JPH0589892A - Matrix for fuel cell - Google Patents

Abstract

PURPOSE:To prevent semi-shortcircuiting and cross-over phenomena and continue superconductive reaction stably for a long period of time by providing different ion resistances along the flow of reaction gas within a plane of matrix layer pinched by a pos. electrode and neg. electrode. CONSTITUTION:The matrix layer 1 of a fuel cell is made so that the inlet 1a and output 1b have different layer compositions along the flow of reaction gas flowing in the direction of arrow. That is, the particle size of SiC constituting the layer 1a is adjusted, and the amount of phosphoric acid impregnation of electroconductive type is reduced, and thereby the ion resistance is increased. The current concentrated on the inlet is dispersed over the whole surface uniformly, and generation of a high temp. part is prevented. This prevents the cross-over and semi-shortcircuiting phenomena to cause cell deterioration likely generated by high temp. according to the conventional arrangement and accomplishes a fuel cell which continues electromotive reactions stably for a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell using phosphoric acid as an electrolyte, and more particularly to a matrix layer having SiC as a main component sandwiched between a positive electrode and a negative electrode.

[0002]

2. Description of the Related Art Conventionally, a fuel cell has been known as a device for directly converting the chemical energy of fuel into electrical energy. As an example of this fuel cell, a basic configuration example of a ribbed electrode fuel cell using phosphoric acid as an electrolyte is shown in FIG. That is, the matrix layer 1 holding phosphoric acid as an electrolyte is sandwiched between the pair of ribbed electrodes 2
The fuel electrode 2a and the oxidant electrode 2b, which are
A unit cell of a fuel cell is constructed. The ribbed electrode 2 is usually made of a carbon material, and a plurality of grooves are provided in parallel in directions orthogonal to each other, and catalyst layers 4a and 4b are respectively formed on the opposite surfaces thereof. Further, the grooves formed in the fuel electrode 2a and the oxidant electrode 2b respectively serve as flow passages for the fuel gas and the oxidant gas. Further, a fuel cell is constructed by stacking a plurality of the unit cells with the separator 3 interposed therebetween. The separator 3 is inductive and impermeable.

[0003]

By the way, in the fuel cell using phosphoric acid as an electrolyte, which is constructed as described above,
Since phosphoric acid which is an electrolyte has a low viscosity, it is very difficult to hold only phosphoric acid between the fuel electrode 2a and the oxidant electrode 2b. Therefore, generally, a suspension of polytetrafluoroethylene (PTFE), which is a fixing agent, and a fine powder having stable electrolyte resistance to phosphoric acid, such as silicon carbide (silicon carbide) powder. The mixed paste consisting of the liquid and additives such as a thickener is directly added to the fuel electrode 2
The matrix layer 1 is formed by coating the surfaces of the catalyst layers 4a and 4b of at least one of the electrodes a or the oxidizer electrode 2b, heat-treating them, and impregnating them with phosphoric acid.

What is important in forming the matrix layer 1 is to form the layer with a uniform thickness.
If the thickness of the matrix layer 1 is not uniform, or if there are defects such as voids, the cell has a lower bubble pressure (crossover phenomenon), a non-uniform current density distribution, or even fuel. This is because the electrode 2a and the oxidant electrode 2b locally contact with each other to cause an internal short circuit (semi-short phenomenon), and the performance thereof deteriorates.

However, even in the matrix layer 1 having the same composition and a uniform thickness so as not to cause such defects, the current density distribution in the cell plane is similar to the case where cells are continuously electromotively reacted. Difference, which causes a difference in the temperature distribution in the cell plane.In particular, at the high temperature part, the scattering of the electrolyte to the outside of the cell is accelerated, etc., and the bubble pressure decreases, and the cell is left for a long time. It may be difficult to stably continue the electromotive reaction. This is because even if the matrix layer is manufactured to have an extremely uniform thickness, the active material concentration is high near the reaction gas inlet of the electrode (particularly on the oxidant gas side), so that the catalytic reaction becomes more active. This causes a difference in current density distribution, which in turn causes a high temperature portion due to the disturbance in the temperature distribution, causing a problem.

From the above, the cell can be used for a long time,
For a stable electromotive reaction, the difference in temperature distribution in the cell plane can be reduced by making the current density distribution in the cell plane uniform, and the generation of high temperature parts can be suppressed over a long period of time. It turns out to be the most important condition essential for operation.

The present invention eliminates the above-mentioned drawbacks and prevents the semi-short phenomenon and crossover phenomenon due to the generation of a high temperature portion of the cell, and enables a stable electromotive reaction for a long time. A battery is provided.

[0008]

In order to achieve the above object, the present invention is such that the resistance of the matrix layer is varied along the flow direction of the reaction gas. That is, as described above, the ionic resistance of the matrix layer at the reaction gas inlet portion where the reaction proceeds more actively because the reaction gas concentration is high,
By increasing the ionic resistance of the reaction gas at the outlet, the concentration of the high current density portion at the inlet is prevented.

[0009]

In the fuel cell having the above means, it is possible to prevent the electric current flowing in the electrode plane from concentrating near the reaction gas inlet as in the conventional case. That is, the heat generation amount (Q) due to the current and the resistance is Q = I ² due to the current (I) and the resistance (R). In the relation of R, current (I)
The heat generation amount (Q) is reduced as

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to FIGS.

As shown in FIG. 1, the matrix layer 1 of the fuel cell according to the present invention has an inlet portion 1a and an outlet portion 1b along the flow of a reaction gas (oxidant gas) flowing in a direction indicated by an arrow.
With this, the composition of the matrix layer 1 is made different.

The entrance portion 1a of the matrix layer 1 shown by diagonal lines
Is composed of SiC (silicon carbide) powder having an average particle diameter of 5 μm, SiC having an average particle diameter of 1 μm, and Teflon (FEP), and a polyethylene oxide solution is used as a dispersant so that the weight ratio is 20: 2: 1. It is kneaded together and is formed on the electrode by the bar casting method.

The outlet portion 1b of the matrix layer 1 is
It is composed of SiC and Teflon (FEP) with an average particle size of 5 μm, and its weight ratio is 20: 1, and is kneaded with a polyethylene oxide solution as a dispersant like the inlet part 1a, and is formed on the electrode by the bar casting method. is there. The matrix layer 1 formed on the electrode is dried in an oven at 260 ° to 280 ° C, and when it is constructed as an electrochemical cell, SiC is used.
Is used by impregnating the solid phase of Teflon with phosphoric acid. A detailed view of the matrix layer 1 of the fuel cell according to the present invention shown in FIG. 1 is shown in FIG.

FIG. 2 is a schematic view of SiC (silicon carbide), which is the main component of the matrix layer 1, in a spherical shape. That is, the inlet portion 1a of the matrix layer 1 is
Since the spheres of 1 μm penetrate between the spheres of 5 μm, the total voids are smaller than the voids of the spheres of 5 μm shown in the outlet portion 1b. When configured as an electrochemical cell,
Since the voids are impregnated with phosphoric acid as the conductive species, the inlet portion 1a having a small amount of voids has a higher ionic resistance than the outlet portion 1b.

Thus, the inlet portion 1a of the matrix layer 1
And the ionic resistance value of the outlet portion 1b are made different, the heat generation amount Q is Q = I ² In relation to R, the inlet portion 1a is reduced as the current I is reduced.

As described above, the matrix layer of the reaction gas inlet portion 1a, the matrix layer of the outlet portion 1b, and the grain size of SiC (silicon carbide) forming the layer are adjusted, and impregnated with phosphoric acid as a conductive species. By reducing the amount, the ionic resistance can be increased. Due to the increase in the ionic resistance of the entrance portion 1a, the current concentrated in the entrance portion 1a can be more evenly distributed over the entire surface, and the high temperature portion of the entrance portion 1a of the matrix layer 1 having a high active material concentration It is possible to prevent the occurrence.

In this embodiment, an example in which the electrode is divided into two in the plane direction as shown in FIG. 1 has been described, but as another example, a local high ion resistance part is formed as shown in FIG. Is also effective in preventing the generation of high temperature parts.

[0018]

As described above, according to the present invention, the composition of the matrix layer, which is one of the constituent members of the fuel cell, is adjusted by adjusting the grain size of silicon carbide, which is the main component of the matrix layer, within its plane. By changing the ionic resistance along the flow direction of the reaction gas, the generation of high current density parts that had been concentrated at the reaction gas (oxidant gas) inlet in the past was eliminated and caused by the current concentration. It is possible to prevent the occurrence of the high temperature part that had been exposed to the heat. Therefore, it is possible to prevent the occurrence of crossover phenomenon, semi-short phenomenon, etc. It is possible to obtain a fuel cell that continues an electromotive reaction.

[Brief description of drawings]

FIG. 1 is a perspective view showing a matrix layer according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining the present invention.

FIG. 3 is a perspective view showing a general configuration of a fuel cell.

FIG. 4 is a perspective view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Matrix layer 1a ... Matrix layer inlet part 1b ... Matrix layer outlet part 2a ... Fuel electrode 2b ... Oxidizer electrode

Claims (2)

[Claims] 1. A fuel cell comprising a positive electrode using an oxidant gas as a reaction gas, a negative electrode using a fuel gas as a reaction gas, and a matrix layer sandwiched between the positive electrode and the negative electrode, wherein the matrix layer has the reaction within its plane. A matrix for a fuel cell, wherein the ionic resistance is made different along the gas flow direction. 2. A fuel cell comprising a positive electrode using an oxidant gas as a reaction gas, a negative electrode using a fuel gas as a reaction gas, and a matrix layer sandwiched between the positive electrode and the negative electrode, wherein the matrix layer is the main component SiC ( The fuel cell is characterized in that the ion resistance value is made different along the flow direction of the reaction gas in the plane by adjusting the particle size of (silicon carbide).