WO2015002287A1

WO2015002287A1 - Electrode for fuel cell and method for manufacturing same, membrane electrode assembly, and solid polymer fuel cell

Info

Publication number: WO2015002287A1
Application number: PCT/JP2014/067876
Authority: WO
Inventors: 雄大東; 志云野田; 灯林; 一成佐々木
Original assignee: 国立大学法人九州大学
Priority date: 2013-07-05
Filing date: 2014-07-04
Publication date: 2015-01-08
Also published as: JPWO2015002287A1; JP6345663B2

Abstract

　Provided is a method for manufacturing an electrode for a fuel cell having excellent durability against electrochemical oxidation and having an electronically conductive oxide that has excellent output characteristics used therefor. An electrode for a fuel cell having a gas diffusion layer, which is electronically conductive, and an electrode catalyst layer formed on the surface of or inside the gas diffusion layer, wherein the electrode for a fuel cell is characterized in that the electrode catalyst layer contains an electronically conductive oxide layer having a gas diffusion property formed by physical vapor deposition and electron catalyst particles carried by the electronically conductive oxide layer. In the electrode for a fuel cell, the electronically conductive oxide particles constituting the electronically conductive oxide layer in the electrode catalyst layer are connected particles in which a plurality of particles are linked. Therefore, electrical resistance caused by grain boundaries is reduced and excellent electron conductivity is obtained in the electrode as a whole.

Description

ELECTRODE FOR FUEL CELL, MANUFACTURING METHOD THEREOF, MEMBRANE ELECTRODE ASSEMBLY AND SOLID POLYMER FUEL CELL

The present invention relates to a fuel cell electrode suitably used as an electrode of a polymer electrolyte fuel cell, a method for producing the same, a membrane electrode assembly, and a polymer electrolyte fuel cell.

Since fuel cells can efficiently convert the chemical energy of hydrogen into electrical energy, the spread of power generation systems using fuel cells is expected. Among the fuel cells, in particular, a polymer electrolyte fuel cell (hereinafter, sometimes referred to as “PEFC”) using a solid polymer membrane as an electrolyte has an operating temperature compared with around 80 ° C. Because of its low temperature, it has been introduced as a small-scale fixed power source for in-vehicle use, home use, and the like. In the polymer electrolyte fuel cell, electric power can be taken out by the following electrochemical reaction.
Anodic reaction: 2H ₂ → 4H ⁺ + 4e ⁻ (reaction 1)
Cathode reaction: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (reaction 2)
Total reaction: 2H ₂ + O ₂ → 2H ₂ O

In PEFC, a membrane electrode assembly (Membrane Electrode Assembly; hereinafter, sometimes referred to as “MEA”) in which a pair of electrodes are arranged on both surfaces of a solid polymer electrolyte membrane is generally used as a gas flow path. It has a structure sandwiched between the formed separators.
An electrode for a fuel cell (especially an electrode for PEFC) is generally composed of an electrode catalyst layer composed of an electrode material having an electrocatalytic activity and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electronic conductivity. The As an electrode material for PEFC, a material in which noble metal particles are dispersed and supported on the surface of a carrier made of a particulate or fibrous carbon-based material is widely used (for example, Patent Documents 1 and 2).

By the way, since the PEFC electrolyte membrane is acidic (pH = 0 to 3), the electrode material of PEFC is used in an acidic atmosphere. The cell voltage during normal operation is 0.4 to 1.0 V, but it is known that the cell voltage rises to 1.5 V when starting and stopping. The state of the cathode and the anode under such PEFC operating conditions is a region in which the carbon-based material as a carrier is decomposed as carbon dioxide (CO ₂ ) at the cathode. Therefore, a reaction occurs in which the carbon-based material used as the carrier is electrochemically oxidized and decomposed into CO ₂ at the cathode (see Non-Patent Document 1).

In addition, not only the cathode, but also the anode, when fuel gas is insufficient at the time of start-up, etc., a voltage drop or concentration polarization occurs at that part and locally becomes a potential opposite to normal, and electrochemical oxidative decomposition of carbon A reaction may occur.

The carbon-based material used as a support for the electrode catalyst particles is electrochemically oxidatively corroded as described above, and becomes a problem particularly when the PEFC is started and stopped or operated for a long time. In order to improve the durability of the carbon-based material against oxidation, there is a method of increasing the crystallization by heat treatment at a high temperature, but the durability against oxidation is still insufficient. Therefore, it is desired to develop a fuel cell electrode using a non-carbon material that is stable under PEFC operating conditions.
In response to such a demand, the inventors of the present application disclose an electrocatalyst material in which noble metal particles are dispersed in a tin oxide support instead of a carbon-based material, and production thereof. Since this electrocatalyst material is thermodynamically stable under PEFC operating conditions, it can be operated for a long time without oxidative corrosion.

Japanese Patent Laid-Open No. 2005-87993 Japanese Patent No. 368364 International Publication No. 2009/060582 Pamphlet

In the method for producing an electrocatalyst material using an oxide support of Patent Document 3, a wet method is employed as in the case of a conventional carbon-based support. In the wet method, for example, an oxide carrier is prepared by a coprecipitation method or the like, and noble metal particles are supported on the oxide carrier by a method such as a colloid method, and a solid polymer electrolyte membrane is formed by a method such as a spray printing method. The electrode catalyst layer is formed by coating on the top.
However, a fuel cell electrode having an electrode catalyst layer produced by a wet method can exhibit sufficient cell performance when using a carbon-based support, but when using an oxide support, it is not necessarily reproducible, It could not be said that sufficient cell performance could be demonstrated.

Under such circumstances, the present invention provides a fuel cell electrode using an electron conductive oxide having excellent durability to electrochemical oxidation and having excellent output characteristics, and a method for producing the same. With the goal. Furthermore, it aims at providing the membrane electrode composite and solid polymer fuel cell which have the said electrode for fuel cells.

The present inventor has described that the electron conductive oxide carrier particles formed by a wet method are secondary particles in which primary particles having an average particle size of about 10 to 500 nm are aggregated. When the electrode catalyst layer is formed using the electrode, the contact between the carrier particles tends to be insufficient because there is no process of firing at a high temperature, resulting in an increase in electrical resistance at the grain boundary and insufficient electron conductivity of the entire electrode. I thought. As a result of intensive studies, the inventors have found that the following invention can solve such problems and have reached the present invention.

That is, the present invention relates to the following inventions.
<1> A fuel cell electrode having a gas diffusion layer having electron conductivity and an electrode catalyst layer formed on or inside the gas diffusion layer,
An electrode for a fuel cell, wherein the electrode catalyst layer includes an electron conductive oxide layer having gas diffusibility formed by physical vapor deposition and electrode catalyst particles supported on the electron conductive oxide layer.
<2> The gas diffusion layer is a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer, and the electrode catalyst layer is formed on or inside the microporous layer. The fuel cell electrode according to <1>.
<3> The fuel cell electrode according to <1> or <2>, wherein the electron conductive oxide layer is made of an oxide mainly composed of tin oxide.
<4> The fuel cell electrode according to any one of <1> to <3>, wherein the electron conductive oxide layer is made of niobium-doped tin oxide doped with 0.1 to 20 mol% of niobium.
<5> The fuel cell electrode according to any one of <1> to <4>, wherein the electrode catalyst layer further contains a proton conductive material.
<6> A method for producing a fuel cell electrode comprising a gas diffusion layer having electron conductivity and an electrode catalyst layer formed on or inside the gas diffusion layer,
A step of forming an electron conductive oxide layer having gas diffusivity on the surface or inside of the gas diffusion layer by a physical vapor deposition method using a vapor deposition source comprising an electron conductive oxide;
A step of supporting electrode catalyst particles on the electron conductive oxide layer;
The manufacturing method of the electrode for fuel cells containing this.
<7> The gas diffusion layer is a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer, and the electrode catalyst layer is formed on the surface of the microporous layer. The manufacturing method of the electrode for fuel cells as described in said <6>.
<8> The method for producing a fuel cell electrode according to <6> or <7>, wherein the vapor deposition source is made of an oxide mainly composed of tin oxide.
<9> The method for producing a fuel cell electrode according to any one of <6> to <8>, wherein the vapor deposition source is made of niobium-doped tin oxide doped with 0.1 to 20 mol% of niobium.
<10> The method for producing an electrode for a fuel cell according to any one of <6> to <9>, wherein the physical vapor deposition method in the step of forming the electron conductive oxide layer is a pulse laser deposition method (PLD). .
<11> The method for producing an electrode for a fuel cell according to any one of <6> to <10>, wherein the supporting method in the step of supporting the electrode catalyst particles is a physical vapor deposition method or a chemical vapor deposition method.
<12> A membrane / electrode assembly having a solid polymer electrolyte membrane, a cathode bonded to one surface of the solid polymer electrolyte membrane, and an anode bonded to the other surface of the solid polymer electrolyte membrane. And
At least one of the cathode and the anode is the fuel cell electrode according to any one of <1> to <5>.
<13> A polymer electrolyte fuel cell comprising the membrane electrode assembly according to <12>.
<14> Manufacture of a membrane / electrode assembly having a solid polymer electrolyte membrane, a cathode joined to one surface of the solid polymer electrolyte membrane, and an anode joined to the other surface of the solid polymer electrolyte membrane A method for producing a fuel cell electrode for each of a cathode and an anode by the method for producing a fuel cell electrode according to <11>, and a solid polymer electrolyte membrane on the produced cathode and anode. A process for producing a membrane electrode assembly, comprising the step of sandwiching and crimping.

According to the present invention, an electrode for a fuel cell that provides both high power generation performance and durability is provided. A polymer electrolyte fuel cell comprising a membrane electrode assembly using the fuel cell electrode has high cycle durability and can generate power for a long period of time.

It is a cross-sectional schematic diagram of the electrode for fuel cells of this invention. It is a cross-sectional schematic diagram of the membrane electrode assembly of this invention. It is a conceptual diagram which shows the typical structure of the polymer electrolyte fuel cell of this invention. It is a cross-sectional SEM image of the electrode for fuel cells of the comparative example 1 (PLD: 5 minutes). It is a cross-sectional SEM image (enlarged view) of the electrode for fuel cells of Comparative Example 1 (PLD: 5 minutes). It is a cross-sectional SEM image of the electrode for fuel cells of Example 1 (PLD: 1 minute). It is an evaluation result of the current-voltage (IV) characteristic of the electrode for fuel cells of Example 1 and Comparative Example 1. It is an evaluation result of the current-voltage (IV) characteristic of the electrode for fuel cells of Example 1 and Comparative Example 2. It is explanatory drawing of a start / stop simulation potential cycle. As a result of the cycle endurance test of the fuel cell electrode of Example 1 (PLD: 1 minute), Comparative Example 2 (wet method) and Reference Example 1 (Pt / C) (initial voltage holding ratio at 200 mA / cm ² ) is there. (A) is an explanatory diagram of a Cole-Cole plot, and (b) is a diagram showing an assumed equivalent circuit. It is a measurement result of the ohmic resistance of the membrane electrode assembly of Example 1 (PLD: 1 minute), Comparative Example 2 (wet method) and Reference Example 1 (Pt / C).

DESCRIPTION OF SYMBOLS 1 Fuel cell electrode 2 Gas diffusion layer 2a Base material layer 2b Microporous layer 3 Electrode catalyst layer 3a Electron conductive oxide layer 4 Cathode 5 Anode 5a Electrode catalyst layer 5b Gas diffusion layer 6 Solid polymer electrolyte membrane 10 Membrane electrode bonding Body (MEA)
20 Polymer electrolyte fuel cell 21 External circuit

Hereinafter, the present invention will be described in detail with reference to examples and the like, but the present invention is not limited to the following examples and the like, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

<1. Fuel Cell Electrode>
The fuel cell electrode of the present invention is a fuel cell electrode having a gas diffusion layer having electronic conductivity and an electrode catalyst layer formed on the surface and / or inside of the gas diffusion layer,
The electrode catalyst layer includes an electron conductive oxide layer having gas diffusibility formed by physical vapor deposition, and electrode catalyst particles supported on the electron conductive oxide layer.

The electrode catalyst layer of the fuel cell electrode needs to have sufficient electronic conductivity along with a gap that allows gas diffusion such as hydrogen and oxygen and water (steam) to be discharged smoothly. However, when the electrode catalyst layer is formed using the electron conductive oxide carrier particles formed by the conventional wet method, the electrical resistance at the grain boundary is increased, and the electron conductivity of the electrode catalyst layer is insufficient. Become. As a result, the electronic conductivity of the entire electrode composed of the electrode catalyst layer and the gas diffusion layer becomes insufficient.
On the other hand, in the fuel cell electrode of the present invention, the electron conductive oxide layer functioning as a conductive support in the electrode catalyst layer is formed by physical vapor deposition. In the physical vapor deposition method, a plurality of electron-conductive oxide particles to be formed are deposited on the surface or inside of a gas diffusion layer as connected particles in which a plurality of particles are connected. Since the plurality of electron conductive oxide particles are continuous in the connected particles, the electrical resistance due to the grain boundary is reduced.
Therefore, compared with the case where the electrode catalyst layer is formed using the electron conductive oxide carrier particles formed by the conventional wet method, the fuel cell electrode of the present invention has a gap having gas diffusibility. Even in this state, since the electrode catalyst layer has excellent electron conductivity, the entire electrode composed of the electrode catalyst layer and the gas diffusion layer is excellent in electron conductivity.

In the fuel cell electrode of the present invention, the gas diffusion layer is a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer, and the electrode catalyst layer is the micro layer. A gas diffusion layer formed on the surface of the porous layer is preferred.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this embodiment is a suitable example of this invention, and this invention is not restrict | limited to the following Examples.

FIG. 1 is a schematic sectional view of a fuel cell electrode according to the present embodiment. The fuel cell electrode 1 was formed on the surface of the microporous layer 2b in the gas diffusion layer 2 and the gas diffusion layer 2 having the base layer 2a and the microporous layer 2b formed on one side of the base layer. And an electrode catalyst layer 3.

(Gas diffusion layer)
The gas diffusion layer 2 includes a base layer 2a and a microporous layer 2b formed on one side of the base layer 2a. The gas diffusion layer 2 has gas diffusibility (gas permeability) for providing fuel gas and air to the electrode catalyst layer 3, water repellency to water generated by power generation, and current generated by the separator. It has the conductivity of.

As the base material layer 2a, a sheet-like member having gas diffusibility and electron conductivity can be used. Specifically, conductive carbon-based sheet-like members having a pore size distribution of about 100 nm to 90 μm, which are conventionally used as a gas diffusion layer of PEFC, can be mentioned. Cloth, carbon paper, carbon non-woven fabric, etc. can be used. The base material layer 2a may be a sheet-like member other than a carbon-based material such as stainless steel. The thickness of the base material layer 2a is not particularly limited, but is usually about 50 μm to 1 mm.

The microporous layer 2b is a layer made of an aggregate of carbon fine particles having an average particle diameter of about 10 to 100 nm and a water repellent provided on one surface of the base material layer 2a. The carbon fine particles may be subjected to a water repellent treatment. The microporous layer 2b has an average pore size smaller than that of the base material layer 2a (high density and excellent surface flatness. The microporous layer 2b preferably has a pore size distribution of 1 nm to 900 nm. The porous layer 2b is suitable for forming an electron conductive oxide layer on its surface by physical vapor deposition as will be described later.The microporous layer 2b is, for example, a coating containing carbon fine particles and a water repellent fluororesin. It can be manufactured by coating and drying the working liquid on the base material layer 2a to make it adhere to the base material layer 2a.

In this embodiment, a gas diffusion layer having a microporous layer is used as the gas diffusion layer, but the present invention is not limited to this. As the gas diffusion layer, it is possible to use only the gas diffusion layer of the base material layer conventionally used in PEFC. However, it is difficult to form the electron conductive oxide layer on the surface, and the electron conductive oxidation is inside. Since the physical layer may be formed discontinuously, a gas diffusion layer having a microporous layer is more preferable for forming the electron conductive oxide layer on the surface of the gas diffusion layer.

As the gas diffusion layer 2, a known gas diffusion layer with a microporous layer may be used. As a suitable commercial item, the GDL25 series made from SIGRACT Gas Diffusion Media can be mentioned, for example.

(Electrode catalyst layer)
The electrode catalyst layer 3 includes an electron conductive oxide layer 3a and electrode catalyst particles (not shown) supported on the electron conductive oxide layer 3a, and is formed on the surface of the microporous layer 2b.

The thickness of the electrode catalyst layer 3 (thickness of the electron conductive oxide layer 3a) may be within a range that has gas permeability and can provide a sufficient electrode catalyst action in a fuel cell. The thickness is appropriately determined in consideration of the porosity of the electron conductive oxide layer 3a constituting the film, and is usually about 0.1 to 50 μm.

The electron conductive oxide layer 3a is formed on the surface (and part of the inside) of the microporous layer 2b by a physical vapor deposition method, and has an electron conductivity and does not impair the electrode reaction of the electrode catalyst layer 3. Has diffusivity. When forming the electron conductive oxide layer 3a, the conditions for physical vapor deposition are appropriately selected under the conditions that the electron conductivity and the gas diffusibility are compatible.
The details of the physical vapor deposition method will be described in the fuel cell electrode manufacturing method of the present invention described later.

The electrode catalyst layer 3 may be composed of only the electron conductive oxide layer and the electrode catalyst particles, but preferably contains a proton conductive material from the viewpoint that the electrode performance can be further improved. As the proton conductive material, the same material as the electrolyte membrane is used, and it is mainly used for fluorine-based electrolyte materials containing fluorine atoms in all or part of the polymer skeleton and hydrocarbon-based electrolyte materials not containing fluorine atoms in the polymer skeleton. They can be used separately as electrolyte materials.

Specific examples of the fluorine-based electrolyte material include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. It is done.

Specific examples of the hydrocarbon electrolyte material include polysulfonic acid, polystyrene sulfonic acid, polyaryl ether ketone sulfonic acid, polyphenyl sulfonic acid, polybenzimidazole alkyl sulfonic acid, and polybenzimidazole alkyl phosphonic acid. Can be mentioned.

The electron conductive oxide constituting the electron conductive oxide layer 3a may be any material that has both sufficient durability and electron conductivity under the operating conditions of a fuel cell (particularly a polymer electrolyte fuel cell). . Specifically, an electron conductive oxide mainly composed of one selected from tin oxide, molybdenum oxide, niobium oxide, tantalum oxide, titanium oxide, and tungsten oxide can be given. Here, in the present invention, the “mainly electron-conducting oxide” means (A) an oxide composed only of a base oxide and (B) an oxide doped with other elements, wherein the base oxide is It means that contained at 80 mol% or more.

Specific examples of the element to be doped include Sn, Ti, Sb, Nb, Ta, W, In, V, Cr, Mn, and Mo (however, they are elements different from the base oxide). The element to be doped is an element having a higher valence than the base oxide. For example, when the base oxide is titanium oxide, an element other than Ti (for example, Nb) is selected from the above doped seed elements. Is done.

Among these, the electron conductive oxide layer 3a is preferably made of an oxide mainly composed of titanium oxide, tungsten oxide or tin oxide, and particularly preferably an oxide mainly composed of tin oxide. Here, the “main oxide” refers to an oxide containing 50 mol% or more of the target oxide.

When the electron conductive oxide is an oxide mainly composed of tin oxide, the fuel cell electrode of the present invention is preferably used as a cathode.
As an element, tin (Sn) is an oxide of SnO _{2 which} is thermodynamically stable and does not undergo oxidative decomposition under PEFC cathode conditions. Further, tin oxide has a sufficient electronic conductivity and becomes a carrier capable of supporting electrode catalyst particles (particularly noble metal particles) with high dispersion.

Among oxides mainly composed of tin oxide, niobium-doped tin oxide doped with 0.1 to 20 mol% of niobium (Nb) is particularly preferable in that a fuel cell electrode having better electrode performance can be formed.

Further, when used as an anode of PEFC, an oxide mainly composed of titanium oxide which is thermodynamically stable under the anode conditions is a suitable example.

The PEFC cathode condition is a condition at the cathode during normal operation of the PEFC, which means a temperature (room temperature to about 150 ° C.) and a condition in which a gas containing oxygen such as air is supplied (oxidizing atmosphere). The condition is a condition in the anode during normal operation of PEFC, and means a condition (reducing atmosphere) in which a temperature of room temperature to about 150 ° C. and a fuel gas containing hydrogen is supplied.

The electrode catalyst particles may have any electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) and can be supported on the electron conductive oxide layer. The electrocatalyst particles may be either a noble metal catalyst or a non-noble metal catalyst, but preferably from noble metals such as Pt, Ru, Ir, Pd, Rh, Os, Au, and Ag, and alloys containing these noble metals. Selected. The “alloy containing a noble metal” includes “an alloy consisting only of the noble metal” and “an alloy consisting of the noble metal and another metal and containing 10% by mass or more of the noble metal”. The “other metals” to be alloyed with the noble metal are not particularly limited, but Co, Ni, W, Ta, Nb, and Sn can be cited as suitable examples, and one or more of these may be used. May be. Moreover, you may use the alloy containing two or more types of said noble metals and noble metals in the state which carried out phase separation.

The method for supporting the electrode catalyst particles may be a wet method or a dry method. However, there is an advantage that the entire electrode catalyst layer can be manufactured by the dry method by using the dry method as the method for supporting the electrode catalyst particles together with the manufacture of the electron conductive oxide layer.
Among the above electrode catalysts, Pt and an alloy containing Pt have high electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) in the temperature range around 80 ° C., which is the operating temperature of the polymer electrolyte fuel cell. In addition, since it can be easily supported on the electron conductive oxide layer by vapor deposition which is a dry method, it can be used particularly suitably.

The amount of the electrode catalyst particles supported is appropriately determined in consideration of conditions such as the type of catalyst and the thickness of the electron conductive oxide layer 3a serving as a carrier. If the amount of the catalyst supported is too small, the electrode performance becomes insufficient, and if it is too large, the catalyst particles may be aggregated to deteriorate the performance. When the catalyst particles are Pt particles, for example, the amount is 0.01 to 5.0 mg / cm ² .

(Applications for fuel cell electrodes)
The fuel cell electrode of the present invention can be used as both a cathode and an anode. In particular, the cathode is excellent in reducing electrochemical catalytic activity of oxygen as shown in (Reaction 2), and does not cause electrochemical oxidative decomposition of the electron-conductive oxide layer under the fuel cell operating conditions (cathode conditions). It is preferable to use as.

The fuel cell electrode of the present invention is suitable as a PEFC electrode. In addition to PEFC, it can be used as an electrode in various fuel cells such as alkaline fuel cells and phosphoric acid fuel cells. It can also be suitably used as an electrode for a water electrolysis apparatus. As a water electrolyzer, a water electrolyzer using a solid polymer electrolyte membrane similar to the fuel cell electrode of the present invention and PEFC can be cited as a preferred example.

<2. Manufacturing Method of Fuel Cell Electrode>
The above-described fuel cell electrode of the present invention is preferably manufactured by the manufacturing method described below (hereinafter referred to as “the manufacturing method of the present invention”).
That is, the method for producing a fuel cell electrode of the present invention is a method for producing a fuel cell electrode having a gas diffusion layer having electron conductivity and an electrode catalyst layer formed on the surface and / or inside of the gas diffusion layer. A method of forming an electron conductive oxide layer having gas diffusibility on the surface and / or inside of a gas diffusion layer by a physical vapor deposition method using a vapor deposition source comprising an electron conductive oxide; And supporting the electrode catalyst particles on the electron conductive oxide layer.
Hereinafter, the step of forming the electron-conductive oxide layer having gas diffusivity may be referred to as “step (1)”, and the step of supporting the electrode catalyst particles may be referred to as “step (2)”.

The production method of the present invention is characterized in that in step (1), an electron conductive oxide layer having gas diffusibility is formed by physical vapor deposition.
In the physical vapor deposition method, a plurality of electron conductive oxide particles to be formed are deposited on the surface or inside of a gas diffusion layer as connected particles in which a plurality of particles are connected. Since the plurality of electron conductive oxide particles are continuous in the connected particles, the electrical resistance due to the grain boundary is reduced, and the electrical resistance of the entire electron conductive oxide layer is reduced. Therefore, compared with the case where the electron conductive oxide layer is formed using the electron conductive oxide carrier particles formed by the conventional wet method, the manufacturing method of the present invention provides an electrode having more excellent electron conductivity. Obtainable.

In addition, the carbon-based material widely used as a conductive support of the electrode catalyst layer of the conventional fuel cell electrode has a low crystallinity and a low durability against oxidative corrosion when produced by a vapor deposition method. It cannot be applied to the method for producing a fuel cell electrode of the present invention.

In the production method of the present invention, when a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer is used as the gas diffusion layer, the electron conductive oxide layer is converted into a surface of the microporous layer. Can be formed. The electrode catalyst layer can be formed on the surface of the fuel cell electrode by supporting the electrode catalyst particles on the electron conductive oxide layer formed on the surface of the microporous layer.

In the step (2), the method for supporting the electrode catalyst particles may be a wet method or a dry method. However, if the electrode catalyst particles are supported by an evaporation method on the electron conductive oxide layer formed in the step (1), The formation of the conductive oxide layer and the loading of the electrode catalyst particles can all be performed by a dry method (dry process).
In the fuel cell electrode of the present invention, when the electrode catalyst particles are supported by a wet method, each of the steps such as preparation of a liquid material containing the raw material, support of the electrode catalyst particles on the support, coating on the gas diffusion layer, etc. Condition adjustment is difficult, and the performance of the manufactured fuel cell electrode tends to be unstable. On the other hand, when the formation of the electron conductive oxide layer and the loading of the electrode catalyst particles are all performed by the dry method (dry process) There is an advantage that a complicated process of adjusting the raw material liquid material in the wet method or performing a heat treatment after coating is unnecessary, and the yield of the manufactured fuel cell electrode is increased.
And since the control of the vapor deposition production conditions in the dry method is easier than the wet conditions, the performance of the fuel cell electrode, and thus the fuel cell electrode, was used by controlling only the vapor deposition production conditions. The performance of the membrane electrode assembly can be controlled.

Hereafter, each process in the manufacturing method of the electrode for fuel cells of this invention is demonstrated in detail.
First, in step (1), an electron conductive oxide layer having gas diffusibility is formed on the gas diffusion layer by a physical vapor deposition method using a vapor deposition source made of an electron conductive oxide.

The gas diffusion layer is composed of a base layer and a microporous layer formed on the base layer. The gas diffusion layer is <1. The fuel cell electrode of the present invention is as described above, and detailed description thereof is omitted here.
The fuel cell electrode manufacturing method of the present invention is characterized in that a gas diffusion layer having a microporous layer on the surface is used. When the electron conductive oxide layer is formed on the surface of the gas diffusion layer by physical vapor deposition, in the gas diffusion layer (base material layer only) that does not have a microporous layer, the gaseous electron conductive oxide that is the vapor deposition species is A gas having a microporous layer that diffuses into the gas diffusion layer and cannot form an electron conductive oxide layer on the surface of the gas diffusion layer, but has a high density and excellent surface flatness compared to the base material layer. In the diffusion layer, since the gaseous electron conductive oxide is difficult to diffuse into the microporous layer, the electron conductive oxide layer can be formed substantially on the surface of the microporous layer. The thickness of the microporous layer is preferably 1 to 100 μm.

The electron conductive oxide used for the vapor deposition source is composed of an electron conductive oxide mainly composed of one selected from tin oxide, molybdenum oxide, niobium oxide, tantalum oxide, titanium oxide and tungsten oxide. The details of the electron conductive oxide used in step (1) are described in <1. The fuel cell electrode of the present invention is as described above, and detailed description thereof is omitted here.

Among these, the deposition source is preferably made of an oxide mainly composed of tin oxide, and niobium-doped tin oxide doped with niobium (Nb) in an amount of 0.1 to 20 mol% is particularly preferable.

The vapor deposition source is used after manufacturing the electron conductive oxide and processing it into a shape suitable for a physical vapor deposition method to be described later (for example, a pellet shape).

Examples of the physical vapor deposition method include a pulsed laser deposition method (Pulsed Laser Deposition (PLD method)), a sputtering vapor deposition method, an electron beam vapor deposition method, and a thermal heating vapor deposition method.
Since the electron conductive oxide layer serves as the skeleton of the electrode catalyst layer of the fuel cell electrode, it must have gas diffusivity. In the physical vapor deposition method, the electron conductivity has a porous structure and gas diffusibility. The conditions under which the oxide is formed are selected as appropriate. The thickness of the electron conductive oxide layer can be prepared by controlling various conditions of the physical vapor deposition method (particularly, the film forming time).

As a preferable physical vapor deposition method in the production method of the present invention, the sputtering vapor deposition method is suitable in terms of productivity. The sputtering deposition method is a method in which a deposition source (target) is irradiated with accelerated ions, and atoms or molecules on the surface of the target are emitted into the space to form a thin film.
The electron-conductive oxide that is the evaporation source in the production method of the present invention is often an oxide having a high melting point, and the thermal heating vapor deposition method may be difficult. There are also advantages that can be applied.

The sputtering deposition method may be either a bipolar method or a magnetron method. Further, since the target has electronic conductivity, the power source applied to the target may be either a DC (direct current) power source or an RF (high frequency) power source.
Sputtering conditions vary depending on the type of electron-conducting oxide as a target, the sputtering method, and the sputtering apparatus, and are appropriately selected within a range in which the gas diffusibility (porous structure) required for the fuel cell electrode can be obtained.

In addition, as a preferable physical vapor deposition method in the production method of the present invention, a PLD method is exemplified. In the PLD method, the deposition source (target) is ablated by intermittently irradiating the deposition source in the vacuum chamber with a pulsed laser, and the fragments (ions, clusters, molecules, atoms) to be emitted are transferred to a predetermined substrate. It is a method of depositing on (a gas diffusion layer in the present invention).

The PLD method can be applied to a case where the evaporation source is an oxide having a high melting point, similarly to the sputtering evaporation method. This is a method suitable for forming an oxide film having a more uniform composition. In particular, when the deposition source is an electron conductive oxide doped with other elements such as niobium-doped tin oxide, the composition is the same as that of the deposition source. It is preferable at the point in which the electron conductive oxide layer which has is formed.

The type of laser used in the PLD method is not particularly limited, and examples thereof include an excimer laser and a YAG laser.
The laser output conditions are appropriately determined in consideration of various conditions such as the type of laser and the porosity and thickness of the electron conductive oxide layer to be formed.

The vapor deposition temperature is determined within a range in which a porous structure capable of obtaining the gas diffusibility required for the fuel cell electrode is formed, and is usually from room temperature to about 200 ° C., preferably from 15 to 40 ° C. If the deposition temperature is too high, a dense thin film may be formed, and the porous structure required for the fuel cell electrode may not be obtained.

The atmosphere in the vacuum chamber during film formation can include oxygen (O ₂ ), for example. Furthermore, the pressure in the vacuum chamber during film formation is preferably set to 30 Pa or less, for example.

In step (2), electrode catalyst particles are supported on the electron conductive oxide layer formed in step (1). Since the electron conductive oxide layer formed in the step (1) has a porous structure, the electrode catalyst particles can be supported not only on the surface but also inside the electron conductive oxide layer.
Hereinafter, the case where the electrode catalyst particles are supported on the electron conductive oxide layer by vapor deposition will be described. However, as described above, the loading method is not limited to vapor deposition.

The electrode catalyst particles to be vapor-deposited may be those having electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation) and can be supported on the electron conductive oxide layer by vapor deposition. The details of the electrode catalyst particles used in the step (2) are described in <1. The fuel cell electrode of the present invention is as described above, and detailed description thereof is omitted here.

As an electrode catalyst particle, an alloy containing Pt and Pt is preferable in that it can be easily supported by vapor deposition having an electrochemical catalytic activity for oxygen reduction (and hydrogen oxidation).

The electrode catalyst particles may be deposited by either physical vapor deposition or chemical vapor deposition.
Examples of the physical vapor deposition method include the sputtering vapor deposition method described in the step (1). When the target electrode catalyst material is used as a vapor deposition source of the physical vapor deposition method and the electrode catalyst is Pt, for example, a Pt plate may be used.
In the case of chemical vapor deposition, generally, a raw material having a high vapor pressure and a low decomposition temperature may be used as a vapor deposition source. For example, in the case of a Pt catalyst, a Pt compound such as a cyclopentadienyltrimethylplatinum (IV)) complex may be mentioned.

The loading amount and particle size of the electrode catalyst particles can be appropriately adjusted by controlling the deposition conditions in consideration of the type of the electrode catalyst particles and the intended performance. The supported amount of the electrode catalyst particles is, for example, 0.01 to 5.0 mg / cm ² .

<3. Membrane electrode assembly (MEA)>
The membrane electrode assembly of the present invention comprises a solid polymer electrolyte membrane, a cathode joined to one surface of the solid polymer electrolyte membrane, and an anode joined to the other surface of the solid polymer electrolyte membrane. In the membrane electrode assembly, at least one of the cathode and the anode is the fuel cell electrode of the present invention. As described above, since the fuel cell electrode of the present invention has high electrode performance and durability under the cathode conditions, it is preferable to use the fuel cell electrode of the present invention at least for the cathode.

As a preferred embodiment of the present invention, a membrane electrode assembly using the fuel cell electrode of the present invention as a cathode will be described.
FIG. 2 schematically shows a cross-sectional structure of the membrane electrode assembly according to the embodiment of the present invention. As shown in FIG. 2, the membrane electrode assembly 10 has a structure in which the cathode 4 and the anode 5 are arranged facing the solid polymer electrolyte membrane 6.

In this embodiment, since the cathode 4 uses the fuel cell electrode 1 of the present invention, detailed description thereof is omitted. In order to further improve the electrode performance, the proton conductive material may be applied to the electrode catalyst layer of the cathode 4 by, for example, dropping a solution containing the proton conductive material. When the fuel cell electrode of the present invention is used as the anode 5, other known cathodes can be used as the cathode 4.

The anode 5 includes an electrode catalyst layer 5a and a gas diffusion layer 5b. As the anode 5, in addition to the fuel cell electrode of the present invention, other known anodes can be used as well. For example, a dispersion of an electrode material carrying noble metal particles as a catalyst on the surface of a conductive support made of a carbon-based material such as graphite, carbon black, activated carbon, carbon nanotube, and glassy carbon, and an electrolyte material for a fuel cell The electrode which formed on the gas diffusion layer 5b the electrode catalyst layer 5a manufactured by apply | coating and drying can be mentioned. The gas diffusion layer 5b of the anode 5 can be the same as the gas diffusion layer described in the fuel cell electrode of the present invention.

As the solid polymer electrolyte membrane 6, a known PEFC electrolyte membrane may be used as long as it has proton conductivity and has chemical stability and thermal stability. In FIG. 2, the thickness is emphasized, but the thickness of the solid polymer electrolyte membrane 6 is usually about 0.05 mm in order to reduce the electric resistance.

Examples of the electrolyte material constituting the solid polymer electrolyte membrane 6 include a fluorine-based electrolyte material and a hydrocarbon-based electrolyte material. In particular, an electrolyte membrane formed of a fluorine-based electrolyte material is preferable because of its excellent heat resistance, chemical stability, and the like. Specific examples include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like.
Examples of the hydrocarbon-based polymer electrolyte material include sulfonated polyether ketone, sulfonated polyether, and sulfonated polyether ether sulfone. Further, as the electrolyte membrane, an electrolyte membrane made of an inorganic proton conductor such as phosphate or sulfate can also be used.

As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.
For example, in the above embodiment, the fuel cell electrode of the present invention is employed only for the cathode, but the fuel cell electrode of the present invention may also be used for the anode.

Here, the manufacturing method of a membrane electrode assembly is a manufacturing method of a membrane electrode assembly in which the fuel cell electrode of the present invention is used for both the cathode and the anode, and the solid polymer electrolyte membrane is sandwiched between these electrodes and pressure-bonded. There is an advantage that all can be made dry.
Since the manufacturing process of the membrane electrode assembly consists only of the production of the fuel cell electrode by physical vapor deposition and the pressure bonding of the fuel cell electrode and the solid polymer electrolyte membrane, the entire process can be continuously made dry. . As a result, the manufacturing cost of the membrane electrode assembly is greatly reduced. If the proton conductive material is applied to the fuel cell electrode and then subjected to the crimping process, the entire process can be almost entirely dry.
In addition, such a dry integrated manufacturing method has an advantage that the performance of the membrane electrode assembly can be controlled by controlling only the vapor deposition conditions when the fuel cell electrode is manufactured.

In the case of using a carbon carrier for a fuel cell electrode, as described above, the vapor deposition method can produce only a carbon carrier with low crystallinity that is extremely inferior in oxidation corrosion durability. Therefore, in the electrode catalyst layer of the fuel cell electrode, Only by using the above-mentioned electron conductive oxide that can be produced by vapor deposition, a dry integrated production method of a membrane electrode assembly becomes possible.

<4. Polymer electrolyte fuel cell>
The polymer electrolyte fuel cell (single cell) of the present invention comprises the membrane electrode assembly of the present invention, and usually has a structure in which the membrane electrode assembly is sandwiched between separators having gas flow paths.

FIG. 3 is a conceptual diagram showing a typical configuration of the polymer electrolyte fuel cell of the present invention. As shown in FIG. 3, in the polymer electrolyte fuel cell 20, hydrogen is supplied to the anode 5, and the proton (H ⁺ ) generated by the above-described (reaction 1) 2H ₂ → 4H ⁺ + 4e ⁻ is solid polymer. The supplied electrons are supplied to the cathode 4 through the electrolyte membrane 6, and the generated electrons are supplied to the cathode through the external circuit 21. (Reaction 2) O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O reacts with oxygen. Produce water. A potential difference is generated between the electrodes by the electrochemical reaction between the anode and the cathode. In the polymer electrolyte fuel cell of the present invention, the components other than the membrane electrode assembly of the present invention are the same as those of the known polymer electrolyte fuel cell, and thus detailed description thereof is omitted.
Actually, a fuel cell stack in which the polymer electrolyte fuel cells (single cells) of the present invention are stacked in the number corresponding to the power generation performance is formed, and by assembling other accompanying devices such as a gas supply device and a cooling device. used.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless the gist thereof is changed.

Example 1
1. Production of Fuel Cell Electrode A fuel cell electrode of Example 1 in which an electrode catalyst layer was formed on one surface of the gas diffusion layer was produced by the following steps (1) and (2).

Step (1):
A carbon paper with a microporous layer (MPL) (manufactured by SIGRACT Gas Diffusion Media, model number: GDL25BC) is used as a gas diffusion layer, 4 mol% niobium-doped tin oxide is used as a deposition source (target), and a PLD apparatus (manufactured by Pascal) , Model number: STD-PLD-11301), an electron conductive oxide layer was formed on the gas diffusion layer under the following conditions.

(PLD film forming conditions)
・ Target: Sn _0.96 Nb _0.04 O ₂ (20mmφ pellet)
・ Laser: Excimer laser (manufactured by Coherent, model number: COMPeXPro50, wavelength 193 nm, output 100 mJ, voltage 22 V, frequency 10 Hz)
Atmosphere: O _2, 2Pa
・ Film forming temperature: 25 ℃
・ Film formation time: 1 minute

Step (2):
A sputtering apparatus (model number E-1010) manufactured by Hitachi High-Technologies Corporation was used as the sputtering apparatus, and a Pt plate was used as the evaporation source (target). Sputtering conditions were set to a current value of 15 mA and a degree of vacuum of 10 Pa, and the sputtering time was set so that the amount of Pt supported on the electron conductive oxide layer was 0.5 mg / cm ^2. The electrode for fuel cells of Example 1 was obtained as an electrode catalyst layer.

2. Production of Membrane Electrode Assembly (MEA) A membrane electrode assembly (MEA) using the fuel cell electrode of Example 1 as a cathode was produced by the following procedure.
First, as an electrolyte membrane, a dispersion solution for anode formation is prepared by dispersing 46 wt% Pt / C (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) in a Nafion membrane (thickness: 50 μm) in a predetermined organic solvent containing a Nafion solution. Was formulated. The obtained dispersion solution was spray-printed on the Nafion membrane, and an anode (electrode catalyst layer) having a predetermined thickness was produced on the Nafion membrane. On the anode (electrode catalyst layer), water-repellent carbon paper (manufactured by Toray Industries, Inc., model number: EC-TP1-060T) was disposed as a gas diffusion layer. In the formation of the anode, the Pt amount was adjusted to 0.2 mg / cm ² .
Next, the fuel cell electrode of Example 1 was placed on the opposite surface of the Nafion membrane on which the anode was formed, and these were pressure-bonded for 190 seconds under predetermined conditions (0.3 kN, 130 ° C.). Obtained.

(Comparative Example 1)
1. Manufacturing of Fuel Cell Electrode A fuel cell electrode of Comparative Example 1 was obtained in the same manner as in Example 1 except that the film forming time was changed to 5 minutes among the PLD film forming conditions in the step (1).

2. Production of MEA The MEA of Comparative Example 1 was prepared in the same manner as the MEA production method of Example 1, except that the fuel cell electrode of Comparative Example 1 was used instead of the fuel cell electrode of Example 1 as the cathode. Got.

(Comparative Example 2)
1. Fuel Cell Electrode Material of Comparative Example 2 As Comparative Example 2, Pt-supported niobium-doped tin oxide particles by a wet method were produced by a method according to the method disclosed in Patent Document 3 above.
First, tin chloride hydrate (SnCl ₂ .2H ₂ O) and niobium chloride (NbCl ₅ ) are dissolved in pure water so as to have a ratio of Sn: Nb = 96: 4 (mol ratio), and then coprecipitation with ammonia. Then, niobium-doped tin oxide particles were prepared, and then Pt was supported on the niobium-doped tin oxide particles by the platinum acetylacetonate method. The amount of Pt precursor (Pt (C ₅ H ₇ O ₂ ) ₂ ) was such that Pt was 20 wt% and was supported in dichloromethane (CH ₂ Cl ₂ ).
The obtained slurry was dried, and then subjected to a reduction treatment at 210 ° C. for 3 hours and at 240 ° C. for 3 hours under an N ₂ atmosphere, whereby a fuel cell electrode material of Comparative Example 2 was obtained.

2. Production of MEA An MEA was produced using a cathode formed from the fuel cell electrode material of Comparative Example 2. First, an anode was formed on the Nafion membrane by the same method as the MEA manufacturing method of Example 1. Next, a cathode-forming dispersion solution was prepared in the same manner as the anode, and the obtained dispersion was spray-printed on the Nafion membrane to produce a cathode (electrode catalyst layer) with a predetermined thickness on the Nafion membrane. . Carbon paper was placed on each of the anode and the cathode and pressure-bonded under predetermined conditions (0.3 kN, 130 ° C.) to obtain an MEA of Comparative Example 2. Note that the Pt amount at the cathode of the MEA of Comparative Example 3 is 0.5 mg / cm ² . The amount of Pt in the anode is 0.2 mg / cm ² .

(Reference Example 1)
Commercially available 46 wt% Pt / C (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was used as the fuel cell electrode material of Reference Example 1, and the same method as Comparative Example 2 except that the fuel cell electrode material was used. The MEA of Reference Example 1 was obtained. In addition, the amount of Pt at the cathode of the MEA of Reference Example 1 is 0.5 mg / cm ² . The anode is 0.2 mg / cm ² .

[Evaluation 1: Microstructure observation]
A cross-sectional SEM image of the fuel cell electrode of Comparative Example 1 is shown in FIG. As shown in FIG. 4, the gas diffusion layer has a microporous layer (MPL) of about 20 μm formed on a carbon paper as a base material layer, and a niobium doped tin oxide layer as an electron conductive oxide layer on the surface of the MPL. It can be seen that is formed. When the film thickness of the niobium-doped tin oxide layer was evaluated at 10 locations, it was 54.3 (± 13.4) μm. As can be seen from the high-magnification cross-sectional SEM image shown in FIG. 5, the niobium-doped tin oxide layer of the fuel cell electrode of Comparative Example 1 had a dense structure.

A cross-sectional SEM image of the fuel cell electrode of Example 1 is shown in FIG. As shown in FIG. 6, it can be seen that a niobium-doped tin oxide layer, which is an electron conductive oxide layer, is formed on the surface of the MPL. When the film thickness of the niobium-doped tin oxide layer was evaluated at 10 locations, it was 15.8 (± 6.2) μm. Moreover, when the magnitude | size of the Pt particle | grains carry | supported by the niobium dope tin oxide layer was evaluated, it was confirmed that it is a particle size of about 30 nm and is distributed not only on the surface of the niobium dope tin oxide layer but also inside.

[Evaluation 2: Electrochemical evaluation]
Using the MEA having the fuel cell electrode of Example 1, Comparative Examples 1 and 2 and Reference Example 1, the IV characteristics and cycle durability were evaluated.

[Evaluation 2-1]
A single cell power generation evaluation jig (self-made) incorporating the MEA of Example 1 and Comparative Example 1 was installed in a thermostat set at 80 ° C., and IV characteristics were evaluated under the following conditions. At that time, a fuel cell evaluation apparatus (manufactured by Toyo Technica, model number: PE-8900K) and potentio / galvanostat (manufactured by Solatron, model number: SI1287) were used. The results are shown in FIG.
(Anode condition)
Electrode area: 0.5 cm ²
Supply gas type: 100% H ₂
Gas supply rate: 100 mL / min
Supply gas humidification temperature: 79 ° C
(Cathode conditions)
Electrode area: 0.5 cm ²
Supply gas type: Air
Gas supply rate: 100 mL / min
Supply gas humidification temperature: 60 ° C

As shown in FIG. 7, the MEA using the fuel cell electrode of Example 1 (film formation time of 1 minute) as a cathode was capable of outputting up to a current density of 600 mA / cm ² . From this, it was confirmed that in the fuel cell electrode of Example 1, an electron conductive oxide layer with high gas diffusibility was formed, and excellent output characteristics were exhibited.
On the other hand, the performance of the MEA using the fuel cell electrode of Comparative Example 1 (film formation time of 5 minutes) as the cathode is significantly lower than that of Example 1. This is because the film formation time is too long, the electron conductive oxide layer is densified, or the film thickness becomes too large, resulting in insufficient gas diffusibility as an electrode catalyst layer.

[Evaluation 2-2]
Further, using the MEA of Comparative Example 2, the IV characteristics were evaluated using the same apparatus and conditions as in [Evaluation 2-1], and compared with the results of Example 1. The MEA of Comparative Example 2 uses a fuel cell electrode having an electrode catalyst layer manufactured by a conventional wet method as a cathode.
As shown in FIG. 8, in Example 1, the cell voltage was low at a low current density compared to Comparative Example 2, but reversed when exceeding 200 mA / cm ² , and Example 1 had a higher cell voltage. showed that. From this, it was found that the fuel cell electrode of Example 1 having an electrode catalyst layer produced by a dry method (physical vapor deposition method) showed superior characteristics at a high current density.

[Evaluation 3] Cycle durability test
[Evaluation 3-1] Evaluation of Initial Pressure Retention Rate Using MEA using the fuel cell electrode of Example 1, Comparative Example 2 and Reference Example 1 as a cathode, the Fuel Cell Practical Use Promotion Council “Solid Polymer Type” In accordance with “III-3-3 Test Name: Potential Cycle Test Method 1/2” (Start / Stop Simulated Potential Cycle) in “Proposal of Fuel Cell Targets / R & D Issues and Evaluation Methods (FY2011 Revised Edition)” The cycle durability test was evaluated. FIG. 9 shows an explanatory diagram of the start / stop simulation potential cycle.
First, using the MEAs of Example 1, Comparative Example 2 and Reference Example, initial IV characteristics were measured using the same apparatus as in the above Evaluation 2. Next, as a start / stop simulation potential cycle, the potential is scanned from 1.0 V to 1.5 V at 0.5 V / sec, an acceleration test is performed with a triangular wave, and IV measurement is performed after a predetermined number of cycles. This operation was repeated and carried out up to 60,000 cycles corresponding to 10 years of use in a fuel cell vehicle (FCV). The results are shown in FIG.

As shown in FIG. 10, in Reference Example 1 in which the support in the electrode catalyst layer is carbon, the voltage was remarkably reduced in about 2000 cycles. As the deterioration factors, the corrosion of the carbon support under the cathode conditions and the desorption of the Pt catalyst particles due to the corrosion of the carbon support are suggested.
On the other hand, in Example 1 and Comparative Example 2 in which the carrier in the electrode catalyst layer is an electron conductive oxide layer, the initial performance is inferior to that of Reference Example 1, but power generation is not significantly degraded from the initial performance after 60,000 cycles. It can be seen that the performance is maintained. From this, the electron-conductive oxide support is thermodynamically stable under the cathode conditions, so it is not corroded like the carbon support and the Pt catalyst particles are not detached, resulting in performance deterioration. It is considered difficult. And it turned out that it does not originate in the preparation methods (Example 1 (physical vapor deposition method), comparative example 2 (wet method)).

[Evaluation 3-2] AC Impedance Measurement Using the MEA using the fuel cell electrode of Example 1, Comparative Example 2 and Reference Example 1 as a cathode, the ohmic resistance of each fuel cell electrode was measured by the AC impedance method. Evaluation was performed.
Using the evaluation apparatus described in [Evaluation 2-1] and the Frequency response analyzer (manufactured by Solartron), the frequency was changed in the range of 100 kHz to 0.1 Hz to obtain a Cole-Cole plot. The anode condition and cathode condition are the same as those in [Evaluation 2-1]. FIG. 11A is an explanatory diagram of a Cole-Cole plot, and FIG. 11B is a diagram illustrating an assumed equivalent circuit. In FIG. 11B, Rs is an ohmic resistance, Rp is a non-ohmic resistance, C is an electric double layer capacitance, and the ohmic resistance and the non-ohmic resistance can be separately evaluated.

FIG. 12 shows the change of the ohmic resistance of the MEA using the fuel cell electrode of Example 1, Comparative Example 2 and Reference Example 1 as the cathode with respect to the number of cycles. The MEAs of Example 1, Comparative Example 2, and Reference Example 1 have the same configuration except for the cathode. Therefore, it was determined that the change in ohmic resistance shown in FIG. 12 is mainly caused by the cathode.

In Reference Example 1 in which carbon is used as the cathode support, the ohmic resistance increases rapidly with the number of cycles, and it is considered that the carbon support is significantly deteriorated with the potential cycle. On the other hand, in Example 1 and Comparative Example 2 in which the cathode carrier is an electron conductive oxide, ohmic with respect to the potential cycle regardless of the physical vapor deposition method (Example 1) or the wet method (Comparative Example 2). The resistance hardly changes, and the electron conductive oxide as the carrier is considered to be stable. On the other hand, it can be seen that the value of ohmic resistance is smaller in Example 1 manufactured by the physical vapor deposition method than in Comparative Example 2 manufactured by the wet method.
From this, the fuel cell electrode of Example 1 in which the electron conductive oxide layer was formed by the connected particles in which a plurality of electron conductive oxide particles were connected by physical vapor deposition was formed by a conventional wet method. It was shown that the electric resistance (ohmic resistance) of the whole electrode was small as compared with the fuel cell electrode of Comparative Example 2 using electron conductive oxide carrier particles.

From the above results, the fuel cell electrode of the present invention (Example 1) has a power generation performance equivalent to or higher than that of a fuel cell electrode using an electron conductive oxide produced by a conventional wet method as a carrier. It has been found that it has a low electrical resistance (ohmic resistance) and has excellent cycle durability under cathode conditions.

According to the present invention, there is provided a fuel cell electrode in which a non-carbon electron conductive oxide having sufficient electron conductivity and excellent durability is used as an electrode catalyst layer. The electrode for a fuel cell is particularly suitable for an electrode for a polymer electrolyte fuel cell that requires long-term operation with start and stop.

Claims

A fuel cell electrode comprising a gas diffusion layer having electron conductivity and an electrode catalyst layer formed on and / or inside the gas diffusion layer,
The electrode catalyst layer includes an electron conductive oxide layer having gas diffusibility formed by physical vapor deposition, and electrode catalyst particles supported on the electron conductive oxide layer. electrode.
The gas diffusion layer is a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer, and the electrode catalyst layer is formed on the surface of the microporous layer. 2. The fuel cell electrode according to 1.
The fuel cell electrode according to claim 1 or 2, wherein the electron conductive oxide layer is made of an oxide mainly composed of tin oxide.
4. The fuel cell electrode according to claim 1, wherein the electron conductive oxide layer is made of niobium-doped tin oxide doped with 0.1 to 20 mol% of niobium.
The electrode for a fuel cell according to any one of claims 1 to 4, wherein the electrode catalyst layer further contains a proton conductive material.
A method for producing a fuel cell electrode comprising a gas diffusion layer having electron conductivity and an electrode catalyst layer formed on and / or inside the gas diffusion layer,
A step of forming an electron conductive oxide layer having gas diffusibility on the surface and / or inside of the gas diffusion layer by a physical vapor deposition method using a vapor deposition source comprising an electron conductive oxide;
A step of supporting electrode catalyst particles on the electron conductive oxide layer;
The manufacturing method of the electrode for fuel cells characterized by including these.
The gas diffusion layer is a gas diffusion layer having a base layer and a microporous layer formed on one side of the base layer, and the electron conductive oxide layer is formed on a surface of the microporous layer. Item 7. A method for producing a fuel cell electrode according to Item 6.
The method for producing an electrode for a fuel cell according to claim 6 or 7, wherein the vapor deposition source is made of an oxide mainly composed of tin oxide.
The method for producing an electrode for a fuel cell according to any one of claims 6 to 8, wherein the vapor deposition source is made of niobium-doped tin oxide doped with 0.1 to 20 mol% of niobium.
The method for producing an electrode for a fuel cell according to any one of claims 6 to 9, wherein the physical vapor deposition method in the step of forming the electron conductive oxide layer is a pulse laser vapor deposition method (PLD).
The method for producing a fuel cell electrode according to any one of claims 6 to 10, wherein the supporting method in the step of supporting the electrode catalyst particles is a physical vapor deposition method or a chemical vapor deposition method.
A membrane electrode assembly comprising: a solid polymer electrolyte membrane; a cathode joined to one surface of the solid polymer electrolyte membrane; and an anode joined to the other surface of the solid polymer electrolyte membrane,
6. A membrane electrode assembly, wherein at least one of the cathode and the anode is a fuel cell electrode according to any one of claims 1 to 5.
A solid polymer fuel cell comprising the membrane electrode assembly according to claim 12.
A method for producing a membrane electrode assembly comprising a solid polymer electrolyte membrane, a cathode joined to one surface of the solid polymer electrolyte membrane, and an anode joined to the other surface of the solid polymer electrolyte membrane. And
A process for producing each of the cathode and anode fuel cell electrodes by the method for producing a fuel cell electrode according to claim 11;
And a step of sandwiching a solid polymer electrolyte membrane between the manufactured cathode and anode and press-bonding the membrane.