JP2023084320A - Fuel battery - Google Patents

Abstract

To enhance durability of a fuel battery.SOLUTION: A solid polymer type fuel battery (10) onto which a catalyst layer (21) is laminated onto both sides of an electrolyte film (1), comprises a microporous layer (22) onto the catalyst layer (21). The microporous layer (22) contains a conductive metal component.SELECTED DRAWING: Figure 2

Description

The present invention relates to fuel cells.

A fuel cell generally has a laminated structure with an anode and a cathode located on opposite sides of an electrolyte membrane. The anode and cathode include catalyst layers in which a platinum catalyst is supported on carrier particles such as carbon particles.

It is known that the material of the catalyst layer deteriorates depending on the operating conditions of the fuel cell. For example, at the high-potential cathode when the fuel cell is started or stopped, the oxidation reaction between carbon and water proceeds, and the carbon in the catalyst layer tends to corrode. In order to improve the durability of the cathode, the use of carrier particles made of metal oxide instead of carbon has been proposed (see, for example, Patent Document 1).

Also in the anode, if the supply of hydrogen is insufficient due to rapid output fluctuations or the like, the oxidation reaction described above may occur and the carbon may corrode. Therefore, the use of water electrolysis catalyst particles such as iridium oxide as a catalyst has been proposed (see, for example, Patent Document 2). In the presence of the water electrocatalyst particles, water is easily electrolyzed and hardly reacts with carbon, so corrosion of carbon can be suppressed.

JP 2017-157353 A JP 2020-47432 A

However, carbon is often used not only in the catalyst layer, but also in microporous layers or gas diffusion layers provided on both sides of the catalyst layer. Therefore, even if corrosion of carbon in the catalyst layer is suppressed, corrosion of carbon in the microporous layer or gas diffusion layer cannot be suppressed. Also, materials such as iridium are expensive, which is a factor in increasing costs.

An object of the present invention is to improve the durability of a fuel cell.

One embodiment of the present invention is a polymer electrolyte fuel cell (10) in which catalyst layers (21) are laminated on both sides of an electrolyte membrane (1). The fuel cell (10) comprises a microporous layer (22) on a catalyst layer (21). The microporous layer (22) contains a conductive metal compound.

ADVANTAGE OF THE INVENTION According to this invention, durability of a fuel cell can be improved.

FIG. 1 is a cross-sectional view showing the cell configuration of the fuel cell of this embodiment. FIG. 2 is a cross-sectional view showing a gas diffusion layer with a microporous layer. FIG. 3 is a cross-sectional view showing a microporous layer provided alone in place of the gas diffusion layer.

Embodiments of the fuel cell of the present invention will be described below with reference to the drawings. The configuration described below is an example (representative example) of the present invention, and the present invention is not limited to this configuration.

(Fuel cell)
FIG. 1 shows the cell structure of a fuel cell 10 of this embodiment. The fuel cell 10 may be a single cell having such a structure, or may be a stack in which a plurality of cells are stacked. The fuel cell 10 of this embodiment is a polymer electrolyte fuel cell. The fuel cell 10 is mounted on a mobile body such as a vehicle, for example, and supplies driving power to the mobile body by chemically reacting fuel gas to generate power. can also apply the present invention.

As shown in FIG. 1, a fuel cell 10 includes a membrane electrode assembly (MEA) 3, a pair of separators 4 arranged on both sides of the MEA 3, and a subgasket 5 surrounding the outer periphery of the MEA 3. , provided. MEA 3 is a laminate in which electrodes 2 are arranged on both sides of electrolyte membrane 1 .

(electrolyte membrane)
The electrolyte membrane 1 is an ion-conducting polymer electrolyte membrane. Examples of polymer electrolytes that can be used for the electrolyte membrane 1 include perfluorosulfonic acid polymers such as Nafion (registered trademark) and Aquivion (registered trademark); Polymer; aliphatic polymers such as polyvinyl sulfonic acid and polyvinyl phosphoric acid.

The electrolyte membrane 1 can be a composite membrane in which a porous substrate 1a is impregnated with a polymer electrolyte, from the viewpoint of improving durability. The porous substrate 1a is not particularly limited as long as it has voids capable of supporting a polymer electrolyte, and porous, woven, nonwoven, fibril, and other membranes can be used. The material of the porous base material 1a is not particularly limited, either, but from the viewpoint of enhancing the ion conductivity, the polymer electrolyte as described above can be used. Among them, fluorine-based polymers such as polytetrafluoroethylene, polytetrafluoroethylene-chlorotrifluoroethylene copolymer, and polychlorotrifluoroethylene are excellent in strength and shape stability.

One electrode 2 of the pair of electrodes 2 is an anode and is also called a fuel electrode. The other electrode 2 is the cathode, also called air electrode. As fuel gas, hydrogen gas is supplied to the anode, and air containing oxygen gas is supplied to the cathode.

At the anode, a reaction occurs to generate electrons (e ⁻ ) and protons (H ⁺ ) from hydrogen gas (H ₂ ), as shown in the following reaction formula (1). The electrons move to the cathode via an external circuit (not shown). This movement of electrons generates a current in an external circuit. Protons move through the electrolyte membrane 1 to the cathode.
(1) 2H ₂ →4H ⁺ +4e ⁻

At the cathode, electrons transferred from the external circuit generate oxygen ions (O 2 ⁻ ) from oxygen gas (O ₂ ) as shown in the following reaction formula ( ₂ ). Oxygen ions combine with protons (2H ⁺ ) transferred from the electrolyte membrane 1 to form water (H ₂ O).
(2) O ₂ +4H ⁺ +4e ⁻ →2H ₂ O

When the cathode reaches a high potential when the fuel cell 10 is started or stopped, an oxidation reaction represented by the following reaction formula (3) occurs, and corrosion of carbon used in the cathode may progress. Also in the anode, if the supply of hydrogen is insufficient due to rapid output fluctuation or the like, a similar oxidation reaction may occur to corrode the carbon.
(3) C+2H ₂ O→CO ₂ +4H ⁺ +4e ⁻

In this embodiment, electrode 2 includes catalyst layer 21 , microporous layer 22 and gas diffusion layer 23 . On both sides of the electrolyte membrane 1, a catalyst layer 21, a microporous layer 22 and a gas diffusion layer 23 are laminated in this order.

The catalyst layer 21 accelerates the reaction of hydrogen gas and oxygen gas with a catalyst. The catalyst layer 21 contains a catalyst, a carrier that supports the catalyst, and an ionomer that coats these. The catalyst layer 21 may further contain water-electrolytic catalyst particles, and it is particularly preferable for the catalyst layer 21 on the anode side to contain them.

Examples of catalysts include particles of metals such as platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), tungsten (W), mixtures of these metals, and alloys. . Among them, platinum, mixtures or alloys containing platinum are preferable from the viewpoint of catalytic activity, carbon monoxide poisoning resistance, heat resistance, and the like.

Examples of the carrier include porous particles of conductive metal compounds such as mesoporous carbon and Pt black. Among them, mesoporous carbon is preferable from the viewpoint of good dispersibility, large surface area, and little particle growth at high temperatures even when a large amount of catalyst is supported.
As the ionomer, an ion-conducting polymer electrolyte similar to that of the electrolyte membrane 1 can be used.

Examples of water-electrolytic catalyst particles include particles of iridium, ruthenium, rhenium, palladium, rhodium, oxides thereof, and the like. Since these particles promote the electrolysis of water, the oxidation reaction between carbon and water in the catalyst layer 21 can be suppressed when hydrogen is depleted, and the durability of the catalyst layer 21 can be increased.

From the viewpoint of suppressing corrosion of carbon, the content of the water-electrolytic catalyst particles in the catalyst layer is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and 1.0% by mass. % or more is more preferable. From the viewpoint of avoiding excessive electrolysis of water, the content is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 2.0% by mass or less.

(microporous layer)
The microporous layer 22 is porous and prevents the flow of fuel gas (hydrogen gas and air containing oxygen) from the gas diffusion layer 23 to the catalyst layer 21 or the flow of waste water from the catalyst layer 21 to the gas diffusion layer 23. can be facilitated.

The catalyst layer 21, the microporous layer 22, and the gas diffusion layer 23 are porous, but the pore size in each layer is generally smaller in the microporous layer 22 than in the gas diffusion layer 23, and in the microporous layer 22. is smaller in the catalyst layer 21 as well. Such gradients tend to favor gas or water flow.

(Gas diffusion layer)
The gas diffusion layer 23 can uniformly diffuse the fuel gas supplied to the fuel cell 10 over the entire surface of the catalyst layer 21 .
Gas diffusion layer 23 comprises an electrically conductive porous substrate. Examples of the porous substrate include fiber sheets such as carbon felt and carbon fiber sheets, foam sheets such as foam metal sheets, and mesh sheets such as expanded metal.

The subgasket 5 is a film or plate provided at the outer peripheral edge of the MEA 3 . Subgasket 5 protects the edge of electrolyte membrane 1 and functions as a support for MEA 3 . As a material for the subgasket 5, a resin having low conductivity can be used. The resin material is not particularly limited and includes, for example, polyphenylene sulfide (PPS), glass-filled polypropylene (PP-G), polystyrene (PS), silicone resin, fluorine-based resin, and the like.

Separator 4 is also called a bipolar plate. As a material for the separator 4, a conductive material such as carbon or stainless steel is used.

The separator 4 of this embodiment has a surface provided with recesses 4a. A flow path is provided between the separator 4 and the MEA 3 when the surface of the separator 4 on which the concave portion 4 a is provided faces the MEA 3 . The channel is not only a fuel gas supply channel, but also a discharge channel for water produced by a chemical reaction during power generation.

(Material of microporous layer)
In this embodiment, the microporous layer 22 is a layer of a composition containing a conductive metal compound. By using such a metal compound that is a non-carbon material, the amount of carbon in the microporous layer 22 can be reduced, and the corrosion of carbon due to the oxidation reaction under high potential or lack of hydrogen gas can be reduced. Therefore, deterioration of the microporous layer 22 can be suppressed, and the durability of the electrode 2 can be enhanced.

From the viewpoint of further reducing corrosion, it is preferable that the content of the conductive metal compound in the composition is high, and it is more preferable that the composition does not contain carbon and instead contains the conductive metal compound. preferable.

The microporous layer 22 is formed by preparing a composition containing a conductive metal compound, forming a porous film of the composition, or coating a porous substrate with the composition, and drying the composition. can be done. The composition can contain a binder, a solvent, etc., in addition to the conductive metal compound.

(Conductive metal compound)
Examples of the conductive metal compound include conductive metal oxides, nitrides, oxynitrides, and the like. These can be used individually by 1 type or in combination of 2 or more types.

Among these, metal compounds of transition metals are preferred from the viewpoint of conductivity or cost, and among metal compounds, metal oxides are more preferred. From the viewpoint of conductivity or cost, the transition metal is preferably a Group 4 element such as titanium or a Group 14 element such as tin, and more preferably titanium or tin. Specific examples of metal compounds include titanium oxide, titanium nitride, tin oxide, palladium oxide, vanadium oxide, and tantalum nitride.

The metal compound may be doped with a metal element different from the transition metal. Holes or electrons are generated by doping, and the conductivity of the metal compound tends to be improved. Metal elements that can be used as dopants include, for example, rare earth elements such as yttrium, Group V elements such as niobium and tantalum, Group VI elements such as tungsten, and Group XV elements such as antimony. Niobium or tantalum is preferred as the dopant from the standpoint of conductivity or cost. Specific doping compounds include, for example, tantalum-doped tin oxide obtained by doping tantalum into tin oxide.

From the viewpoint of durability, the content of the conductive metal compound in the composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The upper limit of the content may be 100% by mass, but it is usually less than 100% by mass due to the content of other components such as a binder.

(binder)
Although the binder is not particularly limited, an ionomer having high proton conductivity is preferable from the viewpoint of conductivity. As the ionomer, the same compound as the ionomer in the catalyst layer 21 can be used, but a water-repellent fluorine-based resin is preferable from the viewpoint of drainage.

As a solvent, water, ethanol, or the like can be appropriately used. By adjusting the viscosity of the composition with the solvent, the composition can be prepared in the form of a solid, a paste, an ink, or the like.

(Structure of microporous layer)
The microporous layer 22 in this embodiment is a layer of the above composition laminated on a part of the surface of the porous substrate of the gas diffusion layer 23, as shown in FIG. For example, a part of the porous substrate of the gas diffusion layer 23 is immersed in the composition to coat the surface of the porous substrate, and then dried to make the layer of the composition porous. It can be laminated to the surface of a substrate.

(material for other layers)
From the viewpoint of further increasing the durability of the electrode 2, it is preferable that the porous base material of the gas diffusion layer 23 is also made of the above composition. A porous substrate comprising the above composition can be produced by forming a fiber sheet, a foamed sheet, a mesh sheet, or the like using the above composition.

In the gas diffusion layer 23 as well, the preferred content of the conductive metal compound in the composition is the same as that of the microporous layer 22 described above. From the viewpoint of reducing corrosion of carbon, it is preferable that the content of the conductive metal compound in each layer is high, and the carbon material of each layer is replaced with the conductive metal compound so that the electrode 2 does not contain carbon. More preferred. The conductive metal compound used for each layer may be the same or different.

As described above, according to this embodiment, a layer of a composition containing a conductive metal compound is provided as the microporous layer 22 on the catalyst layer 21 . Since the metal compound is not carbon, it is possible to reduce the amount of carbon that corrodes under high potential or hydrogen deficiency. Deterioration of the microporous layer 22 can be suppressed, and durability of the electrode 2 can be enhanced.

By using the above conductive metal compound not only for the microporous layer 22 but also for the gas diffusion layer 23, the durability of the electrode 2 as a whole can be enhanced. Moreover, the resistance generated at the interface with the microporous layer 22 due to the corrosion of the gas diffusion layer 23 can also be reduced.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible.

For example, the microporous layer 22 may be a porous substrate made of a composition containing the conductive metal compound. In this case, since the microporous layer 22 can be formed without the gas diffusion layer 23 , the gas diffusion layer 23 may be replaced with the microporous layer 22 . FIG. 3 shows an example of a microporous layer 22 placed alone in place of the gas diffusion layer 23 . In this case the microporous layer 22 contacts the separator 4 .

The microporous layer 22 arranged alone may be a porous substrate made of the above composition, or a layer of the above composition is formed on the surface of a porous substrate made of another material such as carbon or metal. It may be a laminated laminate. From the viewpoint of durability, the microporous layer 22 is preferably a porous substrate made of a conductive metal compound composition.

DESCRIPTION OF SYMBOLS 10... Fuel cell 1... Electrolyte membrane 2... Electrode 21... Catalyst layer 22... Microporous layer 23... Gas diffusion layer 3... Membrane electrode junction body, 4... separator, 5... subgasket

Claims (6)

In a polymer electrolyte fuel cell (10) in which catalyst layers (21) are laminated on both sides of an electrolyte membrane (1),
A microporous layer (22) is provided on the catalyst layer (21),
A fuel cell (10) wherein said microporous layer (22) contains a conductive metal compound. a gas diffusion layer (23) on the microporous layer (22);
2. The fuel cell (10) according to claim 1, wherein said microporous layer (22) is a layer of a composition containing said conductive metal compound laminated on the surface of said gas diffusion layer (23). said gas diffusion layer (23) comprises a porous substrate,
3. The fuel cell (10) of claim 2, wherein the porous substrate comprises a composition containing a conductive metal compound. The microporous layer (22) is a porous substrate made of a composition containing the conductive metal compound, or a laminate in which a layer of the composition is laminated on the surface of a porous substrate. A fuel cell (10) according to claim 1. A fuel cell (10) according to any one of the preceding claims, wherein said metal compound is a metal compound of a transition metal. 6. The fuel cell (10) according to claim 5, wherein said metal compound is doped with a metal element different from said transition metal.

Images