DE29522223U1 - Proton-conducting polymers - Google Patents

Description

PROTON-CONDUCTING POLYMERS

FIELD OF INVENTION

The invention relates to a polymeric solid electrolyte which is useful in fuel cells which operate at elevated temperatures. In particular, the invention relates to the use of a polymer electrolyte membrane which can conduct protons at temperatures up to at least 200 ^° C for use in fuel cells which operate with liquid fuels.

BACKGROUND OF THE INVENTION

Over the past decade, considerable effort has been directed toward the development and characterization of perfluorosulfonic acid polymer electrolytes such as Nafion. These efforts have demonstrated that polymer electrolyte membranes (PEMs) offer a number of advantages over conventional electrolytes when used in electrochemical devices such as fuel cells and water electrolyzers. Unfortunately, these electrolytes must remain hydrated to retain ionic conductivity, which limits their maximum operating temperature to 100 ⁰ C at atmospheric pressure.

This disadvantage of the known PEM materials is therefore highlighted in the systems where a polymer electrolyte with high conductivity at temperatures exceeding 100 ⁰ C would be usable. One such application is the Kb/(^ fuel cell, which uses reformed hydrogen from organic fuels (methane, methanol, etc.) containing a certain amount of CO, which poisons the electrode catalysts. Another such application is the direct methanol fuel cell. Existing direct methanol-air fuel cell designs are severely limited by the lack of sufficiently active catalysts for the methanol anode and, to a lesser extent, for the oxygen anode. This is a direct result of the catalyst poisoning caused by

Caused by carbon monoxide produced by the fuel at operating temperatures of approximately 100 ⁰ C or lower.

Another disadvantage of the known PEM methanol-air fuel cells is the poor performance of the fuel cells due to the high number of methanol crossovers from the anode to the cathode, which leads to a loss of efficiency via chemical reaction of the fuel with oxygen and subsequent depolarization of the cathode.

The use of solid polymeric electrolytes offers new opportunities to overcome these catalyst stability and activity problems, provided that the polymers chosen are stable and maintain acceptable ionic conductivity at temperatures approaching 200 ⁰ C, avoiding anode/cathode poisoning effects. Furthermore, such polymers should have other desirable properties such as low methanol permeability to reduce efficiency losses resulting from crossover.

It has now been discovered that films comprising polymers containing basic groups capable of complexing with stable acids, or polymers containing acidic groups, represent a viable alternative to known PEMs and other conventional electrolytes. Polybenzimidazole (PBI) doped with a strong acid such as phosphoric acid or sulfuric acid is an example of a suitable polymer. Polybenzimidazoles together with other suitable aromatic polymers basic enough to complex with acids exhibit excellent oxidative and thermal stability characteristics, which properties can be further improved by doping at a level of at least 200 mol%. They require low water activity, thus avoiding operating temperature limitations due to the boiling point of water. The ability to operate at elevated temperatures, i.e. up to at least 200 ^° C, also reduces the potential for anode/cathode poisoning. Furthermore, they do not suffer greatly from methanol crossover because of the low methanol swelling with methanol vapor and high glass transition temperatures.

09· 06-Oi

It is therefore an object of the present invention _to provide a polymeric solid electrolyte which does not suffer from known problems associated with catalyst stability and activity.

It is a further object of the invention to provide a polymeric solid electrolyte which is stable and maintains acceptable ionic conductivity up to at least 200 ^° C.

It is a further object of the invention to provide a polymeric solid electrolyte suitable for use in direct methanol fuel cells without exhibiting high methanol permeability which leads to a loss of efficiency due to methanol crossover.

SUMMARY OF THE INVENTION

The present invention relates to polymeric solid electrolyte membranes comprising proton-conducting polymers which are stable at temperatures above 100 ^° C, wherein the polymer is a basic polymer which forms a complex with a strong acid or an acidic polymer. The invention further relates to the use of such membranes in electrolytic cells and acidic fuel cells. In particular, the invention relates to the use of polybenzimidazole as a suitable polymer electrolyte membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph illustrating the conductivity of phosphoric acid-doped PBI as a function of temperature and water partial pressure.

Figure 2 is the scan of the thermogravimetric analysis of an undoped PBI film.

Figure 3 is the scan of the thermogravimetric analysis of a PBI film doped with 20 mol% sulfuric acid.

Figure 4 is a diagram illustrating the dynamic mechanical spectroscopy of a phosphoric acid doped PBI film.

Figures 5a to 5c are diagrams illustrating the polarization and energy density curves of a PBI fuel cell, where Figure 5a shows the cell voltage

as a function of current strength, Figure 5b shows the individual cathode and anode potentials and Figure 5c shows the energy of the cell as a function of current density.

Figure 6 is a graph illustrating the polarization curve of a PBI fuel cell operating with methanol:water fuel and oxygen as the oxidant, comparing a Pt anode and a Pt/Ru anode.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to novel polymeric solid electrolytes which are stable and retain acceptable ionic conductivity at temperatures up to at least 200 ^° C to overcome known catalyst stability and conductivity problems. In particular, the invention relates to the use of polymers containing basic groups capable of forming complexes with stable acids, or polymers containing acidic groups, which can be used to form films suitable for use as polymeric solid electrolyte membranes in methanol-air fuel cells. Examples of such polymers include, but are not limited to, polybenzimidazole, polypyridine, polypyrimidine, polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines, polythiadiazoles, and poly(tetrazapyrenes). Of particular interest is polybenzimidazole (PBI) doped with a strong acid such as phosphoric acid or sulfuric acid. These polymer films exhibit excellent oxidative and thermal stability, with these properties being further enhanced by the acidic nature of the polymer.

The present polymeric solid electrolyte membrane shows stable chemical and electrical properties well above 100 ⁰ C and up to at least 200 ⁰ C, has good mechanical and film properties, shows high proton conductivity and low fuel permeability, and can conduct protons with very low water activity.

The polymer used in the present invention may be a polymer containing basic groups that can form complexes with stable acids. For example, when the PBI polymer is doped with a strong or stable acid such as phosphoric acid or sulfuric acid, it results in a polymer electrolyte that

easily forms a single-phase system in which the acid is dissolved in the polymer, in contrast to conventional phosphoric acid systems in which the acid is only contained in the pores of the inert second phase of the polymer system.

Currently known commercially available sulfonic acid ionomers, for example Nafion 117 and Dow 560, depend on water to solvate the protons generated by the ionization of the sulfonic acid groups. When the polymers are subjected to temperatures above 100 ⁰ C at atmospheric pressure, water is lost, including the water that solvates the hydronium ions. The membrane shrinks and conductivity is lost. The use of a pressurized system can extend the useful temperature range, but at the expense of overall system efficiency, size and weight. For example, temperatures of 120 ⁰ C can be approached at pressures of about 2 atm of water. Furthermore, at an operating temperature of 200 ⁰ C, the pressure required for these membranes is too high to be of practical use.

Suitable basic polymers which form complexes with stable acids include polybenzimidazoles, polypyridines, polypyrimidines, polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines, polythiadiazoles and poly(tetrazapyrenes). The polymers may contain a variety of functional groups as seen below using the polybenzimidazole polymer as an example:

where R

an alkane chain, fluoroalkane chain or similar linkage. Examples of other basic polymers are listed below.

¹ S ₁ X / K_ X U X ^ .R^ -^ ^^ NO _{. 1} X _/

The following polymers may be slightly less stable than the above at 200 ⁰ C for long periods of time, but should still work at lower temperatures above 100 ⁰ C:

--CH ₂ -&sfgr;&EEgr;+ 4-CH ₂ -CH-

^vv -N

-CH ₂ -CtT- V

^CT1

—CH-CH--

-CH-CH ₉ --

.&khgr;

where Ri = H, alkyl, phenyl, pyridyl, each independently of other Ri.

Another suitable polymer that works in the same way is polybenzobisimidazole,

where R and Ri are as defined above.

Furthermore, in the above polymers, the NRi functionality can be replaced by X, where X = O or S.

The basic polymers listed are readily protonated and show improved thermal stability when the molecules consist only of aromatic groups. Other suitable basic polymers that can be substituted with the foregoing R, Ri and X groups include oxazoles:

Thiazoles:

Poly(oxadiazoles) and -thiadiazoles, both as a basic main group and as a linking group for benzimidazoles, benzoxazole and benzthiazole polymers.

·*

·

The listed linkages can be used in any position and copolymers can be formed from any group, as will be known to those skilled in the art.

Of the foregoing, the quinoxalines are the least desirable because they are the least basic of the polymers listed, although when doped they are also suitable as PEMs. The polymers contemplated for use herein which exhibit solubility in dilute acids can be made more stable by known cross-linking techniques, including free radical cross-linking.

Of the foregoing, preferred basic polymers include polypyrimidines, polyimidazoles and polybenzoxazoles, and particularly preferred basic polymers are polybenzimidazoles, which are used as an exemplary polymer in the remainder of this disclosure, and polypyridines.

Suitable polymers also include acidic polymers or polymers containing acidic groups such as sulfonates, phosphonates, boronates, etc. For example

(SO ₃ H) _n (SO ₃ H) _n

¹ I-Tv

J X

S--

SUN ₃ H

CH ₂ -(PO(OH) ₂ ) o—

_CH2 -PQ(OH) ₂

and similar polymers wherein R is as defined herein, Y is -O-, -S-, -SO2-, -CH- or CH2 and η is 0 to 1.

All polymers shown herein containing sulfuric acid groups, with the exception of polybenzimidazoles, can also be prepared with boric acid or phosphoric acid groups. This is achieved by halogenating the polymer backbone and reacting it with trialkyl or aryl borates or trialkyl or aryl phosphates.

Of the foregoing, sulfonates are preferred acidic group-containing polymers, and phosphonates are the most preferred acidic group-containing polymers.

The preferred PEM polybenzimidazole membranes are made by synthesizing the polybenzimidazole Ims which is doped with a strong acid such as sulfuric acid or phosphoric acid to produce a polymer whose acidic anion is bonded to the protonated polybenzimidazole. The protons are ionized by the basic nitrogen atoms in the polybenzimidazole rings as shown below:

In general, any polymer containing a basic group B can be protonated by a strong acid such as phosphoric acid to produce a polymeric solid electrolyte.

(BR) _x

H ⁺

_{H2PO4 -}

The previously mentioned PBIs are known to have excellent oxidative and thermal stability and are further stabilized by reaction with the dope acid. In the case of sulfuric acid, reactions at temperatures exceeding 200 ^° C sulfonate the benzene ring to form bonded SC>3H groups. Proton hopping between basic sites on the polymer compound and/or with imbibed free acid provides enhanced ionic conductivity. Furthermore, the barrier properties of these polymer films are enhanced due to the single-phase morphology of the material as compared to the biphasic nature of nonpolar fluorocarbon/polar ionic membranes. "Single-phase morphology" refers to a microscopic continuous matrix of a single material as opposed to a biphasic system of a polar phase mixed with a nonpolar phase.

When operated in a fuel cell using a suitable fuel such as methanol, the PBI polymer electrolyte membrane conducts protons from the fuel electrode to the oxygen cathode. Carbon monoxide, present in fuels such as reformed hydrogen, poisons the platinum catalyst commonly used in fuel cells. Liquid fuels such as methanol produce even more severe poisoning effects because carbon monoxide is an intermediate in the fuel oxidation process. However, at higher temperatures, approaching 200 ^° C, cell operation promotes carbon monoxide oxidation to carbon dioxide, resulting in significantly improved catalyst activity despite the poisoning effects of the carbon monoxide. However, prior to the present invention, which is operable at temperatures up to at least 200 ^° C, no proton-conducting polymer electrolytes were available.

The foregoing features of the PBI polymer are demonstrated by other polymers of the type described hereinabove which are suitable for use as polymer electrolyte membranes. For example, polybenzimidazoles,

Polypyridines, polypyrimidines, polyimidazoles, polybenzoxazoles, polyoxadiazoles, polyquinoxalines, polythiadiazoles and poly(tetrazapyrenes) each have a single-phase morphology and consequently show high proton conductivity and low methanol permeability.

The invention will now be described with reference to the preferred embodiment of the invention, i.e., the use of the polybenzimidazole polymer. The following examples and associated test data are merely exemplary and are not intended to limit the present invention in any way. Useful variations of the present parameters and also other aspects of the materials, their preparation and their use will be apparent to those skilled in the art and will be covered by the specification and appended claims if they fall within the scope and limitations thereof. For example, those skilled in the art will be able to substitute suitable polymers such as those described herein for the exemplary polymers and obtain reasonable results.

PEM production

Films of polybenzimidazole were prepared by dissolving the polymer (20%) in dimethylacetamide (DMAc) containing LiCl (2%) and spraying it onto a clean glass plate using a Gardner knife. The film was heated at 150 ^0C in air for 15 min. It was removed from the glass plate and heated in a vacuum oven at ⁹⁰ 0C overnight to dry the film. The LiCl was then extracted from the film with water. The films were doped with H2SO4 or H3PO4 by acid sorption from aqueous solutions.

To fully demonstrate the capabilities of the present PBI, additional polymer electrolyte membranes were obtained and evaluated under similar test conditions. In the following text, Nafion membranes were prepared as follows: Nafion 117 membranes (acidic form) were obtained from duPont and hydrated by immersion in boiling water for four hours. Following hydration, samples were either left in distilled water until use or equilibrated with phosphoric acid.

1.2

Conductivity measurements

Conductivity measurements were performed using a four-point probe apparatus. In this apparatus, two platinum foil electrodes were clamped to the end of a 3 cm (L) x 0.5 cm (W) polymer sample. These electrodes were used to pass current through the sample. The magnitude and frequency of the applied current were controlled using a PAR 173 potentiostat/galvanometer and a Wavetek 186 signal generator. Two platinum wires (0.5 mm diameter) spaced 1 cm apart were used to measure the voltage drop at the center of the sample. Voltage measurements were made at three or more current levels to ensure that the voltage-current behavior was resistive. The current was applied at two different frequencies: 100 and 1000 Hz. No frequency dependence was observed. The entire apparatus was contained in a sealed steel vessel located in a furnace and connected to a gas distribution system so that the temperature, pressure and composition of the gas phase in contact with the sample could be controlled. Measurements as a function of water partial pressure above 100 ⁰ C were made by partially evacuating the cell and then injecting sufficient liquid water through a septum to obtain the desired water partial pressure.

Conductivity results are shown below in Table I for films at 170 ⁰ C and 400 Torr water partial pressure. Conductivity and voltage drop for a fuel cell operating at 100 mA/cm ² are shown. This PBI sample contained approximately 250 mol% H ₂ SO ₄ , that is, about 2.5 molecules of H ₂ SO ₄ on each polymer repeat unit.

YYYY J·· · . . .

• · ··· «Y Y Y·*. .J YJ Y

Table I

Membrane conductivity

Membrane/
electrolyte Conditions Conductivity/
OmTi ¹ Cm ¹ Voltage loss
at 100 mA/cm ² Nafion 117
» 80 ⁰ C
SAT H ₂ O 0.07 29mV Nafion 117 120 ⁰ C
400 Torr _H2O 0.0036 555mV
(8mils) PBI _{/ H2SO4} 170°C
400 Torr _H2O 0.02 25mV
(2mils) PBI _{/ H3PO4} 180°C
408 Torr H ₂ O 0.01 5OmV

The conductivity results for the phosphoric acid doped polybenzimidazole material are further shown in Figure 1 as a function of temperature and water partial pressure. The PBI samples contained approximately 334 mol% H3PO4, that is, about 3.35 H3P0 ₄ molecules on each repeat unit. In this graph, the conductivity is shown as a function of water activity for temperatures from 130 ⁰ C to 197 ⁰ C. The conductivity increases with temperature and water activity. The higher the conductivity, the lower the ohmic loss in the fuel cell and hence the greater its efficiency. These conductivities are at least an order of magnitude greater than those of Nafion under similar conditions.

Permeability tsmessu &eegr; ge &agr;

The permeability of oxygen through a PBl film doped with H ₂ SO ₄ according to the present invention was measured using the closed volume technique. The permeability was measured in the same manner for a Nafion 117 film equilibrated with phosphoric acid and Nafion equilibrated with water. The results are summarized in Table 1. The current density column represents the current density corresponding to the flux through the membrane with a pressure differential of one atmosphere as the driving force. The

·

The corresponding current density was calculated as i = nFN, where η = 4 for the oxygen reduction reaction, F is the Faraday constant and N is the flux.

Table 2
Oxygen permeability

Membrane/
electrolyte Temperature/ ⁰ C Current density/mA/cm ² PBI _{/ H2SO4} 80 0.08 Nafion 117/ _H2O 80 0.6 - 0.8 Nafion 117/ H ₃ PO ₄ 123 0.35 - 0.45 Nafion 117/ H ₃ PO ₄ 150 0.25 - 0.67

The permeability of oxygen in the Nafion equilibrated with phosphoric acid at temperatures above 100 ⁰ C is similar to that in Nafion equilibrated with water at 80 ⁰ C. These permeabilities exceed those of oxygen in phosphoric acid. Consequently, the cathode performance is improved by the presence of Nafion because O2 can more easily reach the catalyst sites. The loss of O2 by crossover is not significant because O2 has low solubility. The lowest oxygen permeability was obtained with the polybenzimidazole material, which was expected to show good barrier properties. However, these permeabilities should still be sufficient for fuel cell applications.

The permeabilities of other gases in acid-doped PBI are shown in Table 1. The methanol crossover rate with PBI is on the order of 5 to 11 mA/cm ² . This crossover value is low compared to the values of 100 to 250 mA/cm ² reported for liquid-feed direct methanol fuel cells with Nafion 117 at 80 ⁰ C, as determined by measurements of 250 mA/cm ² , based on pre-evaporation data, in S. Kato et al., T- Membrane Science, 72 (1992).; 100 mA/cm ² in liquid-entry PEM cells in S. Narayanan et al., Extended Abstracts of Electrochemical Society, vol. 93-2, p. 126, Pennington, NJ (1993); and 100 mA/cm ² at 100 ASF in liquid-entry PEM cells in D. Maricle et al., Extended Abstracts of Electrochemical Society, vol. 94-1, p. 58, Pennington, NJ (1994).

· I

·

·

Table III

Permeability of doped polybenzimidazole

Doping

gas

temperature

/ ⁰ C

permeability

Corresponding CD/mA/cm ²

_{H2SO4 ​}

Methanol

175, 320

7.13

_{H2SO4 ​}

Methanol

130

139,156

5.6

_{H3PO4 ​}

Methanol

130

183,186

7.7

_{H3PO4 ​}

Methanol

155

270

11

_{H2SO4 ​}

Water

130

9000,10000

_{H3PO4 ​}

Water

150

4400

SV &iacgr;"'

?' r* µ.'&Uacgr;-&idiagr;&bgr;

_{H3PO4 ​}

hydrogen

150

180

_{H2SO4 ​}

oxygen

125

11.20

0.3, 0.6

_{H3PO4 ​}

oxygen

140

0.3

Permeability coefficients are given in Barrer. Barrer = 10" ¹ cm ³ (STP) cm/cm ² s cmHg
Multiple entries show results from multiple samples. Corresponding current densities assume a pressure differential of one atmosphere

in advance.

H ₂ SO ₄ dope levels 247 mol% HsPO^dope levels 338 mol%

Thermal stability measurements

Thermogravimetric analysis (TGA) was used to investigate the thermal stability of polybenzimidazole and to follow the reaction between PBI film and sulfuric acid. In Figure 2, the TGA scan for an undoped PBI film in nitrogen is shown. The heating rate was 10 °C/min. The PBI film lost water at about 80 ⁰ C and was subjected to thermal degradation at 550 ⁰ C. The TGA of PBI doped with about 20 mol% sulfuric acid is shown in Figure 3. This result shows a water loss at 100 ⁰ C and showed

· · · · 11»» &igr; it &igr;

also two further weight losses starting at 330 ⁰ C and 415 ⁰ C. The first loss at 330 ⁰ C is attributed to the reaction of the acid with BPI to form sulfonic acid groups, while the second loss is probably due to the loss of SO2 or SO3 from the polymer. The weight loss due to thermal degradation has been shifted to 600 °C, indicating that the reaction with the sorbed acid improves the thermal stability of the film.

Figure 4 shows the dynamic mechanical spectroscopy of a PBI film doped with 320 mol% phosphoric acid (this film has about 50 wt% phosphoric acid). The modulus at room temperature before heating is normal for a glassy polymer. On the first heating, the modulus drops and reaches a plateau at about 2 × 10 ⁹ Pascal. Between 160 and 200 ⁰ C, the modulus drops to about δ × 10 ⁸ Pascal and reaches a plateau. On the second heating, the modulus was much higher (1 × 10 ¹⁰ Pascal), which starts to drop at 150 ⁰ C and reaches a plateau of 1 × ^{10 9} Pascal. When used as a fuel cell, the PEM modulus will be about 3 × ^{10 9} Pascal. This value is about 10 ⁴ times higher than Nafion at 150 ⁰ C. The stiffer membrane can be made thinner without deformation when used in a fuel cell. Thinner membranes will have lower electrical resistance and will therefore be more effective.

In Figure 5, the polarization and energy density curves are shown for a PBI cell operating with hydrogen and oxygen at 150 ⁰ C. The membrane was a 0.075 mm PBI film doped with 470 mol% H3PO4. The gases were humidified at very low levels (20 ⁰ C O2, 48 ⁰ C Hi). These tests were performed in a 1 square centimeter micro fuel cell with platinum on carbon supported electrodes (0.5 mg Pt/cm ² ). In Figure 5A, the cell voltage is shown as a function of current. The insulation resistance-free (IJR-free) curve represents the data when the ohmic loss is subtracted. The curve shows the efficiency of the electrodes (more efficient at higher voltage values). The energy of the fuel cell is the product of the voltage and current and is shown in Figure 5C. This curve shows a maximum energy of about 0.25 W/cm ² at about 700 mA/cm ² . This energy level is quite high for a PEM fuel cell, considering the operating temperature and the lack of strong gas humidification.

The curves in Figure 5B show the individual cathode and anode potentials, which show that electrode voltage losses are very low, below 10 mA/cm ² . This fuel cell is not optimized, and performance can be improved with the use of thinner membranes and better electrode structures.

Figure 6 shows the polarization curve of a PBI fuel cell operating with a methanol:water mixture for the fuel and oxygen as the oxidant. The cathode was 4 mg/cm ² Pt on carbon, while the anode was 1.2 mg/cm ² Pt/Ku alloy. The membrane was a 0.075-0.09 mm 450 mol% H ₃ PO ₄ /PBI film. An anode with Pt black catalyst is also given for comparison. In this non-optimized methanol fuel cell operating at "150 ⁰ C, a cell voltage of 0.3 volts at 100 mA/cm ² was achieved.

The invention has been described by way of example. Obviously, changes and modifications will occur to others upon reading and understanding the foregoing detailed description. It is intended that the invention be construed to include all changes and modifications insofar as they come within the scope of the appended claims or their equivalents.

Claims (33)

1. A polymeric solid electrolyte membrane comprising a proton-conducting polymer that is stable at temperatures above 100°C. 2. A polymeric solid electrolyte membrane according to claim 1, characterized in that said proton-conducting polymer is a basic polymer doped with a strong acid at an acid dope level of at least 200 mol%. 3. Polymeric solid electrolyte membrane according to claim 2, characterized in that said basic polymer is selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazapyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinylimidazoles. 4. Polymeric solid electrolyte membrane according to claim 2, characterized in that said basic polymer is selected from the group consisting of poly(pyrimidines), polyimidazoles, polybenzoxazoles, poly(pyridines) and polybenzimidazoles. 5. Polymeric solid electrolyte membrane according to claim 2, characterized in that said basic polymer is polybenzimidazole. 6. Polymeric solid electrolyte membrane according to claim 2, characterized in that said basic polymer is an aromatic polymer. 7. A polymer solid electrolyte membrane according to claim 2, characterized in that said strong acid is selected from the group consisting of sulfuric acid and phosphoric acid. 8. Polymeric solid electrolyte membrane according to claim 1, characterized in that said proton-conducting polymer is an acidic polymer. 9. A polymeric solid electrolyte membrane according to claim 8, characterized in that said acidic polymer is selected from the group consisting of sulfonic acid polymers, phosphonic acid polymers and boronic acid polymers. 10. A polymeric solid electrolyte membrane according to claim 8, characterized in that said acidic polymer is a sulfonic acid polymer. 11. A high temperature proton conducting polymer comprising a basic polymer complexed with a strong acid capable of conducting protons at temperatures above 100°C. 12. A high temperature proton conducting polymer according to claim 11, characterized in that said basic polymer is an aromatic polymer. 13. A high temperature proton conducting polymer according to claim 11, characterized in that said basic polymer is selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazapyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinylimidazoles. 14. A high temperature proton conducting polymer according to claim 11, characterized in that said basic polymer is selected from the group consisting of poly(pyrimidines), polyimidazoles, polybenzoxazoles, poly(pyridines) and polybenzimidazoles. 15. A high temperature proton conducting polymer according to claim 11, characterized in that said basic polymer is polybenzimidazole. 16. A high temperature proton conducting polymer according to claim 11, characterized in that said strong acid is selected from the group consisting of sulfuric acid and phosphoric acid. 17. A hydrogen or direct methanol fuel cell comprising (a) an anode, (b) a cathode, and (c) an electromembrane made of an acid-doped basic polymer that conducts protons at temperatures above 100°C. 18. A hydrogen or direct methanol fuel cell according to claim 17, characterized in that said polymeric electrolyte membrane exhibits low fuel permeability. 19. The direct methanol fuel cell of claim 17, wherein said acid-doped basic polymer electrolyte is derived from a basic polymer selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polyimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazapyrenes), polyoxazoles, polythiazoles, polyvinylpyridines, and polyvinylimidazoles. 20. The direct methanol fuel cell of claim 17, wherein said basic polymer is selected from the group consisting of poly(pyrimidines), polyimidazoles, polybenzoxazoles, poly(pyridines) and polybenzimidazoles. 21. Direct methanol fuel cell according to claim 17, characterized in that said electrolyte is derived from the acid-doped basic polymer of polybenzimidazole. 22. A direct methanol fuel cell according to claim 17, characterized in that said acid is a strong acid. 23. A direct methanol fuel cell according to claim 17, characterized in that said acid is selected from the group consisting of sulfuric acid and phosphoric acid. 24. An acid fuel cell containing a polymeric solid electrolyte membrane comprising an acid-doped basic polymer. 25. The acid fuel cell of claim 24, wherein said basic polymer is selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polyimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazapyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinylimidazoles. 26. The acid fuel cell of claim 24, wherein said basic polymer is selected from the group consisting of poly(pyrimidines), polyimidazoles, polybenzoxazoles, poly(pyridines) and polybenzimidazoles. 27. An acid fuel cell according to claim 24, characterized in that said basic polymer is polybenzimidazole. 28. An acid fuel cell according to claim 24, characterized in that said polymeric solid electrolyte membrane comprises phosphoric acid doped polybenzimidazole. 29. An electrolytic cell containing a polymeric solid electrolyte membrane comprising an acid-doped basic polymer. 30. An electrolytic cell according to claim 299, characterized in that said basic polymer is selected from the group consisting of polybenzimidazole, poly(pyridine), poly(pyrimidine), polyimidazoles, polybenzthiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazapyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinylimidazoles. 31. Electrolytic cell according to claim 29, characterized in that said basic polymer is selected from the group consisting of poly(pyrimidines), polyimidazoles, polybenzoxazoles, poly(pyridines) and polybenzimidazoles. 32. Electrolytic cell according to claim 29, characterized in that said basic polymer is polybenzimidazole. 33. An electrolytic cell according to claim 29, characterized in that said polymeric solid electrolyte membrane comprises phosphoric acid doped polybenzimidazole.