JP2003151577A - Fuel-cell cell unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel-cell cell unit, in which even if an electrolyte layer (film), which consists of proton-conductive gel, is created by the sol-gel processing, the pores in the catalyst layer are not buried by the electrolyte material, and the utilization factor platinum catalyst increases and a high battery performance is obtained since the reaction gas is fully supplied to the catalyst layer. SOLUTION: In the fuel-cell cell unit, which has the cell structure, in which the catalyst layer and a gas diffusion layer are arranged to this order, respectively, on both sides of the main side of the electrolyte layer, the above electrolyte layer consists of the proton-conductive gel, and an interlayer, who contains carbon particles and the electrolyte material at least between the above electrolyte layer and the catalyst layer, is formed. The porosity of the above interlayer is smaller than the porosity of the above catalyst layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell unit having an electrolyte layer made of a proton conductive gel.

[0002]

2. Description of the Related Art A fuel cell has a cell structure in which an electrolyte layer is sandwiched between a fuel electrode catalyst layer and an air electrode catalyst layer on both sides of a main surface, and this is arranged between two gas diffusion layers. A reaction gas containing oxygen and a reaction gas containing oxygen (oxidant gas) are supplied to the air electrode side to react hydrogen with oxygen to generate power. Air is generally used as the reaction gas supplied to the air electrode side. As the reaction gas supplied to the fuel electrode side, in addition to pure hydrogen gas, fuel gas such as natural gas or light hydrocarbon such as naphtha is used as a fuel gas reforming system (reformer, CO modifier, C
A hydrogen-rich reformed gas that has been reformed by using an O remover or the like) is used.

Various types of electrolyte layers are used. Among them, a polymer electrolyte fuel cell using a solid polymer membrane made of a cation exchange resin as an electrolyte is used for vehicles, mobile phones, households. Widely applied as a power source for business.

On the other hand, in recent years, a proton conductive gel has been studied as an electrolyte for fuel cells. This proton-conducting gel is mainly composed of silicon oxide and Bronsted acid (phosphoric acid, etc.) prepared by a sol-gel method, as disclosed in, for example, JP-A-8-249923 and JP-A-11-203936. The fuel cell using the compound as an electrolyte has a higher operating temperature (150 ° C) than the operating temperature (about 60 to 100 ° C) of the polymer electrolyte fuel cell.
Power can be generated at (° C). Therefore, like the conventional polymer electrolyte fuel cell, the high-temperature reformed gas from the fuel gas reforming system is supplied to the operating temperature (about 60 to 100 ° C.) of the fuel cell.
Therefore, it is not necessary to cool it significantly, and the thermal efficiency for power generation can be dramatically improved. In a polymer electrolyte fuel cell, internal resistance increases and power generation efficiency decreases if the polymer electrolyte membrane is not sufficiently wet, but the proton conductive gel requires more water than the polymer electrolyte membrane during power generation. In other words, stable power generation is possible even at relatively high temperatures compared to polymer electrolyte fuel cells. Thus, it is considered that the use of the above-mentioned proton-conducting gel in the electrolyte can solve many of the problems of the polymer electrolyte fuel cell.

[0005]

FIG. 4 is an explanatory view schematically showing a cross section of a conventional fuel cell unit. The conventional fuel cell unit 20 includes a fuel electrode catalyst layer 22 and a fuel electrode gas diffusion layer 2 on both sides of the main surface of an electrolyte layer 21, respectively.
3 and the air electrode catalyst layer 24 and the air electrode gas diffusion layer 25 are arranged in this order to have a cell structure.

To form the electrolyte layer 21 (membrane) by the sol-gel method, for example, a gas diffusion layer 23 (for example, carbon paper filled with carbon powder and polytetrafluoroethylene powder) is joined and laminated. A catalyst layer 22 (for example, a sheet in which carbon particles carrying platinum and polytetrafluoroethylene (PTFE) are mixed) and a gas diffusion layer 25 (for example, carbon paper filled with carbon powder and polytetrafluoroethylene powder) are joined, Laminated air electrode catalyst layer 24 (for example, platinum supporting carbon particles and polytetrafluoroethylene (PT
It is produced by pouring a sol between (sheets mixed with FE) and gelating the solvent by naturally drying the solvent in the air to obtain a proton conductive gel.

However, in the conventional fuel cell unit 20 having such a cell structure, the pores in the catalyst layers 22 and 24 are filled with the electrolyte material, the diffusivity of the reaction gas is lowered, and the electrode reaction site ( Since the electrolyte / catalyst / reaction gas phase (three-phase interface) is reduced and the utilization rate of the platinum catalyst is reduced, there is a problem that the battery performance is reduced.

The object of the present invention is to solve the above problems of the prior art, and even if an electrolyte layer (membrane) made of a proton conductive gel is prepared by the sol-gel method, the pores in the catalyst layer can be filled with the electrolyte material. Since the reaction gas is sufficiently supplied to the catalyst layer, the utilization rate of the platinum catalyst (the rate used for the electrode reaction) is increased, and high battery performance can be obtained. Since the adhesion between the electrolyte layer and the electrolyte layer is maintained well, even if stress is applied from the outside, destruction of micro contact points between the catalyst layer and the electrolyte layer is prevented, and high battery performance can be maintained. Is to provide.

[0009]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the conventional problems, as a result, at least carbon particles and an electrolyte material are contained between the electrolyte layer and the catalyst layer, and specific pores are contained. It has been found that the problem can be solved by the presence of an intermediate layer having a ratio, and the present invention has been accomplished.

That is, the fuel cell unit according to claim 1 of the present invention for solving the above problem has a cell structure in which a catalyst layer and a gas diffusion layer are arranged in this order on both sides of the main surface of the electrolyte layer. In the fuel cell unit, the electrolyte layer is made of a proton conductive gel, an intermediate layer containing at least carbon particles and an electrolyte material is formed between the electrolyte layer and the catalyst layer, and the pores of the intermediate layer are formed. The porosity is smaller than the porosity of the catalyst layer.

A fuel cell unit according to a second aspect of the present invention is the fuel cell unit according to the first aspect, wherein the proton conductive gel is SiO ₂ , Al ₂ O.
₃ , a material selected from TiO ₂ , V ₂ O ₅ , and ZrO ₂ and a material selected from phosphoric acid, perchloric acid, boric acid, and silicic acid.

In the fuel cell unit of the present invention, a proton conductive layer is formed by the sol-gel method by providing an intermediate layer containing at least carbon particles and an electrolyte material and having a specific porosity between the electrolyte layer and the catalyst layer. Even if an electrolyte layer made of a hydrophobic gel is created, the pores in the catalyst layer are not filled with the electrolyte material, so that the reaction gas is sufficiently supplied to the catalyst layer, the utilization rate of the platinum catalyst is increased, and high battery performance is achieved. Therefore, there is an effect that the amount of platinum catalyst can be reduced, and because the carbon particles in the intermediate layer act to enhance the adhesion between the catalyst layer and the electrolyte layer, the adhesion between the catalyst layer and the electrolyte layer is improved. Since it is maintained, even if stress is applied from the outside, destruction of micro contact points between the catalyst layer and the electrolyte layer is prevented, and high battery performance can be maintained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory view schematically showing a cross section of a fuel cell unit of the present invention. Figure 2
[Fig. 2] is an assembly explanatory diagram of a fuel cell unit laminate formed by using the fuel cell unit shown in Fig. 1.

As shown in FIG. 1, the fuel cell unit 1 of the present invention has a fuel electrode catalyst layer 3, a fuel electrode gas diffusion layer 4, and an air electrode catalyst layer 5 on both sides of the main surface of an electrolyte layer 2.
And an air electrode gas diffusion layer 6 are arranged in this order, and at least carbon particles 7 and an electrolyte material 8 are provided between the electrolyte layer 2 and the catalyst layer 3 and between the electrolyte layer 2 and the catalyst layer 5. The intermediate layers 9 including each are formed. The porosity of the mid layer 9 is smaller than that of the catalyst layers 3 and 5. Since the pores 10 are not filled with the electrolyte material 8 in the catalyst layers 3 and 5, the reaction gas is sufficiently supplied to the catalyst layers 3 and 5, and the utilization rate of the platinum catalyst is increased, so that high battery performance is obtained. To be Since the carbon particles 7 in the intermediate layer 9 serve to enhance the adhesiveness between the catalyst layers 3 and 5 and the electrolyte layer 2, the adhesiveness between the catalyst layers 3 and 5 and the electrolyte layer 2 is maintained well. Even if stress is applied to the fuel cell unit 1 from the outside, destruction of micro contact points between the catalyst layers 3 and 5 and the electrolyte layer 2 is prevented, and high battery performance can be maintained.

The porosity in the present invention was measured by the following method. The volume of all pores is measured by the mercury porosimetry using a pore sizer 9310 manufactured by Shimadzu Corporation, and the porosity (volume%) is calculated from the measurement result.

As shown in FIG. 2, the fuel cell unit laminate 30 has a structure in which the fuel cell unit 1 is laminated between the air electrode side channel plate 15 and the fuel electrode side channel plate 16. In the fuel cell unit 1, the intermediate layer 9, the air electrode catalyst layer 5, and the gas diffusion layer 6 are sequentially bonded to one surface of the electrolyte layer 2, and the intermediate layer 9, the fuel electrode catalyst layer 3, and the gas diffusion layer 4 are sequentially bonded to the other surface. It has a laminated structure. The fuel cell is assembled in a structure (cell stack) in which a plurality of stacks 30 are stacked and both ends thereof are fixed by a pair of end plates so that high output power can be taken out. The air electrode catalyst layer 5 and the fuel electrode catalyst layer 3 are formed of, for example, catalyst-supporting particles (platinum-supporting carbon particles and polytetrafluoroethylene (PTF).
It is formed from a mixture of E).

For the gas diffusion layers 4 and 6 used in the present invention, specifically, for example, a base material (carbon paper) having a thickness of about 200 μm is coated and filled with a mixed slurry of a water-repellent resin (for example, PTFE) and carbon powder. Formed. The gas diffusion layers 4 and 6 are also called current collectors, and ensure the flow of current between the air electrode catalyst layer 5, the fuel electrode catalyst layer 3, and the channel plates 15 and 16.

The fuel electrode side channel plate 16 is a member formed by injection-molding a resin material such as phenol resin mixed with carbon powder, and is formed on the surface facing the fuel electrode side gas diffusion layer 4 in the x direction. The ribs 166 are juxtaposed at regular intervals in the y direction with the longitudinal direction as the longitudinal direction, thereby forming a channel 165 through which the fuel gas (hydrogen or hydrogen-rich reformed gas) flows.

The air electrode side channel plate 15 is a member substantially similar to the fuel electrode side channel plate 16, and is arranged on the surface facing the air electrode side gas diffusion layer 6 at regular intervals in the x direction with the y direction as the longitudinal direction. Ribs (not shown) are installed side by side,
As a result, channels are formed to allow the oxidant gas (oxidant such as air) to flow in the same direction.

In order to form the internal manifold, these components 1 to 16 have openings (131) at the four corners of each main surface.
~ 134, 151-154, 161-163 are shown), of which the openings 161, 131,
Reactant gas (fuel gas) is supplied to the channel 165 of the fuel electrode side channel plate 16 by the opening portion including 151 and extending in the z direction, and the opening portion including the opening portions 163, 133 and 153 and extending in the z direction. Thereby supplying a reaction gas (oxidant gas such as air) to a channel (not shown) of the air electrode side channel plate 15, and the openings 132, 162, 15 are formed.
It is discharged through the open hole portion including 2 in the z direction.

During operation of such a fuel cell, the fuel electrode side
Hydrogen gas (hydrogen-rich reformed gas), air on the air electrode side
To supply. This causes hydrogen to become a proton at the fuel electrode.
(H ₂ → 2H⁺ + 2e^- ), In the gel of the electrolyte layer 2
To the air electrode side. On the other hand, oxygen in the air moves
Reacts with incoming protons to produce water (2H⁺ + 2e^-+
1 / 2O₂ → H₂ O). Little water in the electrolyte layer 2
Even if it contains no
The roton is conducted and the power generation reaction is performed.

The electrolyte layer 2 is made of a proton conductive gel.
SiO₂ , Al₂ O₃ , TiO ₂ , V₂ O_Five , Zr
O₂ Materials selected from among
Substance) and Bronsted acid (phosphoric acid, perchloric acid, boric acid,
Of compounds that act as proton donors such as silicic acid)
Bronsted acid comprising a material selected from
High concentration of hydroxyl groups on the terminal surface of silicon oxide etc.
It has a chemical structure that is bound in degrees.

The electrolyte layer 2 is produced by the sol-gel method. First, a solution (sol) of a proton conductive material (electrolyte material)
(For example, ethyl silicate Si (OC ₂ H ₅ ) ₄ + trimethyl phosphate PO (OCH ₃ ) ₃ + water + ethanol C ₂
H ₅ OH + HCl HCl molar ratio 1: 0.04: 1: 1:
Mix (hydrolyze) in a ratio of 0.0027, and mix this solution with water + ethanol C ₂ H ₅ OH + hydrochloric acid HCl in a molar ratio of 4: 1: 0.011 to 1 mol of ethyl silicate. Then, the mixture is stirred for 1 hour to prepare a sol), and the solvent in the sol is naturally dried in the air to cause gelation by a polycondensation reaction.

The above description of the embodiments is for explaining the present invention and does not limit the invention described in the claims or reduce the scope thereof. Further, the configuration of each part of the present invention is not limited to the above embodiment, but various modifications can be made within the technical scope described in the claims.

[0025]

EXAMPLES The contents of the present invention will be described more specifically below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples without departing from the gist of the present invention. (Example 1) (electrolyte material for manufacturing a sol containing) ethyl silicate _{Si (OC 2 H 5) 4} + trimethyl phosphate PO (OCH _{3) 3} + water + ethanol C ₂ H ₅ OH +
HCl with a molar ratio of 1: 0.04: 1: 1: 0.002
Mixed (hydrolyzed) at a ratio of 7. Water + ethanol C ₂ H ₅ OH + hydrochloric acid HCl
In a molar ratio of 4: 1 to 1 mol of ethyl silicate.
The mixture was mixed at a ratio of 0.011 and further stirred for 1 hour or more to proceed with hydrolysis and polycondensation reaction to prepare a sol containing an electrolyte material having an increased viscosity.

(Preparation of Gas Diffusion Layer) Carbon paper was impregnated with 16% by mass of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and then heat-treated at 380 ° C. for 1 hour. A slurry in which carbon powder and PTFE powder were mixed at a mass ratio of 60:40 was applied from both sides of this carbon paper and filled into the carbon paper. Then, it heat-processed at 380 degreeC for 2 hours.

(Preparation of catalyst layer sheet) A mixture of platinum-supporting carbon powder and PTFE powder (mass ratio 70:30) was formed into a sheet having a thickness of 40 μm, and a thickness of 80 μm.
A sheet molded into m was prepared. Incidentally, the amount of platinum per unit area, when the thickness 40μm of the catalyst layer sheet 0.6 mg / cm ^2, when the thickness 80μm of the catalyst layer sheet was 1.2 mg / cm ^2. (Preparation of intermediate layer precursor sheet) Carbon powder and PTFE
A mixture with powder (mass ratio 70:30) was formed into a sheet having a thickness of 40 μm to prepare a sheet. This was used as the intermediate layer precursor.

(Preparation of Fuel Cell Unit A of the Present Invention) A gas diffusion layer, a catalyst layer sheet having a thickness of 40 μm, and an intermediate layer precursor sheet are stacked in this order, and the temperature is 150 ° C. and 20 kgf /
Bonding was performed by hot pressing at 30 cm ² for 30 seconds. The solvent in the sol was placed in the atmosphere in the state where the sol containing the electrolyte material was sandwiched between the two sheets (fuel electrode side and air electrode side) thus prepared with the intermediate layer precursor sheet side facing each other. Air-drying, polycondensation reaction progresses gelation and bonding,
A fuel cell unit A of the present invention whose cross section is schematically shown in FIG. 1 was produced. The electrolyte material penetrated into the intermediate layer precursor sheet to form the intermediate layer, but the electrolyte material did not penetrate much into the catalyst layer sheet, so that the porosity of the intermediate layer was higher than that of the catalyst layer. It was small. The thickness of the electrolyte layer thus formed was 100 μm.

(Comparative Example 1) A gas diffusion layer and a catalyst layer sheet having a thickness of 40 μm were stacked in this order, and the temperature was 150 ° C. and 20 kgf /
Bonding was performed by hot pressing at 30 cm ² for 30 seconds. With the sol containing the electrolyte material sandwiched between the two sheets (fuel electrode side and air electrode side) thus prepared, the catalyst layer sheet side facing each other, the solvent in the sol was naturally dissolved in the atmosphere. A fuel cell unit X for comparison having a cross section schematically shown in FIG. 4 was manufactured by drying and advancing gelation by a polycondensation reaction. The electrolyte material penetrated almost the entire thickness of the catalyst layer sheet. The thickness of the electrolyte layer thus formed is 1
It was 00 μm.

Comparative Example 2 A comparative fuel cell unit Y whose cross section is schematically shown in FIG. 4 was prepared in the same manner as in Comparative Example 1 except that a catalyst layer sheet having a thickness of 80 μm was used.
The electrolyte material penetrated almost half of the thickness of the catalyst layer sheet.
The thickness of the electrolyte layer thus formed is 100 μm
Met.

(Cell characteristic test) Operating temperature of 120 ° C., hydrogen (non-humidified) as a fuel, air (non-humidified) as an oxidant gas, and a fuel cell unit A of the present invention having an electrode area of 25 cm ² and a comparative example. The results of testing the cell voltage-current characteristics of the fuel cell units X and Y are shown in FIG.

From FIG. 3, it can be seen that the fuel cell unit A of the present invention exhibits higher power generation characteristics than the comparative fuel cell unit X. The power generation characteristics of the comparative fuel cell unit X are low because the electrolyte material invades the catalyst layer, the pores in the catalyst layer are filled with the electrolyte material, and the electrode reaction sites are reduced. On the other hand, the comparative fuel cell unit Y exhibits power generation characteristics close to those of the fuel cell unit A of the present invention. This is because the comparative fuel cell unit Y uses a catalyst layer sheet with a thickness of 80 μm, This is because there are many, and the cost is high, so that it is not practical.

[0033]

The fuel cell unit according to claim 1 of the present invention is a fuel cell unit having a cell structure in which a catalyst layer and a gas diffusion layer are arranged in this order on both sides of the main surface of an electrolyte layer. The electrolyte layer is made of a proton conductive gel, an intermediate layer containing at least carbon particles and an electrolyte material is formed between the electrolyte layer and the catalyst layer, and the porosity of the intermediate layer is equal to that of the catalyst layer. Since the porosity is smaller than the porosity, even if an electrolyte layer made of a proton-conductive gel is prepared by the sol-gel method, the pores in the catalyst layer are not filled with the electrolyte material, and the reaction gas is sufficiently supplied to the catalyst layer and the platinum In addition to the remarkable effect that the utilization rate of the catalyst is increased and high battery performance is obtained, since high battery performance is obtained, the platinum catalyst amount can be reduced, and Since the carbon particles function to enhance the adhesion between the catalyst layer and the electrolyte layer, the adhesion between the catalyst layer and the electrolyte layer is maintained well, so that even if external stress is applied, the catalyst layer and the electrolyte layer The remarkable effect that the destruction of micro contact points is prevented and high battery performance can be maintained.

The fuel cell unit according to claim 2 of the present invention is the fuel cell unit according to claim 1, wherein the proton conductive gel is SiO ₂ , Al ₂ O.
_3. A material selected from the group consisting of ₃ , TiO ₂ , V ₂ O ₅ and ZrO ₂ and a material selected from phosphoric acid, perchloric acid, boric acid and silicic acid. In addition to the same effect as that of the fuel cell unit of No. 3, it has a further remarkable effect of being superior in proton conductivity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram schematically illustrating a cross section of a fuel cell unit of the present invention.

FIG. 2 is an assembly explanatory diagram of a fuel cell unit laminated body assembled using the fuel cell unit shown in FIG.

FIG. 3 is a graph showing cell voltage-current characteristics.

FIG. 4 is an explanatory diagram schematically illustrating a cross section of a conventional fuel cell unit.

[Explanation of symbols]

1, 20 Fuel cell unit 2,21 Electrolyte layer 4, 6, 23, 25 Gas diffusion layer 3.22 Fuel electrode catalyst layer 5, 24 Air electrode catalyst layer 7 carbon particles 8 Electrolyte material 9 Middle class

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuo Miyake             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. F-term (reference) 5H018 AA06 AS01 BB01 BB06 BB08                       BB09 BB12 BB16 CC06 DD06                       EE03 EE11 EE12 EE17 EE19                       HH04                 5H026 AA06 EE05 EE12 HH04

Claims (2)

[Claims] 1. A fuel cell unit having a cell structure in which a catalyst layer and a gas diffusion layer are arranged in this order on both sides of a main surface of an electrolyte layer, wherein the electrolyte layer is made of a proton conductive gel, An intermediate layer including at least carbon particles and an electrolyte material is formed between the catalyst layer and the catalyst layer, and the porosity of the intermediate layer is smaller than that of the catalyst layer. 2. The proton conductive gel is SiO₂ ,
Al₂ O₃ , TiO ₂ , V₂ O_Five , ZrO₂ Select from
Whether the material is exposed to phosphoric acid, perchloric acid, boric acid or silicic acid
A material selected from the group consisting of:
1. The fuel cell unit according to 1.