JPS6224565A - Gas diffusion electrode of fuel cell and the like - Google Patents

Abstract

PURPOSE:To prevent wasteful use of catalyst metal by forming a catalyst layer with a skeleton formed by dispersing conductive particles on the surface of water repellent resin, and conductive particles coagulated in spaces of the skele ton, and sypporting catalyst metal on conductive particles. CONSTITUTION:In a fuel gas diffusion electrode comprising a catalyst layer and a gas diffusion layer, a catalyst layer consists of a skeleton formed by dispersing conductive particles 2 on the surface of water repellent resin 3, and conductive particles coagulated in spaces of the skeleton, and catalyst metal 1 is supported on conductive particles 5. Thereby, electrolyte penerates into a hydrophilic part and all the catalyst metals participate in the wetting reaction of electrolyte. On the other hand, gas passes through water repellent part and sufficient gas is supplied to the catalyst.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to positive electrodes and negative electrodes for hydrogen-oxygen fuel cells, electrodes for industrial electrolysis, electrodes for air-zinc batteries, constituent electrodes for galvanic gas sensors, and electrodes for electrolysis. This invention relates to gas diffusion electrodes such as gas generation electrodes, and particularly to improvements in the structure of catalyst layers of gas diffusion electrodes.

(Prior art and its problems) Fuel cells and the like require a catalyst to promote the reaction between fuel and oxidizer at each electrode.

However, the electrochemical reaction of the reactant gas takes place in the presence of the catalytic metal at the point of contact between the electrolyte and the reactant gas at the electrode, ie, in the region forming the three-phase interface. Therefore, the catalyst metal present in other parts is not effectively utilized and is wasted. Catalytic metals commonly used in fuel cells, etc. are expensive precious metals.
In particular, platinum, platinum-rhodium, platinum-ruthenium oxide,
It is a platinum group metal such as platinum-tin, and therefore it is desirable to waste as little as possible and obtain good electrode performance. In order to improve electrode performance, it is necessary to increase the interface area between the electrolyte and the reactant gas.

To make this interface large, only the reactant gas can pass through,
It has been known that a large interface can be obtained by separating a water-repellent gas diffusion layer that does not allow the electrolyte to permeate and a hydrophilic catalyst layer that allows the electrolyte to exist. As a gas diffusion layer having such properties, for example, polyethylene, polypropylene, polytetrafluoroethylene, synthetic rubber, etc. can be used. In addition, a catalyst layer having such properties is generally made by uniformly bonding conductive particles carrying a catalyst with polytetrafluoroethylene, which is a tΩ water-based resin; can be replaced with the above-mentioned gas diffusion layer material.Also, as the conductive particles, for example, carbon black (generally treated with hydrogen gas at high temperature is used, but carbon monoxide or fluorine-containing material is used at high temperature). ), graphite, artificial graphite, activated carbon, and carbon fiber may be used alone or in combination.

Note that the surface of an inorganic oxide such as alumina or silica may be carbonized.

In the ↑Ω water gas diffusion electrode having such a structure, the micro 1Ω aqueous portion in the catalyst layer serves as a gas supply passage, and the hydrophilic portion becomes a portion where the electrolyte permeates and an electrode reaction occurs. By the way, in order to further improve the electrode characteristics with this structure, a considerable amount of ↑water-separating portion is required. However, since the catalyst is uniformly distributed within the electrode, the amount of catalyst present in the hydrophilic portion of the three-phase interface region is usually 20-30%, and at most 75%, so that it is not involved in the reaction. There was a lot of catalyst that was not wasted. As a method to improve this waste of catalyst, Japanese Patent Application Laid-Open No. 51-86734 describes a post-force crease (electrode structure) of an electrode supported by a hydrophobically bonded substrate made of conductive particles. It is disclosed that a good electrode can be obtained by a technique in which a catalyst is supported within the electrode structure after the formation of the catalyst.

However, in this method as well, the catalyst present in areas other than the three-phase interface region is not effectively utilized, and its waste is unavoidable.

(Object of the invention) The present invention has been made to solve such problems,
To provide a gas diffusion electrode for a fuel cell or the like, in which an electrolytic solution completely enters a hydrophilic part and 100% of the catalyst participates in the wetting reaction of the electrolytic solution, while gas passes through a water-repellent part and a sufficient amount of gas can be supplied to the catalyst. The purpose is to

(Structure of the Invention) A gas diffusion electrode for a fuel cell or the like according to the present invention to achieve the above object is a gas diffusion electrode for a fuel cell or the like that includes a catalyst layer and a gas diffusion layer, wherein the catalyst layer has conductive particles. It consists of a skeleton dispersed on the surface of a water-repellent resin and a group of conductive particles aggregated in the space of the skeleton, and is characterized in that a catalytic metal is supported on the group of conductive particles.

First, the configuration of a conventional gas diffusion electrode for a fuel cell or the like will be explained with reference to drawings, and its drawbacks will be pointed out, and then the configuration of the gas diffusion electrode for a fuel cell or the like of the present invention and its effects will be explained.

Figure 2 is a cross-sectional view of a catalyst layer of a conventional gas diffusion electrode such as a fuel cell, in which conductive particles 2 carrying catalyst metal 1 and TA water-based resin 3 are uniformly mixed to form a skeleton. It is. In this catalyst layer, only the catalyst metal 1 in the electrolyte permeation portion 4 contributes, and the catalyst metal 1 in the gas supply passage made of the water-repellent resin 3 is wasted.

FIG. 1 is a schematic cross-sectional view of a catalyst layer of a gas diffusion electrode for a fuel cell or the like according to the present invention, and the numbers are the same as in the conventional example.

In the present invention, the conductive particles 2 are 0401 to 0°06
μ and (θ) are orders of magnitude smaller than the minor axis of the aqueous resin 3, which is around 0.2μ, so the conductive particles 2 aggregate to form a conductive particle group. Since it is hydrophilic, the electrolyte permeates into this group.On the other hand, the conductive particles 2 dispersed on the surface of the 1B aqueous resin 3 form a pair with the conductive particles 2 of the facing conductive particle group 5, and gas A supply passage is formed. This is the same as in the conventional case. However, since this gas supply passage exists very close to the conductive particle group 5, a sufficient amount of gas is supplied for the catalytic reaction of the conductive particle group 5. In order for the electrolytic solution to seep into the entire catalyst layer, it is preferable that the conductive particle groups 5 are connected in a skeleton shape.

In addition, in the gas diffusion electrode of the present invention, the mixing ratio of the water-repellent resin fine powder and the catalyst itself or the catalyst supported on the hydrophilic fine powder is set to a weight mixing ratio of 8:2 to 2:8. The reason for this is that if the weight mixing ratio of both sides is 8:2 or more, the electrolyte will not completely enter the hydrophilic part, and it will be difficult for gas to pass through the other water-repellent part, allowing sufficient gas to be supplied to the catalyst. This is because it will not be possible.

(Example) An example of the water-repellent gas diffusion electrode according to the present invention will be described in the case of an electrode for a Hz/Oz fuel cell using sulfuric acid as an electrolyte.

From a conductive IΩ aqueous porous membrane that is pressure-molded by mixing fine powder of carbon black, which is a conductive material, and fine particles of polytetrafluoroethylene, which is a water-repellent binder, at a weight ratio of 4:6. On the gas diffusion layer consisting of 0.56
Conductive particles of carbon black fine powder supporting mg/cot of platinum catalyst and ↑n aqueous treated carbon black fine powder of polytetrafluoroethylene are dispersed.
A catalyst layer was provided by hot pressing a fine powder mixture containing Ω aqueous resin and a weight ratio of 7:3. Note that this catalyst layer can also appropriately contain, as auxiliary raw materials, water repellency enhancing powder such as wax graphite fluorocarbon powder, reinforcing substance powder such as fluororubber, coloring pigment, and the like. In addition, when preparing the catalyst layer, it is necessary to mix the powder in a mixer, or use petroleum,
Approximately 20 to 200% liquid lubricant of liquid hydrocarbon such as isopropyl alcohol, solvent naphtha, white oil, etc.
Mix and adjust weight %. In this H210□ fuel cell electrode, 60°C 13 mol/7! Oxygen reduction properties and hydrogen oxidation properties were measured in an aqueous sulfuric acid solution. As a result, the oxygen electrode characteristics were 0.8 compared to the hydrogen reference electrode in the same solution.
0.2 A/c at V [J, 3 A/c at 0.7 ■
cal, and oxygen electrode characteristics of 5 A/cal or more at the limiting current were obtained. This is an oxygen electrode characteristic more than twice that of the conventional (Ω) H2102 fuel cell electrode having the structure shown in FIG. 2, which does not contain hydrated conductive particles.

In addition, the hydrogen electrode characteristics are 2.3A/crA at 25mV.
was obtained, and the hydrogen electrode characteristics were 1.3 times that of conventional electrodes.

Next, another example of the gas diffusion electrode according to the present invention will be described in the case of an electrode for an H2102 fuel cell using phosphoric acid as an electrolyte.

A H210□ fuel cell electrode was prepared by disposing a catalyst layer supporting 0.28□/cot of platinum catalyst on a gas diffusion layer made of the same conductive and water-repellent porous membrane as in the above example.
Oxygen reduction properties and hydrogen oxidation properties were measured in 100% phosphoric acid at 0°C. As a result, the oxygen electrode characteristics compared to the hydrogen reference electrode in the same solution were 0.6 A/cm2 at 0.8 .
It was 3.4A/cm2 at 0.7■. This is the conventional H
210□ Oxygen electrode characteristics are more than three times that of fuel cell electrodes. In addition, the hydrogen electrode characteristics were 2.5 A/c+J at 25 mV, which is 1.3 times higher than that of conventional electrodes.

The surface area of the catalyst cluster wetted with the electrolyte of the electrode in each of the above examples was determined by a commonly used electrochemical method (portangram).

In other words, if the cluster surface area determined for an electrode with extremely low water repellency and in which all catalyst clusters are completely wetted is So, and the cluster surface area of the electrode in the example is SPt, then U = S pt/S' pt. The catalyst utilization rate was determined, and the catalyst utilization rate was 100% in terms of the oxygen electrode characteristics of the electrode of Example.

Moreover, the degree of gas supply ability of the electrode of the above example was confirmed as follows. That is, if the gas supply is sufficient and there is no polarization caused by it, the slope of the Tafel plot will theoretically be 80 to 90 mV. Experiments showed that the electrode of the example
Its terfel slope was confirmed to be approximately 90 mV up to a current density of 1.5 A/cnt. From this, it was confirmed that the electrode had no polarization due to gas supply up to a current density of I A / crA or more, and that the electrode could sufficiently supply gas.

In the above embodiments, a platinum catalyst is used as the catalyst, but other metal catalysts, particularly noble metal catalysts or oxide catalysts, may also be used. Further, electrolytic freezing is not limited to sulfuric acid and phosphoric acid, and other materials may also be used. Further, although the above embodiments are for electrodes for fuel cells, the gas diffusion electrode of the present invention can also be used as an electrode for industrial electrolysis, an electrode for an air-zinc battery, a component electrode for a galvanic gas sensor, and a gas generation electrode for electrolysis. It is something that can be done.

(Effects of the Invention) As can be seen from the above explanation, the gas diffusion electrode for fuel cells, etc. according to the present invention allows the electrolyte to completely enter the hydrophilic portion,
% of the catalyst participates in the wetting reaction of the electrolytic solution, while gas passes through the water-repellent portion and sufficient gas is supplied to the catalyst, so the catalyst is not wasted and the electrode properties are significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a catalyst layer of a gas diffusion electrode such as a fuel cell of the present invention, and FIG. 2 is a schematic cross-sectional view of a catalyst layer of a conventional gas diffusion electrode.

Claims (3)

[Claims] (1) In a gas diffusion electrode for a fuel cell or the like that is composed of two layers: a catalyst layer and a gas diffusion layer, the catalyst layer is formed between a skeleton in which conductive particles 2 are dispersed on the surface of a water-repellent resin 3 and a space between the skeletons. A gas diffusion electrode for a fuel cell or the like, comprising a group of aggregated conductive particles, and a catalyst metal 1 is supported on the conductive particle group 5. (2) A gas diffusion electrode for a fuel cell or the like, characterized in that the weight mixing ratio of the conductive particles according to claim (1) and the water-repellent resin is 8:2 to 2:8. (3) A gas diffusion electrode for a fuel cell or the like, wherein the conductive particles according to claims (1) to (2) are carbon black.