JP5090717B2 - Polymer electrolyte fuel cell - Google Patents

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.
Further, the solid polymer electrolyte usually requires water in order to exhibit proton conductivity. Therefore, in order to stably obtain a high output, it is necessary to maintain the solid polymer electrolyte in an appropriate water-containing state regardless of the operating state of the fuel cell.
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 electrolyte membrane obtained by immersing a perfluorocarbon sulfonic acid membrane in an aqueous solution of a zirconium phosphate compound. This document describes that the inclusion of a zirconium phosphate compound in the electrolyte membrane hydrates water molecules with phosphate groups and improves the water retention of the electrolyte membrane.

  Further, in Patent Document 4, nickel and cobalt compounds are supported on carbon powder supporting platinum, alloyed by heat treatment, nickel and cobalt not alloyed by acid treatment are dissolved and extracted, and inert gas is obtained. A process for producing a platinum alloy catalyst that is heat-dried in is disclosed. This document describes that nickel and the like that are not alloyed with platinum are removed by acid treatment, so that a stable potential can be maintained for a long time.

  Patent Document 5 discloses an electrode catalyst for a polymer electrolyte fuel cell obtained by annealing a platinum-based noble metal catalyst supported on a conductive carrier at 50 to 90 ° C. in air. This document describes that the durability of the catalyst is improved because a predetermined amount of oxygen is held and fixed on the surface of the platinum-based noble metal catalyst by the annealing treatment.

  Further, Patent Document 6 discloses a phosphoric acid fuel cell cathode catalyst which is made of an alloy of platinum and cobalt and has a platinum ratio of 67% or more and 75%. This document describes that the alloy phase is stabilized by alloying platinum and cobalt, so that the durability of the catalyst is improved.

JP 2001-118591 A JP 2000-106203 A JP-A-6-103983 JP-A-6-246160 JP 2004-349113 A JP 2001-345107 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 certain transition metal oxides have an action of decomposing hydrogen peroxide, and are cheaper than noble metals, but have low electron conductivity. Therefore, when a large amount of these compounds is added to the electrode in order to improve the durability of MEA, there is a problem that the internal resistance or the contact resistance is increased and the battery performance is lowered.

In addition, it has been conventionally considered that perfluorinated electrolytes have high resistance to peroxide radicals and do not deteriorate even when used for a long time in an environment where peroxide radicals coexist. However, even a perfluorinated electrolyte may deteriorate over 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.
Furthermore, Patent Documents 4 to 6 propose various methods for suppressing deterioration of the electrode catalyst. However, the conventional method is insufficient in the effect of suppressing the deterioration of the electrode catalyst. Moreover, the cause of deterioration of the electrode catalyst has not been clarified.

The problem to be solved by the present invention is to provide a polymer electrolyte fuel cell that is practical, has high battery performance, and is 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 using a perfluorinated electrolyte.
Furthermore, another problem to be solved by the present invention is to provide a polymer electrolyte fuel cell that can suppress deterioration of the electrode catalyst and stably obtain a high output over a long period of time.

In order to solve the above problems, the solid polymer fuel cell according to the present invention is summarized as having the following configuration.
(1) The polymer electrolyte fuel cell is
A membrane electrode assembly having electrodes bonded to both surfaces of the electrolyte membranes,
A sparingly soluble inorganic anion exchanger substantially not containing Fe, which is added to one or more of the electrolyte membrane and the electrode .
(2) The electrode has a two-layer structure of a catalyst layer and a diffusion layer,
The hardly soluble inorganic anion exchanger is added to the catalyst layer.
(3) The hardly soluble inorganic anion exchanger is a hydrated oxide of Ce.
(4) The amount of the hardly soluble inorganic anion exchanger added to the catalyst layer (= weight of the hardly soluble inorganic anion exchanger × 100 / weight of the solid content of the catalyst layer) is 5.0 wt% to 10. 0 wt%.

When peroxide radicals are generated during operation of the fuel cell, the electrolyte and the carbon material are deteriorated, resulting in an increase in cross leak and a decrease in voltage. On the other hand, the sparingly soluble inorganic anion exchanger has the effect of decomposing and detoxifying peroxides or peroxide radicals. Therefore, if this is added to any one or more of the electrolyte membrane and the electrode, it is possible to suppress a decrease in output due to deterioration of the electrolyte and the carbon material due to peroxide radicals without significantly increasing the manufacturing cost.
Further, in an environment where a potential fluctuation occurs as in a fuel cell, elution and grain growth of a noble metal catalyst such as Pt occurs particularly on the air electrode side, and the catalytic performance is reduced. This deterioration is further promoted by the coexistence of halogen ions. In addition, the halogen ions cause corrosion of the metal material in the fuel cell. On the other hand, the hardly soluble inorganic anion exchanger has an action of adsorbing halogen ions. Therefore, if this is added to the electrolyte membrane or the electrode, a trace amount of halogen ions in the fuel cell can be removed, and the reduction in catalytic ability and corrosion of the metal material due to the halogen ions can be suppressed.

  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-based electrolyte containing a C—H bond in the polymer chain and not containing a 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 electrolyte group provided in the solid polymer electrolyte is not particularly limited. 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,
(1) 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 hydrocarbons) System electrolyte),
(2) Polystyrene having an electrolyte 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 electrolyte 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 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 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 solid polymer fuel cell according to the present invention is characterized in that a hardly soluble inorganic anion exchanger is added to any of the solid polymer electrolyte membrane and the electrodes constituting the MEA.
Here, the “slightly soluble inorganic anion exchanger” is a poorly soluble compound having a peroxide decomposing action and an anion adsorbing action, and includes at least one OH group, crystal water, or halogen ion (especially Cl ^−). An anion group exchangeable with (ion). The hardly soluble inorganic anion exchanger is preferably substantially free of Fe.

In order to obtain a fuel cell system with excellent durability, a hardly soluble inorganic anion exchanger is one in which when a metal element exhibiting an H ₂ O ₂ decomposition action comes into contact with water, the metal element does not easily elute from a fixed place. (Slightly soluble).
Here, the pH of water under the normal operating environment of the fuel cell is not neutral due to the influence of CO ₂ , NO _x , SO _x in the atmosphere and organic acids and halogen ions eluted from the constituent materials, The pH is about 4 to 6 which is weakly acidic. In some cases, the pH may be lowered to about 3 by F ⁻ ions from the fluorine-based electrolyte membrane or 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 reality, it is required to be hardly soluble in these severe environments, but the degree of poor solubility in the operating environment of such a fuel cell is the hardly soluble inorganic at room temperature (18-25 ° C.). The solubility product size of the anion exchanger can be substituted.
In order to obtain a fuel cell system with excellent durability, the sparingly soluble inorganic anion exchanger preferably has a solubility product at room temperature (18 to 25 ° C.) of 1 × 10 ⁻³ or less.

“Substantially free of Fe” means that the concentration as an inevitable impurity is low in addition to not containing Fe as an active component. Specifically, the content of Fe is preferably 0.1 wt% or less (1000 ppm or less) in terms of hydroxide, hydrated oxide, or oxyhydroxide. When the Fe content exceeds 0.1 wt% in terms of hydroxide or the like, Fe dissolves out as ions and hydrogen peroxide undergoes radical decomposition. That is, the .OH radical generated by the catalytic action of Fe ions may attack the electrolyte in the catalyst layer or the electrolyte membrane and cause a decrease in battery performance. In addition, .OH radicals attack (oxidize) the diffusion layer and the C material of the electrode carrier to reduce water repellency and easily cause deterioration of battery performance. Therefore, when the Fe content exceeds 0.1 wt% in terms of hydroxide, hydrated oxide or oxyhydroxide, it is necessary to remove these by pretreatment.
As a removal method,
(1) A method of magnetically sorting powder with a magnetic material (magnet) to remove foreign matters such as iron oxide and iron oxyhydroxide,
(2) A method of neutralizing and washing with water after removing an iron compound with an acid (sulfuric acid, nitric acid, hydrochloric acid),
and so on.

The poorly soluble inorganic anion exchanger is
(1) Decomposes hydrogen peroxide, prevents the deterioration of electrolytes and carbon materials due to OH radicals, and
(2) an action of adsorbing anions such as halogen ions to prevent the catalyst metal (for example, Pt) in the catalyst layer from being dissolved and consumed as a halogen complex (for example, PtCl ₄ ²⁻ );
have.
Here, the degree of decomposition of the peroxide (decomposition ability) of a certain compound can be expressed by the decomposition rate η shown in the following equation (1).
η = {(1.0−C) /1.0} × 100 (1)
However, C is a peroxide concentration after 100 ppm of a hardly soluble inorganic anion exchanger having an average particle size of 50 μm or less is added to 50 ml of an aqueous solution containing 1 wt% of peroxide and left standing at 100 ° C. for 1 hour.
In order to improve the durability of the polymer electrolyte fuel cell, it is preferable that the hardly soluble inorganic anion exchanger has a hydrogen peroxide (H ₂ O ₂ ) decomposition rate of 30% or more. The decomposition rate is more preferably 40% or more, and still more preferably 50% or more.

Specific examples of the hardly soluble inorganic anion exchanger having a peroxide decomposition action and an anion adsorption action include rare earth elements (La to Lu), transition metal elements (3d to 5d transition metal elements), and alkaline earth metals. There are any one or more hydroxides, hydrated hydroxides, hydrated oxides, oxyhydroxides, or oxyoxides selected from the group consisting of elements.
Further, the hardly soluble inorganic anion exchanger is particularly a group consisting of Y, Zr, La, Ce, Pr, Gd, Yb, Tb, Co, Cu, Ti, Al, Nb, Bi, Mg, Ca, Sr and Ba. A hydroxide, a hydrated hydroxide, a hydrated oxide, an oxyhydroxide, or an oxyoxide containing at least one element selected from These are characterized in that the peroxide decomposition action and / or the anion adsorption action are larger than those of other hardly soluble inorganic anion exchangers.
The MEA may contain any one of these poorly soluble inorganic anion exchangers, or may contain two or more. Moreover, when a slightly soluble inorganic anion exchanger is contained in several places of MEA, the hardly soluble inorganic anion exchanger contained in each place may mutually be the same kind, and may differ.

Here, the “hydroxide” is represented by a general formula: M _x (OH) _y (where Z is the valence of M, Z × X = Y, and X and Y are positive integers). A compound of a hydroxyl group and a cation.
The “hydrated hydroxide” refers to a compound in which water is further bonded to the hydroxide. Examples of the hydrated hydroxide include LiOH · H ₂ O, CsOH · H ₂ O, and Cr (OH) ₃ · nH ₂ O.
The “hydrated oxide (or hydrated oxide)” refers to an oxide in which water is bonded. Examples of the hydrous oxide include CeO ₂ · nH ₂ O. Note that n is usually a positive integer, but n does not necessarily take an integer depending on the degree of dehydration. These may be described as acidic oxides of the corresponding cation. For example, WO ₂ .H ₂ O = H ₂ WO ₃ , WO ₃ .H ₂ O = H ₂ WO ₄ , TiO ₂ .H ₂ O = H ₂ TiO ₃ , TiO ₂ .2H ₂ O = H ₄ TiO _4, etc. It is.
“Oxyhydroxide” refers to an oxide having a hydroxyl group (OH) bonded thereto. Examples of the oxyhydroxide include FeOOH, CrOOH, and AlOOH. However, for example, when AlOOH is further added with crystallization water (AlOOH · H ₂ O), it is also described as Al (OH) _3, so that oxyhydroxide and hydroxide cannot be clearly distinguished.
The "oxy oxide", all or a portion of the OH groups contained in oxyhydroxide or hydrated oxyhydroxide halogen ions (in particular, Cl ^- ions) and other anions having an exchange capacity (e.g., NO ^3- , SO ₄ ^2-, etc.). Examples of the oxyoxide include BiO (NO ₃ ) · nH ₂ O.

Further, the hardly soluble inorganic anion exchanger is preferably subjected to a heat history of 400 ° C. or less. In the production process of the hardly soluble inorganic anion exchanger and the MEA production process, when the poorly soluble inorganic anion exchanger receives a heat history exceeding 400 ° C., the peroxide decomposition action and / or the anion adsorption action are lowered.
The reason why the hardly soluble inorganic anion exchanger having a heat history of 400 ° C. or less has a high peroxide decomposition action and / or anion adsorption action is considered to be as follows.
(1) Since it does not receive a high-temperature thermal history, the necking (sintering) of the particles hardly occurs, and the reduction ratio of the specific surface area is small, so that the peroxide decomposition action is large.
(2) Since the decrease in ion exchange capacity due to the loss (dehydration) of OH groups and crystal water is small, the adsorption capacity of halogen ions such as F and Cl is large.

  The fixing place of the hardly soluble inorganic anion exchanger may be either the electrolyte membrane or the electrode. Moreover, when fixing to an electrode, any of a catalyst layer and a diffusion layer may be sufficient as the fixing place of a hardly soluble inorganic anion exchanger. 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 hardly soluble anion exchanger at least on the cathode and in the vicinity thereof.

  Further, in general, solid polymer fuel cells are humidified using an auxiliary machine 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 cases, the discharged water may contain peroxides, so the water will circulate on the separator surface, the inner surface of the piping, the inner surface of the water retention tank, etc. A hardly soluble inorganic anion exchanger may be fixed.

The form of the hardly soluble inorganic anion exchanger is not particularly limited, and can take various forms depending on the kind of the hardly soluble inorganic anion exchanger, the fixing location, and the like.
For example, when the hardly soluble inorganic anion exchanger is fixed to the electrolyte membrane, the particulate hardly soluble inorganic anion exchanger may be uniformly dispersed in and / or on the surface of the electrolyte membrane. In addition, when the electrolyte membrane is a composite of a solid polymer electrolyte and a reinforcing material, a particulate hardly soluble inorganic anion exchanger may be fixed on the surface of the reinforcing material.
Further, for example, when fixing a sparingly soluble inorganic anion exchanger to the catalyst layer, a particulate sparingly soluble inorganic anion exchanger is provided on the surface of the electrode catalyst or the carrier for supporting the electrode catalyst and / or the electrolyte in the catalyst layer. It may be fixed, or may be fixed inside the support and / or the electrolyte in the catalyst layer. Moreover, after forming a catalyst layer, you may fix a fine particle form hardly soluble inorganic anion exchanger to the surface.
Further, when fixing the hardly soluble inorganic anion exchanger to the diffusion layer, the finely particulate hardly soluble inorganic anion exchanger may be uniformly dispersed in or on the surface of the diffusion layer, or the catalyst layer side surface of the diffusion layer. The water repellent layer formed on the surface may be uniformly dispersed in or on the surface.

Moreover, when fixing a fine particle form slightly soluble inorganic anion exchanger to either of MEA, the particle size selects an optimal particle size according to a fixing location.
For example, when fixing the particulate hardly soluble inorganic anion exchanger to the electrolyte membrane or the catalyst layer, the particle size is preferably 10 μm or less. When the particle diameter exceeds 10 μm, it is difficult to uniformly disperse the hardly soluble inorganic anion exchanger, or there is a possibility that the electrolyte membrane is mechanically damaged. In general, the smaller the particle size, the higher the peroxide decomposition action and / or the anion adsorption action 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 diameter of the hardly soluble inorganic anion exchanger is preferably 0.1 μm or more.
On the other hand, when fixing a fine particle form slightly soluble inorganic anion exchanger to a diffused layer, even a thing with a somewhat large particle size of 0.1-50 micrometers 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.

  The fixing amount of the hardly soluble inorganic anion exchanger is selected in accordance with the type, form, fixing location, etc. of the peroxide decomposition catalyst. In general, the higher the decomposition ability of peroxide and / or the anion adsorption capacity and the less soluble inorganic anion exchanger having a large specific surface area, the higher the peroxide decomposition action and / or the relatively small amount of fixation. Anion adsorption action is obtained. In general, the durability increases as the amount of the hardly soluble inorganic anion exchanger fixed increases. However, even if the poorly soluble inorganic anion exchanger is fixed excessively, there is no profit, but rather, the cost may be increased, the mechanical properties may be lowered, and the battery performance may be lowered.

  For example, when fixing a particulate hardly soluble inorganic anion exchanger to the inside of the electrolyte membrane, the surface of the electrolyte membrane, and / or the surface of the reinforcing material, the addition amount of the hardly soluble inorganic anion exchanger (= the hardly soluble inorganic anion exchanger) The weight of the anion exchanger / (weight of the hardly soluble inorganic anion exchanger + weight of the electrolyte membrane) is preferably 0.01 to 1.0 wt%. If the addition amount of the hardly soluble inorganic anion exchanger is less than 0.01 wt%, a sufficient effect cannot be obtained. On the other hand, when the amount of the hardly soluble inorganic anion exchanger exceeds 1.0 wt%, the mechanical properties of the electrolyte membrane may be impaired.

  Further, for example, in the case where fine particulate hardly soluble inorganic anion exchanger is fixed on the surface and / or inside of the catalyst layer, the addition amount of the hardly soluble inorganic anion exchanger (= weight of the hardly soluble inorganic anion exchanger × / catalyst layer) Is preferably 0.01 to 10.0 wt%. If the addition amount of the hardly soluble inorganic anion exchanger is less than 0.01 wt%, a sufficient effect cannot be obtained. On the other hand, if the addition amount of the hardly soluble inorganic anion exchanger exceeds 10.0 wt%, the internal resistance may increase and the battery performance may deteriorate.

In addition, for example, when fixing a poorly soluble inorganic anion exchanger on the surface of the diffusion layer (including the surface and the inside of the water repellent layer when a water repellent layer is formed on the surface of the diffusion layer), the poorly soluble inorganic anion The addition amount of the exchanger is preferably 0.01 to 5.0 mg / cm ² . If the addition amount of the hardly soluble inorganic anion exchanger is less than 0.01 mg / cm ² , a sufficient effect cannot be obtained. On the other hand, when the addition amount of the sparingly soluble inorganic anion exchanger exceeds 5.0 mg / cm ² , 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 constituent elements of MEA, the electrolyte membrane on which the hardly soluble inorganic anion exchanger is fixed is as follows:
(1) First, a particulate, hardly soluble inorganic anion exchanger is kneaded with a solid polymer electrolyte or a precursor thereof (for example, Nafion (registered trademark) sulfonyl fluoride) in a wet or dry manner to form a membrane. the method of,
(2) Second method of spraying, spraying, or applying (including a doctor blade; the same applies hereinafter) to a surface of an electrolyte membrane or a precursor thereof with a finely particulate hardly soluble inorganic anion exchanger or a slurry in which the finely dispersed inorganic anion exchanger is dispersed. ,
(3) A particulate hardly soluble inorganic anion exchanger is fixed to the surface of the reinforcing material using the second method described above, and the reinforcing material and the solid polymer electrolyte or precursor thereof are combined in a wet or dry manner. A third method of
(4) these combinations,
Etc. can be manufactured.

In addition, among the constituent elements of MEA, the catalyst layer to which the sparingly soluble inorganic anion exchanger is fixed,
(1) To a solution containing an electrode catalyst or an electrode catalyst-supported carrier and a polymer electrolyte (hereinafter referred to as “catalyst ink”), a particulate hardly soluble inorganic anion exchanger is added, and polytetrafluoroethylene is added. A first method of spraying or applying to a surface of a substrate made of a polymer material such as a sheet;
(2) a second method of spraying or coating a catalyst ink containing a particulate hardly soluble inorganic anion exchanger 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 that does not contain a sparingly soluble inorganic anion exchanger, and a particulate sparingly soluble inorganic anion exchanger or a slurry in which this is dispersed is sprayed, sprayed or applied on the surface of the catalyst layer. A third way to
(4) (a) A compound containing a metal element constituting a sparingly soluble inorganic anion exchanger, which is liquid at room temperature or can be dissolved in an appropriate solvent (for example, salt, chloride, alkoxide) , Alcoholate, acetylacetonate, etc.) is added to the catalyst carrier, and the compound containing the metal element is adsorbed on the surface of the catalyst carrier,
(B) performing hydrolysis, thermal decomposition, electrolysis, photolysis, etc. of the compound containing the metal element to form a particulate hardly soluble inorganic anion exchanger on the surface of the catalyst carrier;
(C) a fourth method of adding the catalyst carrier to the catalyst ink to form a catalyst layer;
(5) a combination of these,
Etc. can be manufactured.

In addition, among the constituent elements of MEA, the diffusion layer to which the sparingly soluble inorganic anion exchanger is fixed,
(1) A first method of spraying, spraying, or coating a finely divided hardly soluble inorganic anion exchanger or a slurry in which the finely dispersed inorganic anion exchanger is dispersed on the surface of carbon paper or the like,
(2) Spraying or applying a slurry containing carbon particles, water-repellent powder (for example, polytetrafluoroethylene powder), and finely particulate hardly soluble inorganic anion exchanger on the surface of carbon paper or the like to cause poorly soluble inorganic anion exchange A second method of forming a water repellent layer comprising a body,
(3) A water-repellent layer that does not contain a poorly soluble inorganic anion exchanger is formed on the surface of carbon paper or the like, and a finely particulate hardly soluble inorganic anion exchanger or a slurry in which this is dispersed is dispersed on the surface of the water-repellent layer. A third method of spraying or applying;
(4) According to the same procedure as the fourth method for fixing the sparingly soluble inorganic anion exchanger to the catalyst layer, the particulate sparingly soluble inorganic anion exchanger is fixed on the surface of the carbon particles, and this is used to A fourth method of forming a water repellent layer on the surface of paper or the like;
(5) When the diffusion layer is a C-based material, it is a compound containing a metal element constituting a sparingly soluble inorganic anion exchanger, which is liquid at room temperature or can be dissolved in an appropriate solvent ( For example, a C-based material is immersed in a solution containing a salt, chloride, alkoxide, alcoholate, acetylacetonate, etc.) to adsorb the sparingly soluble inorganic anion exchanger on the surface and / or inside of the C-based material. Method,
(6) a combination of these,
Etc. can be manufactured.

  In each of these methods, the fixing conditions of the hardly soluble inorganic anion exchanger (for example, the type of solvent used, the solution concentration, the composition of the catalyst ink, the decomposition conditions of the compound containing a metal element, etc.) are the electrolyte membrane, the catalyst layer, The optimum conditions are selected according to the material and composition of the diffusion layer and the hardly soluble inorganic anion exchanger, the fixing method, and the like.

After fixing the sparingly soluble inorganic anion exchanger to at least one of the electrolyte membrane, the catalyst layer, and the diffusion layer using the various methods described above, the catalyst layer is bonded to both surfaces of the electrolyte membrane, and if necessary, If a diffusion layer is bonded to the surface of the catalyst layer, MEA is obtained. The joining of the electrolyte membrane, the catalyst layer, and the diffusion layer is usually performed by hot pressing. In this case, the heat history in the MEA manufacturing process (for example, the firing temperature and hot press temperature when forming the water repellent layer on the surface of the diffusion layer) is preferably 400 ° C. or lower.
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.

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, the above-mentioned hardly soluble inorganic anion exchanger has the effect | action which suppresses degradation by a peroxide radical. This is because, on the solid surface of the hardly soluble inorganic anion exchanger, before the peroxide is radically decomposed, it is ion-decomposed by the following reduction reaction (4) or oxidation reaction (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)

Therefore, when a poorly soluble inorganic anion exchanger 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. Alteration of compounds, lower molecular weight, etc. 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. 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.
Furthermore, peroxide radicals attack carbon materials such as a diffusion layer and a catalyst carrier, causing a decrease in battery performance. However, when a poorly soluble inorganic anion exchanger is fixed to any of the MEAs, it is possible to suppress deterioration in battery performance due to the peroxide radical attacking the carbon material.

  In addition, the sparingly soluble inorganic anion exchanger has a relatively low solubility in high-temperature or low-pH water, so that even if it is used in a fuel cell environment for a long period of time, it is less likely to be eluted. Therefore, if this is fixed to any part of the MEA, a polymer electrolyte fuel cell exhibiting high durability over a long period of time can be obtained.

  In addition, rare earth elements, transition metal elements, and typical metal elements are relatively rich in resources and are less expensive than noble metals such as Pt. Therefore, if a hardly soluble inorganic anion exchanger containing these metal elements is fixed to any of the MEAs, it is not necessary to use a large amount of noble metal elements 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, sparingly soluble inorganic anion exchangers containing Ce, La, Y, Zr and the like are relatively inexpensive and have a high peroxide decomposition action, so that the high cost of the polymer electrolyte fuel cell is high. Durability can be dramatically improved without incurring any increase in the cost.

Further, in an environment where a potential fluctuation occurs as in a fuel cell, elution and grain growth of a noble metal catalyst such as Pt occurs particularly on the air electrode side, and the catalytic performance deteriorates. This deterioration is further promoted by the coexistence of halogen ions. This point was first discovered by the present inventors.
In particular, Cl ^- ions are contained in atmospheric dust (seawater splashes, snowmelt salt, etc.), rainwater, etc., and these may pass through the filter on the air electrode side during operation and enter the fuel cell. . In addition, halogen ions are also present in the catalyst carrier, catalyst metal, and electrolyte in a new state at a level of several ppm, and are also mixed in the MEA manufacturing process and the stack manufacturing process. Therefore, electrode deterioration has progressed with long-term use, and it has been difficult to ensure long-term durability.
Furthermore, the halogen ions cause corrosion of the metal material in the fuel cell.

On the other hand, the hardly soluble inorganic anion exchanger has an anion group exchangeable with OH group, crystal water, or halogen ion, and therefore has an action of adsorbing an anion such as halogen ion.
For example, it is considered that La (OH) ₃ , which is a kind of hardly soluble inorganic anion exchanger, adsorbs F ⁻ ions according to the following formulas (7) to (9).
La (OH) ₃ + F ⁻ → La (OH) ₂ F + OH ⁻ (7)
La (OH) ₂ F + F ⁻ → La (OH) F ₂ + OH ⁻ (8)
La (OH) F ₂ + F ⁻ → LaF ₃ + OH ⁻ (9)
For example, BiO (NO ₃ ) · nH ₂ O (5/3 ≧ n> 0), which is a kind of Bi-containing oxyoxide, is composed of bismuth oxide (Bi ₂ O ₃ ) powder and bismuth nitrate pentahydrate. (Bi (NO ₃ ) ₃ .5H ₂ O) powder is mixed at a molar ratio of 1: 1 and reacted at room temperature to 80 ° C. (Japanese Patent Laid-Open No. 2000-016814). When a sparingly soluble inorganic anion exchanger containing this hydrous oxyoxide as an active ingredient is reacted with a halogen ion, the halogen ion can be removed as BiOX (X = I, Br, Cl, F).
Therefore, if such a poorly soluble inorganic anion exchanger is added to the electrolyte membrane or electrode, a trace amount of halogen ions in the fuel cell can be removed, and the catalytic ability is reduced due to the halogen ions and the corrosion of the metal material. Can be suppressed.

(Platinum dissolution test (1): Relationship between weight change by QCM method and platinum dissolution amount)
Using the quartz crystal microbalance (QCM) method, the relationship between platinum weight change and platinum dissolution was investigated.
A quartz crystal unit was attached to a platinum plate and immersed in an aqueous solution containing 100 ppm of Cl ^- ions. After a predetermined time, the change in weight of the platinum plate with a crystal resonator was determined from the resonance frequency. At the same time, a solution was collected and the platinum concentration in the solution was analyzed by ICP. Hereinafter, in the same manner, the weight change of the platinum plate with a crystal resonator and the platinum concentration in the solution were measured by changing the immersion time in the solution.
FIG. 1 shows the relationship between the platinum dissolution amount determined by the QCM method and the platinum dissolution amount determined by ICP analysis. From FIG. 1, it can be seen that the two are in a proportional relationship, and the weight loss of platinum (QCM method) corresponds to the dissolution amount of platinum (ICP analysis).
The QCM method is a method for obtaining a change in weight of the crystal resonator from the resonance frequency. Possible causes of weight change include adsorption / desorption of water molecules and anions, and dissolution / precipitation of platinum. The weight change due to the former need not be considered when the adsorption state of water molecules and anions (electrode potential of the working electrode) is the same. The cause of the weight change in that case is considered to be all due to dissolution and precipitation of platinum.
The reason why the amount of dissolved platinum obtained by ICP is slightly less than the weight loss obtained by the QCM method is that the latter uses a theoretical formula, so there is a slight difference between the weight loss obtained by calculation and the actual weight loss. It is thought that it was because of.

(Platinum dissolution test (2): Cl to platinum dissolution rate ^- Concentration Effect of)
The effect of Cl ^- concentration on the dissolution rate of platinum was investigated using the QCM method. As the solution, a 0.1 M sulfuric acid aqueous solution containing a predetermined amount of NaCl was used. The temperature was set to room temperature, and cycling was performed while sweeping the potential of the working electrode (platinum plate with a quartz resonator attached) between 0.5 V and 1.4 V at 9.9 V · s ⁻¹ .
FIG. 2 shows the weight loss (platinum dissolution) amount after 2000 cycles. From FIG. 2, Cl ^- with increasing concentration, platinum dissolution rate seen to increase linearly. This is because when Cl ⁻ ions coexist, stable [PtCl ₄ ] ²⁻ or [PtCl ₆ ] ⁴⁻ is formed compared to aqua ions (Pt ²⁺ , Pt ⁴⁺ ), and the dissolution of platinum is promoted. It is thought to be for this purpose.
From the above, in the actual fuel cell, Cl present in the vicinity of the catalyst ^- to remove the, considered can be suppressed dissolution of platinum.

(Cl in the catalyst ^- Quantification)
In order to examine how much Cl ⁻ is present as an impurity in the platinum-supported carbon used in the preparation of the catalyst ink described later, the following experiment was conducted.
(1) 0.5 g of platinum-supporting carbon was immersed in 10 mL of distilled water and held at 80 ° C. for 24 hours.
(2) The solution was analyzed by ion chromatography.
The Cl ⁻ concentration in the solution was 0.3 ppm. In tests performed without a platinum-supported carbon as a background measurement, Cl ^- since is not detected, the Cl ^- is what was present as an impurity in carbon-supported platinum. From this value, the Cl ⁻ concentration in the vicinity of platinum in an actual fuel cell is estimated to be 50 ppm (the water content of Nafion (registered trademark) is 30% at 100% relative humidity, and all Cl ⁻ is Nafion (registered trademark). )). Actually, Cl ^- is taken in during the manufacturing process and operation of the fuel cell, and the Cl ^- concentration may be higher than the above-mentioned estimation. As can be seen from FIG. 2, the estimated Cl ⁻ concentration is sufficient to promote platinum elution, and removal of this Cl ⁻ is essential for improving the durability of the catalyst.

(Example 1, Reference Examples 2-9, Comparative Examples 1-9: F ion adsorption test)
A container with cap made of polytetrafluoroethylene (PTFE), 50 mL of a 1 wt% hydrogen peroxide aqueous solution containing 20 ppm of F ions (using an NaF aqueous solution having an F concentration of 1000 ppm), and various hydrous oxides or hydroxides (particle size: 1 ˜6 μm) was added, and the mixture was sufficiently dispersed in water by applying ultrasonic waves for 2 minutes. Further, in order to generate peroxide radicals in the solution, FeCl ₂ was added so as to be 10 ppm of Fe, and heated at 100 ° C. for 8 hours. Then, after filtering with PTFE filter paper having a pore size of 0.1 μm, the F concentration in the filtrate was measured with an ion selective electrode manufactured by Orion Research.
The reagent used was a product manufactured by Wako Pure Chemical Industries, Ltd., Kishida Chemical Co., Ltd., or High Purity Chemical Laboratory. In addition, the value of n of the hydrous oxide is about 2, and when M is a tetravalent metal element, it can be expressed as M (OH) ₄ .

Table 1 shows the F ion concentration remaining in the solution. A low F ion concentration in the solution indicates a high F ion adsorption ability in an environment where peroxide radicals exist.
From Table 1, the hydrous oxide or hydroxide used in Example 1 and Reference Examples 2 to 9 has higher F ion adsorption power than α-FeOOH which is an oxyhydroxide excellent in anion adsorption power and catalytic activity. I understand that. It can also be seen that the Ce ion-containing oxide CeO ₂ · nH ₂ O has a much larger F ion adsorption power per unit weight than Ce oxides, phosphates, carbonates and fluorides.

( Example 10, Reference Examples 11-19 , Comparative Examples 10-14: Hydrogen peroxide decomposition rate)
Add 100 mL of 1.0 wt% aqueous hydrogen peroxide solution and 100 ppm of various hydrous oxides or hydroxides (particle size: 1 to 6 μm) to a PTFE capped container and apply ultrasonic waves for 2 minutes. Dispersed. Thereafter, it was heated at 100 ° C. for 1 hour to decompose hydrogen peroxide. After the test solution was filtered with qualitative filter paper, the hydrogen peroxide concentration C (wt%) in the filtrate was measured. For the sample electrode, a Pt smooth plate was used, and constant potential oxidation was performed at 0.1 V vs. NHE in 0.1 MH ₂ SO ₄ , and the hydrogen peroxide concentration C was electrochemically determined from the current value after 10 minutes. . The decomposition rate of hydrogen peroxide was determined by equation (1).

Table 2 shows the decomposition rate of hydrogen peroxide. The decomposition rate η of hydrogen peroxide in Example 10 and Reference Examples 11 to 19 are all Ce phosphate (Comparative Example 10), Ce fluoride (Comparative Example 11), and La oxide (Comparative Example 12). ) And Fe oxyhydroxide (Comparative Example 13). The decomposition rate of Bi ₂ O ₃ (Comparative Example 14) was 22%, while the decomposition rate of Bi (OH) ₃ ( Reference Example 15 ) was 45.3%.

(Examples 20 to 23, Reference Examples 24 to 26 , Comparative Examples 15 to 16: Influence of the amount added to the catalyst layer)
CeO ₂ · nH ₂ O powder with an average particle diameter of 2 μm was added to 0.5 g of 60 wt% Pt / C catalyst, and 2.0 g of distilled water, 2.5 g of ethanol, 1.0 g of propylene glycol, and 22 wt% Nafion (registered) (Trademark) solution (manufactured by DuPont) 0.9 g was added in this order, and dispersed with an ultrasonic homogenizer to prepare a catalyst ink. This was applied onto a PTFE sheet and dried to obtain a transfer electrode. The amount of CeO ₂ · nH ₂ O powder added was 0.005 to 15.0 wt% of the solid content of the catalyst layer. Further, Pt usage, cathode 0.5~0.6mg / cm ^2, the anode is constant in the range of 0.3~0.4mg / cm ^2.
These electrodes were cut into 36 mm squares, and thermocompression-bonded (120 ° C., 50 kgf / cm ² (4.9 MPa)) on both sides of the F-based electrolyte to prepare an MEA. CeO ₂ · nH ₂ O powder was added only to the air electrode, only the hydrogen electrode, and both electrodes, and Nafion (registered trademark) 112 was used as the F-based electrolyte membrane. Diffusion layer, using a carbon cloth made of carbon fiber fabric, a water-repellent layer made of acetylene black and PTFE particles to the electrode surface by spray coating so that the basis weight of 10 mg / cm ^2, in N ₂ atmosphere furnace 200 A baking treatment at 30 ° C. for 30 minutes was performed.

The durability test was performed on the obtained MEA. The durability test conditions are as follows.
Anode gas: H ₂ (100 mL / min)
Cathode gas: air (100 mL / min)
Cell temperature: 80 ° C
Humidifier temperature: 80 ° C (both anode and cathode)
Test time: Open circuit 1 minute, cycle test with 1 cycle of power generation per minute at 0.1 A / cm ² for 150 hours.

The voltage value at 0.8 A / cm ² was measured before and after the endurance test, and the rate of decrease in this voltage value (= ΔV / V _0. V ₀ is the voltage value before the endurance test, and ΔV is the endurance test. The absolute value of the change in voltage before and after.) Was compared. Moreover, the air electrode side drain water collect | recovered between 24hr-48hr after the test start was sampled, and F density | concentration was measured with the ion selective electrode by Orion Research.
As a comparison, the durability test was similarly performed for the catalyst layer with 10.0 wt% of α-FeOOH added (Comparative Example 16) and with nothing added (Comparative Example 15).

Table 3 shows the results. From Table 3, it can be seen that when CeO ₂ · nH ₂ O powder is added to the catalyst layer, the voltage drop is smaller and the concentration of F discharged into the solution is lower than when no addition and α-FeOOH are added. When the addition amount of CeO ₂ · nH ₂ O powder is 15.0 wt% ( Reference Example 26 ), the cell resistance increases, and power generation of 0.8 A / cm ² cannot be stably performed, and the durability test is performed. Could not do. However, it was found that when the addition amount of the CeO ₂ · nH ₂ O powder is 0.01 to 10.0 wt%, the voltage drop and the F discharge amount can be significantly reduced as compared with Comparative Examples 15 and 16.

( Reference Examples 27 to 28 , Comparative Example 17: Influence of Temperature History (1))
To 100 mL of 0.1 M Ce (NO ₃ ) ₃ aqueous solution, 100 mL of 1.0 M NH ₃ aqueous solution was added and reacted with stirring at 80 ° C. for 4 hours to form a cerium hydroxide precipitate. In the middle, 10 mL of 30 wt% hydrogen peroxide water was added to promote conversion from Ce ³⁺ to Ce ⁴⁺ . The gel was filtered and washed thoroughly with cold water to remove excess ammonia. Furthermore, the obtained gel (hydrous oxide) was dried in the atmosphere at 80 ° C., 400 ° C., and 500 ° C. for 4 hours.
About the dried gel, F adsorption | suction performance was measured using the same method as Example 1 and Reference Examples 2-9 . Further, the dried gel was further dried at 600 ° C. × 2 hr, and the water content was determined from the change in weight before and after drying at 600 ° C.

Table 4 shows the water content and the F ion concentration remaining in the solution. From Table 4, it can be seen that the higher the drying temperature, the lower the water content, and the F ion concentration in the solution increases (F adsorption capacity decreases). In addition, as a result of the powder XRD, when subjected to drying at 500 ° C. and 600 ° C., a wide diffraction line derived from water-containing CeO ₂ was not observed, but a sharp diffraction line derived from cubic anhydrous CeO ₂ was observed. .

( Reference Example 29 , Comparative Example 18: Influence of Temperature History (2))
Implemented except that Ce (OH) ₄ ( Reference Example 29 ) dried at 80 ° C. and Ce (OH) ₄ (Comparative Example 18) dried at 500 ° C. were used in place of CeO ₂ .nH ₂ O. A MEA was prepared following the same procedure as in Example 20. The amount of Ce (OH) ₄ added was 5.0 wt% in all cases.
For the obtained MEA, the voltage drop rate and the F concentration in the air electrode side drain water were measured under the same conditions as in Example 20.
Table 5 shows the results. From Table 5, it can be seen that 80 ° C. drying significantly suppresses battery deterioration compared to 500 ° C. drying.

( Reference Examples 30 to 34 , Comparative Example 19: Influence of the amount added to the electrolyte membrane)
ZrO ₂ · nH ₂ O (manufactured by Kishida Chemical) was added to the electrolyte membrane. The addition method to the electrolyte membrane was a casting method using a glass petri dish. That is, 0.005 to 1.5 wt% was added to the solid resin component of Nafion (registered trademark) solution (manufactured by DuPont), and the mixture was cast into a glass petri dish after ultrasonic stirring for 4 minutes. The solvent was then removed at 60 ° C. and finally dried at 120 ° C. for 2 hours.
Next, 0.5 g of 60 wt% Pt / C catalyst was charged with 2.0 g of distilled water, 2.5 g of ethanol, 1.0 g of propylene glycol, and 0.9 g of 22 wt% Nafion (registered trademark) solution (manufactured by DuPont) in this order. In addition, a catalyst ink was prepared by dispersing with an ultrasonic homogenizer. This was applied onto a PTFE sheet and dried to obtain a transfer electrode. Pt usage, cathode 0.5~0.6mg / cm ^2, the anode is constant in the range of 0.3~0.4mg / cm ^2. These electrodes were cut into 36 mm squares and thermocompression-bonded (120 ° C., 50 kgf / cm ² (4.9 MPa)) on both sides of the cast film to prepare MEAs. The same diffusion layer as that used in Example 20 was used.

After the cast film was manufactured, the film formation state was examined visually. In addition, a case where a lot of cracks occurred and a non-uniform film was formed was designated as “X”, and a case where a uniform film was formed was designated as “◯”.
Moreover, the durability test was done about MEA. The durability test was performed under the same conditions as in Example 20, and the voltage value decrease rate at 0.8 A / cm ² was compared before and after the durability test.
Table 6 shows the results. When the addition amount was 1.5 wt%, a self-supporting film could not be obtained and the power generation test could not be performed. On the other hand, it was found that when the addition amount was 0.01 to 1.0 wt%, the voltage drop could be suppressed without reducing the film forming property.

( Reference Examples 35 to 39 , Comparative Example 20: Influence of the amount added to the diffusion layer)
The diffusion layer is made of carbon cloth made of carbon fiber fabric, and sprayed with a water repellent paste containing acetylene black, PTFE particles, and La (OH) ₃ powder (manufactured by Wako Pure Chemical Industries, Ltd.) on the electrode surface side. A water repellent layer was formed. The total basis weight of the water repellent layer was 10 mg / cm ^2, and the amount of La (OH) ₃ powder added was 0.005 to 6.0 mg / cm ² .
An MEA was produced using the obtained diffusion layer. The diffusion layer containing La (OH) ₃ was used only for both electrodes, only the air electrode, or only the fuel electrode. The MEA production conditions were the same as in Example 20 except that no CeO ₂ · nH ₂ O powder was added to the catalyst layer.
Furthermore, a durability test was performed using the obtained MEA. The durability test conditions were the same as in Example 20.

Table 7 shows the results. When the amount of La (OH) ₃ added to the diffusion layer is 6.0 mg / cm ² , the hydrophilicity is too high, and the voltage value at 0.8 A / cm ² becomes unstable, and a durability test should be performed. I could not. On the other hand, it was found that the voltage drop can be suppressed when the addition amount is 0.01 to 5.0 mg / cm ² .

( Reference Examples 40 to 42 , Comparative Example 21: Addition of a commercially available inorganic anion exchanger to the catalyst layer)
[1. Preparation of catalyst ink containing inorganic anion exchanger]
0.025 g of ion exchanger (IXE-550 (manufactured by Toagosei Co., Ltd.)) and 4 g of distilled water are added to 0.5 g of platinum-supported carbon (45 wt% of Pt supported), and ultrasonic dispersion (3 minutes) And left for 30 minutes. 2 g of ethanol, 1 g of propylene glycol, and 1 g of Nafion (registered trademark) solution were added to this solution and subjected to ultrasonic dispersion (3 minutes) to obtain a catalyst ink (hereinafter referred to as “catalyst ink (A)”).
[2. Preparation of catalyst ink containing no inorganic anion exchanger]
4 g of distilled water was added to 0.5 g of platinum-supporting carbon, and after ultrasonic dispersion (3 minutes), the mixture was allowed to stand for 30 minutes. 2 g of ethanol, 1 g of propylene glycol and 1 g of Nafion (registered trademark) solution are added to this solution and ultrasonically dispersed (3 minutes) to obtain a catalyst ink (hereinafter referred to as “catalyst ink (B)”). It was.

[3. Preparation of catalyst sheet]
A PTFE sheet was prepared, and the catalyst ink (A) or the catalyst ink (B) was applied on the PTFE sheet so as to have a uniform thickness, and was vacuum-dried at 60 ° C. for 6 hours. The catalyst sheets thus produced are referred to as “catalyst sheet (A)” and “catalyst sheet (B)”, respectively.
[4. Production of MEA]
The catalyst sheet (A) or (B) (3.6 cm × 3.6 cm) was transferred to the surface of a 6 cm × 6 cm Nafion (registered trademark) 112 membrane, and four levels of MEA ( Reference Examples 40 to 42 , Comparative Example 21). ) Was produced.

[5. An endurance test]
A durability test was performed using the obtained MEA. The durability test was performed under the same conditions as in Example 20, and the voltage value decrease rate at 0.8 A / cm ² was compared before and after the durability test.
Table 8 shows the results. It can be seen that the MEA with the ion exchanger added has less voltage drop than the non-added one.

(Comparative Example 22)
Add 100 mL of 1.0 M NH ₃ aqueous solution to 100 mL of 0.1 M Ce (NO ₃ ) ₃ aqueous solution, and add 0.002 M of Fe ₂ (SO ₄ ) ₃ .5H ₂ O to this, and stir at 80 ° C. × 4 hr. Reaction was carried out to coprecipitate cerium hydroxide. In the middle, 10 mL of 30 wt% hydrogen peroxide water was added to promote conversion from Ce ³⁺ to Ce ⁴⁺ . The gel was filtered and washed thoroughly with cold water to remove excess ammonia. The obtained gel (hydrous oxide) was dried in air at 80 ° C. for 4 hours.
Further, an MEA including the dried gel in the catalyst layer was produced. The manufacturing conditions for MEA were the same as those in Example 20 except that a gel containing Fe was used instead of CeO ₂ · nH ₂ O powder.

When the weight of Fe contained in the gel synthesized in Reference Example 27 was analyzed by ICP, it was 30 ppm. On the other hand, the weight of Fe contained in the gel obtained in Comparative Example 22 was 0.13 wt%. Furthermore, when the durability test was conducted using MEA obtained by adding the gel obtained in Comparative Example 22 to the catalyst layer, the voltage drop rate was 6.8%, and the gel synthesized in Reference Example 27 was used. Significant increase over MEA ( Reference Example 29 ).

  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 hardly soluble inorganic anion exchanger is fixed is not limited to the electrolyte membrane of the polymer electrolyte fuel cell or the electrolyte in the catalyst layer. It can also be used as electrolyte membranes, electrode materials, etc. used in various electrochemical devices such as electrolyzers, salt electrolyzers, oxygen and / or hydrogen concentrators, humidity sensors, and gas sensors.

It is a figure which shows the relationship between the platinum dissolution amount calculated | required by QCM method, and the platinum dissolution amount calculated | required by ICP analysis. It is a figure which shows the relationship between the Cl density | concentration contained in a solution, and the weight reduction | decrease amount (platinum melt | dissolution) amount in 2000 cycles progress.

Claims (2)

A polymer electrolyte fuel cell having the following configuration.
(1) The polymer electrolyte fuel cell is
A membrane electrode assembly having electrodes bonded to both surfaces of the electrolyte membranes,
A sparingly soluble inorganic anion exchanger substantially not containing Fe, which is added to one or more of the electrolyte membrane and the electrode .
(2) The electrode has a two-layer structure of a catalyst layer and a diffusion layer,
The hardly soluble inorganic anion exchanger is added to the catalyst layer.
(3) The hardly soluble inorganic anion exchanger is a hydrated oxide of Ce.
(4) The amount of the hardly soluble inorganic anion exchanger added to the catalyst layer (= weight of the hardly soluble inorganic anion exchanger × 100 / weight of the solid content of the catalyst layer) is 5.0 wt% to 10. 0 wt%. The polymer electrolyte fuel cell according to claim 1, wherein the hardly soluble inorganic anion exchanger is subjected to a thermal history of 400 ° C. or less.

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