JPS63116366A - Fuel cell - Google Patents

Abstract

PURPOSE:To reduce the quantity of a precious metal catalyst used for a unit cell and obtain a cell structure effectively utilizing the precious metal catalyst without deteriorating the cell performance by changing a material constituting the supply path of a phosphoric acid electrolyte from precious metal-borne carbon powder to precious metal-unborne carbon powder. CONSTITUTION:In a catalyst layer 20a constituted of a hydrophilic material, the diffusivity of a reaction gas is very bad due to the wetting by an electrolyte, and catalyst activity rarely exists. Therefore, a material not containing a precious metal catalyst, i.e., precious metal catalyst-unborne carbon powder and silicon carbide, is used instead of a material containing a precious metal catalyst such as precious metal-borne carbon powder to form the material constituting a supply path formed in a band shape. Accordingly, the utilization factor of the precious metal catalyst used for a unit cell is improved, and the quantity of the precious metal catalyst can be reduced without deteriorating the cell performance.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to fuel cells, and particularly aims to effectively utilize a precious metal catalyst, and to increase the amount of precious metal catalyst used without causing a decrease in cell performance. This invention relates to a fuel cell that has been improved in order to reduce the

(Prior Art) Fuel cells are conventionally known as devices that directly convert chemical energy contained in fuel into electrical energy. This fuel cell usually has a pair of porous electrodes sandwiched between a matrix holding an electrolyte, and a fuel gas such as hydrogen is brought into contact with the back surface of one, and an oxidizing agent gas such as oxygen is brought into contact with the back surface of the other electrode. It is constructed by stacking a plurality of unit cells that output electrical energy from between the electrodes by making use of the electrochemical reaction that occurs when the fuel gas and oxidizing gas are brought into contact with each other. Electrical energy can be extracted with high conversion efficiency as long as it is supplied.

FIG. 5 shows an example of the structure of a unit cell in a bipolar fuel cell based on the above principle and using phosphoric acid as an electrolyte. That is, a pair of opposing gas diffusion electrodes (anode electrode 2, cathode electrode 3) coated with catalyst layers 1a and 1b.
) A matrix 4 holding phosphoric acid as an electrolyte is disposed between the cells, and is integrated to form a unit cell. A conductive separator 5 having gas flow passages is disposed on both sides of this unit cell, and a fuel gas 6 and an oxidizing gas 7 are normally flowed in directions perpendicular to each other to perform a power generation reaction.

(Problems to be Solved by the Invention) However, in such a unit cell configuration, when the battery is operated for a long time, the phosphoric acid electrolyte dissipates and disappears, resulting in a decrease in battery performance.

Therefore, in order to eliminate such drawbacks, recently, the 6th
Apply catalyst layers 1a and lb on one side as shown in the figure,
A unit cell is constructed by sandwiching a matrix 4 between a pair of porous electrodes, so-called ribbed electrodes (anode electrode 10 and cathode electrode 11), each having reaction gas flow passages 8 and 9 formed on the other surface. Ribbed to extend battery life by holding phosphoric acid electrolyte uniformly over the entire surface, and to reduce contact resistance by improving adhesion of porous parts when tightening batteries when stacking unit cells. An electrode type has been proposed.

Here, the purpose of holding the phosphoric acid electrolyte in the anode electrode lO is to prevent the phosphoric acid electrolyte in the matrix 4 from being depleted as the single power generation reaction progresses, and to allow the phosphoric acid electrolyte to be replenished as appropriate. be. Therefore, the catalyst layer 1a applied to the anode electrode 10 is made of a hydrophilic substance so that the retained phosphoric acid electrolyte can be easily replenished.

In addition, an anode electrode 10 and a cathode electrode 1 with ribs
Even if the phosphoric acid electrolyte is simultaneously held in both of the cathode electrode 11 side, H and O are generated by the power generation reaction on the cathode electrode 11 side, so the held phosphoric acid electrolyte gets wet, and as a result, the cathode electrode 11 The oxidant gas supplied from the back side of the cell becomes difficult to be supplied to the reaction interface, significantly deteriorating the battery characteristics.

Therefore, it is common to have the phosphoric acid electrolyte held only in the anode electrode 10.

Furthermore, if the catalyst layer 1a applied to the anode electrode 10 is made of a material that is too hydrophilic, the anode electrode 10
The diffusion of fuel gas supplied from the back side of the
It had the disadvantage of being hindered by the retained phosphate electrolyte.

In addition, in order to improve the diffusion of the fuel gas supplied from the back surface of the anode electrode 10 to the reaction interface, the catalyst layer 1a is
When water repellency was imparted to the fuel cell, there was a drawback that the retained phosphoric acid electrolyte could not be sufficiently replenished.8 Therefore, as shown in Figure 2, a fuel gas flow passage 8 was provided on the back side. Catalyst layers 20 coated on the other surface of the ribbed anode electrode 10 were arranged at regular intervals in a direction perpendicular to the fuel gas flow path 8 . A fuel cell has been devised and manufactured that includes a band-shaped catalyst layer 208 made of a water-based substance and a water-repellent catalyst JW20b disposed therebetween.

However, it was found that the catalyst layer 20a made of a hydrophilic substance had extremely poor diffusion of the reaction gas due to wetting by the electrolyte, and had almost no catalytic activity.

[Structure of the invention]

(Means for Solving the Problems and Their Effects) Accordingly, the present invention provides a fuel cell of a type having a strip-shaped supply channel formed in an anode catalyst layer. By forming the material from a material containing a noble metal catalyst, such as carbon powder supporting a noble metal, to a material not containing a noble metal catalyst, that is, using carbon powder and silicon carbide powder that do not support a noble metal catalyst, the amount used per unit cell can be changed. This makes it possible to increase the utilization of precious metal catalysts and reduce the amount of precious metal catalysts without deteriorating cell performance.

(Example) The present invention will be described in detail below based on examples.

(First Example) In this example, as shown in FIG. band-shaped carbon layers 20a made of a hydrophilic substance arranged at regular intervals in a direction perpendicular to the fuel gas flow path 8;
and a water-repellent catalyst layer 20b disposed between them.

Here, the catalyst J120 is formed as follows.

That is, the hydrophilic carbon layer 2 serves as a phosphoric acid supply path.
For 0a, Slaflon 30J (manufactured by Mitsui Fluorochemical Co., Ltd.) was used by kneading distilled water (700aQ), carbon powder not carrying a noble metal catalyst (30i), and Teflon dispersion solution (14.3mQ).

Then, this coating mixture is applied onto the anode electrode substrate by a spray method. At this time, the water-repellent catalyst layer 20
The area to be coated with b is sealed to prevent the hydrophilic catalyst layer from being formed during the coating operation.

Next, the water-repellent catalyst layer 20b is coated with distilled water (700%
Co., Ltd.), platinum-supported carbon black (301)).

By kneading Teflon solution (14.3 mQ),
A similar coating mixture is synthesized and applied by spraying in the same manner as the hydrophilic coating mixture. In this case as well, the portion where the hydrophilic catalyst layer 20a is formed is sealed to prevent the formation of a water-repellent catalyst layer during the coating operation.

The catalyst layer 20 coated as described above was applied at a weight of 20 kg/cn.
After pressing at i, heat treatment was performed at 327° C. for 30 minutes in a N2 atmosphere to form an anode electrode.

(Second Example) The components of the slurry-like coating mixture shown in the first example were distilled water (700aQ), carbon powder not supported with a noble metal catalyst (30i), and Teflon dispersion solution (14,3
It was synthesized by kneading d) and silicon carbide I (5g). Note that the carbon powder was used to form an anode electrode under all other conditions similar to those of the first example.

A small cell was constructed using the anode electrodes formed according to the first example and the second example, and an electromotive test was conducted under the following conditions. The results are shown in FIG.

The line shown in FIG. 1 shows the result according to the first embodiment, the -111 line shows the result according to the second embodiment, and the -1 line shows an example using conventional precious metal-supported carbon for comparison.

〔Effect of the invention〕

As described above, according to the present invention, the amount of precious metal catalyst used per unit cell can be reduced by changing the material constituting the supply path for the phosphoric acid electrolyte from carbon powder supporting precious metals to carbon powder not supporting precious metals. It has now become possible to create a cell configuration that effectively utilizes precious metal catalysts without reducing battery performance.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of the fuel cell of the present invention, FIG. 2 is a block diagram of the fuel cell of the present invention, and a block diagram of a third same-position cell. la, lb...catalyst layer, 2...anode electrode, 3...cathode electrode, 4...matrix, 5...separator, 6...fuel gas, 7...oxidant gas, 8... Fuel gas flow path, 9... Oxidizing gas flow path, 10... Anode electrode, 11... Cathode electrode, zO... Catalyst layer, 2
0a...Catalyst layer having hydrophilicity, 20b...Catalyst layer having water repellency, 30...Catalyst layer having water repellency N'71 Time 1fl (/1rS) Fig. 1 Fig. 2 Fig. 3 Figure 4

Claims (2)

[Claims] (1) A flow path for fuel gas or oxidizing gas is formed on one side of a conductive porous substrate that sandwiches a matrix holding an electrolyte, and a catalyst layer is coated on the other side. The anode electrode is configured by stacking a plurality of unit cells that output electrical energy under conditions in which fuel gas or oxidant gas is distributed through each of the reaction gas flow paths. In a fuel cell in which a phosphoric acid electrolyte for replenishment is held in an electrode and a belt-shaped phosphoric acid replenishment path is formed in a catalyst layer in a direction perpendicular to a fuel gas flow path formed in an anode electrode, the belt-shaped replenishment path is formed in a catalyst layer. 1. A fuel cell characterized in that the channel is formed from a mixture of carbon powder and fluororesin that does not support a noble metal catalyst. (2) The fuel cell according to claim 1, wherein the phosphoric acid supply path is made of carbon powder, silicon carbide (SiC), and fluororesin that do not carry a noble metal catalyst.