JPH02207457A - Fuel cell - Google Patents

Abstract

PURPOSE:To enhance the reliability of a cell by forming grooves in which highly hydrophilic substances are filled in the same direction as gas passages in a porous electrode substrate. CONSTITUTION:A plurality of grooves 12 are formed on one side of each of porous substrates 10, 11 having a pair of ribs arranged on both sides of a matrix layer 1. The grooves 12 are formed in the same direction as gas flow passages 6, 7, and highly hydrophilic substances are filled in the grooves 12. By installing the grooves filled with highly hydrophilic substances, the matrix layer is directly connected to the porous electrode substrate retained with a phosphoric acid electrolyte, and the electrolyte is easily supplied to the reaction interface and the matrix layer from the electrode substrate. A fuel cell having high reliability can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a fuel cell having a gas diffusion electrode made of a ribbed porous substrate and using phosphoric acid as an electrolyte. .

(Prior Art) Fuel cells are conventionally known as devices that directly convert chemical energy contained in fuel into electrical energy. This fuel cell usually consists of a pair of porous electrodes placed with an electrolyte-impregnated matrix in between, and a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidizing gas such as oxygen is brought into contact with the back surface of the other electrode. This system extracts electrical energy from between the electrodes by bringing the oxidant gas into contact and utilizing the electrochemical reaction that occurs at this time.As long as the fuel gas and oxidant gas are supplied, the conversion efficiency is high. It is something that can extract electrical energy.

Incidentally, a unit cell of a fuel cell using phosphoric acid as an electrolyte is constructed as shown in FIG. 3, and a fuel cell stack is constructed by stacking a plurality of these unit cells. That is, in FIG. 3, the unit cell includes a matrix layer 1 impregnated with phosphoric acid as an electrolyte, and
On both sides thereof, a pair of ribbed electrodes 4.5 made of a porous body made of carbon material and having catalyst layers 2 and 3 added to one surface (matrix side) are arranged. Further, in the pair of ribbed electrodes 4 and 5, a fuel gas flow passage 6 and an oxidant gas flow passage 7 are formed, respectively, on the side opposite to the added surfaces of the catalyst layers 2 and 3. A fuel cell stack is constructed by alternately stacking a plurality of these unit cells with gas separation plates 8 in between.

In a fuel cell using an acidic electrolyte such as phosphoric acid as described above, the electrode reaction occurs in a solid phase consisting of a carbon base material supporting a catalyst, a liquid phase consisting of an electrolyte such as a phosphoric acid solution, or
This occurs in the coexistence of three gaseous phases consisting of a fuel gas and a reactant gas such as an oxidant gas. A place where three phases coexist in this way is generally called a three-phase zone, and the area of this three-phase zone greatly influences the electrode reaction of the fuel cell, that is, the cell characteristics. In other words, the smaller the area of the three-phase zone,
The cell characteristics deteriorate, and on the contrary, the larger the area, the more active the electromotive reaction becomes, making it possible to obtain a high-performance fuel cell.

In this way, when considering the area of the three-phase zone that affects the characteristics of the fuel cell, the supply of phosphoric acid to the liquid phase reaction interface activates the electromotive reaction in the fuel cell, and
It is an essential element in keeping the activated electromotive reaction stable for a long period of time. The electrolyte is also an important element in keeping the internal resistance of the cell to a minimum. In other words,
Depletion of electrolytes in the matrix leads to a decrease in cations, which are conductive species, in the matrix, increasing the electrical resistance of the cell and degrading the cell properties.

(Problems to be Solved by the Invention) However, in the conventional fuel cell as described above, there were problems to be solved as described below. That is, in a phosphoric acid electrolyte fuel cell, when an electromotive reaction is continued for a long period of time, a phenomenon is observed in which the phosphoric acid electrolyte inside the cell is carried out to the outside of the cell. Therefore, in order to supplement the phosphoric acid carried out from the reaction interface and the matrix layer, many systems have been proposed in which phosphoric acid is supplied by holding phosphoric acid in a porous body constituting the electrode. However, a technique for supplying phosphoric acid held in a porous electrode substrate to a phosphoric acid depleted area with sufficient efficiency has not yet been established.

The present invention was proposed to solve the above-mentioned drawbacks, and its purpose is to provide a highly reliable fuel cell that facilitates the supply of phosphoric acid electrolyte to the reaction interface and matrix layer. .

[Configuration of the Invention (Means for Solving the Problems)] The present invention comprises a matrix layer impregnated with an electrolyte,
A pair of ribbed electrodes made of a porous substrate having gas flow passages through which fuel gas and oxidizing gas flow are arranged on the back surface thereof, and the fuel gas and oxidizing gas are supplied to the gas flow passages, respectively. In a fuel cell for obtaining electrical energy, at least one of the pair of porous electrode substrates,
A plurality of grooves are formed in the same direction as the gas flow passages on a surface opposite to the gas flow passage formed on one side, and a substance having higher hydrophilicity than the matrix layer is filled in the grooves. This is a characteristic feature.

(Function) According to the fuel cell of the present invention, a plurality of grooves are formed on the surface of at least one of the pair of ribbed porous electrode substrates to be bonded to the matrix layer, and the catalyst layer in this portion is removed. By filling the groove with a hydrophilic substance, the matrix layer and the porous electrode substrate holding phosphoric acid can be directly bonded, and the movement of the held phosphoric acid to the reaction interface and matrix layer is prevented. It becomes very easy.

(Example) Hereinafter, an example of the present invention will be specifically described based on FIGS. 1 and 2. Incidentally, the same members as those of the conventional type shown in FIG. 3 are given the same reference numerals, and the description thereof will be omitted.

In this embodiment, as shown in FIG. 1, gas flow channels are formed on at least one surface of a pair of ribbed porous electrode substrates 10 and 11 that are placed opposite each other with a matrix layer 1 in between. A plurality of grooves 12 are formed on the surface opposite to the gas flow passages 6 and 7 in the same direction as the gas flow passages 6 and 7. Note that the catalyst layer 2.3 is not provided in the portion where the groove 12 is formed. Furthermore, the grooves 12 are filled with a substance (for example, silicon carbide) that is more hydrophilic than the matrix layer.

Next, an example of a method for manufacturing a porous electrode substrate according to the present invention will be described. That is, a porous substrate (about 3 mm thick) made of carbon fiber with a porosity of about 50 to 70% was shaped to a thickness of 2 mm. Next, a depth of 1.0 mm and a width of 1.5 mm will be used as a gas flow path.
A groove was formed. In addition, a groove according to the present invention with a depth of 0.8 mm and a width of 2 mm was formed on the opposite surface from the gas flow passage. At this time, the interval between the gas flow passage and the groove according to the present invention is 1 mm.
And so. Further, after forming the porous electrode substrate as described above, the groove portion according to the present invention was sealed and a catalyst layer was applied. The powder electrostatic coating method was used as the coating method, but
The method is not particularly limited.

In addition, the powder electrostatic coating method was used as a method for forming the matrix layer, but the adhesion to the porous electrode substrate is tight;
The method is not particularly limited as long as there are no voids or the like.

Furthermore, a hydrophilic substance was filled into the grooves of the porous electrode base formed in this manner. This hydrophilic substance may be any substance as long as it is more hydrophilic than the matrix layer, has phosphoric acid affinity, and is heat resistant (230°C). Here, silicon carbide having a smaller particle size than the silicon carbide used for the matrix layer was used.

In the fuel cell of this example having such a configuration,
By forming a groove for filling a hydrophilic substance in at least one of a pair of porous electrode substrates placed opposite each other, the matrix layer and the porous electrode substrate holding phosphoric acid are directly bonded. This facilitates the supply of phosphate electrolyte from the porous electrode substrate to the reaction interface and matrix layer.

Further, a unit cell was formed using such a porous electrode substrate, and an electromotive test was conducted under the following conditions. The results are shown in FIG. In addition, in the figure, the solid line shows the case where the porous electrode base according to the present invention is used, and the dotted line shows the case where the conventional porous electrode base is used. In addition, in FIG. 2, the vertical axis shows the cell voltage, and the horizontal axis shows the time scale, and the transition of the cell voltage is shown.

(Test conditions) Normal pressure, 205°C, 220 mA/am2 Fuel gas utilization rate 30% Oxidizing gas utilization rate 30% As described above, when a unit cell is constructed using the porous electrode substrate of the present invention, it will last for a long time. A stable cell voltage can be maintained.

Note that the present invention is not limited to the embodiments described above, and the number of grooves formed in the porous electrode base can be set as appropriate. Further, the hydrophilic substance filled in the grooves may be any substance as long as it is more hydrophilic than the matrix layer and has phosphoric acid affinity and heat resistance.

[Effects of the Invention] As described above, according to the present invention, at least one of a pair of porous electrode substrates has four gas flow passages formed on one surface thereof, and four gas flow passages formed on the opposite surface thereof in the same direction. A reliable method that facilitates the supply of phosphate electrolyte to the reaction interface and matrix layer by forming multiple grooves and filling the grooves with a substance that is more hydrophilic than the matrix layer. It is possible to provide high fuel cells.

[Brief explanation of the drawing]

FIG. 1 is an enlarged perspective view of a unit cell showing an embodiment of the fuel cell of the present invention, FIG. 2 is a cell characteristic diagram showing the effects of the fuel cell of the present invention, and FIG. 3 is a unit cell of a conventional fuel cell. FIG. 1... Matrix layer, 2.3... Catalyst layer, 4.5
... Ribbed electrode, 6... Fuel gas flow path, 7...
- Oxidizing gas flow path, 8... gas separation plate, 10.11
...Porous electrode base, 12...grooves. 10o0 (clear weather). Figure ys Figure

Claims (1)

[Scope of Claims] A pair of ribbed electrodes made of a porous substrate are arranged with a matrix layer impregnated with an electrolyte sandwiched therebetween, and gas flow passages through which fuel gas and oxidizing gas flow are formed on the back surface of the electrodes. In a fuel cell that obtains electrical energy by supplying a fuel gas and an oxidant gas to the gas flow passages, respectively, a surface opposite to the gas flow passage formed on at least one surface of the pair of porous electrode substrates. A fuel cell characterized in that a plurality of grooves are formed in the same direction as the gas flow passage, and the grooves are filled with a substance having higher hydrophilicity than the matrix layer.