JP2010257990A - Polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte fuel cell and a fuel cell system of low cost, high battery performance, and excellent durability. <P>SOLUTION: The polymer electrolyte fuel cell includes a membrane-electrode assembly with electrodes jointed to both sides of an electrolyte membrane, and peroxide decomposing catalyst containing hardly-soluble carbonate fixed to the electrolyte membrane and/or the electrode. The fuel cell system includes: the polymer electrolyte fuel cell; humidifying channels for supplying water and/or water vapor to the polymer electrolyte fuel cell and/or for collecting water and/or water vapor exhausted from the polymer electrolyte fuel cell; and the peroxide decomposing catalyst containing hardly-soluble carbonate fixed to either of the humidifying channels. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  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.
Moreover, in order to advance an electrode reaction efficiently, it is necessary to ensure the three-phase interface in which an electrode catalyst, electrolyte, and reaction gas coexist in a catalyst layer. However, on the cathode side in particular, there is a problem that so-called flooding occurs in which the three-phase interface is clogged with water generated by the electrode reaction or water contained in the reaction gas, and the reaction efficiency tends to be lowered.
Furthermore, in order to reduce the cost of the polymer electrolyte fuel cell, it is necessary to reduce the amount of expensive noble metal catalyst such as platinum, and for that purpose, it is necessary to uniformly disperse fine catalyst particles. . However, the noble metal catalyst has a problem that it easily aggregates on the surface of the support.

In order to solve this problem, various proposals have heretofore been made.
For example, Patent Document 1 discloses a highly durable solid polymer electrolyte in which transition metal oxide fine particles such as manganese oxide, ruthenium oxide, and iridium oxide are dispersed in a hydrocarbon electrolyte. This document describes that the oxidation resistance of the membrane is improved by dispersing ruthenium oxide or the like in the hydrocarbon electrolyte membrane.

  Patent Document 2 discloses a solid polymer electrolyte membrane in which a transition metal oxide catalyst such as manganese oxide or ruthenium oxide or a macrocyclic metal complex catalyst such as iron phthalocyanine or copper phthalocyanine is added to a hydrocarbon solid polymer electrolyte membrane. A molecular electrolyte membrane is disclosed. In this document, when a transition metal oxide catalyst or a macrocyclic metal complex catalyst is added to a hydrocarbon-based electrolyte, hydrogen peroxide generated by the side reaction of the electrode reaction is decomposed by the transition metal oxide catalyst or the macrocyclic metal complex catalyst. The point that the oxidation resistance of the hydrocarbon electrolyte is improved is described.

  Patent Document 3 discloses an electrode manufacturing method in which electrolysis is performed using carbon paper as an anode in an electrolytic solution containing anhydrous hydrofluoric acid, potassium fluoride, and a fluorine-based surfactant. In this document, the water repellent carbon fluoride layer can be formed on the surface of the electrode substrate by such a method, and the electrode obtained by such a method has excellent water repellency. Are listed.

In Patent Document 4, a titanium layer is formed on the surface of carbon particles, and catalyst-supporting particles for fuel cells in which platinum particles are supported on the titanium layer, and a zirconium carbide layer is formed on the surface of the carbon particles. Further, there are disclosed fuel cell catalyst supporting particles in which platinum particles are supported on a zirconium carbide layer. In this document, the formation of an adhesion layer composed of a titanium layer, a zirconium carbide layer, or the like on the surface of carbon particles, and supporting platinum particles thereon, the aggregation of platinum particles is suppressed, and the platinum particles The point that the contact area between the carbon particle and the carbon particle increases and the contact resistance between the two decreases is described.
Further, Patent Document 5 describes that Sc, La, Yb, and Y are particularly effective in the use of a hydrogen peroxide solution and a rare earth salt of a sulfonic acid having a perfluoroalkyl group as a catalyst for the olefin oxidation reaction. ing. Patent Document 6 describes that when wastewater treatment is performed using hydrogen peroxide, transition metal ions, for example, ions such as Fe and Cu have a catalytic action on oxidation of organic substances.

JP 2001-118591 A JP 2000-106203 A Japanese Patent Laid-Open No. 10-284088 JP 2003-346814 A JP 2001-79417 A JP 2003-154332 A

Noble metals such as Pt, Ru, Ir, Rh or their oxides have an action of decomposing peroxides. Therefore, when these powders are added to a hydrocarbon-based electrolyte or a partial fluorine-based electrolyte, generation of peroxide radicals is suppressed, and oxidation resistance can be improved. However, this method is not practical because noble metals are low in resources and expensive.
On the other hand, macrocyclic metal complexes and transition metal oxides have an action of decomposing hydrogen peroxide and are less expensive than noble metals. However, many of these have insufficient chemical stability, and in some cases, sufficient durability for practical use cannot be obtained.

  Further, perfluorinated electrolytes have hitherto been considered to be highly resistant to peroxide radicals and not deteriorate even when used for a long time in an environment where peroxide radicals coexist. However, the present inventors have found that even a perfluorinated electrolyte deteriorates with time when used for a long time under the operating conditions of a fuel cell. Therefore, it is desired to further improve the durability of the electrolyte for applications requiring a high level of oxidation resistance.

  The problem to be solved by the present invention is to provide a polymer electrolyte fuel cell and a fuel cell system that are low in cost, high in battery performance, and excellent in durability. Another problem to be solved by the present invention is to improve the durability of a perfluorinated electrolyte in a polymer electrolyte fuel cell and a fuel cell system using a perfluorinated electrolyte.

In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention includes a membrane electrode assembly in which electrodes are joined to both surfaces of an electrolyte membrane, and a poorly soluble material fixed to the electrolyte membrane and / or the electrode. And a peroxide decomposition catalyst containing a carbonate of the above.
The fuel cell system according to the present invention includes a polymer electrolyte fuel cell, and supplies water and / or water vapor to the polymer electrolyte fuel cell and / or is discharged from the polymer electrolyte fuel cell. And a peroxide decomposition catalyst containing a sparingly soluble carbonate fixed to any one of the humidification paths.

Certain carbonates are relatively stable in water at high temperature and low pH, have a relatively high peroxide decomposition action, and are less expensive than noble metal-based peroxide decomposition catalysts. Therefore, if this is fixed to the electrolyte membrane and / or electrode, deterioration of the electrolyte due to peroxide radicals can be suppressed without significantly increasing the manufacturing cost. In addition, when a peroxide decomposition catalyst is fixed to any membrane electrode assembly using a perfluorinated electrolyte, deterioration of the perfluorinated electrolyte is suppressed, and the durability of the polymer electrolyte fuel cell is further improved.
Furthermore, in the fuel cell system according to the present invention, the peroxide decomposition catalyst containing a hardly soluble carbonate is fixed to any one of the humidification pathways, so that the peroxide radical can be obtained without significantly increasing the production cost. It is possible to suppress the deterioration of the electrolyte due to.

It is a figure which shows the decomposition rate of hydrogen peroxide of various carbonates and oxalates.

  Hereinafter, an embodiment of the present invention will be described in detail. The polymer electrolyte fuel cell according to the present invention 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 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 (for example, —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 electrolyte group provided in the solid polymer electrolyte is not particularly limited. Suitable examples of the electrolyte group include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. The solid polymer electrolyte may contain only one kind of these electrolyte groups, or may contain two or more kinds. Furthermore, these electrolyte 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, polyamide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, etc. in which an electrolyte group such as a sulfonic acid group is introduced into any of the polymer chains, And derivatives thereof (aliphatic hydrocarbon electrolytes), polystyrene in which an electrolyte group such as a sulfonic acid group is introduced into any of the polymer chains, polyamides having aromatic rings, polyamideimides, polyimides, polyesters, polysulfones, polyethers Imide, polyethersulfone, polycarbonate and the like, and derivatives thereof (partial aromatic hydrocarbon electrolyte), polyetheretherketone, polyetherketone in which an electrolyte group such as sulfonic acid group is introduced into any of the polymer chains, Polysulfone, polyethersulfone, poly Imides, polyetherimides, polyphenylene, polyphenylene ether, polycarbonate, polyamide, polyamideimide, polyester, polyphenylene sulfide, etc., and their derivatives (fully aromatic hydrocarbon-based electrolytes), etc. are mentioned as suitable examples.

  Further, as the partial fluorine-based electrolyte, specifically, a polystyrene-graft-ethylenetetrafluoroethylene copolymer (hereinafter referred to as “PS”) in which an electrolyte 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, platinum alloy, 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 materials of the electrode catalyst and the catalyst carrier, the use of the MEA, 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 solid polymer fuel cell according to the present invention is characterized in that a peroxide decomposition catalyst is fixed to any one of the solid polymer electrolyte membrane and the electrodes constituting the MEA. Here, the “peroxide decomposition catalyst” refers to a compound having a peroxide decomposition action and containing a hardly soluble carbonate.

The “slightly soluble compound” includes not only a compound that is hardly soluble in water but also a compound that becomes hardly soluble by reacting with hydrolysis or other dissolved ions. In order to obtain a fuel cell system with excellent durability, a peroxide decomposition catalyst is one in which when a metal element exhibiting an H ₂ O ₂ decomposition action comes into contact with water, the metal element is unlikely to elute from a fixed place. There must be.
Here, the pH of water under the operating environment of a normal fuel cell is the atmospheric CO ₂ , NO _x , SO _x , organic acids and halogen ions eluted from the constituent materials, and in some cases, a fluorine-based electrolyte membrane The pH is about 4 to 6 which is not neutral but weakly acidic due to the F ⁻ ions from the SO ₂ and SO ₃ ⁻ ions due to sulfonic acid elimination. In addition, due to the effect of by-product H ₂ O ₂ , the environment is such that ions are more likely to be eluted from the material. Furthermore, the operating temperature of the polymer electrolyte fuel cell is generally about 80 ° C.

Therefore, in practice, it is required to be poorly soluble in these harsh environments, but the degree of poor solubility in the operating environment of such a fuel cell is that of the constituent elements at room temperature (18-25 ° C.). The size of the hydroxide solubility product can be substituted.
That is, for example, when CaC ₂ comes into contact with water, calcium hydroxide (Ca (OH) ₂ ) is generated by a hydrolysis reaction as shown in the following formula (1).
CaC ₂ + 2H ₂ O → Ca (OH) ₂ + C ₂ H ₂ (1)
If the hydroxide produced | generated by such a hydrolysis reaction is hardly soluble with respect to water, since reaction of Formula (1) does not advance to the right, the elution of a peroxide decomposition catalyst can be suppressed. In order to obtain a fuel cell system with excellent durability, the peroxide decomposition catalyst should contain a metal element having a hydroxide solubility product of 1 × 10 ⁻¹² or less at room temperature (18 to 25 ° C.). preferable. The solubility product of hydroxide is more preferably 1 × 10 ⁻²⁰ or less.

The degree of peroxide decomposition action (decomposition ability) of a compound can be expressed by the decomposition rate ΔE shown in the following equation (2).
ΔE = (1−E ₂ ) × 100 (2)
However, E ₂ is the peroxide concentration after adding 0.1 g of powder having an average particle size of 50 μm or less to 30 ml of an aqueous solution containing 1 wt% of peroxide and leaving it to stand at 100 ° C. for 1 hour.
In order to obtain a solid polymer electrolyte having excellent durability, the peroxide decomposition catalyst has a decomposition rate of hydrogen peroxide (H ₂ O ₂ ) represented by the formula (2) of 10% or more. Preferably, it is 30% or more, more preferably 50% or more.

  Rare earth elements (Sc of atomic number 21 and Y of atomic number 39, and lanthanoid elements from La of atomic number 57 to Lu of atomic number 71) and carbonates (including hydrates) containing transition metal elements. Hereinafter, the same)) has a relatively high peroxide decomposition action.

Specific examples of the carbonate having a relatively high peroxide decomposition action and hardly soluble include Y ₂ (CO ₃ ) ₃ , Y ₂ (CO ₃ ) ₃ · 3H ₂ O, Ce ( CO _{3) 2,
Ce 2 (CO 3) 3 ·} 8H 2 O, La 2 (CO 3) 3, La 2 (CO 3) 3 · 8H 2 O,
Nd ₂ (CO ₃ ) ₃ , Nd ₂ (CO ₃ ) ₃ · 8H ₂ O, MnCO ₃ , NiCO ₃ ,
NiCO ₃ .6H ₂ O, CoCO ₃ , Ag ₂ CO _{3 and the} like.

  Furthermore, these series of poorly soluble carbonates need not necessarily be pure. For example, during the refining of the ore containing rare earth elements, a mixture of rare earth elements called Misch metal (with La, Ce, and Nd as main components) is obtained. This misch metal may be carbonated as it is and used as a peroxide decomposition catalyst. Since the peroxide decomposition catalyst using natural mineral as a raw material is inexpensive, the cost increase of the solid polymer fuel cell can be reduced.

  That is, the peroxide decomposition catalyst may be composed of any one of the carbonates described above, or may be a mixture or composite compound containing two or more. Further, the peroxide decomposition catalyst may be composed only of the above-mentioned carbonate, or the above-described carbonate and the above-mentioned rare earth element, transition metal element and / or typical element fluoride, hydroxide and / or Alternatively, it may be a mixture with oxide or a composite compound.

Specifically, as a composite compound that can be used as a peroxide decomposition catalyst,
CeCO ₃ F, (Ce, La) ₂ (CO ₃ ) ₃ · 4H ₂ O, Ce (CO ₃ ) ₂ O · H ₂ O,
Ce ₂ O (CO ₃ ) ₂ .H ₂ O, CeCO ₃ OH, Ce ₂ (CO ₃ ) ₂ (OH) ₂ .H ₂ O,
CaY (CO ₃ ) ₂ F, CaY ₂ (CO ₃ ) ₄ · 6H ₂ O, Y ₂ (CO ₃ ) ₃ · 2H ₂ O,
Y (OH) CO ₃ or the like is.

  Among these, carbonates containing any one or more of Ce, Y, La, and Ag are suitable as peroxide decomposition catalysts because they all have a large peroxide decomposition action and are hardly soluble.

  The place for fixing the peroxide decomposition catalyst may be either the electrolyte membrane or the electrode. When fixing to the electrode, the peroxide decomposition catalyst may be fixed at either the catalyst layer or the diffusion layer. However, in the polymer electrolyte fuel cell, it is considered that the peroxide is generated by a side reaction of the electrode reaction generated at the cathode, and the generated peroxide diffuses to the anode side through the electrolyte membrane. Therefore, it is preferable to fix the peroxide decomposition catalyst at least on the cathode and in the vicinity thereof.

  Further, in a fuel cell system including a solid polymer fuel cell, in general, humidification is performed using an auxiliary device in order to maintain the electrical conductivity of the electrolyte membrane. On the cathode side, water is generated by the electrode reaction. These waters are usually discharged out of the fuel cell as they are, but the discharged water may be reused for humidifying the electrolyte membrane in order to reduce the water retention amount of the entire fuel cell system. In such a case, the discharged water may contain peroxide, so the water circulation path (the separator surface, the inner surface of the piping, the inner surface of the water retention tank, etc.) In other words, the water and / or water vapor is supplied to the polymer electrolyte fuel cell and / or the water and / or water vapor discharged from the polymer electrolyte fuel cell is recovered. An oxide decomposition catalyst may be fixed.

The form of the peroxide decomposition catalyst is not particularly limited, and various forms can be taken according to the kind of the peroxide decomposition catalyst, the fixing location, and the like.
For example, when the peroxide decomposition catalyst is fixed to the electrolyte membrane, the fine particle peroxide decomposition catalyst may be uniformly dispersed inside and / or on the surface of the electrolyte membrane, or the membrane may be formed on the surface of the electrolyte membrane. It may be fixed to. Further, when the electrolyte membrane is a composite of a solid polymer electrolyte and a reinforcing material, a particulate or thin film peroxide decomposition catalyst may be fixed on the surface of the reinforcing material.
For example, when fixing a peroxide decomposition catalyst to a catalyst layer, a fine particle or thin film peroxide decomposition catalyst is formed on the surface of the electrode catalyst or the carrier for supporting the electrode catalyst and / or the electrolyte in the catalyst layer. May be fixed, or may be fixed inside the carrier and / or the electrolyte in the catalyst layer. In addition, after forming the catalyst layer, a fine particle or thin film peroxide decomposition catalyst may be fixed on the surface thereof.
Further, when the peroxide decomposition catalyst is fixed to the diffusion layer, the fine particle peroxide decomposition catalyst may be uniformly dispersed inside or on the surface of the diffusion layer, or formed on the catalyst layer side surface of the diffusion layer. You may disperse | distribute uniformly in the inside or surface of the water-repellent layer. Further, a thin-film peroxide decomposition catalyst may be fixed to the catalyst layer side surface or the separator side surface of the diffusion layer.

In addition, when fixing the fine particle peroxide decomposition catalyst to any of the MEAs, the optimal particle size is selected according to the fixing location.
For example, when fixing the fine particle peroxide decomposition catalyst to the electrolyte membrane or the catalyst layer, the particle size is preferably 5 μm or less. When the particle diameter exceeds 5 μm, it is difficult to uniformly disperse the peroxide decomposition catalyst, or there is a risk of causing mechanical damage to the electrolyte membrane. In general, the smaller the particle size, the higher the peroxide decomposition effect with a small amount of fixation. However, if the particle size becomes too small, the solubility becomes high and the long-term stability may be inferior. Therefore, the particle size of the peroxide decomposition catalyst is preferably 0.01 μm or more.
On the other hand, when fixing the fine particle peroxide decomposition catalyst to the diffusion layer, a catalyst having a slightly large particle size of 0.01 to 50 μm or less can be used. However, when a powder having a relatively large particle size is used, it is preferable to fix it in a place where it does not directly contact the electrolyte membrane or the catalyst layer.

  As the fixed amount of the peroxide decomposition catalyst, an optimal amount is selected according to the kind, form, fixing location, etc. of the peroxide decomposition catalyst. In general, the higher the peroxide decomposition ability and the larger the specific surface area of the peroxide decomposition catalyst, the higher the peroxide decomposition action can be achieved with a relatively small amount of fixation. Generally, durability increases as the amount of peroxide decomposition catalyst fixed increases. However, even if the peroxide decomposition catalyst is excessively fixed, there is no actual benefit, but rather it may increase the cost, decrease the mechanical properties, decrease the battery performance, and the like.

For example, when a particulate peroxide decomposition catalyst is fixed to the inside of the electrolyte membrane, the surface of the electrolyte membrane, and / or the surface of the reinforcing material, the fixed amount of the peroxide decomposition catalyst is 0 with respect to the electrolyte. .1 to 1 wt% is preferable. When the fixed amount of the peroxide decomposition catalyst is less than 0.1 wt%, a sufficient effect cannot be obtained. On the other hand, when the peroxide decomposition catalyst fixing amount exceeds 1 wt%, the mechanical properties of the electrolyte membrane may be impaired.
In addition, for example, when a fine particle peroxide decomposition catalyst is fixed on the surface and / or inside of the catalyst layer, the fixed amount of the peroxide decomposition catalyst is preferably 0.1 to 10 wt% with respect to the weight of the catalyst layer. . When the fixed amount of the peroxide decomposition catalyst is less than 0.1 wt%, a sufficient effect cannot be obtained. On the other hand, when the fixed amount of the peroxide decomposition catalyst exceeds 10 wt%, the internal resistance may increase and the battery performance may deteriorate.

For example, when fixing a thin film-like peroxide decomposition catalyst to the catalyst layer side surface and / or separator side surface of the diffusion layer by laser ablation, sputtering, or the like, the thickness of the thin film is preferably 2 to 20 nm. If the thickness of the thin film is less than 2 nm, sufficient effects cannot be obtained. On the other hand, when the thickness of the thin film exceeds 20 nm, the contact resistance may increase and the battery performance may be deteriorated.
Further, for example, when a water repellent layer is formed on the surface of the diffusion layer and the particulate hydrogen peroxide decomposition catalyst is fixed on the surface and / or inside of the water repellent layer, the fixed amount of the hydrogen peroxide decomposition catalyst is solid 0.1-20 wt% is preferable with respect to quantity. When the fixed amount of the peroxide decomposition catalyst is less than 0.1 wt%, a sufficient effect cannot be obtained. On the other hand, when the fixed amount of the hydrogen peroxide decomposition catalyst exceeds 20 wt%, the contact resistance may increase and the battery performance may deteriorate.

Next, a method for producing a polymer electrolyte fuel cell according to the present invention will be described.
Among the MEA components, the electrolyte membrane with the peroxide decomposition catalyst fixed is
(1) First, a particulate peroxide decomposition catalyst is added to a solid polymer electrolyte or a precursor thereof (for example, Nafion (registered trademark) sulfonyl fluoride) and kneaded in a wet or dry manner to form a film. Method,
(2) a second method of spraying, spraying, or applying (including a doctor blade; the same applies hereinafter) to the surface of the electrolyte membrane or its precursor with a fine particle peroxide decomposition catalyst or a slurry in which the fine particle decomposition catalyst is dispersed;
(3) a third method for forming a thin-film peroxide decomposition catalyst on the surface of the electrolyte membrane or its precursor by sputtering, laser ablation or the like of a target material having an appropriate composition;
(4) A fine particle or thin film peroxide decomposition catalyst is fixed on the surface of the reinforcing material by using the second or third method described above, and the reinforcing material and the solid polymer electrolyte or a precursor thereof are fixed. A fourth method of compounding in a wet or dry manner;
(5) a combination of these,
Etc. can be manufactured.

In addition, among the constituent elements of MEA, the catalyst layer to which the peroxide decomposition catalyst is fixed is
(1) A polytetrafluoroethylene sheet prepared by adding a particulate peroxide decomposition catalyst to a solution containing an electrode catalyst or a carrier carrying an electrode catalyst and a polymer electrolyte (hereinafter referred to as “catalyst ink”) A first method of spraying or applying to the surface of a substrate made of a polymer material such as
(2) A second method of spraying or applying a catalyst ink containing a particulate peroxide decomposition catalyst directly on the surface of the electrolyte membrane or the surface of the diffusion layer,
(3) A catalyst layer is formed using a catalyst ink not containing a peroxide decomposition catalyst, and a fine particle peroxide decomposition catalyst or a slurry in which this is dispersed is dispersed, sprayed or applied to the surface of the catalyst layer. 3 methods,
(4) A catalyst layer is formed using a catalyst ink not containing a peroxide decomposition catalyst, and a thin film peroxide decomposition catalyst is formed on the surface of the catalyst layer by sputtering, laser ablation, etc. of a target material having an appropriate composition. A fourth method of fixing,
(5) (a) a compound containing a metal element constituting the peroxide decomposition catalyst, which is liquid at room temperature or can be dissolved in an appropriate solvent (for example, salt, chloride, alkoxide, A catalyst carrier is added to a solution containing alcoholate, acetylacetonate, etc.), a compound containing a metal element is adsorbed on the surface of the catalyst carrier, and hydrolyzed to produce a hydroxide.
(B) Carbonate treatment is performed by bringing the metal element-containing compound into contact with an aqueous solution containing carbonate ions (sodium carbonate, potassium carbonate, ammonium carbonate, etc.), and peroxide decomposition in the form of fine particles or thin film on the catalyst carrier surface Forming a catalyst,
(C) a fifth method of adding the catalyst carrier to the catalyst ink to form a catalyst layer;
(6) a combination of these,
Etc. can be manufactured.

In addition, among the components of MEA, the diffusion layer to which the peroxide decomposition catalyst is fixed is
(1) A first method of spraying, spraying or applying a fine particle peroxide decomposition catalyst or a slurry in which the fine particle decomposition catalyst is dispersed on the surface of carbon paper or the like,
(2) A slurry containing carbon particles, water-repellent powder (for example, polytetrafluoroethylene powder) and fine particle peroxide decomposition catalyst is sprayed or applied on the surface of carbon paper or the like, and the peroxide decomposition catalyst is applied. A second method of forming a water repellent layer comprising:
(3) A water repellent layer not containing a peroxide decomposition catalyst is formed on the surface of carbon paper or the like, and a fine particle peroxide decomposition catalyst or a slurry in which this is dispersed is dispersed and sprayed on the surface of the water repellent layer. Or a third method of applying,
(4) A water-repellent layer that does not contain a peroxide decomposition catalyst is formed on the surface of carbon paper, etc., and a thin-film peroxide decomposition catalyst is formed on the surface of the water-repellent layer by sputtering, laser ablation, etc. A fourth method of fixing,
(5) According to the same procedure as the fifth method for fixing the peroxide decomposition catalyst to the catalyst layer, the fine particle or thin film peroxide decomposition catalyst is fixed to the surface of the carbon particles, and this is used. A fifth method of forming a water repellent layer on the surface of carbon paper or the like;
(6) A compound containing a metal element constituting a peroxide decomposition catalyst, which is liquid at room temperature, or can be dissolved in an appropriate solvent (for example, salt, chloride, alkoxide, alcoholate, acetyl) A diffusion layer is immersed in a solution containing acetonate, etc., and a compound containing a metal element is adsorbed on the surface and / or inside of the diffusion layer, and after hydrolysis, a solution containing carbonate ions (sodium carbonate, potassium carbonate, carbonic acid) A sixth method of performing a carbonation treatment in contact with ammonium or the like),
(7) a combination of these,
Etc. can be manufactured.

  In each of these methods, the conditions for fixing the peroxide decomposition catalyst (for example, the type of solvent used, the solution concentration, the composition of the catalyst ink, the decomposition condition of the compound containing the metal element, the composition of the target material, the sputtering condition, or the laser ablation) For the conditions, etc., the optimum conditions are selected according to the materials and compositions of the electrolyte membrane, the catalyst layer, the diffusion layer, and the peroxide decomposition catalyst, the fixing method, and the like. Moreover, when forming a thin film-like peroxide decomposition catalyst using a target material, you may use 1 type of target material containing 1 type, or 2 or more types of metal elements, or 1 type or 2 types or more. Two or more kinds of target materials containing these metal elements may be used.

After fixing the peroxide decomposition catalyst to at least one of the electrolyte membrane, the catalyst layer, and the diffusion layer using the various methods described above, the catalyst layers are joined to both surfaces of the electrolyte membrane, and if necessary, MEA can be obtained by bonding a diffusion layer to the surface of the catalyst layer. The joining of the electrolyte membrane, the catalyst layer, and the diffusion layer is usually performed by hot pressing. Furthermore, the polymer electrolyte fuel cell according to the present invention can be obtained by sandwiching both sides of the obtained MEA with a separator having a gas flow path to form a unit cell, and stacking a plurality of unit cells.
In addition, a reaction gas supply path and a humidification path are attached to a polymer electrolyte fuel cell in which a peroxide decomposition catalyst is fixed or not fixed to one of the MEAs, and the peroxide decomposition catalyst is fixed to one of the humidification paths. Then, the fuel cell system according to the present invention can be obtained. In this case, the method for fixing the hydrogen peroxide decomposition catalyst to the humidification route is not particularly limited, and the above-described method for fixing to the MEA can be used as it is or with appropriate modifications and changes.

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 (3) or (4) It is known to undergo radical decomposition by the reduction reaction of the formula.
HOOH + M ^{(n + 1) +} → HOO. + H ⁺ + M ^{n +} (3)
HOOH + M ^{n +} → HO · + OH ⁻ + M ^{(n + 1) +} (4)

  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 certain kind of carbonate has an action of suppressing deterioration due to peroxide radicals. This is thought to be because, on the solid surface of the carbonate, the peroxide is ion-decomposed by the reduction reaction of the following formula (5) or the oxidation reaction of the following formula (6) before radical decomposition. .
H ₂ O ₂ + 2H ⁺ + 2e ⁻ → 2H ₂ O (5)
H ₂ O ₂ → O ₂ + 2H ⁺ + 2e ⁻ (6)
The reaction on the surface of the solid is eventually the so-called two-molecule hydrogen peroxide colliding and decomposing into water and oxygen as shown in the following equation (7) from the equations (5) and (6). Expressed as catalytic cracking reaction.
2HOOH → H ₂ O + O ₂ (7)

Therefore, when carbonate is fixed to any one or more of the solid polymer electrolyte membrane, the catalyst layer, and the diffusion layer, generation of peroxide radicals is suppressed, and as a result, alteration of organic compounds by peroxide radicals, Lower molecular weight and the like are suppressed. In addition, even when a hydrocarbon electrolyte membrane or a partial fluorine electrolyte membrane is used as the solid polymer electrolyte membrane, a solid polymer fuel cell having high durability can be obtained. This is because the carbonate added as a catalyst does not elute even when CO ₂ is generated due to deterioration of the hydrocarbon-based electrolyte, part of which is dissolved as carbonate ions, and the pH of the generated water is lowered. This is because the catalytic activity can be maintained. Furthermore, when a perfluorinated electrolyte is used as the solid polymer electrolyte membrane, the deterioration of the perfluorinated electrolyte due to peroxide radicals and the elution of F ions due to this are suppressed, and the solid has excellent durability. A polymer fuel cell is obtained.

Further, transition metal oxide, it is known that there is a peroxide decomposition, the solubility of the transition metal oxide, fuel cells use environment (i.e., NO x from the _atmosphere, SO _x, It is not always small in an environment where impurity anions such as Cl ₂ gas contamination and Cl ions eluted from constituent materials in the system exist. To solve this problem, a transition metal oxide and F ^- ions, is bound to an anion such as PO ₄ ^2-ionic or C ^₂ O ₄ ^2- ions, also conceivable to hardly soluble. However, the allowable concentration of these anions in the environment is small and some are toxic. For this reason, when a combined product of transition metal oxide and these anions is used as a hydrogen peroxide decomposition catalyst, there is a special treatment (for example, adjustment of particle size or improvement of crystallinity) to reduce the solubility of the combined product. Necessary.
In contrast, certain carbonates have relatively low solubility in high temperature or low pH water and high chemical stability. Moreover, even if it elutes, since the load with respect to an environment is small, the special process for insolubilization is unnecessary. Therefore, if this is fixed to any part of the MEA and / or the humidification path, a polymer electrolyte fuel cell having high durability over a long period of time can be obtained without increasing the manufacturing cost and environmental load. It is done.

  Moreover, rare earth elements and transition metal elements are relatively rich in resources and are less expensive than noble metals such as Pt. Therefore, if a carbonate containing these metal elements is fixed to any of the MEAs, it is not necessary to use a large amount of a noble metal element such as Pt as a peroxide decomposition catalyst. That is, the durability of the polymer electrolyte fuel cell can be improved without increasing the cost. In particular, carbonates containing Ce, Y, La or Ag are relatively inexpensive and have a high peroxide decomposition action, so that the cost of the polymer electrolyte fuel cell is not increased. , Durability can be dramatically improved.

  Furthermore, even in the same salt, oxalates of rare earth elements or transition metal elements have a smaller hydrogen peroxide decomposition action than carbonates. Although the details of the cause are not clear, it is thought to be due to the following reasons. That is, oxalate ions have a higher complex stability than carbonate ions. Therefore, when oxalate is fixed to one of the humidification pathways, the oxalate ions are dissolved in water under the environment where the fuel cell is used, and the dissolved oxalate ions are adsorbed on the active sites of the peroxide decomposition catalyst. This is considered to decrease the catalytic activity.

(Examples 1-4)
According to the following procedure, the decomposition ability of the peroxide decomposition catalyst was investigated. That is, 30 ml of a 1 wt% aqueous solution of H ₂ O ₂ is placed in a container whose inner cylinder is made of polytetrafluoroethylene, and Ce ₂ (CO ₃ ) ₃ · 8H ₂ O (Example 1) is used as a peroxide decomposition catalyst. , Y ₂ (CO) ₃ .3H ₂ O (Example 2), Ag ₂ CO ₃ (Example 3), or La ₂ (CO ₃ ) ₃ (Example 4) was added in an amount of 0.1 g. After standing at 100 ° C. × 1 hr, the hydrogen peroxide concentration E ₂ in the solution was measured, and the decomposition rate ΔE was determined by the above-described equation (2).
Note that the hydrogen peroxide concentration _{E 2} of the test solution, the relationship between the hydrogen peroxide concentration of the solution constant potential oxidation current (after 10 minutes) at 1.2V in 0.1M sulfuric acid (vs SHE) (A calibration curve of hydrogen peroxide-current value) was obtained in advance, and was calculated using a calibration curve based on the measured constant potential oxidation current of the solution to be tested (constant potential electrochemical oxidation method).

(Comparative Example 1)
The decomposition rate ΔE was determined according to the same procedure as in Examples 1 to 4, except that cerium oxalate (Ce ₂ (C ₂ O ₄ ) ₃ · 9H ₂ O) was used instead of carbonate.

  FIG. 1 shows the decomposition rate ΔE of various carbonates and oxalates. From FIG. 1, it can be seen that carbonate has a higher hydrogen peroxide decomposition action than oxalate. The reason why the hydrogen peroxide decomposition action of oxalate is lower than that of carbonate is thought to be because oxalate ions eluted in water are adsorbed on the active sites (rare earth elements or transition metals) to reduce the catalytic activity.

  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 the solid polymer electrolyte to which the predetermined carbonate is fixed is not limited to the electrolyte membrane or the electrolyte in the catalyst layer of the solid polymer fuel cell, but a water electrolysis device, hydrohalic acid electrolysis device It can also be used as electrolyte membranes, electrode materials, etc. used in various electrochemical devices such as salt electrolyzers, oxygen and / or hydrogen concentrators, humidity sensors, gas sensors and the like.

Claims (7)

A membrane electrode assembly in which electrodes are bonded to both surfaces of the electrolyte membrane;
A polymer electrolyte fuel cell comprising a peroxide decomposition catalyst containing a hardly soluble carbonate fixed to the electrolyte membrane and / or electrode. 2. The polymer electrolyte fuel cell according to claim 1, wherein the peroxide decomposition catalyst includes a carbonate of a metal element having a hydroxide solubility product _Ksp of 1 × 10 ²⁰ or less at room temperature.   2. The polymer electrolyte fuel cell according to claim 1, wherein the peroxide decomposition catalyst contains a rare earth element and / or a transition metal element carbonate. The peroxide decomposition catalyst includes Y ₂ (CO ₃ ) ₃ , Y ₂ (CO ₃ ) ₃ · 3H ₂ O,
Ce (CO ₃ ) ₂ , Ce ₂ (CO ₃ ) ₃ · 8H ₂ O, La ₂ (CO ₃ ) ₃ ,
La ₂ (CO ₃ ) ₃ · 8H ₂ O, Nd ₂ (CO ₃ ) ₃ , Nd ₂ (CO ₃ ) ₃ · 8H ₂ O,
_{MnCO 3, NiCO 3, NiCO 3} · 6H 2 O, CoCO 3, Ag 2 CO 3,
CeCO ₃ F, (Ce, La) ₂ (CO ₃ ) ₃ · 4H ₂ O, Ce (CO ₃ ) ₂ O · H ₂ O,
Ce ₂ O (CO ₃ ) ₂ .H ₂ O, CeCO ₃ OH, Ce ₂ (CO ₃ ) ₂ (OH) ₂ .H ₂ O,
CaY (CO ₃ ) ₂ F, CaY ₂ (CO ₃ ) ₄ · 6H ₂ O, Y ₂ (CO ₃ ) ₃ · 2H ₂ O,
And Y (OH) CO ₃
The polymer electrolyte fuel cell according to claim 1, which is at least one selected from the group consisting of:   The polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the peroxide decomposition catalyst is a fine particle having a particle size of 0.01 µm to 5 µm.   The polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the peroxide decomposition catalyst has a decomposition rate of hydrogen peroxide of 10% or more. A polymer electrolyte fuel cell;
A humidification path for supplying water and / or water vapor to the polymer electrolyte fuel cell and / or recovering water and / or water vapor discharged from the polymer electrolyte fuel cell;
A fuel cell system comprising the peroxide decomposition catalyst according to any one of claims 1 to 6, which is fixed to any one of the humidification paths.

Images