JPH0393165A - Manufacture of electrode catalytic layer for fuel cell - Google Patents

Abstract

PURPOSE:To obtain an excellent gas diffusing property by enlarging an empty hole diameter so that reaction gas may easily diffuse through empty holes of an empty catalytic layer. CONSTITUTION:An electrolyte 7, in which a carbon carrier carries a noble metal, fluorine-contained polymers 8 and fine grains of a base metal are mixed to form an application liquid, and the application liquid is applied on an electrode substrate 5. Later, base metal corpuscules are electrolytic-liquated in an electrolyte for being shaved out. That is, base metal corpuscules mixed with electrolytic grains, fluorine-contained polymers are shaved out and removed after electrode manufacture so as to be able to manufacture empty holes having the same size with the base metal grains on the spots occupied before by the base metal grains. Accordingly, these empty holes smooth reaction gas supply to the empty holes existing from before. A sufficient amount of reaction gas can be supplied in a high electric wave density region 4 requiring a large amount of reaction gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing an electrode catalyst layer for a fuel cell, and more particularly to a method for manufacturing an electrode catalyst layer in which reactive gases can easily diffuse. [Prior art] Figure 3 shows the electrical system for fuel cells. The electrode is a porous electrode substrate 5 made of carbon material with excellent electrical conductivity.
An electrode catalyst layer 4 is made of a uniform mixture of a catalyst 7 on which precious metals such as platinum are supported and a fluororesin 8 as a floating wood.
A matrix 3 made of a mixture of silicon carbide 6, which has excellent electrical insulation properties, and fluororesin 8 as a binder, is laminated on the electrode. The matrix 3 is impregnated with phosphoric acid as an electrolytic solution, and the electrolytic solution is supplied to the electrode catalyst layer 4 from the matrix 3 and the reaction gas is supplied from the electrode substrate 5. Inside the electrode catalyst layer, a three-phase interface of the catalyst (solid), electrolyte (liquid), and reaction gas (gas) is formed, and an electrochemical reaction occurs, allowing electrical energy to be taken out of the system. [Problems to be Solved by the Invention] However, in conventional fuel cells, there was a problem in which the single cell voltage of the fuel cell suddenly decreased when the current density was increased. Figure 2 shows the single cell voltage. Fig. 9 is a diagram showing the current density dependence of .Curve 9 shows the characteristics of a conventional battery.This shows that when the current density of the battery is increased, the reaction gas supply to the inside of the electrode catalyst layer This occurs because the amount becomes insufficient to maintain 0. Figure 1 is a diagram showing the pore size distribution of the electrode catalyst layer. Curve 2 is the pore size distribution of the conventional battery
．． There are peaks near OIIrm and IIs. Of these, 0
．． The 01μ pores are pores in the catalyst particles themselves, and the 1μ pores are pores existing between the fluororesin and the mass of the catalyst particles. These 1μ holes play the role of gas supply channels. In order to smoothly supply the reaction gas inside the electrode catalyst layer,
It is necessary to increase the pore diameter so that the reactant gas can easily diffuse through the pores in the electrode catalyst layer. In the electrode catalyst layer mentioned above, the pore size formed by the mixing of catalyst particles and fluororesin particles is too small. That is, the above-mentioned pore diameter is in the Wl region of Knudsen diffusion, and the pore diameter largely controls gas diffusivity. This invention has been made in view of the above-mentioned points, and its purpose is to provide a method for manufacturing an electrode catalyst layer that has a larger pore diameter than conventional ones and has excellent gas diffusivity. [Means for Solving the Problems] According to the present invention, the above-mentioned object has a first step, a second step, and a third step, and the first step includes supporting a precious metal on a carbon carrier. This is a step of mixing the catalyst 7, the fluorine tree 1118, and fine particles of a base metal to form a coating liquid, in which the base metal particles have a particle size of 5 to 50B, and the second step This is a step of applying a liquid onto the electrode substrate 5, and the third step is achieved by electrolytically eluting and removing base gold II fine particles in the electrolytic solution after the second step. Nickel, iron, cobalt, etc., which do not poison the catalyst, can be used as base metals. [Operation] Base metal particles mixed with catalyst particles and fluororesin particles are eluted after electrode activation. By removing it, pores with the same size as the base metal particles can be created in the locations where the base metal particles existed. [Example] Next, an example of this invention will be explained based on the drawings. First, a dispersion solution is prepared by adding 38 to 57% by weight of fluororesin (PTFB) to a catalyst supporting a noble metal. Furthermore, nickel particles with a particle size of 5 to 50 μm are added to this dispersion system in a ratio of 1 to 10 times the weight of the catalyst. Next, this dispersion system is applied onto the electrode substrate, and the electrode catalyst layer is shaped by suction, and the shaping and moisture removal are carried out at a temperature of 110 degrees Celsius and a pressure of 3 to 20 degrees Celsius. The nickel particles contained in the catalyst layer thus obtained are removed by using a potentiometer in a solution of acid such as dilute nitric acid or dilute sulfuric acid or salt such as Ha@So@ using a potentiometer.
Nickel particles are electrolytically removed at a potential of +1000 mV (vs.sflE) from V. The end of electrolysis can be determined by the decrease in electrolytic current. A lower electrolytic potential is preferable because it has less negative effect on the catalyst, but a higher potential requires a shorter electrolysis time, so it is +500 mV (vs. sH
E) degree is desirable. The electrode with nickel particles electrolytically eluted is immersed in pure water to elute the nickel particles. The electrode is then made by drying and removing the moisture. The amount of residual nickel in the obtained electrode was about 0.1%. The pore size distribution of this electrode is shown in curve &lI1 of Figure 1. Pores of 5 to 50 nm are used as gas passages. The gas permeation amount of the obtained electrode catalyst layer was 10 to 200 cc/
hr-csa 810 ・Conventional catalyst layer 1~
lOOcc/hr-cs greater than LO-1. In the high current density region, the electrode created in this way can
Compared to electrodes with conventional structure, there is less deterioration in characteristics due to gas diffusion. The current-voltage characteristic of the electrode according to the invention is shown by curve 10 in FIG. It can be seen that the deterioration of characteristics in the high current density region is smaller. [Effects of the Invention] According to the present invention, there are a first step, a second step, and a third step, and the first step includes a catalyst in which a noble metal is supported on a carbon carrier, a fluororesin, and a base metal. The step is to form a coating solution by mixing fine particles of the base metal, wherein the fine particles of the base metal have a particle size of 5 to 50 mm, and the second step is a step of coating the coating solution on the electrode substrate. In the third step, after the second step, base metal particles are electrolytically eluted in an electrolytic solution. Since this is a removal process, pores of the same size as the base metal particles are left after the base metal electrolytic elution, and these pores facilitate the supply of reaction gas to the conventionally existing pores of about 0.1 μm, allowing a large amount of In the high current density region where reactive gas is required, a sufficient amount of reactive gas is supplied to the three-phase interface, resulting in a fuel cell with excellent characteristics in the high current density region. Another advantage is that the pore size and its distribution can be freely controlled by adjusting the particle size and amount of base metal added.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the pore size distribution of the electrode catalyst layer according to the embodiment of the present invention in comparison with the conventional pore diameter distribution, and FIG. 2 is a diagram showing the pore size distribution of the electrode catalyst layer according to the embodiment of the present invention. A diagram showing a comparison of polarization characteristics with conventional polarization characteristics, and Figure 3 is a cross-sectional view showing the electrodes and matrix of a fuel cell. l: pore size distribution of the electrode catalyst layer according to the example of the present invention, 2
: Pore size distribution of conventional electrode catalyst layer, 5;

Claims (1)

[Claims] 1) It has a first step, a second step, and a third step, and the first step includes a catalyst in which a precious metal is supported on a carbon carrier;
This is a step of mixing a fluororesin and fine particles of a base metal to form a coating solution, wherein the fine particles of the base metal have a particle size of 5 to 50 μm, and the second step is to mix the coating solution on an electrode substrate. A method for manufacturing an electrode catalyst layer for a fuel cell, characterized in that the third step is a step of electrolytically eluting and removing base metal fine particles in an electrolytic solution after the second step.