JPH03252058A - Electrode catalyst layer for fuel cells - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode catalyst layer of a gas diffusion electrode for a fuel cell, and more particularly to a gas diffusion electrode for a fuel cell that has excellent characteristics and reliability.

[Conventional technology]

A phosphoric acid fuel cell is a device that directly converts the chemical energy of fuel into electrical energy, and its configuration consists of a carbon electrode base material 7 as shown in Figure 1 with a matrix (not shown) in between. Gas diffusion electrodes each having an electrode catalyst layer 6 are placed facing each other, and a fuel gas and an oxidant gas are separately supplied to each electrode from an external gas supply system, and the oxidant gas is distributed over the catalyst particles of the electrode catalyst layer. This is a power generation device that electrochemically reacts the fuel gas and fuel gas individually, and extracts electrical energy from the system as a result. The electrode catalyst layer 6 is prepared by supporting noble metal particles 3 on a carbon catalyst carrier 2 to form catalyst particles 4, and binding them with fluororesin particles 5. In the electrode catalyst layer 6 of such a fuel cell, phosphoric acid as an electrolyte is mainly retained in the inner pores 14 of the catalyst particles 4, and the reactive gas is retained in the interparticle pores between the catalyst particles 4 and the fluororesin particles 5. Hole 8
A, or flows through the pores 8B between the catalyst particles, and reaches the noble metal particles 3 of the catalyst particles 4. The noble metal particles 3 are wetted with phosphoric acid, which is an electrolyte, and a three-phase interface is formed.
An electrochemical reaction of oxidation or reduction occurs.

[Problem to be solved by the invention]

However, in such a conventional electrode catalyst layer 6, the phosphoric acid in the catalyst particles 4 is absorbed into the interparticle pores 8A formed between the fluororesin particles 5 and the catalyst particles 4 or the interparticle pores between the catalyst particles 4 over time. There was a problem in that the characteristics of the fuel cell deteriorated because the reaction gas moved to 8B and blocked them, preventing the flow of the reaction gas. The primary particle size of conventional carbon black was 700 particles.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an electrode catalyst layer for a fuel cell whose properties are less likely to deteriorate over time and have excellent reliability by increasing the ability of catalyst particles to retain phosphoric acid.

[Means to solve the problem]

According to the present invention, the above-mentioned purpose is to have catalyst particles 4 and fluororesin particles 5, and the fluororesin particles bind the catalyst particles, and at this time, the fluororesin particles bind the catalyst particles and the interparticle pores 8A formed with the catalyst particles. The reaction gas is flowed through, and the catalyst particles are precious metal particles supported on a catalyst carrier.The catalyst carrier is an agglomeration of primary particles of carbon black, and the secondary particle size is in the range of 200 to 500 particles. This is achieved by impregnating the internal holes 14 of the catalyst particles with an electrolytic solution.

[Effect]

When the primary particle size is in the range of 200 to 500 particles, phosphoric acid is well retained within the catalyst particles by capillary action. 500
When the amount exceeds that of humans, the ability to retain phosphoric acid decreases.

If the number of participants is less than 200, it will be difficult to form an electrode catalyst layer.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

- Arithmetic mean particle size of particles is 300, bulk density is 0.1g
/cc, 100 g of carbon blank powder with a specific surface area of 100 m" was dispersed in ion-exchanged water, a predetermined amount of chloroplatinic acid solution whose concentration was adjusted so that 10% platinum was supported per unit weight of carbon was added, and the temperature was 50°. After homogeneous dispersion with C, a reducing agent such as formic acid or hydrazine with a 0.1 to 0.3 molar concentration is removed to reduce chloroplatinic acid and at the same time deposit microcrystals of platinum on the surface of the carbon powder. The resulting platinum-supported carbon dispersion was filtered, thoroughly washed with ion exchange solution, and then dried in a vacuum dryer with adjustable atmosphere to obtain a catalyst.Next, the above catalyst was soaked in ion exchange water. After uniformly dispersing, add 100% of the fluororesin based on the weight of the catalyst and mix uniformly to create a dispersion of the catalyst and fluororesin.Next, the above dispersion is poured into a porous carbon material. It was coated on top by a blade method, a spray method, etc., dried, and fired to obtain a fuel cell electrode in which an electrode catalyst layer was laminated on a porous carbon base material.

FIG. 3 is a diagram showing the pore distribution of the electrode catalyst layer according to the example of the present invention, and the peak 1 is the internal pore 14 in the catalyst particle 4. The peak 12 corresponds to the interparticle pores 8A between the catalyst particles 4 and the fluororesin particles 5, and the interparticle pores 8B between the catalyst particles. Fourth
The figure is a diagram showing the pore distribution of a conventional electrode catalyst layer with peak 1.
3, the peaks of interparticle pores 8A and 8B corresponding to the internal pores 14 in the catalyst particles 4 are masked by the peak 13.

It can be seen from FIGS. 3 and 4 that by reducing the primary particle diameter, the internal pores 14 within the catalyst particles become smaller.

FIG. 2 is a diagram showing changes over time in the characteristics of a fuel cell using an electrode catalyst layer according to an embodiment of the present invention (characteristic line 9) in comparison with the characteristics of a conventional fuel cell (characteristic line 10). Since the fuel cell electrode catalyst layer according to the embodiment of the present invention has a high ability to retain phosphoric acid, the interparticle pores 8A and 8B through which the reaction gas passes are not blocked, and high characteristics can be maintained for a long period of time.

It is effective that the particle diameter is within the range of 200 to 500 people, including the above-mentioned 300 people. If the number exceeds 500, the internal pores of the catalyst particles will become larger and the phosphoric acid retention capacity will decrease. 2
If the particle size is smaller than 0.00, the particles are too fine to form an electrode catalyst layer.

[Effects of the Invention] According to the present invention, the catalyst has catalyst particles and fluororesin particles, and the fluororesin particles bind the catalyst particles, and at this time, the reaction gas enters the interparticle pores formed with the catalyst particles. The catalyst particles are made by supporting precious metal particles on a catalyst carrier, and the catalyst carrier is an agglomeration of primary particles of carbon black, and the primary particle size is in the range of 200 to 500 particles. Since the internal pores of the catalyst particles are impregnated with electrolyte, the internal pore diameter of the catalyst particles becomes smaller, and as a result, the phosphoric acid retention capacity of the catalyst particles increases, and the pores between the catalyst particles and the fluororesin particles become smaller. Since phosphoric acid does not migrate into the pores between particles, a fuel cell electrode catalyst layer with excellent reliability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the electrode catalyst layer of a fuel cell, FIG. 2 is a diagram showing the characteristics of the electrode catalyst layer according to an embodiment of the present invention in comparison with the characteristics of a conventional electrode catalyst layer, and FIG. 4 is a diagram showing the pore distribution of the electrode catalyst layer according to the example of the present invention, and FIG. 4 is a diagram showing the pore distribution of the conventional electrode catalyst layer. 4: Catalyst particles, 5: Fluororesin particles, 8A, 8B: Patent attorney Iwao Yamaguchi - 2nd Figure 1 10' Wheel stroke per hour Figure 2

Claims (1)

[Scope of Claims] 1) A device that has catalyst particles and fluororesin particles, where the fluororesin particles bind the catalyst particles, and at this time, a reaction gas is flowed into the interparticle pores formed with the catalyst particles. The catalyst particles are made by supporting noble metal particles on a catalyst carrier, and the catalyst carrier is an agglomeration of primary particles of carbon black, and the primary particle diameter is in the range of 200 to 500 Å, and the inner fineness of the catalyst particles is An electrode catalyst layer for a fuel cell, characterized in that the pores are impregnated with an electrolyte.