JPH025365A - Electrode catalyst for fuel cell - Google Patents

Abstract

PURPOSE:To more promote activation to obtain an electrode catalyst layer having a good polarization characteristic by decreasing a quantity of the fine grains of fluororesin as water repellent material to a quantity necessary for binding taking advantage of the water repellency of acetylene black. CONSTITUTION:A fine grain of catalyst 7 and a fine grain of acetylene black 8 are bound by a fine grain of fluororesin 3. A water repelling action is made by the fine grain of acetylene black 8 and the fine grain of fluororesin 3. The purity of the fine grain of acetylene black 8 is high and does not have a group having electrolyte and affinity (e.g., carbonyl group, carboxyl group, aldehyde group, etc.) on the surface. Its water repellency, therefore, is higher than the other carbon carriers. This water repelling action makes it possible to reduce fluororesin as water repellent material and therefore, the degree that a fine grain is covered with fluororesin decreases and the electrode catalyst can be more activated than before; as a result, it is possible to obtain an electrode catalyst layer for fuel cell having a good polarization characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrode catalyst layer for a fuel cell, and particularly to an electrode catalyst layer with excellent activity.

[Conventional technology]

A fuel cell is a device that directly converts the chemical energy of fuel into electrical energy, and its configuration is as shown in Figure 3, with an electrolyte layer (not shown) made of phosphoric acid in between.
6 (electrode catalyst layer 5 fused onto carbon electrode base material 4) are arranged facing each other, and fuel gas and oxidant gas are supplied to each electrode from an external gas supply system, and each electrode The oxidant gas and the fuel gas are individually electrochemically reacted on the catalyst fine particles 7, and as a result, electrical energy can be taken out of the system.

The fine catalyst particles 7 used are those in which fine metal particles 1 such as platinum are supported on a catalyst carrier 2 such as carbon black, and the fine catalyst particles 7 are bonded by fine particles 3 of fluororesin made of polytetrafluoroethylene (PTFE). The electrode catalyst layer 5 is formed.

In such an electrode catalyst layer, the fluororesin fine particles not only bind the catalyst fine particles 7, but also perform a water repellency function so that the electrolyte impregnated into the electrode catalyst layer has an appropriate level of water repellency.

Since the contact angle of the electrolyte on the blue gold i fine particles covering the surface of the catalyst carrier such as carbon black is small, the electrode catalyst layer is easily wetted by the electrolyte, and the pores of the electrode catalyst layer are blocked by the electrolyte, which inhibits the diffusion of the reaction gas, resulting in 1. This is because performance deteriorates. Conventionally, the solution to this problem was to mix in large amounts of fine particles of fluororesin, which has strong water repellency.

(Problem to be solved by the invention) However, since the fluororesin also functions as a binder for the catalyst fine particles, it needs to be melted, and since the molten fluororesin covers the surface of the catalyst fine particles, a large amount of fluororesin is required. There was a problem in that if mixed, the electrode performance would deteriorate.

The present invention has been made in view of the above-mentioned points, and its object is to provide a catalyst layer for fuel cells, which is less active, by using non-melting creeping wood.

[Means to solve the problem]

According to the present invention, the above-mentioned purpose is achieved by transferring catalyst fine particles 7 supported on a catalyst carrier to fluororesin fine particles 3.
This is achieved by forming an electrocatalyst layer consisting of fine catalyst particles, fine particles 8 of acetylene black, and fine particles of fluororesin in the first scraped catalyst layer 5 for fuel cells bound and water-repellent.

The acetylene black fine particles 8 have high purity and do not have groups on the surface that have an affinity for electron Mf (for example, carbonyl groups, carboxyl groups, aldehyde groups, hydroxyl groups, etc.). Therefore, it has stronger water repellency than other carbon carriers.

[Effect]

By utilizing the water repellency of the acetylene platter, it is possible to reduce the amount of fluororesin fine particles used as a repellent material. The fine particles of fluororesin need only be as strong as necessary for binding. Since the acetylene blank does not melt, it does not cover the surface of the catalyst fine particles.

〔Example〕

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

(Example 1) FIG. 1 is a schematic cross-sectional view of an electrode containing an electrolyte catalyst according to an example of the present invention. The catalyst fine particles 7 and the acetylene blank fine particles 8 are bound by the fluororesin fine particles 3. The water-repellent action is performed by the acetylene black fine particles 8 and the fluororesin fine particles 3. Such an electrocatalyst layer and electrode can be prepared as follows.

40 of an aqueous solution containing 0.1% nonionic surfactant by volume.
Prepare 0-. 1 piece of platinum is placed on a catalyst carrier 2 made of activated carbon.
Catalyst fine particles 7 supported at a ratio of 0% by weight are prepared.

6 g of this catalyst fine particle 7 and 6 g of acetylene black were added to the surfactant aqueous solution, and then PTFE disvergyran (PTFE) containing 5% surfactant by weight was added.
Add 13- (containing 60% by weight) and disperse using ultrasonic waves.

The dispersion obtained by the above method was heated at a temperature of 60°C to 100°C.
Heat and concentrate while stirring. When approximately 360% of water is evaporated, a highly viscous mixed concentrate is obtained.

Next, the mixed concentrate is kneaded using a double-arm kneader. At this time, the fine particles of PTFE are made into fibers and are well entangled. The kneader is operated at a rotation speed of 50 rpm for 4 to 5 minutes. In this step, the PTFE The fibers of the particles are not aligned in a fixed direction but are intertwined in arbitrary directions.

The paste obtained by kneading is extruded using an extrusion molding machine into a plate-shaped molded body with a thickness of 5 days and a length of 50 m. In this extrusion molding, the fine particles of PTFH are arranged in a fixed direction. This orientation increases the mechanical strength of the electrocatalyst layer sheet, and this extrusion molding also serves as a preliminary step for the next calender roll step.

The plate-shaped molded body, which was extruded to a thickness of 5 m, was formed into a sheet-shaped electrode catalyst layer having a thickness of 0.2 mm using a calender roll.

The obtained sheet-like electrode catalyst layer was placed on the carbon electrode base material 4 and hot press bonded at a temperature of 350 to 370°C and a pressure of LO kg/- to prepare a fuel cell electrode contact 6A having an electrocatalyst layer 5. can do.

(Example 2) Electrode 6B is prepared in the same manner as in Example 1 except that the activated carbon in Example 1 is replaced with furnace black.

(Comparative example) In Example 1, acetylene black was not used, and PTFH disvergyran was used instead of 13-26-
Electrode 6C is prepared in the same manner as in Example 1 except that .

Polarization characteristics are determined using these electrodes 6A, 6B, and 6G as oxygen species and a 7N alkaline solution as an electrolyte. The results are shown in FIG. The electrode potential of electrodes 6A and 6B is H
It exhibits a more noble potential than electrode 6C based on g/Hg0t polar standard,
It turns out that it is less than a minute. This is because the activity of electrodes 6A and 6B is higher than that of tFIj6c. Also, the 1st pole potential during continuous discharge at a current density of 100mA/- is the 3rd
Even in the time-dependent change in electrode potential shown in the figure, the electrode 6A
, 6B is slightly superior to electrode 6C. It can be seen that it has a long lifespan.

〔Effect of the invention〕

According to this invention, in an electrode catalyst layer for a fuel cell in which catalyst fine particles, in which precious metal fine particles are supported on a catalyst carrier, are bound with fine fluororesin particles and made water repellent, catalyst fine particles, acetylene black fine particles, and a fluororesin are combined. Since an electrode catalyst layer consisting of fine particles is used, the water-repellent action of acetylene black can reduce the amount of fluororesin as repellent wood, which reduces the degree to which the catalyst fine particles are covered with fluororesin, and the electrode catalyst -i layer than before
As a result, it is possible to provide an electrode catalyst layer for a fuel cell that can be activated and has excellent decentralization characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an electrode including an electrode catalyst layer according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of an electrode including an electrode catalyst layer according to an embodiment of the present invention and a conventional electrode. The figure is a schematic cross-sectional view of the t-pole according to an embodiment of the present invention. 3: Fluororesin fine particles, 5: Electrode catalyst layer, 7: Catalyst fine particles, 8: Acetylene black fine particles. 1. Current GnA/crn)

Claims (1)

[Claims] 1) In a fuel cell electrode catalyst layer in which fine catalyst particles, in which fine metal particles are supported on a catalyst carrier, are bound with fine particles of fluororesin and made water repellent, the fine particles of catalyst, fine particles of acetylene black, and fine particles of fluororesin are combined. An electrode catalyst layer for a fuel cell characterized by: