JP2008159343A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell with little degradation of electrolyte and excellent in durability. <P>SOLUTION: The solid polymer fuel cell comprises a membrane electrode assembly with an electrode containing catalyst jointed to an electrolyte membrane, and one or two kinds or more compounds containing W and/or Mo and transition metal (except W and Mo) added to either the electrolyte membrane or the electrode, and that, includes a degradation inhibitor with a ratio of the transition metal to the W and or the Mo expressed in formula (1): transition metal/(W+Mo)(mol/mol)=0.01 to 0.6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte fuel cell, and more particularly to a polymer electrolyte fuel cell suitable as an in-vehicle power source, a stationary small power generator, a cogeneration system, and the like.

  A solid polymer fuel cell has a membrane electrode assembly (MEA) in which electrodes are bonded to both surfaces of a solid polymer electrolyte membrane as a basic unit. In the polymer electrolyte fuel cell, the electrode generally has a two-layer structure of a diffusion layer and a catalyst layer. The diffusion layer is for supplying reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, or the like is used. The catalyst layer is a part that becomes a reaction field for electrode reaction, and generally comprises a composite of carbon carrying an electrode catalyst such as platinum and a solid polymer electrolyte.

The electrolyte membrane or the catalyst layer electrolyte that constitutes such an MEA includes a perfluorinated electrolyte excellent in oxidation resistance (an electrolyte that does not contain a C—H bond in the polymer chain. For example, Nafion (registered trademark, DuPont). ), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), etc.) are generally used.
In addition, perfluorinated electrolytes are excellent in oxidation resistance but are generally very expensive. Therefore, in order to reduce the cost of the solid polymer fuel cell, a hydrocarbon electrolyte (an electrolyte that includes a C—H bond and does not include a C—F bond in a polymer chain) or a partial fluorine electrolyte The use of (electrolytes containing both C—H bonds and C—F bonds in the polymer chain) has also been studied.

  However, in order to put the polymer electrolyte fuel cell into practical use as a vehicle-mounted power source, there remain problems to be solved. For example, hydrocarbon electrolytes are less expensive than perfluorinated electrolytes, but have a problem that they are easily degraded by peroxide radicals.

In order to solve this problem, various proposals have heretofore been made.
For example, Patent Literature 1 includes an electrolyte membrane having ionic conductivity and a pair of electrodes provided on both sides of the electrolyte membrane, and it is difficult to decompose peroxide into at least one of the electrolyte membrane and the pair of electrodes. An electrolyte membrane electrode assembly for a polymer electrolyte fuel cell containing a soluble tungstate is disclosed. In the same document, Ce ₂ (WO ₄ ) ₃ , La ₂ (WO ₄ ) ₃ , Y ₂ (WO ₄ ) ₃ , FeWO ₄ , CaWO ₄ , BiWO ₄ , Gd ₂ (WO ₄ ) ₃ , It is described that when Ag ₂ WO ₄ or MnWO ₄ is added, the F ion concentration or fluorine discharge rate decreases.

Japanese Patent Laid-Open No. 2005-93234

As described in Patent Document 1, when a poorly soluble tungstate with a stoichiometric ratio such as Ce ₂ (WO ₄ ) ₃ is added to an electrolyte membrane or an electrode, deterioration of the electrolyte due to radicals can be suppressed to some extent. it can. However, the effect of suppressing the deterioration of the electrolyte is insufficient only by adding a stoichiometric poorly soluble tungstate, and it is desired to further improve the deterioration suppressing effect.

  The problem to be solved by the present invention is to provide a polymer electrolyte fuel cell with little electrolyte deterioration and excellent durability.

In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention is
A membrane electrode assembly in which an electrode including a catalyst layer is bonded to an electrolyte membrane;
Consisting of one or more compounds including W and / or Mo and transition metals (excluding W and Mo) added to any one or more portions of the electrolyte membrane or the electrode; and A ratio of the transition metal to W and / or Mo is provided with a deterioration inhibitor represented by the following (1).
Transition metal / (W + Mo) (mol / mol) = 0.01-0.6 (1)

  When a deterioration inhibitor satisfying the formula (1) is added to the electrolyte membrane and / or the electrode, the deterioration of the electrolyte is suppressed as compared with the case where a stoichiometric poorly soluble tungstate is added. The This means that the stoichiometric poorly soluble tungstate not only ionically decomposes hydrogen peroxide but also causes radical decomposition, whereas the deterioration inhibitor satisfying the formula (1) is peroxidized. This is considered to reduce the rate at which hydrogen undergoes radical decomposition and to preferentially advance ion decomposition.

Hereinafter, an embodiment of the present invention will be described in detail.
A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which electrodes are bonded to both surfaces of a solid polymer electrolyte membrane. In addition, the polymer electrolyte fuel cell is usually formed by sandwiching both sides of such an MEA with a separator having a gas flow path and laminating a plurality of them.

In the present invention, the material of the solid polymer electrolyte membrane is not particularly limited, and various materials can be used.
That is, the material of the solid polymer electrolyte membrane is a hydrocarbon-based electrolyte containing a C—H bond in the polymer chain and no C—F bond, and a fluorine-based material containing a C—F bond in the polymer chain. Any of electrolytes may be used. Further, the fluorine-based electrolyte may be a partial fluorine-based electrolyte containing both C—H bonds and C—F bonds in the polymer chain, or contains C—F bonds in the polymer chain, and A perfluorinated electrolyte containing no C—H bond may be used.
In addition to the fluorocarbon structure (—CF ₂ —, —CFCl—), the fluorine-based electrolyte includes a chlorocarbon structure (—CCl ₂ —) and other structures (eg, —O—, —S—, —C ( ═O) —, —N (R) —, etc. provided that “R” may be an alkyl group). The molecular structure of the polymer constituting the solid polymer electrolyte membrane is not particularly limited, and may be either linear or branched, or may have a cyclic structure.

  Also, the type of acid group provided in the solid polymer electrolyte is not particularly limited. Examples of the acid group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. Only one of these acid groups may be contained in the solid polymer electrolyte, or two or more of them may be contained. Furthermore, these acid groups may be directly bonded to the linear solid polymer compound, or may be bonded to either the main chain or the side chain of the branched solid polymer compound.

Specifically, as the hydrocarbon electrolyte,
(1) Polyamide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, etc. in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, and derivatives thereof (aliphatic hydrocarbons) System electrolyte),
(2) Polystyrene having an acid group such as a sulfonic acid group introduced into any of the polymer chains, polyamide having an aromatic ring, polyamideimide, polyimide, polyester, polysulfone, polyetherimide, polyethersulfone, polycarbonate, and the like, and These derivatives (partial aromatic hydrocarbon electrolytes),
(3) Polyetheretherketone, polyetherketone, polysulfone, polyethersulfone, polyimide, polyetherimide, polyphenylene, polyphenylene ether, polycarbonate, in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, Polyamide, polyamideimide, polyester, polyphenylene sulfide, etc., and derivatives thereof (fully aromatic hydrocarbon electrolytes),
Etc. are mentioned as a suitable example.

Further, as the partial fluorine-based electrolyte, specifically, a polystyrene-graft-ethylenetetrafluoroethylene copolymer (hereinafter referred to as “PS”) in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains. -G-ETFE "), polystyrene-graft-polytetrafluoroethylene, and derivatives thereof.
Further, as the perfluorinated electrolyte, specifically, Nafion (registered trademark) manufactured by DuPont, Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., etc. A suitable example is a derivative.

  Furthermore, in the present invention, the solid polymer electrolyte membrane constituting the MEA may be composed only of a solid polymer electrolyte, or a reinforcing material composed of a porous material, a long fiber material, a short fiber material, or the like. It may be a complex containing.

  Among these, fluorinated electrolytes, particularly perfluorinated electrolytes, have a C—F bond in the polymer chain and are excellent in oxidation resistance. Therefore, if the present invention is applied thereto, A polymer electrolyte fuel cell excellent in oxidation resistance and durability can be obtained.

  The electrode constituting the MEA usually has a two-layer structure of a catalyst layer and a diffusion layer, but may be constituted only by the catalyst layer. When the electrode has a two-layer structure of a catalyst layer and a diffusion layer, the electrode is joined to the electrolyte membrane via the catalyst layer.

  The catalyst layer is a part serving as a reaction field for the electrode reaction, and includes an electrode catalyst or a carrier carrying the electrode catalyst, and an electrolyte in the catalyst layer covering the periphery thereof. In general, an optimum electrode catalyst is used depending on the purpose of use of MEA, use conditions, and the like. In the case of a polymer electrolyte fuel cell, platinum, palladium, ruthenium, rhodium or the like or an alloy thereof is used as the electrode catalyst. As the amount of the electrode catalyst contained in the catalyst layer, an optimal amount is selected according to the use of MEA, use conditions, and the like.

  The catalyst carrier is for carrying a fine electrode catalyst and simultaneously transferring electrons in the catalyst layer. Generally, carbon, activated carbon, fullerene, carbon nanophone, carbon nanotube or the like is used for the catalyst carrier. As the amount of the electrode catalyst supported on the surface of the catalyst carrier, an optimum amount is selected according to the material of the electrode catalyst and the catalyst carrier, the use of the MEA, the use conditions, and the like.

  The electrolyte in the catalyst layer is for exchanging protons between the solid polymer electrolyte membrane and the electrode. For the electrolyte in the catalyst layer, the same material as that constituting the solid polymer electrolyte membrane is usually used, but a different material may be used. As the amount of the electrolyte in the catalyst layer, an optimal amount is selected according to the use of MEA, use conditions, and the like.

  The diffusion layer is for supplying and receiving a reaction gas to the catalyst layer at the same time as transferring electrons to and from the catalyst layer. Generally, carbon paper, carbon cloth, or the like is used for the diffusion layer. In order to increase water repellency, a surface of carbon paper or the like coated with a mixture of water repellent polymer powder such as polytetrafluoroethylene and carbon powder (water repellent layer) is used as a diffusion layer. Also good.

The polymer electrolyte fuel cell according to the present invention includes a deterioration inhibitor in any one or more portions of the electrolyte membrane or the electrode.
The deterioration inhibitor may be contained only in one of the electrolyte membrane and the electrode, or may be contained in both. Further, when the electrode has a two-layer structure of a catalyst layer and a diffusion layer, the deterioration inhibitor may be contained only in either the catalyst layer or the diffusion layer, or may be contained in both. .
Further, when a deterioration inhibitor is added to the diffusion layer, the deterioration inhibitor is preferably added in the vicinity of the catalyst layer (in the case of forming a water repellent layer, the water repellent layer).

  The amount of the deterioration inhibitor added to the electrolyte membrane, the catalyst layer, or the diffusion layer can be arbitrarily selected according to the purpose. In general, the smaller the amount of deterioration inhibitor added, the smaller the effect of suppressing electrolyte deterioration. On the other hand, when the addition amount of the deterioration inhibitor is excessive, the proton conductivity of the electrolyte membrane or the catalyst layer is inhibited, or the electron conductivity of the catalyst layer or the diffusion layer is inhibited.

In the present invention, the “degradation inhibitor” is composed of one or more compounds including W and / or Mo and a transition metal (excluding W and Mo, hereinafter the same), and W And / or the ratio of the transition metal to Mo is expressed by the following (1).
Transition metal / (W + Mo) (mol / mol) = 0.01-0.6 (1)
“Consisting of one or more compounds” means
(A) a mixture of one or more compounds containing W and / or Mo and one or more compounds containing a transition metal;
(B) one or two or more complex compounds containing W and / or Mo and a transition metal, or
(C) a combination of (a) and (b) above,
Say.
The ratio represented by the formula (1) means that the ratio of transition metal to W and / or Mo is less than the stoichiometry. When the transition metal / (W + Mo) ratio is less than 0.01 and when the ratio exceeds 0.6, the effect of suppressing the deterioration of the electrolyte decreases.

  In both cases where the deterioration inhibitor is composed of a mixture and a composite compound, the deterioration inhibitor may be either a poorly soluble compound or a water-soluble compound. However, since water is always present in the MEA, if the deterioration inhibitor is water-soluble, the deterioration inhibitor is likely to elute from the MEA during use. On the other hand, since the elution from MEA is suppressed as the deterioration inhibitor is poorly soluble, the effect of suppressing deterioration of the electrolyte can be maintained for a long time.

The transition metal contained in the deterioration inhibitor is not particularly limited, and the first transition element ( ₂₁ Sc- ₃₀ Zn), the second transition element ( ₃₉ Y- ₄₈ Cd), and the third transition element ( ₅₇ La— ₈₀ Hg) or a fourth transition element ( ₈₉ Ac to ₁₀₃ Lr). Among these, the transition metal is preferably one or more selected from the group consisting of Fe, Cu, Mn, Ce, Ru, Zr, Ni, Co, Zn, and Pd.

Specifically, the following deterioration inhibitors are preferable.
The first specific example of the deterioration inhibitor is
(1) A mixture of a W compound containing one or more selected from the group consisting of tungsten oxide, tungsten carbide, tungsten nitride, and tungsten boride, and a transition metal compound (A) containing a transition metal, or
(2) A composite compound obtained by mixing a W compound and a transition metal compound (A) in a solvent.
As will be described later, when the W compound and the transition metal compound (A) are dispersed or dissolved in an appropriate solvent, a mixture of the W compound and the transition metal compound (A) or a W compound and the transition metal compound (A) is obtained. A composite compound obtained by reacting in a solvent is obtained.

The W compound is particularly preferably tungsten oxide. Tungsten oxide is composed of WO _x .nH ₂ O (0 <x ≦ 3, 0 ≦ n. For example, WO ₂ , WO ₃ etc.), H ₂ WO ₄ , and M _x WO ₄ (M = alkali metal). Any one or more selected from the group consisting of alkaline earth metals, x = 2 / α, and α is the valence of M).
When tungsten oxide is used as the W compound, a deterioration inhibitor having a high electrolyte deterioration suppressing action can be obtained. This is presumably because the OH group on the surface of tungsten oxide reacts with the transition metal compound (A) in a solvent, and a composite compound having a stoichiometric ratio or less is easily generated.

The transition metal compound (A) may be any of oxide, carbide, nitride, hydroxide, and salt (for example, halide, nitrate, sulfate, etc.).
In particular, the transition metal compound (A) is preferably a solvent-soluble compound. When a solvent-soluble compound is used as the transition metal compound (A), a deterioration inhibitor having a high electrolyte deterioration suppressing action can be obtained. This is considered to be because the use of the solvent-soluble transition metal compound (A) promotes the reaction with the W compound (particularly tungsten oxide) in the solvent, and easily produces a composite compound having a stoichiometric ratio or less. It is done.

The second specific example of the deterioration inhibitor is
(1) A mixture of a Mo compound containing any one or more selected from the group consisting of molybdenum oxide, molybdenum carbide, molybdenum nitride, and molybdenum boride, and a transition metal compound (B) containing a transition metal, or
(2) A composite compound obtained by mixing the Mo compound and the transition metal compound (B) in a solvent.
As will be described later, when the Mo compound and the transition metal compound (B) are dispersed or dissolved in an appropriate solvent, a mixture of the Mo compound and the transition metal compound (B) or the Mo compound and the transition metal compound (B) is obtained. A composite compound obtained by reacting in a solvent is obtained.

The Mo compound is particularly preferably molybdenum oxide. Molybdenum oxide includes MoO _x .nH ₂ O (0 <x ≦ 3, 0 ≦ n. For example, MoO ₂ , MoO _3, etc.), H ₂ MoO ₄ , and M _x MoO ₄ (M = alkali metal). Any one or more selected from the group consisting of alkaline earth metals, x = 2 / α, and α is the valence of M).
When molybdenum oxide is used as the Mo compound, a deterioration inhibitor having a high electrolyte deterioration suppression effect can be obtained. This is presumably because the OH group on the surface of molybdenum oxide and the transition metal compound (B) react in a solvent, and a composite compound having a stoichiometric ratio or less is easily generated.

The transition metal compound (B) may be any of oxide, carbide, nitride, hydroxide, and salt (for example, halide, nitrate, sulfate, etc.).
In particular, the transition metal compound (B) is preferably a solvent-soluble compound. When a solvent-soluble compound is used as the transition metal compound (B), a degradation inhibitor having a high electrolyte degradation suppression effect can be obtained. This is thought to be because the use of the solvent-soluble transition metal compound (B) facilitates the reaction with the Mo compound (particularly molybdenum oxide) in the solvent, and easily produces a composite compound having a stoichiometric ratio or less. It is done.
When a combination of a W-based degradation inhibitor and a Mo-based degradation inhibitor is used, the transition metal compound (A) and the transition metal compound (B) may be the same or different from each other. good.

Next, a method for producing a polymer electrolyte fuel cell according to the present invention will be described.
[1. Method for producing electrolyte membrane]
Specifically, the electrolyte membrane containing the deterioration inhibitor is
(1) The electrolyte is dissolved in an appropriate solvent (for example, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide or the like, or a water mixed solvent or an alcohol mixed solvent thereof). Compound or transition metal compound (A) and / or Mo compound and transition metal compound (B) are dispersed or dissolved to form a mixed solution,
(2) The mixed solution can be produced by casting on the surface of an appropriate substrate (for example, polytetrafluoroethylene substrate) and removing the solvent.

Moreover, the electrolyte membrane containing a deterioration inhibitor is
(1) A solution in which W compound and transition metal compound (A) and / or Mo compound and transition metal compound (B) are dispersed or dissolved in an appropriate first solvent (for example, water, methanol, ethanol, etc.) (A)
(2) The electrolyte is dissolved in a second solvent (for example, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, etc.) that is compatible with the first solvent and can dissolve the electrolyte. Solution (B),
(3) By mixing the solution (A) and the solution (B), casting the mixed solution on the surface of an appropriate substrate (for example, polytetrafluoroethylene substrate), and removing the first solvent and the second solvent It can also be manufactured.

  The MEA can be obtained by joining the catalyst layer to both surfaces of the electrolyte membrane thus obtained, or joining the catalyst layer and the diffusion layer in this order. Furthermore, if both surfaces of the MEA are sandwiched between separators having gas flow paths, the polymer electrolyte fuel cell according to the present invention can be obtained. In this case, the catalyst layer and the diffusion layer may be obtained by a usual method, or may contain a deterioration inhibitor obtained by the method described later.

[2. Method for producing catalyst layer]
Specifically, the catalyst layer containing the degradation inhibitor is
(1) In a catalyst ink in which an electrolyte and an electrode catalyst (Pt / C, etc.) are dissolved or dispersed in an appropriate solvent (for example, water, alcohol, etc.), W compound and transition metal compound (A), and / or Mo Dispersing or dissolving the compound and the transition metal compound (B),
(2) Applying this catalyst ink to the surface of an appropriate substrate (for example, polytetrafluoroethylene substrate) to remove the solvent,
(3) Transfer the catalyst layer to the electrolyte membrane.
Can be manufactured.

  As another method, there is a method in which a catalyst ink containing a W (Mo) compound and a transition metal compound is directly spray-coated on an electrolyte membrane.

  If diffusion layers are bonded to both surfaces of the thus obtained electrolyte membrane / catalyst layer assembly as required, an MEA can be obtained. Furthermore, if both surfaces of the MEA are sandwiched between separators having gas flow paths, the polymer electrolyte fuel cell according to the present invention can be obtained. In this case, the electrolyte membrane and the diffusion layer may be obtained by a normal method, or may contain a deterioration inhibitor obtained by the method described above or below.

[3. Diffusion layer manufacturing method]
Specifically, the diffusion layer containing the degradation inhibitor is
(1) A W compound, a transition metal compound (A), and / or a solution in which carbon and a water-repellent material (for example, polytetrafluoroethylene) are dissolved or dispersed in a suitable solvent (for example, water, alcohol, etc.) Alternatively, the Mo compound and the transition metal compound (B) are dispersed or dissolved to form a mixed solution,
(2) It can manufacture by apply | coating this mixed solution to the surface of a diffusion layer, and removing a solvent.

  As another method, there is a method in which a solution containing a W (Mo) compound and a transition metal compound is spray-coated on a diffusion layer.

  After joining the catalyst layer to both surfaces of the electrolyte membrane, the diffusion layer obtained in this way is joined to both surfaces of the catalyst layer to obtain MEA. Furthermore, if both surfaces of the MEA are sandwiched between separators having gas flow paths, the polymer electrolyte fuel cell according to the present invention can be obtained. In this case, the electrolyte membrane and the catalyst layer may be obtained by a normal method, or may contain a deterioration inhibitor obtained by the above-described method.

Next, the operation of the polymer electrolyte fuel cell according to the present invention will be described.
Under the operating environment of the polymer electrolyte fuel cell, a peroxide such as hydrogen peroxide is generated as a side reaction of the electrode reaction. In the presence of transition metal ions (M ^{n +} / M ^{(n + 1) +} ) whose valence changes such as Fe ²⁺ / Fe ³⁺ ions, this peroxide is oxidized in the following formula (2): Alternatively, radical decomposition is known by the reduction reaction of the formula (3).
HOOH + M ^{(n + 1) +} → HOO · + H ⁺ + M ^{n +} (2)
HOOH + M ^{n +} → HO · + OH ⁻ + M ^{(n + 1) +} (3)

  In the polymer electrolyte fuel cell, the electrolyte membrane is generally humidified by using an auxiliary device, and transition metal ions derived from piping and the like exist in the vicinity of the MEA. It is in an environment where product radicals are easily generated. On the other hand, peroxide radicals (HOO, HO, etc.) generated by peroxide radical decomposition break the C—H bond of the organic polymer compound, leading to alteration of the organic polymer compound and reduction in molecular weight. It is known. Therefore, if a conventional hydrocarbon-based electrolyte or a partial fluorine-based electrolyte is used as it is in a polymer electrolyte fuel cell, practically sufficient durability cannot be obtained.

  In addition, since perfluorinated electrolytes do not contain C—H bonds in their polymer chains, it has been conventionally thought that they do not deteriorate due to peroxide radicals. However, the present inventors have found that even if it is a perfluorinated electrolyte, it deteriorates in the operating environment of the fuel cell, and F ions are discharged from the fuel cell due to the deterioration, and the causative substance is a peroxide. It is found to be a radical.

On the other hand, a hardly soluble tungstate having a stoichiometric ratio as described in Patent Document 1 has an effect of suppressing deterioration due to peroxide radicals. This is because, on a solid surface of a sparingly soluble tungstate, before the peroxide is radically decomposed, it is ion-decomposed by a reduction reaction of the following formula (4) or an oxidation reaction of the following formula (5). This is probably because of this.
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O (4)
H ₂ O ₂ → O ₂ + 2H ⁺ + 2e ⁻ (5)
The reaction on the solid surface is the so-called two-molecule hydrogen peroxide colliding into water and oxygen as shown in the following equation (6) from the equations (4) and (5). Expressed as catalytic cracking reaction.
2HOOH → 2H ₂ O + O ₂ (6)

On the other hand, when a deterioration inhibitor satisfying the formula (1) is added to the electrolyte membrane or electrode, the deterioration of the electrolyte is further improved as compared with the case where a stoichiometric hardly soluble tungstate is added. It is suppressed. this is,
(A) The degradation inhibitor satisfying the formula (1) has a higher decomposition rate of hydrogen peroxide than a stoichiometric hardly soluble tungstate, and
(B) The stoichiometric poorly soluble tungstate not only ionically decomposes hydrogen peroxide but also causes radical decomposition, whereas the deterioration inhibitor satisfying the formula (1) is peroxidized. This is considered to reduce the rate at which hydrogen undergoes radical decomposition and to preferentially advance ion decomposition.

(Examples 1 to 21, Comparative Examples 1 to 12)
[1. experimental method]
A hydrogen peroxide test was conducted using benzenesulfonic acid as a model compound. That is, benzenesulfonic acid, W compound and transition metal compound were added to 1% H ₂ O ₂ aqueous solution and heated at 80 ° C. for a predetermined time. After a predetermined time, the hydrogen peroxide decomposition rate and the residual rate of benzenesulfonic acid were determined by ¹ H-NMR. Table 1 shows the test conditions for the hydrogen peroxide test.

[2. result]
Table 2 shows the test results of the hydrogen peroxide test. A substance having a high hydrogen peroxide decomposition rate and a large residual ratio of benzenesulfonic acid rapidly ionizes hydrogen peroxide, indicating that it is excellent as a deterioration inhibitor.
For example, the H ₂ O ₂ decomposition rate of H ₂ WO ₄ (Comparative Example 1) was 25% after 24 hours. Further, the H ₂ O ₂ decomposition rate of FeWO ₄ (Comparative Example 2) was 64% after 5 hours and 100% after 24 hours.
On the other hand, when 0.01 to 0.6 mol of FeCl ₂ was added to H ₂ WO ₄ , the H ₂ O ₂ decomposition rate became 100% after 1 to 5 hours had elapsed.

Cu (NO ₃ ) ₂ (Examples 6 and 7), Mn (NO ₃ ) ₂ (Example 8), Ce (NO ₃ ) ₂ (Examples 9 and 10) below stoichiometric with respect to H ₂ WO ₄ , Zr (NO ₃ ) ₂ (Example 11), Ni (NO ₃ ) ₂ (Example 12), Co (NO ₃ ) ₂ (Example 13), Zn (NO ₃ ) ₂ (Example 14), Ru The same applies when (NO) (NO ₃ ) _x (OH) _y (Examples 15 to 17) or PdCl ₂ (Example 18) is added, and when a stoichiometric compound is added (Comparative Example) Compared with 3-9), the H ₂ O ₂ decomposition rate reached 100% in a short time.
The same applies to the case of adding FeCl ₂ below the stoichiometry to WO ₂ (Example 19), WO ₃ (Example 20), or Na ₂ WO ₄ (Example 21). The H ₂ O ₂ decomposition rate reached 100% in a short time as compared with the case where the ratio ratio compounds were added (Comparative Examples 10 to 12).

(Examples 22-24, Comparative Examples 13-15)
[1. experimental method]
A hydrogen peroxide test was performed according to the same procedure as in Examples 1 to 21, except that the Mo compound was used instead of the W compound.
[2. result]
Table 3 shows the test results of the hydrogen peroxide test. The same applies to the Mo compound. When FeCl ₂ of less than the stoichiometry is added to MoO ₂ (Example 22), MoO ₃ (Example 23), or Na ₂ MoO ₄ (Example 24), the stoichiometric ratio is increased. Compared with the case of adding the compound (Comparative Examples 13 to 15), the H ₂ O ₂ decomposition rate reached 100% in a short time.

(Examples 25-28, Comparative Examples 16-19)
[1. Production of MEA]
A catalyst ink was prepared by mixing and stirring a 20 wt% Nafion (registered trademark) solution in a water / ethanol mixed solution in which carbon carrying 45 wt% platinum was dispersed. The mixing ratio of water, ethanol, platinum-supported carbon, and Nafion (registered trademark) was 2.5: 2.0: 0.5: 1.0 by weight.
To this catalyst ink, 0.25-fold moles of H ₂ WO ₄ and 0.05-fold moles of Ru ions (Ru (NO) (NO ₃ ) _{x with} respect to the molar amount of sulfonic acid groups in Nafion (registered trademark) (OH) _y aqueous solution (made by Aldrich) was added and stirred. This catalyst ink was placed on a polytetrafluoroethylene sheet and the thickness was made uniform using a doctor blade method, and then the solvent was dried and removed to prepare a catalyst sheet. By hot pressing at 130 ° C. for 6 minutes, the catalyst sheet was thermally transferred to a sulfonated polyether ether sulfone membrane (equivalent weight: 630 meq./g) to prepare an MEA (Example 25). The electrode area was 13 cm ² .

Also,
(1) Catalyst ink to which 0.25 times mole of H ₂ WO ₄ and 0.02 times mole of FeCl ₂ were added relative to the number of moles of sulfonic acid groups in Nafion (registered trademark) (Example 26) ,
(2) Catalyst ink containing 0.25 times moles of H ₂ WO ₄ and 0.05 times moles of Ce (NO ₃ ) ₃ with respect to the number of moles of sulfonic acid groups in Nafion (registered trademark) ( Example 27),
(3) A catalyst ink in which 0.25 times moles of H ₂ WO ₄ and 0.05 times moles of Mn (NO ₃ ) ₃ are added to the number of moles of sulfonic acid groups in Nafion (registered trademark) ( Example 28),
(4) Catalyst ink without addition of deterioration inhibitor (Comparative Example 16)
(5) A catalyst ink (Comparative Example 17) to which 0.25 times mole of FeWO ₄ was added relative to the number of moles of sulfonic acid groups in Nafion (registered trademark)
(6) Catalyst ink (Comparative Example 18) to which 0.25 times moles of Ce ₂ (WO ₄ ) ₃ was added relative to the number of moles of sulfonic acid groups in Nafion (registered trademark),
(7) A catalyst ink (Comparative Example 19) in which 0.25 times mole of MnWO ₄ was added to the number of moles of sulfonic acid groups in Nafion (registered trademark)
An MEA was produced in the same manner as in Example 25 except that was used.

[2. Test method]
The produced MEA was sandwiched between carbon paper diffusion layers (manufactured by Toray), set in an evaluation cell, tested for a predetermined time under the following pattern conditions, and the durability of the electrolyte membrane was evaluated.
Endurance test conditions Cell temperature: 80 ° C
Gas: Hydrogen / Air Flow rate: 54/140 (cc / min)
Bubbler temperature: Anode / cathode: 50/50 (° C)
Test pattern: Open circuit state (3 minutes) ⇔ 0.1 A / cm ² discharge (1 minute)
Time: 250 hours

  The MEA after the durability test was taken out from the cell, the electrode was peeled off, the electrolyte membrane was dissolved in dimethylacetamide, and the molecular weight was measured by gel permeation chromatography (GPC). The molecular weight in terms of polystyrene was determined from the peak top of the GPC chart using a standard polyethylene calibration curve.

[3. result]
Table 4 shows the FC cell test results. The molecular weight maintenance rate of MEA (Examples 25 to 28) in which a deterioration inhibitor equal to or less than the stoichiometric amount was added to the catalyst ink was as follows: the MEA without addition (Comparative Example 16) and the MEA with the stoichiometric W salt added Compared with (Comparative Examples 17-19), it turns out that a molecular weight maintenance factor is high. This is presumably because the use of a compound having a stoichiometric amount or less as a deterioration inhibitor reduced the rate of radical decomposition of hydrogen peroxide and promoted ionic decomposition.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

The polymer electrolyte fuel cell according to the present invention can be applied to an in-vehicle power source, a stationary small power generator, a cogeneration system, and the like.
In addition, the use of a solid polymer electrolyte to which a deterioration inhibitor of less than the stoichiometry is added is not limited to an electrolyte membrane or an electrolyte in a catalyst layer of a solid polymer fuel cell. It can also be used as an electrolyte membrane, an electrode material, etc. used in various electrochemical devices such as an acid electrolysis apparatus, a salt electrolysis apparatus, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor.

Claims (6)

A membrane electrode assembly in which an electrode including a catalyst layer is bonded to an electrolyte membrane;
Consisting of one or more compounds including W and / or Mo and transition metals (excluding W and Mo) added to any one or more portions of the electrolyte membrane or the electrode; and A polymer electrolyte fuel cell comprising a deterioration inhibitor, wherein the ratio of the transition metal to W and / or Mo is represented by the following (1).
Transition metal / (W + Mo) (mol / mol) = 0.01-0.6 (1)   2. The polymer electrolyte fuel cell according to claim 1, wherein the transition metal is at least one selected from the group consisting of Fe, Cu, Mn, Ce, Ru, Zr, Ni, Co, Zn, and Pd. . The deterioration inhibitor is
(1) A mixture of a W compound containing at least one selected from the group consisting of tungsten oxide, tungsten carbide, tungsten nitride, and tungsten boride, and a transition metal compound (A) containing the transition metal, or
(2) The polymer electrolyte fuel cell according to claim 1 or 2, comprising a composite compound obtained by mixing the W compound and the transition metal compound (A) in a solvent. The tungsten oxide contains WO _x · nH ₂ O (0 <x ≦ 3, 0 ≦ n), H ₂ WO ₄ , and M _x WO ₄ (M = alkali metal, alkaline earth metal, x = 2 / α). The solid polymer fuel cell according to claim 3, wherein α is any one or more selected from the group consisting of: a valence of M). The deterioration inhibitor is
(1) A mixture of a Mo compound containing any one or more selected from the group consisting of molybdenum oxide, molybdenum carbide, molybdenum nitride, and molybdenum boride, and a transition metal compound (B) containing the transition metal, or
(2) The polymer electrolyte fuel cell according to any one of claims 1 to 4, comprising a composite compound obtained by mixing the Mo compound and the transition metal compound (B) in a solvent. The molybdenum oxide includes MoO _x .nH ₂ O (0 <x ≦ 3, 0 ≦ n), H ₂ MoO ₄ , and M _x MoO ₄ (M = alkali metal, alkaline earth metal, x = 2 / α). The solid polymer fuel cell according to claim 5, wherein α is any one or more selected from the group consisting of: a valence of M).