JP2006120620A - Electrolyte material, electrolyte membrane, catalyst paste, membrane electrode assembly, and fuel cell - Google Patents

Abstract

Provided is a hydrocarbon-based electrolyte material that has excellent oxidation resistance and can exhibit high performance.
SOLUTION: A hydrocarbon electrolyte material having an ion exchange capacity of 0.5 meq / g or more and 2.1 meq / g or less, and a heteropolyester in an amount of 10 mass% or more and less than 300 mass% based on the hydrocarbon electrolyte material. It contains an acid. It has been discovered that the oxidation resistance of hydrocarbon-based electrolyte materials is improved within a relatively small range of ion exchange capacity. And with respect to the hydrocarbon-based electrolyte material whose ion exchange capacity is controlled within a low range, by mixing a heteropoly acid as a proton conductive auxiliary agent, oxidation resistance (the higher the oxidation resistance, the higher the mass retention rate) and We succeeded in achieving both proton conductivity. We have also succeeded in improving the carbon monoxide resistance.
[Selection] Figure 1

Description

  The present invention relates to an electrolyte material and an electrolyte membrane, a catalyst paste, a membrane electrode assembly, and a fuel cell that employ the electrolyte material.

  As electrolyte materials applicable to fuel cells, perfluoro-based electrolyte materials and hydrocarbon-based electrolyte materials (in this specification, electrolyte materials that are not completely substituted by fluorine are included in the “hydrocarbon-based electrolyte materials”) )

  The perfluoro-based electrolyte material is represented by Nafion (trademark), and is a material generally employed in fuel cells, and is a material excellent in oxidation resistance. In the fuel cell, when protons produced at the anode reach the cathode through the electrolyte membrane during the electrode reaction process, they are oxidized by oxygen supplied to the cathode to produce water. The hydroxyl radicals may diffuse and decompose fuel cell components.

  Further, due to the nature of the resin skeleton, a segment having a water repellent structure and a segment having a hydrophilic structure are mixed, and the water repellent layer and the hydrophilic layer have a phase separation structure. For this reason, the structure has a well-balanced function of water retention and gas diffusibility.

  However, although perfluoro-based electrolyte material has high performance when applied to a fuel cell, it is a material synthesized through a complicated process and has a high fluorine content, so the cost is very high. It is an obstacle to the spread of batteries.

  On the other hand, hydrocarbon electrolyte materials can generally be reduced in cost, but there is a tendency that sufficient performance cannot be exhibited as compared with perfluoro electrolyte materials. The reason for this is that hydrocarbon-based electrolyte materials often have a predominant hydrophilic structure and a water-repellent structure that is not sufficient, leading to a decrease in proton conductivity.

In addition, it is known that the oxidation resistance of hydrocarbon electrolyte materials is much less than that of perfluoro electrolyte materials. That is, since the bond energy between carbon and hydrogen is smaller than the bond energy between carbon and fluorine, it is considered that the oxidation resistance is not sufficient. This can also be confirmed by an oxidation resistance evaluation test such as the Fenton test described later.
JP-A-5-3418 JP 2002-298855 A JP 2002-164055 A JP 2004-123794 A JP 2003-292608 A JP 2004-119242 A JP 2004-149786 A JP 2003-317737 A

  The present invention has been made in view of the above circumstances, and an object to be solved is to provide an electrolyte material mainly composed of a hydrocarbon-based electrolyte material that has excellent oxidation resistance and can exhibit high performance. Another object to be solved is to provide an electrolyte membrane, a catalyst paste, a membrane electrode assembly, and a fuel cell that employ the electrolyte material.

  As a result of intensive studies aimed at solving the above problems, the present inventors have obtained the following knowledge. That is, when the oxidation resistance of the hydrocarbon-based electrolyte material is evaluated, the ion-exchange capacity is relatively small, and if it is in the range of 0.5 meq / g to 2.1 meq / g, high oxidation resistance is exhibited. discovered. This is considered that the oxidation resistance was improved by reducing the number of ion exchange groups that can act as reaction sites due to hydroxy radicals and the like. It can be presumed that the effect of improving oxidation resistance by reducing the number of ion exchange groups is also valid for perfluoro-based electrolyte materials.

  And it succeeded in making oxidation resistance and proton conductivity compatible by mixing heteropoly acid as a proton-conductive auxiliary agent with respect to the hydrocarbon-type electrolyte material which controlled the ion exchange capacity in the low range.

  The present invention has been completed based on the above findings, and the electrolyte material of the present invention includes a hydrocarbon-based electrolyte material having an ion exchange capacity of 0.5 meq / g to 2.1 meq / g, and the hydrocarbon The heteropolyacid is contained in an amount of 10% by mass or more and less than 300% by mass based on the system electrolyte material. In addition, in determining the above-mentioned mixing ratio, the value calculated in terms of the anhydride is used as the mass of the heteropolyacid.

  In other words, high performance is achieved by mixing a heteropoly acid that can improve proton conductivity with a hydrocarbon-based electrolyte material that has improved oxidation resistance by controlling the ion exchange capacity within a relatively low range. An electrolyte material can be provided.

  Further, it has been found that the heteropolyacid exhibits higher performance than that of a single substance when mixed with a hydrocarbon electrolyte material. For example, the heteropolyacid can be mixed with a hydrocarbon-based electrolyte material to improve the stability (morphological stability, solubility in water, etc.) as an electrolyte.

  The heteropolyacid is a polyacid having a polynuclear structure in which two or more oxo acids are condensed. The skeleton excluding protons is called a heteropolyacid ion (heteropolyanion), and has a structure containing a small number of heteroatoms (referred to as heteroatoms) oxygen acid in the acid condensation structure forming the skeleton. The central atom of the other skeletal acid is called a poly atom.

  Examples of the hetero atom include P, Si, As, and Ge. The poly atom is selected from transition metals, and examples thereof include W, Mo, Nb, V, and Ta. And it is also possible to substitute a partly different transition metal. There are also structures in which some of the poly atoms are missing. A preferred heteropolyacid is silicotungstic acid.

  And the electrolyte membrane of this invention which solves the said subject has the electrolyte material of this invention mentioned above, and the porous membrane which impregnates the electrolyte material, It is characterized by the above-mentioned. Sufficient mechanical strength is given by impregnating the above-mentioned electrolyte material in the porous membrane. The porous membrane is preferably composed of polyimide. Moreover, the catalyst paste of the present invention that solves the above-described problems includes the above-described electrolyte material of the present invention and a catalyst.

  Furthermore, the membrane electrode assembly of the present invention that solves the above problems includes an electrolyte membrane, a catalyst layer laminated on both sides of the electrolyte membrane, and a diffusion layer laminated on the opposite side of the catalyst layer to the electrolyte membrane. A membrane electrode assembly for a fuel cell, wherein the electrolyte membrane is the electrolyte membrane of the present invention described above and / or the catalyst layer is a layer formed from the catalyst paste of the present invention described above. It is characterized by. And the fuel cell of this invention which solves the said subject has this membrane electrode assembly of this invention, It is characterized by the above-mentioned.

  The electrolyte material and catalyst paste of the present invention can achieve both oxidation resistance and proton conductivity. The electrolyte membrane and membrane electrode assembly of the present invention can achieve both oxidation resistance and proton conductivity and can provide sufficient strength. The fuel cell of the present invention can achieve both high durability and performance.

  Furthermore, it has been discovered that the effect of carbon monoxide contained in the fuel gas or the like can be reduced as an incidental effect due to the inclusion of the heteropolyacid. That is, as fuel for the fuel cell, in addition to the case of using pure hydrogen, there are cases where fuel gas is produced by reforming hydrocarbons, and in that case, carbon monoxide may be mixed. When carbon monoxide is mixed, the power generation capability of the fuel cell is lowered. However, when the electrolyte material and catalyst paste of the present invention are employed, the drop in cell performance can be reduced even if carbon monoxide is mixed in the fuel gas. This is probably because the water retention performance of the electrolyte material containing the heteropolyacid is improved because the heteropolyacid is a hydrate.

(Electrolyte material)
The electrolyte material of the present embodiment is characterized by containing a hydrocarbon-based electrolyte material, a heteropolyacid, and other materials mixed as necessary. The electrolyte material can be formed by simply mixing the hydrocarbon-based electrolyte material and the heteropolyacid. As will be described later, when the hydrocarbon-based electrolyte material is formed from a monomer polymer, the monomer can be polymerized in a state where the heteropolyacid is mixed.

  The hydrocarbon electrolyte material is not particularly limited except that the ion exchange capacity is not less than 0.5 meq / g and not more than 2.1 meq / g. For example, a material composed of a base material (skeleton) made of a hydrocarbon-based compound and an ion conductive group such as a sulfo group, a phosphate group, or a carboxylic acid group introduced into the base material is exemplified. As the base material, it is preferable to employ a polymer, more preferably a polymer, from the viewpoints of stability (including stability against moisture) when applied to a fuel cell and mechanical strength. By adopting a material having a molecular weight of a certain level or more such as a polymer, various performances such as water resistance are improved, and stability in the fuel cell is improved. In addition, by adjusting the molecular weight of the base material portion, the final form of the electrolyte material can be freely controlled from a liquid state to a solid state. The form of the electrolyte material is preferably solid.

  Examples of specific materials that can be used for the substrate include polymers of monomers (such as styrene). In addition to a linear structure, the polymer can have a ladder-like structure, a three-dimensional network-like structure, etc. by adding an appropriate crosslinking agent. Moreover, ETFE containing a fluorine atom in part can also be employed. The ion exchange capacity can be controlled within an appropriate range by adjusting the amount of proton conductive group introduced.

  Furthermore, the upper limit of the ion exchange capacity of the hydrocarbon-based electrolyte material is 2.1 meq / g or less, 2.01 meq / g or less, less than 2.01 meq / g, 1.75 meq / g or less, 1.5 meq / g or less. And each value below 1.1 meq / g can be arbitrarily adopted. Moreover, the lower limit of the ion exchange capacity can be arbitrarily selected from values of 0.75 meq / g or more and 1.0 meq / g or more in addition to 0.5 meq / g or more. The upper and lower limits of the ion exchange capacity can be independently selected and can be arbitrarily combined. Further, only the upper limit can be adopted from the viewpoint of improving the oxidation resistance.

  The ion exchange capacity was measured by substituting the ion exchange group for the test sample of the hydrocarbon-based electrolyte material with the H type, and then the mass of the test sample after the replacement with the dry H type based on the mass after dissolution. Dissolve in ethanol to a concentration of 3%, use phenolphthalein as an indicator, and titrate with 0.05 mol / L sodium hydroxide aqueous solution at the point where the color change of the solution is kept for several seconds. It is a value calculated according to the following formula based on the obtained value.

(Ion exchange capacity) (meq / g) = (0.05 × Titration volume (ml)) / (Dry mass of dissolved test sample (g))
The heteropolyacid is contained in an amount of 10% by mass or more and less than 300% by mass based on the aforementioned hydrocarbon electrolyte material. The poly atom of the heteropolyacid is selected from transition metal atoms, and W, Mo, Nb, V and Ta are particularly preferable examples. Tungsten is particularly preferable. These polyatoms are considered to exist in the form of W ⁶⁺ , Mo ⁶⁺ , Nb ⁵⁺ , V ⁵⁺ , Ta ^5+, etc. in the heteropolyacid. Examples of the hetero atom include P, Si, As, Ge, and B. Silicon is particularly preferable. As a preferred heteropolyacid employing tungsten as a polyatom and silicon as a heteroatom, silicotungstic acid: H ₄ [SiW ₁₂ O ₄₀ ] · nH ₂ O is exemplified. Other heteropolyacids applicable to this embodiment include phosphotungstic acid: H ₃ [PW ₁₂ O ₄₀ ] · nH ₂ O, phosphomolybdic acid: H ₃ [PMo ₁₂ O ₄₀ ] · nH ₂ O, phosphomolybdenum. Sodium acid: Na ₃ [PMo ₁₂ O ₄₀ ] · nH ₂ O, Lintungsto molybdic acid: H ₃ [PW _12-X Mo _x O ₄₀ ] · nH ₂ O (0 <x <12), phosphovanadomolybdic acid: Examples thereof include H _15-X [PV _12-X Mo _X O ₄₀ ] · nH ₂ O (6 <x <12), silicomolybdic acid: H ₄ [SiMo ₁₂ O ₄₀ ] · nH ₂ O. In addition, the value of n which shows the quantity of the hydrate in the heteropoly acid shown above is all about 30 (n≈30). The ratio of the number of atoms between the heteroatom and the polyatom (heteroatom / polyatom) is not particularly limited, but the number ratio of 1/6, 1/9, 1/12, 2/18, etc. frequently appears.

  The upper limit of the content of the heteropolyacid may be arbitrarily selected from values of less than 300% by mass, 200% by mass or less, 150% by mass or less, and 100% by mass or less based on the hydrocarbon electrolyte material. . The lower limit of the content of the heteropolyacid is arbitrarily selected from 10 mass% or more, 33 mass% or more, more than 33 mass%, 50 mass% or more, and 75 mass% or more based on the hydrocarbon electrolyte material. Can be adopted. The upper limit and the lower limit of the content of the heteropolyacid can be independently selected and can be arbitrarily combined.

(Electrolyte membrane)
The electrolyte membrane of this embodiment has an electrolyte material and a porous membrane. Since the electrolyte material of the present embodiment described above can be employed as it is as the electrolyte material, further explanation is omitted here.

  The porous film is a thin film having a large number of pores communicating with the front and back surfaces of the film. The pores are impregnated with an electrolyte material. The porosity of the porous membrane is preferably high from the viewpoint of proton conductivity. Further, from the viewpoint of the strength of the film, it is preferable to limit it to a value below to some extent. For example, the porosity of the porous membrane is preferably about 90% to 20%, and more preferably about 70% to 40%.

  The porous membrane is preferably composed of a polymer material regardless of organic or inorganic. As the polymer material, a material having high chemical and physical stability under the environment in the fuel cell is desirable. For example, organic polymer materials such as engineering plastics (polyimide, fluororesin, etc.), polyolefins (polyethylene, polypropylene, etc.), carbon materials (carbon paper, porous carbon, etc.), ceramic materials (glass, alumina, etc.) may be adopted. it can. In particular, it is preferable to employ an organic polymer material (such as polyimide) having excellent film strength and high flexibility.

  As a method for forming holes in these materials, conventional methods can be employed. For example, a method of stretching a film without pores (polymer material, etc.), a method of forming a non-woven fabric or woven fabric after making it into a fiber (polymer material, carbon material, ceramic material, etc.), kneading fine powder that can be dissolved and removed, etc. Examples thereof include a method of forming a film after dispersion and dissolving and removing fine powder (polymer material, carbon material, ceramic material, etc.), a mechanical method, and the like.

  The electrolyte material is preferably a solid material. The solid electrolyte material is impregnated into the pores by permeating or press-fitting into the porous membrane in a state melted by heating or dissolved in a solvent, and then the liquid electrolyte material is cooled or dried. Thus, a stable film can be formed by returning to a solid state.

(Catalyst paste and membrane electrode assembly)
The catalyst paste of this embodiment has an electrolyte material and a catalyst. The catalyst paste preferably contains an appropriate solvent. A catalyst layer can be formed by applying this catalyst paste to an electrolyte membrane or a diffusion layer. Since the electrolyte material of the present embodiment described above can be employed as it is as the electrolyte material, further explanation is omitted here. The catalyst is generally used as a catalyst-supported powder in which a catalyst is supported on a supported powder. As the catalyst, platinum or a noble metal catalyst obtained by alloying platinum with another element (ruthenium, palladium, etc.) is used. Carbon powder or the like is used as the support powder. Platinum-supported carbon using carbon powder as the support powder and platinum as the catalyst is widely used. Platinum of the platinum-supporting carbon may be alloyed with other elements, or may be used by mixing with other elements. The catalyst itself may be used as a powder without using the supported powder.

  The membrane electrode assembly of this embodiment has an electrolyte membrane, a catalyst layer, and a diffusion layer. Here, the electrolyte membrane is a member that mainly exhibits proton conductivity in the film thickness direction, the catalyst layer is a member that catalyzes the oxidation-reduction reaction, and the diffusion layer is permeable to gases such as fuel gas and air and moisture. It is a member that has excellent properties and can also exhibit electrical and thermal conductivity. The diffusion layer is known to be composed of surface-treated carbon paper or the like. The catalyst layer can be formed by applying a catalyst paste on the surface of the electrolyte membrane and / or the diffusion layer. The membrane electrode assembly employs the electrolyte membrane of the present embodiment relative to the electrolyte membrane and / or employs a layer formed from the catalyst paste of the present embodiment as the catalyst layer.

(Fuel cell)
The fuel cell of this embodiment is a solid polymer electrolyte fuel cell. As the fuel cell of this embodiment, a fuel cell is used alone or a stack in which a plurality of layers are stacked is formed. The fuel cell has the membrane electrode assembly of the present embodiment described above, and the membrane electrode assembly is sandwiched between separators.

  The separator can be of a generally used material and form. A flow path through which the fuel gas or oxidant gas flows is formed in the separator, and a gas supply device is connected to the separator.

(Test Example 1)
(Manufacture of hydrocarbon electrolyte materials)
A styrene polymer was selected as the base material for the hydrocarbon electrolyte material. The synthesis of the styrene polymer was carried out by adding dropwise 200 mL of styrene in which 0.2 g of benzoyl peroxide was dissolved in 200 mL of xylene heated to 90 ° C. in a nitrogen atmosphere over 3 hours, and then holding at 90 ° C. for 1 hour. It was done by doing. Thereafter, the reaction solution cooled to room temperature was dropped into a large amount of methanol to precipitate a produced styrene polymer. The precipitate was collected by filtration and dried at 110 ° C. for 3 hours. When the molecular weight of the obtained styrene polymer was measured by GPC, Mw was 124,000.

  150 g of the obtained styrene polymer was dissolved in 500 mL of 1,2-dichloroethane. While the solution was heated to 60 ° C. and stirred, the amount of chlorosulfonic acid shown in Synthesis Examples 1 to 3 in Table 1 was added dropwise and held at 60 ° C. for 1 hour. The obtained chlorosulfonated styrene polymers of Synthesis Examples 1 to 3 were washed with 1,2-dichloroethane and then ion-exchanged water in that order, and then left in ion-exchanged water at room temperature for 1 hour to hydrogenate ion-exchange groups. Turned into. Thereafter, it was vacuum dried to obtain a powdered sulfonated styrene polymer (corresponding to a hydrocarbon electrolyte material). Table 1 also shows the ion exchange capacity of the sulfonated styrene polymers of Synthesis Examples 1 to 3 obtained. The ion exchange capacity was performed by the method described in the section of the embodiment described above.

(Manufacture of electrolyte membrane)
To the water / ethanol (1/1) solution in which the hydrocarbon-based electrolyte materials of Synthesis Examples 1 to 3 are dissolved at a concentration of 10% by mass, silicotungstic acid is added to the ratio shown in Table 2 and stirred and mixed. And the solution containing the electrolyte material of Examples 1-4 and Comparative Examples 1-5 was obtained. After impregnating a porous polyimide film having a film thickness of 40 μm and a porosity of 60% with a solution containing the electrolyte material of each Example and Comparative Example, it was dried at 90 ° C. for 1 hour. Furthermore, it vacuum-dried and obtained the electrolyte membrane of each Example and the comparative example. The properties of the obtained electrolyte membrane are also shown in Table 2. Proton conductivity was measured by the AC impedance method.

(Evaluation of oxidation resistance)
About the electrolyte membrane of Examples 1-4 and Comparative Examples 1-5, oxidation resistance was evaluated by the Fenton test. The Fenton test was carried out by maintaining an aqueous solution containing 2 ppm of Fe ²⁺ and 3% hydrogen peroxide at 60 ° C., and measuring the mass change when the electrolyte membrane was immersed therein. Here, the higher the oxidation resistance, the smaller the mass change in the Fenton test.

  The results are shown in FIG. 1 (Synthesis Example 2: ion exchange capacity 2.01 meq / g), FIG. 2 (Synthesis Example 3: ion exchange capacity 1.09 meq / g), and FIG. 3 (hydrocarbon electrolyte materials of Synthesis Examples 1 to 3). Independently). As is clear from FIGS. 1 and 2, it was found that there is an appropriate range for the addition amount of heteropolyacid (silicotungstic acid). That is, the oxidation resistance and proton conductivity of the electrolyte membrane obtained by setting the addition amount of the heteropolyacid within the range of 33.3 mass% or more and 300 mass% or less based on the hydrocarbon-based electrolyte material is high. We were able to. In particular, preferable properties were exhibited when the addition amount was around 100% by mass (50 to 140% by mass). Further, as is clear from FIG. 3, it was found that the hydrocarbon-based electrolyte material improved in oxidation resistance as the ion exchange capacity was reduced.

(Manufacture of catalyst paste)
50 g of a solution in which a heteropoly acid is mixed so as to have a ratio shown in Table 2 with respect to a water / ethanol (1/1) solution in which the hydrocarbon-based electrolyte materials of Synthesis Examples 1 to 3 are dissolved at a concentration of 10% by mass. On the other hand, 20 g of platinum-supported carbon containing platinum as a catalyst (platinum supported amount 50 mass%) is added to form a slurry. Thereafter, 60 g of ion-exchanged water and 60 g of ethanol are added and mixed and dispersed until the particle size of the platinum-supporting carbon becomes 1.0 μm or less. Final mixing and dispersion were performed with a high-speed homogenizer to obtain catalyst pastes of Examples and Comparative Examples.

(Manufacture of membrane electrode assembly)
A bar coater so that the amount of platinum supported is 1 mg / cm ² on carbon paper (thickness 180 μm, porosity 65%) subjected to water repellent treatment as a gas diffusion base material (diffusion layer) from the catalyst paste of each example and comparative example. It was coated by. After coating, heating and drying were performed at 80 ° C. for 30 minutes to obtain an electrode having a catalyst layer formed thereon. After sandwiching the electrolyte membranes of the corresponding examples and comparative examples by two electrodes respectively arranged in the direction of contact on the catalyst layer side, they were hot-pressed at 170 ° C. and 8 MPa for 3 minutes to be joined. A membrane electrode assembly of a comparative example was obtained.

(Evaluation of battery performance)
The membrane electrode assemblies of Examples 1 to 4 and Comparative Examples 1 to 5 were incorporated into a single cell for fuel cell evaluation and evaluated. Evaluation was made by measuring the change in output voltage when the current density was changed. The evaluation (operation) conditions of the single cell for fuel cell evaluation are electrode area 9 cm ² , cell internal temperature 75 ° C., supplied gas is pure hydrogen corresponding to 90% utilization on the anode side, and 40% utilization on the cathode side. The corresponding air. As the humidification amount for the gas, 0.2 mol of water was used in a molar ratio with respect to 1 mol of each gas.

  The results are shown in FIG. 4 (Synthesis Example 2: ion exchange capacity 2.01 meq / g) and FIG. 5 (Synthesis Example 3: ion exchange capacity 1.09 meq / g). As is clear from FIGS. 4 and 5, it was revealed that there is an appropriate range for the addition amount of silicotungstic acid. That is, the cell characteristics of the fuel cell obtained by adding the amount of the heteropolyacid within the range of 33.3 mass% or more and less than 300 mass% based on the hydrocarbon electrolyte material could be improved. . In particular, preferable properties were exhibited when the addition amount was around 100% by mass (50 to 140% by mass).

(Test Example 2)
(Manufacture of hydrocarbon electrolyte solution)
The water / ethanol (1/1) solution in which the hydrocarbon-based electrolyte material of Synthesis Example 2 shown in Test Example 1 was dissolved at a concentration of 10% by mass was used as the electrolyte solution of Comparative Example 6.

  25 g of a solution containing 20 g / w% of silicotungstic acid (water / ethanol = 1/1) was mixed and stirred in 50 g of the electrolyte solution of Comparative Example 6 to obtain the electrolyte solution of Example 5.

  Further, 25 g of a solution (water / ethanol = 1/1) containing phosphomolybdic acid at 20 w / w% was mixed and stirred in 50 g of the electrolyte solution of Comparative Example 6 to obtain the electrolyte solution of Example 6.

(Manufacture of catalyst paste)
20 g of platinum-supported carbon containing platinum as a catalyst (platinum supported amount 50 mass%) was added to 75 g of each of the electrolyte solutions of Examples 5 and 6 and 50 g of the electrolyte solution of Comparative Example 6 to form a slurry. Thereafter, 60 g of ion-exchanged water and 60 g of ethanol are added and mixed and dispersed until the particle size of the platinum-supporting carbon becomes 1.0 μm or less. Final mixing and dispersion were performed with a high-speed homogenizer, and catalyst pastes of Examples 5 and 6 and Comparative Example 6 were obtained.

(Manufacture of membrane electrode assembly)
The amount of platinum supported on the carbon paste (thickness 180 μm, porosity 65%) treated with the catalyst pastes of Examples 5 and 6 and Comparative Example 6 as a gas diffusion base material (diffusion layer) becomes 1 mg / cm ² . As shown in FIG. After coating, heating and drying were performed at 80 ° C. for 30 minutes to obtain an electrode having a catalyst layer formed thereon. A commercially available electrolyte membrane (Nafion 112: manufactured by DuPont Co., Ltd.) After sandwiching the electrolyte membranes of the corresponding Examples and Comparative Examples by two electrodes respectively arranged in contact directions on the catalyst layer side, 140 ° C. and 10 MPa The membrane electrode assembly of each Example and the comparative example was obtained by hot-pressing for 3 minutes and joining.

(Evaluation of battery performance)
The membrane electrode assemblies of Examples 5 and 6 and Comparative Example 6 were incorporated into a single cell for fuel cell evaluation and evaluated. In the evaluation, the change in the output voltage of the single cell was measured when the current density was 0.26 A / cm ² and the concentration of carbon monoxide contained in the gas flowing to the anode side was changed from 10 to 250 ppm. Evaluation (operation) conditions of a single cell for fuel cell evaluation are electrode area 9 cm ² , cell temperature 75 ° C., supplied gas is 76% hydrogen, 4% nitrogen, 19% carbon dioxide and 1% methane as anode side gas. Then, a gas having a composition in which carbon monoxide was added in the range of 10 to 250 ppm was used, and an amount corresponding to a hydrogen utilization rate of 90% was circulated. The cathode side gas was air corresponding to a utilization rate of 40%. As the humidification amount for the gas, 0.2 mol of water was used in a molar ratio with respect to 1 mol of each gas. The results are shown in Table 3 and FIG.

  As is apparent from Table 3 and FIG. 6, the fuel cells of Examples 5 and 6 containing the heteropolyacid in the electrolyte and the electrode catalyst are more affected by carbon monoxide than the fuel cell of Comparative Example 6 containing no heteropolyacid. It became clear that it was difficult. For example, in the fuel cell of Comparative Example 6, the concentration of carbon monoxide increased and the cell voltage decreased to 0.577 V when the concentration reached 250 ppm, but in the fuel cells of Examples 5 and 6, the monoxide was oxidized. Even when the carbon concentration is 250 ppm, the voltage drop is as small as 0.608 V (Example 5) and 0.579 V (Example 6). This tendency is remarkable when the carbon monoxide concentration is 100 ppm or more. In addition, the value of the initial voltage was not significantly different between the fuel cells of Examples 5 and 6 and the fuel cell of Comparative Example 6, and it was found that the heteropolyacid had no adverse effect on the fuel cell or very little.

It is the graph which showed the oxidation resistance and proton conductivity of the electrolyte membrane in an Example. It is the graph which showed the oxidation resistance and proton conductivity of the electrolyte membrane in an Example. It is the graph which showed the oxidation resistance and proton conductivity of the electrolyte membrane in an Example. It is the graph which showed the IV characteristic of the fuel cell using the electrolyte material in an Example. It is the graph which showed the IV characteristic of the fuel cell using the electrolyte material in an Example. It is the graph which showed the IV characteristic in the presence of carbon monoxide of the fuel cell using the electrolyte material in an Example.

Claims (7)

A hydrocarbon electrolyte material having an ion exchange capacity of 0.5 meq / g or more and 2.1 meq / g or less;
An electrolyte material comprising a heteropolyacid in an amount of 10% by mass or more and less than 300% by mass based on the hydrocarbon electrolyte material.   The electrolyte material according to claim 1, wherein the heteropolyacid is silicotungstic acid. The electrolyte material according to claim 1 or 2,
An electrolyte membrane comprising a porous membrane impregnated with the electrolyte material.   The electrolyte membrane according to claim 3, wherein the porous membrane is made of polyimide.   A catalyst paste comprising the electrolyte material according to claim 1 or 2 and a catalyst. A membrane electrode assembly for a fuel cell, comprising an electrolyte membrane, a catalyst layer laminated on both sides of the electrolyte membrane, and a diffusion layer laminated on the catalyst layer opposite to the electrolyte membrane,
A membrane electrode assembly, wherein the electrolyte membrane is the electrolyte membrane according to claim 3 or 4 and / or the catalyst layer is a layer formed from the catalyst paste according to claim 5. A fuel cell comprising the membrane electrode assembly according to claim 6.

Images