JPH02226659A - Electrode construction for fuel cell - Google Patents

Abstract

PURPOSE:To enable the coexistence of good conductivity and gas permeability by forming an electrode base material with a bonding layer comprising a mixture of a conductive powder and water repellent agent. CONSTITUTION:An anode 1 and a cathode 2 are made in such a way that a catalytic layer 5 is integrally laminated on respective base materials 4 and the layer 5 is so positioned as to oppose the side of a matrix layer 5. The base material 4 has porous structure and the layer 5 has the porous structure wherein carbon black powder carrying platinum is bonded with PTFE as a water repellent binder. Also, the layer 5 comprises porous structure obtainable from the sintering of the kneaded material of silicon carbide powder and PTFE, and is impregnated with an electrolyte. The base materials 4 proper has strength necessary for an electrode base material, the characteristics of both good conductivity and gas permeability pertain thereto and the aforesaid characteristics can be made to coexist.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to the structure of an electrode plate constituting a fuel cell cell.

[Prior Art] A fuel cell is constructed by interposing a matrix layer for holding an electrolyte between an anode and a cathode. Further, electrodes such as anodes and cathodes are generally constructed by using carbon paper made of carbon fiber as a substrate and integrally laminating a catalyst layer on the surface of the substrate facing the matrix layer side. In such a configuration, air (oxygen) is supplied and transmitted to the back surface of the anode, and hydrogen is supplied and transmitted to the back surface of the cathode,
Each is ionized by the electrolyte in the matrix layer in the catalyst layer and reacts with each other to generate water and electrical energy to generate electricity.

The electrode substrate in such a fuel cell must have electrical conductivity and gas permeability to allow gases such as oxygen and hydrogen to pass therethrough, and must also have sufficient strength to withstand pressure. However, conventional electrode substrates are made of carbon paper in which carbon fibers are treated with a water repellent such as polytetrafluoroethylene (PTFE). However, with this carbon paper, if the amount of salt water repellent is large, the electrical resistance increases and the conductivity is inhibited, and conversely, if the amount of water repellent is small, the electrolyte penetrates and inhibits gas permeability. There was a problem with the stripes.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned conventional problems and provide an electrode structure for a fuel cell that can achieve both electrical conductivity and gas permeability.

[Means to solve the problem]

The electrode structure of the present invention that achieves the above object uses a binding layer formed by press-molding a mixture of conductive powder and a water repellent as an electrode substrate, and a catalyst layer is integrally laminated on the electrode substrate. It is characterized by:

Further, in another electrode structure of the present invention, a plate-like body in which a binding layer formed by binding a mixture of conductive powder and a water repellent agent is integrally laminated on carbon paper made of carbon fiber is used as an electrode substrate. , is characterized in that a catalyst layer is integrally laminated on the electrode substrate.

In the present invention, the conductive powder used in the binding layer of the electrode base material has good conductivity, chemical resistance that does not corrode against electrolytes such as phosphoric acid, and is suitable for fuel cells. It is not particularly limited as long as it has characteristics that are stable against the generated temperature of about 200°C. A particularly preferred example of such conductive powder is carbon black powder.

In addition, the water repellent used as a binder for the above-mentioned conductive powder has good water repellency, has chemical resistance that does not corrode against electrolyte, and has a temperature of about 20"C, which is generated by fuel cells. The water repellent is not particularly limited as long as it has the property of being stable at a temperature of
Examples include fluororesins such as TFE), fluorinated alkoxyethylene (PFA), and fluorinated ethylene propylene ether (FEP).

The above-mentioned conductive powder and water repellent are sintered to form a binder layer with a plate-like porous structure, and the mixing ratio of the two (conductive powder/water-clear binder) is determined by weight. 4 in ratio
It is preferably in the range of 0/60 to 70/30. Among such binder layers, a press-molded one exhibits high strength by itself and can therefore be used alone as an electrode substrate. In addition, in the case of a binder layer that is not press-molded, it does not have sufficient strength to be used alone, so it is recommended to use it in combination with carbon paper to supplement the strength. However, since the carbon paper at this time does not need to have as much strength as that used for conventional electrode substrates, it is better to use carbon paper with a small amount of water repellent.

The above-mentioned porous structure binder layer has a conductive powder and a water repellent mixed and dispersed at a microscopic level, so even if the amount of TA water agent is small, it has good water clearing ability and has excellent water repellency. It has gas permeability. Furthermore, since the conductive powder is a large component, the conductivity is high and the electrical resistance is reduced. In particular, in the case of a press-molded binding layer, it exhibits a low electrical resistance, and can perfectly achieve both electrical conductivity and gas permeability as an electrode base material.

In the present invention, any conventionally known catalyst layer can be used as the catalyst layer that is integrally stacked on the electrode substrate. Such a catalyst layer may be made of, for example, a porous structure obtained by sintering a paste-like mixture of carbon black powder supporting a catalyst such as platinum and a fluororesin such as PTFB on carbon paper made of carbon fibers. Preferably used. Of course, as a binder for the catalyst layer, in addition to the above-mentioned PTFE, PF^, Ft! P etc. can also be used.

FIG. 1 is an explanatory diagram of a fuel cell having an electrode structure according to an embodiment of the present invention.

In the figure, 1 is an anode, 2 is a cathode, and a matrix layer 3 is interposed between the picture electrodes. The two electrodes each have a catalyst layer 5 laminated integrally on a base material 4, and are arranged so that the catalyst layer 5 faces the matrix layer 3 side.

In this embodiment, the base material 4 has a porous structure in which a mixture of 45% by weight of carbon black powder and 55% by weight of PTFE is press-molded. The catalyst layer 5 has a porous structure in which carbon black powder supporting platinum is bound using PTFE as a water-repellent binder. Moreover, the matrix layer 3 is made of silicon carbide powder and PT.
It has a porous structure created by sintering a kneaded material of FE, and is impregnated with an electrolyte such as phosphoric acid. Of course,
The water repellent used in any of the porous structures mentioned above is also the above-mentioned PTPI! In addition to PFA.

Fluororesins such as FEP can also be used.

The electrode base material 4 has the strength required for an electrode base material by itself, has good electrical conductivity and gas permeability, and can achieve both electrical conductivity and gas permeability.

FIG. 2 shows another embodiment of the electrode (anode 1 or cathode 2). The base material 4 is a binding layer made by press-molding a mixture of carbon black powder and a fluororesin such as PTFH as in the case of FIG. 1, but the surface in contact with the catalyst layer 5 has irregularities. It is formed.

By forming the surface into an uneven shape and stacking it together with the catalyst layer 5, the gas diffusion distance from the outer surface of the base material 4 to the reaction point of the catalyst layer 5 is reduced, thereby reducing the diffusion overvoltage and improving the output. can be achieved.

FIG. 3 shows an electrode according to yet another embodiment. The base material 4 of this electrode is made of the same mixed material as in FIG. 2, but is different in that it is not press-molded. Therefore, since the strength is not high, the carbon paper 6 is used as a reinforcing material and is integrally laminated thereon. The water repellent contained in the carbon paper 6 in this case is less than that of the carbon paper used in the conventional electrode base material.

The electrode base materials shown in FIGS. 2 and 3 also have high water repellency as in the embodiment shown in FIG. 1, and have both excellent electrical conductivity and gas permeability.

〔Effect of the invention〕

As mentioned above, in the electrode structure of the present invention, since the electrode base 4° plate is made of a binding layer of a mixture of conductive powder and water repellent, the conductive powder and water repellent are mixed at a microscopic level. This makes it possible to achieve both good electrical conductivity and gas permeability.

In particular, in the case of a binder layer formed by press-molding the electrode base material, it has great strength by itself, so it can be used alone.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a fuel cell having an electrode structure according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic explanatory diagrams of electrode structures according to other embodiments. 1... Anode, 2... Cathode, 4... Base material, 5...
catalyst layer.

Claims (2)

[Claims] (1) An electrode structure for a fuel cell in which a binding layer formed by press-molding a mixture of conductive powder and a water repellent agent is used as an electrode substrate, and a catalyst layer is integrally laminated on the electrode substrate. (2) An electrode substrate is a plate-like body in which a binding layer formed by binding a mixture of conductive powder and a water repellent is laminated on carbon paper made of carbon fiber, and a catalyst is placed on the electrode substrate. A fuel cell electrode structure consisting of layers stacked together.