JP2005063902A - Electrolyte membrane electrode junction for solid polymer type fuel cell, and solid polymer type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane electrode junction for solid polymer fuel cell of which the electrolyte membrane and the electrode are hardly deteriorated, and a solid polymer fuel cell in which the deterioration of battery performance is small even in the case of operation for a long period of time. <P>SOLUTION: In the electrolyte membrane electrode junction for a solid polymer fuel cell which is constructed of an electrolyte membrane having ion conductivity and a pair of electrodes provided on both sides of the electrolyte membrane, a peroxide decomposition substance composed of at least one kind of an iron-contained oxide and an iron-contained hydroxide is contained in at least one of the electrolyte membrane and the pair of the electrodes. And the solid polymer fuel cell is structured by using such electrolyte membrane electrode junction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell, and more particularly to an electrolyte membrane electrode assembly used in a polymer electrolyte fuel cell.

  A fuel cell that generates electricity by an electrochemical reaction of gas has high power generation efficiency, clean gas discharged, and extremely little influence on the environment. Therefore, in recent years, various uses such as power generation and low-pollution automobile power supplies are expected.

  Among these, the polymer electrolyte fuel cell can be operated at a low temperature of about 80 ° C. and has a large output density. In general, a polymer electrolyte fuel cell uses a proton conductive polymer membrane as an electrolyte. A pair of electrodes each serving as a fuel electrode and an oxygen electrode are provided on both sides of the polymer film serving as an electrolyte to form an electrolyte membrane electrode assembly (MEA). A single cell in which the electrolyte membrane electrode assembly is sandwiched between separators serves as a power generation unit. Then, a fuel gas such as hydrogen or hydrocarbon is supplied to the fuel electrode, and an oxidant gas such as oxygen or air is supplied to the oxygen electrode, and power is generated by an electrochemical reaction at the three-phase interface between the gas, the electrolyte, and the electrode.

  However, the polymer electrolyte fuel cell has a problem that the battery performance is deteriorated by long-term operation. As a cause of the decrease in battery performance, for example, deterioration of an electrolyte membrane or an electrode can be mentioned. In addition, corrosion of metal materials used for separators, piping constituting a fuel cell system, manifolds, and the like can be given. When the metal material is corroded, the eluted metal ions are ion-exchanged with protons of sulfonic acid groups in the polymer constituting the electrolyte membrane and the electrode. Thereby, the proton conductivity of the electrolyte membrane is inhibited, and the resistance increases. Moreover, the electrochemical reaction in an electrode is also inhibited.

Usually, when the polymer electrolyte fuel cell is operated, water is generated from hydrogen and oxygen at the oxygen electrode. However, depending on the operating conditions, the reduction of oxygen at the oxygen electrode may be stopped by a two-electron reaction, and hydrogen peroxide (H ₂ O ₂ ) may be generated. The generated hydrogen peroxide undergoes radical decomposition in the presence of, for example, metal ions. The hydrogen peroxide radical is thought to damage and deteriorate the electrolyte membrane and the electrode.

  As an attempt to suppress the deterioration of electrolyte membranes caused by hydrogen peroxide and improve the durability of fuel cells, for example, it is proposed to include oxides such as manganese oxide, ruthenium oxide, and tungsten oxide in electrolyte membranes and electrodes (For example, refer to Patent Documents 1 and 2).

On the other hand, Patent Document 3 discloses a fuel cell electrode in which a magnetic substance such as iron ferrite is blended in an electrode catalyst layer from the viewpoint of radicalizing a supplied fuel gas and improving output characteristics.
JP 2001-118591 A JP 2000-106203 A JP 2001-110431 A

  However, the methods disclosed in Patent Documents 1 and 2 have problems in terms of practicality and cost because they use an expensive metal with a small amount of resources as the oxide to be contained. On the other hand, Patent Document 3 has no idea of suppressing radicalization of hydrogen peroxide. That is, the fuel cell electrode disclosed in Patent Document 3 aims to radicalize the fuel gas. Therefore, in order to promote ionization of the fuel gas, a large amount of magnetic substance is blended in the electrode catalyst layer in which the electrochemical reaction proceeds.

  Many of the polymer electrolyte fuel cells use a polymer membrane made of a hydrocarbon material or a fluorine material as an electrolyte membrane. Conventionally, it has been considered that a fluorine-based electrolyte membrane is hardly damaged by hydrogen peroxide. Therefore, also in the said patent documents 1, 2, examination is made about the hydrocarbon type electrolyte membrane. However, as a result of various studies, the present inventor has obtained knowledge that even a fluorine-based electrolyte membrane may be damaged by hydrogen peroxide. In this case, since the C—F bond is decomposed by hydrogen peroxide, harmful substances such as hydrofluoric acid may be generated.

  The present invention has been made in view of such a situation, and by decomposing and detoxifying hydrogen peroxide generated in the battery, the solid content is low even when operated for a long period of time. It is an object to provide a molecular fuel cell. It is another object of the present invention to provide an electrolyte membrane electrode assembly that can constitute such a polymer electrolyte fuel cell.

  An electrolyte membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises an electrolyte membrane having ionic conductivity and a pair of electrodes provided on both sides of the electrolyte membrane, and the electrolyte membrane and the pair of electrodes At least one of the electrodes includes a peroxide decomposing substance composed of one or more of an iron-containing oxide and an iron-containing hydroxide.

  In the electrolyte membrane electrode assembly of the present invention (hereinafter referred to as “MEA” where appropriate), a pair of electrodes that respectively serve as a fuel electrode and an oxygen electrode are disposed on both sides of the electrolyte membrane. Therefore, in the MEA of the present invention, a peroxide decomposition substance is contained in at least one of the electrolyte membrane, the fuel electrode, and the oxygen electrode. When the peroxide decomposition substance is contained in two or more of them, the decomposition effect of the peroxide becomes higher.

  The peroxide-decomposing substance contained in the MEA of the present invention comprises one or more of iron-containing oxides and iron-containing hydroxides (hereinafter referred to as “iron-containing oxides” as appropriate). Usually, when the polymer electrolyte fuel cell is operated, the inside is subjected to severe conditions such as an acidic atmosphere at a high temperature of about 80 ° C. Therefore, peroxide-decomposing substances are required to be difficult to elute under high temperature and acidic conditions. Iron-containing oxides and the like are relatively stable even under high temperature and acidic conditions, and are difficult to elute. Moreover, the resolution of peroxides such as hydrogen peroxide is high. Hereinafter, decomposition of hydrogen peroxide will be described as an example.

Hydrogen peroxide undergoes radical decomposition in the presence of transition metal ions (M ^{n +} / M ^{(n + 1) +} ) as shown in formulas (1) and (2).
HOOH ^{+ M (n + 1) +} → HOO · + H + + M n + ··· (1)
HOOH + M ^{n +} → HO · + OH ⁻ + M ^{(n + 1) +} (2)
The peroxide-decomposing substance can be reduced or decomposed as shown in formula (3) or oxidatively decomposed as shown in formula (4) before hydrogen peroxide is radically decomposed in this way. .
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O ... (3)
H ₂ O ₂ → O ₂ + 2H ⁺ + 2e ⁻ (4)
On the surface of the peroxide-decomposing substance, from the formula [(3) + (4)], as shown in the formula (5), two molecules of hydrogen peroxide collide and decompose into water and oxygen. This is a so-called catalytic decomposition reaction.
2H ₂ O ₂ → 2H ₂ O + O ₂ (5)
In this way, hydrogen peroxide generated during operation is decomposed by peroxide-decomposing substances before radicalization, so that decomposition of fluorine-based materials and the like and reduction in molecular weight due to hydrogen peroxide radicals are suppressed. . As a result, deterioration of the electrolyte membrane and the electrode is suppressed. Moreover, since the hydrogen peroxide which moves to a separator, piping, a manifold, etc. which comprise a fuel cell system reduces, corrosion of these metal materials is also suppressed.

Here, the corrosion of the metal material will be described. The corrosion reaction in which the metal M elutes in divalent is represented by the formula (6).
^{M → M 2+ + 2e - ···} (6)
On the other hand, in the presence of hydrogen peroxide, hydrogen peroxide is responsible for the corrosion reduction reaction as shown in equation (7).
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O ... (7)
Therefore, corrosion of the metal material can be effectively suppressed by decomposing hydrogen peroxide with the MEA and reducing the amount of hydrogen peroxide that moves to the outside of the MEA.

  A polymer electrolyte fuel cell according to the present invention includes the above-described electrolyte membrane electrode assembly according to the present invention. That is, in the polymer electrolyte fuel cell of the present invention, even if hydrogen peroxide is generated during operation, the hydrogen peroxide is rapidly decomposed by the peroxide decomposition substance. For this reason, there is little deterioration of the electrolyte membrane and the electrode during operation, and there is little decrease in battery performance even when operated for a long period.

  In the electrolyte membrane electrode assembly of the present invention, at least one of the electrolyte membrane and the pair of electrodes contains a peroxide decomposing substance composed of one or more of an iron-containing oxide and an iron-containing hydroxide. Therefore, hydrogen peroxide generated during operation is quickly decomposed and detoxified by the peroxide decomposition substance. Therefore, in the polymer electrolyte fuel cell provided with the electrolyte membrane electrode assembly of the present invention, there is little deterioration of the electrode and the electrolyte membrane, and even when the battery is operated for a long time, the battery performance is hardly lowered.

  Hereinafter, embodiments of the electrolyte membrane electrode assembly for a polymer electrolyte fuel cell and the polymer electrolyte fuel cell of the present invention will be described. In addition, the electrolyte membrane electrode assembly for polymer electrolyte fuel cells and the polymer electrolyte fuel cell of the present invention are not limited to the following embodiments. The electrolyte membrane electrode assembly for a polymer electrolyte fuel cell and the polymer electrolyte fuel cell of the present invention are in various forms that have been modified or improved by those skilled in the art without departing from the gist of the present invention. Can be implemented.

<Electrolyte membrane electrode assembly for polymer electrolyte fuel cell>
An electrolyte membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises an electrolyte membrane having ionic conductivity and a pair of electrodes provided on both sides of the electrolyte membrane, and the electrolyte membrane and the pair of electrodes At least one of the electrodes includes a peroxide decomposing material composed of one or more of an iron-containing oxide and an iron-containing hydroxide.

Examples of the iron-containing oxide that becomes a peroxide-decomposing substance include FeO, Fe ₂ O ₃ , Fe ₃ O ₄ (iron ferrite: FeO · Fe ₂ O ₃ ), and the like. Examples of the iron-containing hydroxide include Fe (OH) ₂ and Fe (OH) ₃ , and oxyhydroxide such as FeOOH. One of these may be used alone, or a mixture of two or more may be used. In particular, it is desirable to use iron ferrite (Fe ₃ O ₄ ) as a peroxide decomposing substance because of its low solubility in acid and the ability to stably exhibit the resolution of hydrogen peroxide for a long period of time. Also, oxides in which a part of iron (Fe) is substituted with other elements such as alkaline earth metals and transition metals, such as BaFe ₁₂ O ₁₉ , MnFe ₂ O ₄ , and Ni _x Fe _3−x O ₄ . May be used. These oxides have good electronic conductivity. Therefore, if these oxides are contained in the electrode, hydrogen peroxide can be decomposed without significantly reducing the electronic conductivity of the electrode.

  The particle diameter of the iron-containing oxide or the like is not particularly limited. However, if the particle diameter of the iron-containing oxide or the like is too small, it is easy to elute under acidic conditions, which causes a problem in terms of long-term stability. Therefore, the particle diameter of the iron-containing oxide or the like is desirably 0.05 μm or more. On the other hand, when the particle diameter of the iron-containing oxide or the like is too large, the dispersibility is lowered. Accordingly, the particle diameter of the iron-containing oxide or the like is desirably 5 μm or less.

  The peroxide decomposing substance is contained in at least one of the electrolyte membrane, the fuel electrode, and the oxygen electrode. For example, when the peroxide decomposing substance is contained in the electrolyte membrane, the content ratio of the peroxide decomposing substance is preferably 0.1 wt% or more when the total weight of the electrolyte membrane is 100 wt%. This is because when the amount is less than 0.1 wt%, the effect of decomposing peroxide is small. More preferably, it is 0.5 wt% or more. On the other hand, in consideration of proton conductivity, it is desirable that the content ratio of the peroxide decomposing substance is 5 wt% or less. More preferably, it is 1 wt% or less.

  In general, the fuel electrode and the oxygen electrode are each composed of a catalyst layer and a diffusion layer. The catalyst layer is a reaction field for electrochemical reaction, and includes a catalyst such as platinum supported on carbon and a solid polymer electrolyte. The diffusion layer serves to supply a reaction gas to the catalyst layer and exchange electrons with the catalyst layer, and is made of a porous material such as carbon cloth. Therefore, for example, when a peroxide decomposition substance is contained in the catalyst layer of the electrode, the content ratio of the peroxide decomposition substance is that of a platinum catalyst (hereinafter referred to as “Pt / C catalyst”) supported on carbon. It is desirable to set it to 0.2 wt% or more when the weight is 100 wt%. This is because when the amount is less than 0.2 wt%, the effect of decomposing the peracid is small. More preferably, it is 0.5 wt% or more. On the other hand, when the influence on the electrochemical reaction in the electrode is taken into consideration, it is desirable that the content rate of the peroxide decomposition substance is 5 wt% or less. More preferably, it is 1 wt% or less.

  Further, when the peroxide decomposition substance is contained in the diffusion layer of the electrode, the content ratio of the peroxide decomposition substance is 0.2 wt% or more when the weight of the porous material constituting the diffusion layer is 100 wt%. It is desirable to do. This is because when the amount is less than 0.2 wt%, the effect of decomposing the peracid is small. More preferably, it is 1 wt% or more. On the other hand, it is desirable that the content rate of the peroxide decomposing substance is 10 wt% or less from the viewpoint of suppressing a decrease in the discharge performance of the generated water due to a decrease in water repellency of the diffusion layer. More preferably, it is 5 wt% or less. When the catalyst layer and the diffusion layer are integrated to form an electrode, the content ratio of the peroxide decomposing substance may be the same as that for fixing to the catalyst layer.

  The peroxide decomposition substance may be contained in any of the electrolyte membrane, the fuel electrode, and the oxygen electrode. From the viewpoint of promptly decomposing the generated hydrogen peroxide, it is desirable to contain a peroxide decomposing substance in the oxygen electrode. Further, from the viewpoint of effectively suppressing deterioration of the electrolyte membrane and generation of hydrofluoric acid or the like, it is desirable to contain a peroxide decomposing substance in the electrolyte membrane. More preferably, the peroxide decomposition substance is contained in both the electrolyte membrane and the oxygen electrode. Moreover, when an electrode is comprised from a catalyst layer and a diffusion layer, it is desirable to contain a peroxide decomposition substance in at least one of the diffusion layer and the electrolyte membrane. By containing a peroxide-decomposing substance in the diffusion layer, hydrogen peroxide moving to the outside of the MEA can be reduced, and corrosion of metal materials such as piping constituting the fuel cell system can be effectively suppressed. Can do.

  The method for incorporating the peroxide decomposing substance into the electrolyte membrane and the electrode is not particularly limited. Examples thereof include a method of mixing a powdery peroxide-decomposing substance into an electrolyte membrane or the like, or fixing to a electrolyte membrane or the like by a sol-gel method. The sol-gel method is preferable because fine particles of a peroxide decomposing substance can be uniformly dispersed in an electrolyte membrane or the like. Hereinafter, each method will be described.

(1) Mixing method (a) Electrolyte membrane A powdery peroxide-decomposing substance may be kneaded with a polymer to be an electrolyte membrane, and the polymer is formed into an electrolyte membrane.

(B) Electrode When contained in the catalyst layer of the electrode, a powdery peroxide decomposition substance may be mixed with the catalyst ink for forming the catalyst layer. Specifically, a catalyst ink may be prepared by dispersing a powdery peroxide-decomposing substance, an electrode catalyst, and a polymer as a binder in a solvent such as water or alcohol.

  When it is contained in the diffusion layer of the electrode, a water repellent layer containing a powdery peroxide-decomposing substance may be formed on the surface of carbon cloth or the like that becomes the diffusion layer. Specifically, first, a powdery peroxide-decomposing substance, a conductive substance such as carbon powder, a water repellent such as polytetrafluoroethylene (PTFE), a surfactant or the like, if necessary, water or alcohol Etc. to produce a paste. Next, the paste may be applied to the surface of carbon cloth or the like by a doctor blade method, a spray method, or the like, and dried to form a water repellent layer.

(2) Sol-gel method In this method, a peroxide decomposing substance is deposited and fixed on the electrolyte membrane or the electrolyte in the catalyst layer of the electrode. For example, the electrolyte membrane or the like may be hydrolyzed by immersing it in a metal salt aqueous solution in which a metal salt containing iron is dissolved in water or an organic complex solution in which an organic complex of metal containing iron is dissolved in an organic solvent. Here, the metal salt containing iron includes acetate, oxalate, nitrate, sulfate, chloride, and the like as salts having high solubility in water. Moreover, as for the metal organic complex containing iron, those t-butoxide, ethyl hexanate, octane dionate, isopropoxide, etc. are mentioned. Moreover, in the case of a hydrolysis, you may heat as needed and you may add an acid or an alkali. In particular, when an aqueous metal salt solution is used, it is desirable to perform hydrolysis by adding a complexing agent such as acetic acid or citric acid.

Further, a precursor such as an electrolyte membrane may be immersed in the metal salt aqueous solution or the organic complex solution and hydrolyzed. This method is efficient because the conversion from a precursor such as an electrolyte membrane to the electrolyte membrane and the like and the fixation of the peroxide decomposition substance proceed simultaneously. Here, a precursor such as an electrolyte membrane refers to a material in which an electrolyte group such as an electrolyte membrane is replaced with an electrolyte group precursor. The electrolyte group precursor means a functional group that can be easily converted into an electrolyte group by hydrolysis. Specific examples of the electrolyte group precursor include halide groups such as a sulfonyl halide group (—SO ₂ X: X is a halogen element, the same shall apply hereinafter), and alkalis such as —SO ₃ M (M is an alkali metal element, the same applies hereinafter). A metal salt etc. are mentioned.

When a precursor such as an electrolyte membrane is immersed in an alkaline metal salt aqueous solution or the like, for example, the halide group is hydrolyzed to become an alkali metal salt (—SO ₂ X → —SO ₃ M). Next, by contacting with an acid, the electrolyte group precursor is converted into an acid form to be an electrolyte group (—SO ₃ M → —SO ₃ H). Phosphoric acid, hydrofluoric acid, sulfuric acid, hydrochloric acid, nitric acid, etc. may be used as the acid for making the electrolyte group precursor an acid electrolyte group. Among these, phosphoric acid and hydrofluoric acid are preferable because the surface of the iron-containing oxide or the like to be fixed can be hardly soluble.

  The MEA of the present invention can be produced according to a usual method except that a peroxide decomposing substance is contained in the electrolyte membrane and the electrode. For example, first, each catalyst ink for oxygen electrode and fuel electrode is applied to the surface of a PTFE sheet and dried to form a catalyst layer for each electrode on the sheet surface. Subsequently, the catalyst layer of each electrode formed on the sheet surface is pressure-bonded to both surfaces of the electrolyte membrane by hot pressing or the like. After crimping, only the sheet is peeled off. As a result, a catalyst layer constituting the oxygen electrode is formed on one surface of the electrolyte membrane, and a catalyst layer constituting the fuel electrode is formed on the other surface. Finally, a carbon cloth or the like serving as a diffusion layer may be pressure-bonded to the surfaces of the catalyst layers of both electrodes by hot pressing or the like to form an MEA.

  In the MEA of the present invention, the type of electrolyte membrane is not particularly limited. For example, a perfluorinated sulfonic acid film, a perfluorinated phosphonic acid film, a perfluorinated carboxylic acid film, a fluorinated hydrocarbon-based graft film, a perhydrocarbon-based graft film, a wholly aromatic film, or the like can be used. Moreover, you may use the composite polymer film which strengthened mechanical characteristics containing reinforcement materials, such as PTFE and a polyimide. In particular, when considering durability and the like, it is desirable to use a perfluorinated polymer film. Among these, it is desirable to use a perfluorinated sulfonic acid membrane because of its high performance as an electrolyte. Examples of perfluorinated sulfonic acid membranes include “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. Can be mentioned.

<Solid polymer fuel cell>
The polymer electrolyte fuel cell of the present invention includes the above-described electrolyte membrane electrode assembly of the present invention. For example, what is necessary is just to comprise the electrolyte membrane electrode assembly of this invention by laminating | stacking two or more through a separator. As a separator for sandwiching an electrolyte membrane electrode assembly, a fired carbon, a molded carbon, or a stainless steel material coated with a noble metal or a carbon material, which has high current collecting performance and is relatively stable even in an oxidizing water vapor atmosphere, is used. That's fine.

  Based on the above embodiment, an electrolyte membrane containing a peroxide-decomposing substance was manufactured and its durability was evaluated. In addition, an MEA containing a peroxide decomposing substance in at least one of the electrolyte membrane and the oxygen electrode was produced. A battery reaction was performed using the produced MEA, and the degree of deterioration of the electrolyte membrane and the electrode was investigated. Hereinafter, it demonstrates in order.

<Manufacture and evaluation of electrolyte membranes containing peroxide-decomposing substances>
(1) Manufacture of electrolyte membrane containing peroxide decomposing substance (1-a) First, FeCl ₂ · 6H ₂ O is dissolved in 100 ml of water so that the amount of Fe is 0.05 wt% to prepare an iron chloride aqueous solution. did. A perfluorinated sulfonic acid membrane (7 cm × 7 cm, thickness 45 μm, hereinafter simply referred to as “membrane” in this production process) was immersed in the prepared aqueous iron chloride solution and maintained at 90 ° C. for 1 hour. Subsequently, a 0.1 M aqueous sodium acetate solution was added and maintained at 90 ° C. for 1 hour. Then, the film gradually became black and Fe ₃ O ₄ was fixed to the film. Further, the sulfonic acid group (—SO ₃ H) of the membrane became —SO ₃ Na. To return the -SO ₃ Na again -SO ₃ H, washed several times the membrane with deionized water, and immersed for 10 minutes at 90 ° C. in 0.1M sulfuric acid, was converted to the acid form. Thereafter, Fe ₃ O ₄ takes out a fixed film, placed in deionized water to remove excess sulfuric acid by maintaining 10 minutes at 90 ° C.. The obtained film was vacuum dried and its weight was measured. The weight of the fixed Fe ₃ O ₄ was 1.6 wt%. The obtained membrane was used as the electrolyte membrane of Example 1.

(1-b) An electrolyte membrane in which Fe ₃ O ₄ was fixed was produced in the same manner as the electrolyte membrane of Example 1 except that phosphoric acid was used instead of sulfuric acid when the membrane was converted to the acid type. . The obtained membrane was used as the electrolyte membrane of Example 2.

(1-c) When the membrane is converted to the acid form, an electrolyte membrane in which Fe ₃ O ₄ is fixed is obtained in the same manner as the electrolyte membrane of Example 1 except that hydrofluoric acid is used instead of sulfuric acid. Manufactured. The obtained membrane was used as the electrolyte membrane of Example 3.

(2) Durability Evaluation The electrolyte membranes of Examples 1 to 3 manufactured above were mixed in an aqueous solution containing 1 wt% hydrogen peroxide and 14 ppm iron ions (Fe ²⁺ ) in a PTFE sealed container ( 200 ml), heated to 100 ° C. and held for 24 hours. After the aqueous solution was cooled, the concentration of fluoride ions (F ⁻ ) eluted in the aqueous solution was measured. For the measurement of F ⁻ concentration, an ion selective electrode (manufactured by Orion) was used. Moreover, each electrolyte membrane was vacuum-dried and the weight of each was measured. The F ⁻ concentration and the change in weight before and after the immersion of the electrolyte membrane serve as indices indicating the degree of deterioration of each electrolyte membrane. For comparison, an electrolyte membrane of the same kind (Comparative Example 1) in which Fe ₃ O ₄ is not fixed was immersed in the same aqueous solution as described above, and the F ⁻ concentration and weight change were measured. The results are shown in Table 1. In Table 1, “film weight reduction rate (%)” was calculated from the formula [{(film weight after immersion−film weight before immersion) / film weight before immersion} × 100].

As shown in Table 1, in the electrolyte membranes of Examples 1 to 3 in which Fe ₃ O ₄ was fixed, the F ⁻ concentration and the membrane weight reduction rate were smaller than those of the electrolyte membrane of Comparative Example 1 of the related art. . In particular, F in the electrolyte membrane of Example 2, 3 ^- concentration and film weight loss was smaller. This is probably because in the electrolyte membranes of Examples 2 and ₃ , elution of the fixed Fe ₃ O _{4 into} the aqueous solution was suppressed by using phosphoric acid and hydrofluoric acid for conversion of the acid type. . Thus, it can be seen that the electrolyte membranes of Examples 1 to 3 are hardly decomposed and hardly deteriorated even in the presence of hydrogen peroxide and Fe ²⁺ .

<Production and degradation investigation of MEA>
(1) Production of MEA Various MEAs were produced by appropriately combining oxygen electrode catalyst ink, fuel electrode catalyst ink, carbon cloth, and electrolyte membrane shown below.

First, two types of oxygen electrode catalyst inks for forming an oxygen electrode catalyst layer were prepared. Add 0.0025 g Fe ₃ O ₄ powder to 0.5 g Pt / C catalyst (platinum support rate 60 wt%), and further add 2.0 g distilled water, 2.5 g ethanol, 1.0 g propylene glycol, Nafion solution 0.9 g (22 wt%, manufactured by DuPont) was added in this order. Then, a catalyst ink containing Fe ₃ O ₄ was prepared by dispersing with an ultrasonic homogenizer. Also, a catalyst ink containing no Fe ₃ O ₄ was prepared without adding Fe ₃ O ₄ powder.

Next, a fuel electrode catalyst ink for forming a fuel electrode catalyst layer was prepared. Except for not adding Fe ₃ O ₄ powder and using a Pt / C catalyst having a platinum content of 30 wt% as the fuel electrode catalyst, the same method as the preparation of the oxygen electrode catalyst ink was used. A fuel electrode catalyst ink was prepared.

Next, two types of carbon cloths serving as diffusion layers were produced. Fe ₃ O ₄ powder, carbon powder (Denka black (average particle size 0.03 μm), manufactured by Denki Kagaku Kogyo Co., Ltd.) and PTFE powder were mixed in water to produce a paste. The paste was applied to the surface of the carbon cloth with a spray gun and dried to form a water repellent layer containing Fe ₃ O ₄ . The basis weight of the water repellent layer on the surface of the carbon cloth was 12 mg / cm ² by weight after drying. The content ratio of each material in the water repellent layer is 10 wt% Fe ₃ O ₄ powder, 45 wt% carbon powder, and 45 wt% PTFE powder. Further, a water repellent layer not containing Fe ₃ O ₄ was formed on the surface of the carbon cloth without using Fe ₃ O ₄ powder. In this case, the content ratio of each material in the water repellent layer is 50 wt% carbon powder and 50 wt% PTFE powder.

The electrolyte membrane, Fe ₃ electrolyte of Example 1 containing O ₄ film or Fe ₃ O ₄ containing no Nafion 112 (trade name, manufactured by DuPont), we decided to use the film. Hereinafter, the production procedure of MEA will be described.

The prepared oxygen electrode catalyst ink and fuel electrode catalyst ink were each applied to the surface of a sheet made of Teflon (registered trademark, manufactured by DuPont) by a doctor blade method. Thereafter, the solvent was removed by vacuum drying at room temperature, and a catalyst layer of each electrode was formed on the sheet surface. In the catalyst layer of the oxygen electrode, the platinum amount per unit area was set to 0.5 to 0.6 mg / cm ² . In the catalyst layer of the fuel electrode, the amount of platinum per unit area was 0.2 mg / cm ² . After the sheet with each catalyst layer formed is cut into 36 mm square, the sheet with the fuel electrode catalyst layer formed on one surface of the electrolyte membrane and the sheet with the oxygen electrode catalyst layer formed on the electrolyte The other surface of the membrane was hot pressed at a pressure of about 4.9 MPa and a temperature of about 120 ° C. Thereafter, only the sheet was peeled off. And the carbon cloth used as a diffused layer was hot-pressed on the surface of the catalyst layer of each electrode, and it was set as MEA. For the diffusion layer of the fuel electrode, a carbon cloth containing no Fe ₃ O ₄ in the water repellent layer was used.

(2) Investigation of deterioration of electrolyte, etc. The produced various MEAs were incorporated into a small (electrode area 13 cm ² ) solid polymer fuel cell. That is, carbon separators with gas flow paths formed on both sides of the MEA were placed and held by a SUS support. Then, humidified air was supplied to the oxygen electrode, and humidified hydrogen was supplied to the fuel electrode, and the polymer electrolyte fuel cell was operated for 24 hours. The humidification temperature of air and hydrogen was 90 ° C., the flow rate was 100 ml / min, and the operating temperature of the battery was 90 ° C. During the operation of the battery, water discharged from the oxygen electrode and the fuel electrode was collected. The fluoride ion (F ⁻ ) concentration in each recovered water was measured with an ion chromatograph PIA-1000 (manufactured by Shimadzu Corporation), and the fluorine discharge rate (μg / (cm ² · hr)) was determined. The fluorine discharge rate is the amount of fluorine discharged per unit time and unit electrode area, and is calculated from the amount of recovered water from each electrode and the F ⁻ concentration in the recovered water. The fluorine discharge rate is an index indicating the degree of deterioration of the electrolyte membrane and the electrode. Table 2 shows the configuration of each MEA and the fluorine discharge rate (μg / (cm ² · hr)). In Table 2, ○ mark, shown to contain Fe ₃ O _4, - mark indicating that it does not contain the Fe ₃ O _4.

As shown in Table 2, the MEA (Examples 4 to 8) containing Fe ₃ O ₄ in at least one of the electrolyte membrane and the oxygen electrode was compared with the MEA containing no Fe ₃ O ₄ (Comparative Example 2). The fluorine discharge rate decreased at both the fuel electrode and the oxygen electrode. From this, it can be seen that in the MEA containing Fe ₃ O ₄ , deterioration of the electrolyte membrane and the electrode was suppressed. In addition, in the MEA containing Fe ₃ O ₄ in the electrolyte membrane and the diffusion layer (Examples 4 to 7), the fluorine discharge rate is higher than in the MEA containing Fe ₃ O ₄ only in the catalyst layer (Example 8). It has become smaller. From this, it is understood that the deterioration of the electrolyte membrane and the electrode can be more effectively suppressed by including Fe ₃ O ₄ in the electrolyte membrane and the diffusion layer.

  From the above, it was confirmed that in the MEA of the present invention in which at least one of the electrolyte membrane and the pair of electrodes contains a peroxide decomposing substance, the electrolyte membrane and the electrode are hardly deteriorated. Therefore, by using the MEA of the present invention, it is possible to economically realize a polymer electrolyte fuel cell with little deterioration in battery performance even when operated for a long time.

Claims (4)

An electrolyte membrane having ionic conductivity, and a pair of electrodes provided on both sides of the electrolyte membrane,
An electrolyte membrane electrode assembly for a polymer electrolyte fuel cell, wherein at least one of the electrolyte membrane and the pair of electrodes contains a peroxide decomposing substance comprising at least one of an iron-containing oxide and an iron-containing hydroxide. Each of the pair of electrodes includes a catalyst layer and a diffusion layer,
The electrolyte membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the peroxide decomposition substance is contained in at least one of the diffusion layer and the electrolyte membrane. The electrolyte membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the peroxide decomposing substance includes iron ferrite (Fe ₃ O ₄ ).   A polymer electrolyte fuel cell comprising the electrolyte membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1.