JPS62154464A - Electrode catalyst layer for fuel cell - Google Patents

Abstract

PURPOSE:To advance electrochemical corrosion reaction of carbon and to prevent decrease in the surface area caused by aggregation of noble metal catalyst to retain stable three phase interface over a long period of time by adding noble metal non-supporting carbon powder to an electrode catalyst layer. CONSTITUTION:Electrodes comprising porous carbon paper 2, 4 supported with electrode catalysts 1, 3 are arranged on both sides of an electrolyte layer 5, and a bipolar separating plate 6 having fuel gas and oxidizing agent gas supply grooves 7, 8 is arranged in the outside of each electrode. They are stacked to form a phosphric acid electrolyte fuel cell. In the cell, noble metal non- supporting carbon powder is added to the electrode catalyst layers 1, 3. Thereby, decrease in cell voltage of the fuel cell does not appear and high voltage is retained even after long continuous operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell electrode catalyst layer comprising carbon powder supporting a noble metal catalyst and a binder.

[Technical background of the invention and its problems] A fuel cell is a device that directly converts the energy released in the oxidation reaction into electrical energy by oxidizing the chemical energy of fuel through an electrochemical process. A power generation system using this fuel cell has a thermal efficiency of 40 to 50% even on a relatively small scale, and is expected to far surpass new thermal power generation. In addition, SO, which is a pollution factor that has become a major social problem in recent years,
x.

It emits extremely low NOx and does not require a large amount of cooling water as it does not contain a combustion cycle within the power generation device.
In principle, high energy conversion efficiency can be expected, such as low noise, and there are few environmental problems such as noise and exhaust gas, as well as good responsiveness to load fluctuations. There are high expectations and interest in research into practical application.

By the way, the above-mentioned fuel cell usually has a pair of porous electrodes arranged with an electrolyte in between, and a fuel electrode such as hydrogen is brought into contact with the back surface of one N electrode, and the other electrode is An oxidizing agent such as oxygen is brought into contact with the back surface of the electrode to form an oxidizing agent electrode, and the electrical energy generated by the electrochemical reaction occurring at this time is extracted from between the pair of electrodes. In this case, an acidic solution such as phosphoric acid is generally used as the electrolyte.

Further, the porous electrode is usually made of carbon paper J:
A noble metal catalyst is supported on a porous carbon substrate.

In a fuel cell that uses an acidic electrolyte such as phosphoric acid, the electrode reaction is performed, for example, as described above, using a solid phase consisting of a carbon base material supporting a member Kinnagi catalyst, or an electrolyte such as a phosphoric acid solution. This occurs where three phases coexist: a liquid phase consisting of a fuel gas and a gas phase consisting of a reactant gas such as a fuel gas and an oxidant gas. A place where these three phases coexist is generally called a three-phase zone, and the electrode reaction and cell characteristics of the fuel cell are affected by the area of this three-phase zone. That is, the smaller the area, the lower the battery characteristics, and conversely, the larger the area, the better the battery characteristics, making it possible to obtain a high-performance fuel cell.

As mentioned above, when considering the area of the three-phase zone that affects the fuel cell characteristics, it is essential to maintain the surface area of the 5-metal catalyst disposed in the porous electrode. However, the surface area of such an electrode catalyst decreases as the fuel R4 battery operates, and as a result, the area of the three-phase interface decreases, so the electrode reaction does not take place sufficiently, leading to a decline in battery characteristics. It was something that connected us.

Possible factors that cause such a decrease in the surface area of the electrode catalyst include dissolution of the noble metal catalyst in the electrolytic shell solution, granulation due to aggregation of the noble metal catalyst, and aggregation of the supported catalyst due to corrosion of the carbon support. Therefore, conventional countermeasures have been taken such as preventing dissolution by alloying noble metal catalysts and preventing corrosion of carrier carbon by using crystallized carbon carriers.

[Object of the Invention] The present invention solves the problems of the conventional electrode catalyst layer for fuel cells described above. The purpose is to create an electrode catalyst layer for fuel cells that can maintain high cell characteristics by preventing the surface area of the precious metal catalyst from decreasing and maintaining the area of the three-phase interface. It is about providing.

[Summary of JIIi Akira] The fuel cell m-electrode catalyst base of the present invention is a fuel cell m-electrode catalyst base made of carbon powder supporting a noble metal catalyst and a binder, in which carbon not supported with a noble metal catalyst is contained in the electrode catalyst layer. By adding the powder, the electrochemical corrosion reaction of carbon is prevented from occurring in the carbon powder supported by the mountain metal, and instead, the corrosion reaction is allowed to proceed in the added carbon, and the corrosion reaction is caused by the agglomeration of the member Kinnagi catalyst. This prevents the surface area from decreasing and allows a stable three-phase interface to be maintained over a long period of time.

[Example of the Invention] An example of the present invention will be specifically described below with reference to FIGS. 1 to 3.

■First Example *Structure* In the serious tM example, as shown in Fig. 1, ? 1! Electrodes made of porous carbon paper 2.4 holding an electrode catalyst 1.3 are arranged on both sides of the solute layer 5, and supply grooves 7 for supplying fuel gas and oxidizing gas to both outsides of these electrodes are arranged. In this phosphoric acid electrolyte fuel cell, a bipolar separator 6 having a polarity of .8 is disposed and laminated, and a carbon layer not carrying a noble metal catalyst is added to the electrode catalyst layer 1.3.

Note that the cathode electrode used in this example was VX
It was produced by heat-treating C-72R (manufactured by Cabot, USA) carbon black at 2600°C for 2 hours, supporting 7% platinum, and adding 10% activated carbon as carbon powder that does not support a noble metal catalyst. It is something.

*Function* In this example having the 8I structure as described above, the battery characteristics as shown in FIG. 2 were exhibited. That is, in the figure, the curve shown by solid line A shows the cell characteristics when the fuel cell electrode catalyst layer of this example is used for the cathode electrode, and the curve shown by point IB shows the cell characteristics when the fuel cell electrode catalyst layer of this example is used as the cathode electrode. Conventional fuel cell without added carbon powder 9!1. This is a diagram showing the characteristics of a tS pond when the layer is used as a cathode electrode. The battery used here was the fuel-flour battery shown in FIG. 1, and was operated continuously under conditions of a discharge current of 220 mA, /Cm2, 205° C1, and normal pressure.

As shown in Fig. 2, in the fuel cell using the fuel cell electrode catalyst layer of this example, no decrease in the cell voltage of the fuel cell was observed even after continuous operation for a long time, and the cell voltage was high. Characteristics can be maintained.

In addition, after 8,000 hours of continuous operation, X-ray diffraction of the cathode catalysts used in these fuel cells revealed an increase in particle size (after the conventional noble metal catalyst particle time) and due to solidification. The noble metal catalyst particle diameter of the catalyst layer according to this example was 60A, and no change was observed.

As described above, by adding and covering the Xfi electrode catalyst layer for a fuel cell with carbon powder supporting a noble metal catalyst, the increase in the particle size of the noble metal catalyst was suppressed and the cell properties were improved.

*Other practical examples: Toy T The present invention is not limited to the above-described embodiments, and similar effects can be obtained with an anode electrode.

■Second Example By the way, the 7-node electrode catalyst contains H2S, NH3, C
There is a problem in that the performance of the fuel cell cannot be maintained for a long period of time because the fuel gas is mixed with impurities that poison the electrode catalyst, such as carbon dioxide.

Therefore, among these impurities, platinum-ruthenium and gold supported on carbon are resistant to CO, which is difficult to remove.
Rhenium, tantalum, tungsten, molybdenum, silver,
A ternary alloy consisting of one selected from rhodium, osmium, iridium, etc. (USP No. 35064)
94>, or as another method, a method in which an alloy of platinum and aluminum is applied on the body and then the aluminum is eluted and removed (USP 342849)
0), etc., but these methods are not sufficient, and when a fuel cell is operated for a long period of time,
Its performance sometimes deteriorated.

The second actual flow example is a non-membered metal bending catalyst of the first embodiment.
In addition to the method of adding carbon powder, platinum-palladium (Pt/Pd
) By using graphitized carbon that supports fine alloy particles, even when the fuel cell is operated for a long time,
This makes it possible to maintain high performance.

*Structure* In this example, as the graphitized carbon, 1 q of VVal canXC-72R manufactured by Kabotsu 1 was activated with steam at 900° C. and used. Further, the platinum-palladium alloy used is one obtained by impregnating graphitized carbon with a mixture of platinum and palladium chlorides and then reducing the mixture with a hydrogen stream according to US Pat. No. 3,510,355.

The negative metal content in the catalyst is 2 to 10 wt%, and the atomic ratio of platinum to palladium is 5 conehart (USP440
7906) showed optimal characteristics in the thighs of 50:50
The ratio of The graphitized carbon-supported alloy catalyst thus obtained was heated at 350°C in a C atmosphere for 20 minutes, and then at 900°C in a N2 atmosphere for 1 hour.
Further, the material was heat-treated at 350° C. for 20 minutes in a CO atmosphere.

In addition, as an electrode, Teflon dispersion (manufactured by Mitsui Fluorochemical Co., Ltd., TCflon30-
J) was added so that the amount of Teflon in the total catalyst mixture was 40 wt%, and this suspension was applied on a porous substrate.
The sample was fired at 330° C. for 20 minutes in 2 atmospheres.

Nido effect* In this example J3 with grooves formed in this way, the above electrode was cut out as an electrode for a half cell, and 100% phosphoric acid, 18
When the change in 200 mA/hour was investigated in a bubbling gas of 70% H2 + 30% CO at 0°C, the results shown in Figure 3 were obtained. For comparison, FIG. 3 shows the change in polarization characteristics over time when the same electrode catalyst without heat treatment was used in a CO atmosphere.

That is, as is clear from Fig. 3, in an electrode using a catalyst heat-treated in a CO atmosphere, the magnitude of the overvoltage of the hydrogen oxidation reaction remains almost constant over a long period of time, as shown by solid line C. However, the hydrogen overvoltage of the electrode using an unheated catalyst in a CO atmosphere is
As shown by the dotted line, it increases rapidly after about i ooo time.

In this way, in the electrode using the catalyst of this example, the polarization is small even at a high COW concentration of 30% in the fuel gas, and even when the battery is operated for a long period of time,
Able to maintain high performance.

[Effects of the Invention] As described above, the present invention provides an electrode contact for fuel cells that can maintain high cell characteristics by preventing a decrease in the surface area of the noble metal catalyst and maintaining the area of the three-phase interface! I
The I+ layer can be provided.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view showing the structure of a fuel cell using the fuel cell electrode catalyst layer X layer of the present invention, and FIG. 2 is a perspective view showing the structure of a fuel cell using the fuel cell electrode catalyst layer X layer of the present invention. FIG. 3 shows the i! in a fuel cell using the fuel cell electrode catalyst layer of the present invention. This shows how the polarization characteristics of the poles change over time. 1.3... Catalyst layer, 2,4... Carbon paper,
5... Electrolyte layer, 6... Bipolar separator, 7.8...
- Supply groove. Figure 1 FJ'1 (hrs) during operation 112 Figure 2 and Figure 3

Claims (3)

[Claims] (1) In a fuel cell electrode catalyst layer formed by applying carbon powder supporting a noble metal catalyst and a binder on a porous conductive substrate, carbon powder not supporting a noble metal catalyst is added to the catalyst layer. Characteristic electrode catalyst layer for fuel cells. (2) The electrode catalyst for a fuel cell according to claim 1, wherein the carbon powder supporting a noble metal catalyst is a highly crystallized carbon powder, and the carbon powder not supporting a noble metal catalyst is amorphous carbon. layer. (3) The noble metal supported carbon powder supports a platinum-palladium alloy on graphitized carbon, and furthermore, CO
The electrode catalyst layer for a fuel cell according to claim 1, which is heat-treated in an atmosphere and an N_2 atmosphere.