Datta R. Thermodynamics and proton 17(7):1691e7.
transport in Nafion. J Electrochem Soc 2005;152(3):E84e9. [106] Thomassin JM, Pagnaulle C, Caldarella G, Germain A,
[88] Choi P, Jalani NH, Datta R. Thermodynamics and proton J’erôme R. Impact of acid containing montmorillonite on the
transport in nafion. J Electrochem Soc 2005;152(3): properties of Nafion membranes. Polymer 2005;46(25):
E123e30. 11389e95.
[89] Choi P, Jalani NH, Datta R. Thermodynamics and proton [107] Antonucci PL, Arico AS, Creti P, Ramunni E, Antonucci V.
transport in nafion. J Electrochem Soc 2005;152(8): Investigation of a direct methanol fuel cell based on
A1548e54. a composite Nafion-silica electrolyte for high temperature
[90] Jalani NH, Dunn K, Datta R. Synthesis and characterization operation. Solid State Ionics 1999;125(1e4):431e7.
of Nafion-MO2 (M¼Zr, Si, Ti) nanocomposite membranes [108] Pourcelly G, Gavach C, Colomban P. Proton conductors. New
for higher temperature PEM fuel cells. Electrochimica Acta York: Cambridge University Press; 1992.
2005;51:553e60. [109] Lin YF, Yen CY, Hung CH, Hsiao YH, Ma CCM. A novel
[91] Satterfield MB, Majsztrik PW, OTA H, Benziger JB, composite membranes based on sulfonated
Bocarsly A. Mechanical properties of Nafion and Titania/ Montmorillonite modified Nafion for DMFCs. J Power Sourc
Nafion composite membranes for polymer electrolyte 2007;168(1):162e6.
membrane fuel cells. J Polym Sci Part B Polym Phys 2006;44 [110] Liang ZX, Zhao TS, Prabhuram J. Diphenylsilicate-
(16):2327e45. incorporated Nafion membranes for reduction of
methanol crossover in direct methanol fuel cells. J Membr [133] Benyaich A, Deslouis C, El Moustafid T, Musiani MM,
Sci 2006;283(1e2):219e24. Tribollet B. Electrochemical properties of PANI films for
[111] Hibino T, Akimoto T, Iwahara H. Protonic conduction of different counter-ions in acidic pH analysed by impedance
mordenite-type zeolite. Solid State Ionics 1993;67(1e2):71e6. techniques. Electochim Acta 1996;41(11e12):1781e5.
[112] Yamamoto N, Okubo T. Ionic conductivity of single-crystal [134] Ladewig B, Martin D, Knott R, Diniz da Costa JC, Lu GQ.
ferrierite. Microporous Mesoporous Mater 2000;40(1e3): Nafion-MPMDMS nanocomposite membranes with low
283e8. methanol permeability. Electrochem Comm 2007;9(4):
[113] Berry MB, Libby BE, Rose K, Hass KH, Thompson RW. 781e6.
Incorporation of zeolites into composite matrices. [135] Roelofs KS, Hirth T, Schiestel T. Sulfonated poly(ether ether
Microporous Mesoporous Mater 2000;39(1e2):205e17. ketone)-based silica nanocomposite membranes for direct
[114] Caro J, Noack M, Kölsch P, Schäfer R. Zeolite membranes e ethanol fuel cells. J Membr Sci 2010;346:215e26.
state of their development and perspective. Microporous [136] Colicchio I, Demco DE, Baias M, Keul H, Moeller M.
Mesoporous Mater 2000;38(1):3e24. Influence of the silica content in sPEEK-silica membranes
[115] Libby B, Smyrl WH, Cussler EL. Polymer-zeolite composite prepared from the sol-gel process of polyethoxysiloxane:
membranes for direct methanol fuel cells. AIChE J 2003;49 morphology and proton mobility. J Membr Sci 2009;337:
(4):991e1001. 125e35.
[116] Rao N, Andersen TP, Ge P. Tin mordenite membranes for [137] Yang J, Shen PK, Varcoe J, Wei Z. Nafion/polyaniline
direct methanol fuel cells. Solid State Ionics 1994;72:334e7. composite membranes specifically designed to allow proton
[117] Qui P, Huang Y, Secco RA, Balong PS. Effect of multi-stage exchange membrane fuel cells operation at low humidity. J
dehydration on electrical conductivity of zeolite A. Solid Power Sourc 2009;189:1016e9.
State Ionics 1999;118:281e5. [138] Barthet C, Gugliemi M. Mixed electronic and ionic
[118] Mikhailenko SD, Kaliaguine S, Ghali E. Water-assisted ionic conductors: a new route to Nafion-doped polyaniline. J
conductance of zeolites with ZSM-5 structure. Microporous Electronal Chem 1995;388(1e2):35e44.
Mater 1997;11(1e2):37e44. [139] Chen CY, Rodriguez JIG, Duke MC, Dalla Costa RF, Dicks AL,
[119] Sancho T, Soler J, Pina MP. Conductivity in zeolite - polymer Da Costa JCD. Nafion/polyaniline/silica composite
composite membranes for PEMFCs. J Power Sourc 2007;169 membranes for direct methanol fuel cell application. J
(1):92e7. Power Sourc 2007;166(2):324e30.
[120] Yang T. Composite membrane of sulfonated poly(ether [140] Rivin CE, Kendrick PW, Gibson NS. Schneider Solubility and
ether ketone) and sulfated poly(vinyl alcohol) for use in transport behavior of water and alcohols in Nafion.
direct methanol fuel cells. J Membr Sci 2009;342:221e6. Polymer 2001;42(2):623e35.
[121] Dillon R, Srinivasan S, Arico AS, Antonucci B. International [141] Tan S, Laforgue A, Belanger D. Characterization of a cation
activities in DMFC R&D: status of technologies and potential exchange/polyaniline composite membrane. Langmuir
applications. J Power Sourc 2004;127(1e2):112e26. 2003;19(3):744e51.
[122] Sauk J, Byun J, Kim H. Grafting of styrene on to Nafion [142] Alpatova NM, Adreev VN, Danilov AI, Molodkina EB,
membranes using supercritical CO2 impregnation for direct Poukarov YM, Berezina NP, et al. Electrochemical template
methanol fuel cells. J Power Sourc 2004;132(1e2):59e63. synthesis of an polyaniline composite with polymeric
[123] Yamaguchi T, Miyata F, Macao S. Pore-filling type polymer perfluorinated sulfo cationite. J Electrochem 2002;38(8):
electrolyte membranes for a direct methanol fuel cell. J 913e8.
Membr Sci 2003;214(2):283e92. [143] Carter R, Wycisk R, Yoo H, Pintauro PN. Blended
[124] Shao ZG, Wang X, Hsing IM. Composite Nafion/polyvinyl polyphosphazene/polyacrylonitrile membranes for direct
alcohol membranes for the direct methanol fuel cell. J methanol fuel cells. Electrochem Solid-State Lett 2002;5:
Membr Sci 2002;210(1):147e53. A195e7.
[125] Smit MA, Ocampo AL, Espinosa-Medina MA, Sebastian PJ. [144] Narang S, Ventura SC, Olmeijer DL. Polymer membrane
A modified Nafion membrane with in situ polymerized composition. WO/2001/094450; 2001.
polypyrrole for the direct methanol fuel cell. J Power Sourc [145] Wang J, Yue Z, Economy J. Preparation of proton-conducting
2003;124(1):59e64. composite membranes from sulfonated poly(ether ether
[126] Dimitrova P, Friedrich KA, Vogt B, Stimming U. Transport ketone) and polyacrylonitrile. J Membr Sci 2007;291(1e2):
properties of ionomer composite membranes for direct 210e9.
methanol fuel cells. J Electroanal Chem 2002;532(1e2): [146] Kerres J, Ullrich A, Meier F, Thomas Haring T. Synthesis and
75e83. characterization of novel acidebase polymer blends for
[127] Tan S, Belanger D. Characterization and transport application in membrane fuel cells. Solid State Ionics 1999;
properties of nafion/polyaniline composite membranes. 125:243e9.
J Phys Chem B 2005;109(49):23480e90. [147] Keruer KD. On the development of proton conducting
[128] Tung S, Hwang B. High proton conductive glass electrolyte polymer membranes for hydrogen and methanol fuel cells.
synthesized by an accelerated sol-gel process with water/ J Membr Sci 2001;185(1):29e39.
vapor management. J Membr Sci 2004;241(2):315e23. [148] Xing DM, Yi BL, Fu YZ. Pt-C/sPEEK/PTFE self-humidifying
[129] Geniès EM, Boyle A, Lapkowski M, Tsintavis C. Polyaniline: composite membrane for fuel cells. Electrochem Solid-State
a historical survey. Synth Met 1990;36(2):139e82. Lett 2004;7(10):315e7.
[130] Duic L, Mandic Z, Kovac S. Polymer-dimer distribution in [149] Wang L, Xing DM, Liu YH, Cai YH, Shao ZG, Zhai YF, et al. Pt/
the electrochemical synthesis of polyaniline. Electrochim SiO2 catalyst as an addition to Nafion/PTFE self-humidifying
Acta 1995;40(11):1681e8. composite membrane. J Power Sourc 2006;161(1):61e7.
[131] Pud A, Ogurtsov N, Korzhenko A, Shapoval G. Some aspects [150] Ramani V, Kunz HR, Fenton JM. Stabilized heteropolyacid/
of preparation methods and properties of polyaniline Nafion composite membranes for elevated temperature/
blends and composites with organic polymers. Prog Polym low relative humidity PEFC operation. Electrochim Acta
Sci 2003;28(12):1701e53. 2005;50(5):1181e7.
[132] Deslouis C, Musiani MM, Tribollet B. AC impedance study of [151] Lee H, Kim J, Park J, Lee T. A study on self-humidifying
transport processes in polyaniline membranes. J Phys Chem PEMFC using PteZrPeNafion composite membrane.
1994;98(11):2936e40. Electrochim Acta 2004;50(2e3):761e8.
[152] Choi JK, Lee DK, Kim YW, Min BR, Kim JH. Composite conductive membranes via in situ mixed sol-gel process.
polymer electrolyte membranes comprising triblock J Membr Sci 2007;296:156e61.
copolymer and heteropolyacid for fuel cell applications. [170] Tripathi BP, Shahi VK. Surface redox polymerized
J Polym Sci Part B Polym Phys 2008;46:691e701. sPEEKeMO2ePANi (M¼ Si, Zr and Ti) composite
[153] Limoges BR, Stains RJ, Turner JA, Herring AM. polyelectrolyte membranes impervious to methanol.
Electrocatalyst materials for fuel cells based on the Colloids Surf A Physicochem Eng Aspects 2009;340:
polyoxometalates [PMo(12 n)VnO40](3 þ n)(n ¼ 0e3). 10e9.
Electrochim Acta 2005;50(5):1169e79. [171] Watanabe M, Uchida H, Emori M. Polymer electrolyte
[154] Giordano N, Staiti P, Hocevar S, Arico AS. High performance membranes incorporated with nanometer-size particles of
fuel cell based on phosphotungstic acid as proton conducting pt and/or metal-oxides: experimental analysis of the self-
electrolyte. Electrochim Acta 1996;41(3):397e403. humidification and suppression of gas-crossover in fuel
[155] Zhang Y, Zhang H, Bi C, Zhu X. An inorganic/organic self- cells. J Phys Chem B 1998;102:3129e37.
humidifying composite membranes for proton exchange [172] Nunes SP, Ruffmann B, Rikowski E, Vetter S, Richau K.
membrane fuel cell application. Electrochimica Acta 2008; Inorganic modification of proton conductive polymer
53:4096e103. membranes for direct methanol fuel cells. J Membr Sci 2002;
[156] Wang L, Yi BL, Zhang HM, Xing DM. Cs2.5H0.5PW12O40/SiO2 203:215e25.
as addition self-humidifying composite membrane for [173] Silva VS, Ruffmann B, Silva H, Silva VB, Mendes A,
proton exchange membrane fuel cells. Electrochimica Acta Madeira LM, Nunes SP. zirconium oxide hybrid membranes
2007;52(17):5479e83. for direct methanol fuel cells-evaluation of transport
[157] Asensio JA, Borros S, Pedro GR. Enhanced conductivity in properties. J Membr Sci 2006;284:137e44.
polyanion-containing polybenzimidazoles. Improved [174] Kalappa P, Lee JH. Proton conducting membranes based on
materials for proton-exchange membranes and PEM fuel sulfonated poly(ether ether ketone)/TiO2 nanocomposites
cells. Electrochem Commun 2003;5(11):967e72. for a direct methanol fuel cell. Polym Int 2007;56:371e5.
[158] Shao ZG, Joghee P, Hsing IM. Preparation and [175] Helen M, Viswanathan B, Murthy VS. Fabrication and
characterization of hybrid Nafionesilica membrane doped properties of hybrid membranes based on salts of
with phosphotungstic acid for high temperature operation heteropolyacid, zirconium phosphate and polyvinyl
of proton exchange membrane fuel cells. J Membr Sci 2004; alcohol. J Power Sourc 2006;163:433e9.
229(1e2):43e51. [176] Krishnan P, Park JS, Yang TH, Lee WY, Kim CS. Sulfonated
[159] Kerres J, Ullrich A, Meier F, Häring T. Synthesis and poly(ether ether ketone)-based composite membrane for
characterization of novel acidebase polymer blends for polymer electrolyte membrane fuel cells. J Power Sourc
application in membrane fuel cells. Solid State Ionics 1999; 2006;163:2e8.
125(1e4):243e9. [177] Helen M, Viswanathan B, Srinivasa Murthy V. Synthesis and
[160] Li QF, He RH, Jensen JO, Bjerrum NJ. Approaches and recent characterization of composite membranes based on a-
development of polymer electrolyte membranes for fuel zirconium phosphate and silicotungstic acid. J Membr Sci
cells operating above 100 C. Chem Mater 2003;15(26): 2007;292:98e105.
4896e915. [178] Ismail AF, Othman NH, Mustafa A. Sulfonated polyether
[161] Suryani, Liu YL. Preparation and properties of ether ketone composite membrane using tungstosilicic acid
nanocomposite membranes of polybenzimidazole/ supported on silica-aluminium oxide for direct methanol
sulfonated silica nanoparticles for proton exchange fuel cell (DMFC). J Membr Sci 2009;329:18e29.
membranes. J Membr Sci 2009;332:121e8. [179] Krishnan P, Park JS, Kim CS. Preparation of proton-
[162] Savadogo O. Emerging membranes for electrochemical conducting sulfonated poly(ether ether ketone)/boron
systems: part II. High temperature composite membranes phosphate composite membranes by an in situ sol-gel
for polymer electrolyte fuel cell (PEFC) applications. J Power process. J Membr Sci 2006;279:220e9.
Sourc 2004;127(1e2):135e61. [180] Deb PC, Rajputy LD, Hande VR, Sasane S, Kumar A.
[163] Wang JT, Savinell RF. A H2/O2 fuel cell using acid doped Modification of sulfonated poly(ether ether ketone) with
polybenzimidazole as polymer electrolyte. Electrochim Acta phenolic resin. Polym Adv Technol 2007;18:419e26.
1996;41(2):193e7. [181] Cai H, Shao K, Zhong S, Zhao C, Zhang G, Li X, et al.
[164] Mecerreyes D, Grande H, Miguel O, Marcilla R, Cantero I. Properties of composite membranes based on sulfonated
Porous polybenzimidazole membranes doped with poly(ether ether ketone)s (sPEEK)/phenoxy resin (PHR) for
phosphoric acid: highly proton-conducting solid direct methanol fuel cells usages. J Membr Sci 2007;297
electrolytes. Chem Mater 2004;16(4):604e7. (1e2):162e73.
[165] Zhai Y, Zhang H, Zhang Y, Xing D. A novel H3PO4/ [182] Sambandam S, Ramani V. sPEEK/functionalized silica
NafionePBI composite membrane for enhanced durability composite membranes for polymer electrolyte fuel cells.
of high temperature PEM fuel cells. J Power Sourc 2007;169 J Power Sourc 2007;170:259e67.
(2):259e64. [183] Gosalawit R, Chirachanchai C, Shishatskiy S, Nunes SP.
[166] Zhai Y, Zhang H, Liu G, Hu J, Yi B. Degradation study on MEA Sulfonated montmorillonite/sulfonated poly(ether ether
in H3PO4/PBI high-temperature pemfc life test. J ketone) (sMMT/sPEEK) nanocomposite membrane for direct
Electrochem Soc 2007;154(1):B72e6. methanol fuel cells (DMFCs). J Membr Sci 2008;323:337e46.
[167] Zhang Y, Zhang H, Zhu X, Gang L, Bi C, Liang Y. Fabrication [184] Lavrenc ic
U, Stangar B, Orel JV, Jovanovski V, Spreizer H,
and characterization of a PTFE-reinforced integral Vuk AS, et al. Silicotungstic acid/organically modified silane
composite membrane for self-humidifying PEMFC. J Power proton-conducting membranes. J Solid State Electrochem
Sourc 2007;165:786e92. 2005;9:106e13.
[168] Zhu X, Zhang H, Zhang Y, Liang Y, Wang X, Yi B. An [185] Kim YS, Wang F, Heckler M, Zawodzinski TA, McGrath JE.
ultrathin self-humidifying membrane for pem fuel cell Fabrication and characterization of heteropolyacid
application: fabrication, characterization, and experimental (H3PW12O40)/directly polymerized sulfonated poly(arylene
analysis. J Phys Chem B 2006;110:14240e8. ether sulfone) copolymer composite membranes for higher
[169] Luisa Di Vona M, Ahmed Z, Bellitto S, Lenci A, Traversa E, temperature fuel cell applications. J Membr Sci 2003;212:
Licoccia S. sPEEK-TiO2 nanocomposite hybrid proton 263e82.
[186] Guzman-Garcia AG, Pintauro PN, Verbugge MW, Hill RF. [206] Zhou C, Guerra MA, Qiu ZM, Zawodzinski Jr TA,
Development of a space-charge transport model for ion- Schiraldi DA. Chemical durability studies of perfluorinated
exchange membranes. AIChE J 1990;36:1061e74. sulfonic acid polymers and model compounds under
[187] Yang Y, Pintauro PN. Multicomponent space-charge mimic fuel cell conditions. Macromolecules 2007;40:
transport model for ion-exchange membranes. AIChE J 8695e707.
2000;46:1177e90. [207] Merlo L, Ghielmi A, Cirillo L, Gebert M, Arcella V. Resistance
[188] Fernandez FJ, Compan V, Riande E. Hybrid ion-exchange to peroxide degradation of Hyflon Ion membranes. J Power
membranes for fuel cell and separation processes. J Power Sourc 2007;171:140e7.
Sourc 2007;173:68e76. [208] Aoki M, Asano N, Miyatake K, Uchida H, Watanabe M.
[189] Silva VS, Schirmer J, Reissner R, Ruffmann B, Silva H, Durability of sulfonated polyimide membrane evaluated by
Mendes A, LM, et al. Proton electrolyte membrane long-term polymer electrolyte fuel cell operation.
properties and direct methanol fuel cell performance II. J Electrochem Soc 2006;153:A1154e8.
Fuel cell performance and membrane properties effects. J [209] Kundu S, Fowler MW, Simon LC, Abouatallah R,
Power Sourc 2005;140:41e9. Beydokhti N. Degradation analysis and modeling of
[190] Elabd YA, Napadensky E, Sloan JM, Crawford DM, reinforced catalyst coated membranes operated under OCV
Walker CW. Triblock copolymer ionomer membranes: part conditions. J Power Sourc 2008;183:619e28.
I. Methanol and proton transport. J Membr Sci 2003;217 [210] Xing DM, Zhang HM, Wang L, Zhai YF, Yi BL. Investigation
(1e2):227e42. of the Ag-SiO2/sulfonated poly(biphenyl ether sulfone)
[191] Thomassin JM, Pagnoulle C, Bizzari D, Caldarella G, composite membranes for fuel cell. J Membr Sci 2007;296:
Germain A, Jerome R. Nafion-layered silicate 9e14.
nanocomposite membrane for fuel cell application. e- [211] Trogadas P, Ramani V. Pt/C/MnO2 hybrid electrocatalysts
Polymers 2004;18:1. for degradation mitigation in polymer electrolyte fuel cells.
[192] Li L, Xu L, Wang Y. Novel proton conducting composite J Power Sourc 2007;174:159e63.
membranes for direct methanol fuel cell. Mater Lett 2003;57 [212] Aoki M, Uchida H, Watanabe M. Decomposition mechanism
(8):1406e10. of perfluorosulfonic acid electrolyte in polymer electrolyte
[193] Kim D, Scibioh M, Kwak S, Oh IH, Ha HY. Nano-silica layered fuel cells. Electrochem Commun 2006;8:1509e13.
composite membranes prepared by PECVD for direct methanol [213] Xu H, Hou X. Synergistic effect of CeO2 modified Pt/C
fuel cells. Electrochem Commun 2004;6(10):1069e74. electrocatalysts on the performance of PEM fuel cells. Int J
[194] Li L, Zhang J, Wang Y. Sulfonated poly(ether ether ketone) Hydrogen Energy 2007;32:4397e401.
membranes for direct methanol fuel cell. J Membr Sci 2003; [214] La Conti AB, Hamdan M, Mc Donald RC. In: Vielstic W,
226(1e2):159e67. Gasteiger HA, Lamm A, editors. Handbook of fuel cells-
[195] Elabd YA, Walker CW, Beyer FL. Triblock copolymer fundamentals, technology, applications. John Wiley & Sons;
ionomer membranes: part II. Structure characterization 2003. p. 659.
and its effects on transport properties and direct [215] Trogadas P, Parrondo J, Ramani V. Degradation mitigation
methanol fuel cell performance. J Membr Sci 2004;231 in polymer electrolyte membranes using cerium oxide as
(1e2):181e8. a regenerative free-radical scavenger. Electrochem Solid
[196] DeLuca Nicholas W, Elabd Yossef A. Nafion/poly(vinyl State Lett 2008;11(7):B113e6.
alcohol) blends: effect of composition and annealing [216] Zhao D, Yi BL, Zhang HM, Yu HM, Wang L, Ma YW, et al.
temperature on transport properties. J Membr Sci 2006;282 Cesium substituted 12-tungstophosphoric (Cs xH3- xPW12O40)
(1e2):217e24. loaded on ceria-degradation mitigation in polymer
[197] Chang JH, Hyeok JP, Park GG, Kim CS, Park OO. Proton- electrolyte membranes. J Power Sourc 2009;190:301e6.
conducting composite membranes derived from sulfonated [217] Surowiec J, Bogoczek R. Studies on the thermal stability of
hydrocarbon and inorganic materials. J Power Sourc 2003; the perfluorinated cation-exchange membrane Nafion-417.
124:18e25. J Thermal Anal Calorimetry 1988;33:1097e102.
[198] He R, Li Q, Bach A, Jensen JO, Bjerrum NJ. Physicochemical [218] Samms SR, Wasmus S, Savinell RF. Thermal stability of
properties of phosphoric acid doped polybenzimidazole nafion in simulated fuel cell environments. J Electrochem
membranes for fuel cells. J Membr Sci 2006;277:38e45. Soc 1996;143:1498e504.
[199] Liu W, Zuckerboard D. Growth of single crystal cuprous [219] Kyu T, Hashiyama M, Eisenberg A. Dynamic mechanical
oxide from the melt and luminescence of cuprous oxide. studies of partially ionized and neutralized nafion
J Electrochem Soc 2005;152:A1165e70. polymers. Can J Chem 1983;61:680e7.
[200] Scherer GG, Bunsen-Ges B. Phys Chem 1990;94:1008e14. [220] Jang IY, Kweon OH, Kim KE, Hwang GJ, Moon SB,
[201] Qiao J, Saito M, Hayamizu K, Okadaz T. Degradation of Kang AS. Application of polysulfone (PSf)e and polyether
perfluorinated ionomer membranes for PEM fuel cells ether ketone (PEEK)etungstophosphoric acid (TPA)
during processing with H2O2. J Electrochem Soc 2006;153(6): composite membranes for water electrolysis. J Membr Sci
A967e74. 2008;322:154.
[202] Teranishi K, Kawata K, Tsushima S, Hirai S. Degradation [221] Sengul E, Erdener H, Gultekin Akay R, Yucel H, Bac N,
mechanism of PEMFC under open circuit operation. Eroglu I. International Journal of Hydrogen Energy. Effects
Electrochem Solid State Lett 2006;9(10):A475e7. of sulfonated polyether-etherketone (SPEEK) and composite
[203] Guo Q, Pintauro PN, Tang H, O’Connor S. Sulfonated and membranes on the proton exchange membrane fuel cell
crosslinked polyphosphazene-based proton-exchange (PEMFC) performance 2009;34(10):4645e52.
membranes. J Membr Sci 1999;154:175e81. [222] Tripathi BP, Kumar M, Shahi VK. Highly stable proton
[204] Buchi FN, Gupta B, Haas O, Scherer GG. Study of radiation- conducting nanocomposite polymer electrolyte membrane
grafted FEP-G-polystyrene membranes as polymer (PEM) prepared by pore modifications: an extremely low
electrolytes in fuel cells. Electrochimica Acta 1995;40: methanol permeable PEM. J Membr Sci 2009;327:145.
345e53. [223] Carbone A, Sacca A, Gatto I, Pedicini R, Passalacqua E.
[205] Xie J, Wood DL, Wayne DM, Zawodzinski TA, Atanassov P, Investigation on composite sPEEK/H-BETA MEAs for
Borup RL. Durability of PEFCs at high humidity conditions. medium temperature PEFC. Int Journal Hydrogen Energy
J Electrochem Soc 2005;152:A104e13. 2008;33:3153.
[224] Su YH, Liu YL, Sun YM, Lai JY, Wang DM, Gaoe Y, et al. poly(ether ether ketone) membrane transport properties
Proton exchange membranes modified with sulfonated and direct methanol fuel cell performance. Separat Sci
silica nanoparticles for direct methanol fuel cells. J Membr Technol 2007;42:2909.
Sci 2007;296:21. [230] Dimitrova PG, Baradie B, Foscallo D, Poinsignon C,
[225] Tan AR, de Carvalho LM, de Ramos Filho FG, de Souza Sanchez JY. Ionomeric membranes for proton exchange
Gomes A. Nanocomposite membranes based on sulfonated membrane fuel cell (PEMFC): sulfonated polysulfone
poly(etheretherketone) structured with modified silica for associated with phosphatoantimonic acid. J Membr Sci
direct ethanol fuel cell. Macromolcular Symposia 2006; 2001;185:59.
245e246:470. [231] Jang W, Choi S, Lee S, Shul Y, Han H. Characterizations and
[226] Gaowen Z, Zhentao Z. Organic/inorganic composite stability of polyimideephosphotungstic acid composite
membranes for application in DMFC. J Membr Sci 2005;261: electrolyte membranes for fuel cell. Polym Degrad Stab
107. 2007;92:1289.
[227] Karthikeyan CS, Nunes SP, Prado LASA, Ponce ML, Silva H, [232] Gosalawit R, Chirachanchai S, Shishatskiy S, Nunes SP.
Ruffmann B, et al. Polymer nanocomposite membranes for KrytoxeMontmorilloniteeNafion nanocomposite
DMFC application. J Membr Sci 2005;254:139. membrane for effective methanol crossover reduction in
[228] Li X, Liu C, Xu D, Zhao C, Wang Z, Zhang G, et al. Preparation DMFCs. Solid State Ionics 2007;178:1627.
and properties of sulfonated poly(ether ether ketone)s [233] Amjadi M, Rowshanzamir S, Peighambardoust SJ,
(SPEEK)/polypyrrole composite membranes for direct Hosseini MG, Eikani MH. Investigation of physical
methanol fuel cells. J Power Sourc 2006;162:1. properties and cell performance of Nafion/TiO2
[229] Silva VS, Silva VB, Mendes A, Madeira LM, Silva H, nanocomposite membranes for high temperature PEM fuel
Michaelmann J, et al. Pre-treatment effect on the sulfonated cells. Int J Hydrogen Energy 2010;35:9252e60.

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 9 3 4 9 e9 3 8 4

journal homepage: www.elsevier.com/locate/he

Review of the proton exchange membranes for fuel

S.J. Peighambardoust a, S. Rowshanzamir a,b,*, M. Amjadi a

article info abstract

Fuel cells due to their particular properties are on the verge of

Anode electrode: H2 / 2Hþ þ 2e

AFC [2] 60e90 100e200 40e60 >10,000 >200 Space, Mobile

with shorter side chains and a higher ratio of SO3H to CF2

Table 2 e Properties of commercial cation-exchange membranes.

Asahi Chemical Industry Company Ltd., Chiyoda-ku, Tokyo, Japan [10]

exchange membrane which allow the transferring of the

benzene ring structures in the polymeric backbone of

Table 3 e The most important blends in the preparation of acidebase complex.

5.4. Solegel method

The solegel method provides the easier introduction of pure

Condensation reactions: M e OH þ HO e M / M e O e Recently, the modification of the fluorinated membranes such

Nafion 117 [100] 185 205 30 11

the composite one (Nafion/Lp-g) can reach 500 mA cm2, as

Fig. 18 e Polarization curves for Nafion-115 (B) and

As a result, The Nafion/MMT-POPD400- PS composite

6.3. Modified Nafion membrane with types of zeolites

Zeolites are a class of crystalline aluminosilicates, which form

Fig. 22 e Proton conductivity versus temperature curves for

100 C [116]. Above this value, conductivity in zeolites is

condensation of TEOS as described elsewhere [134e136] to

proton transport via the Grotthus mechanism and the global

6.5. Modified Nafion blend membrane with sPEEK and

Table 5 e IEC and swell ratios of composite membranes

sPEEK without 2.10 Dissolved in

Table 6 e Methanol permeability of Nafion L117 and

Thickness Slope Methanol permeability

Nafion 117 0.022 1.444 27.4

Thickness Slope Methanol permeability

3500 [145] 0.0068 0.114 0.67

conductivity, which was a result of the increase in perme-

7. Measurement and investigation methods

In this section, methods of evaluation and characterization of

durability, thermal stability and fuel cell performance of the 

A is a constant proportional to the number of charge carriers,

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