JPH056771A - Fuel cell - Google Patents

Abstract

PURPOSE:To provide a fuel cell excellent in reliability having no electrode breakage caused by corrosion by making the effective area of the electrode catalytic layer of an oxidizing agent electrode equal to or smaller than the effective area of the electrode catalytic layer of a fuel electrode. CONSTITUTION:The electrode catalytic layer of an oxidizing agent electrode forms a reacting seed preventing part by partial treatment with a fluorine resin, and has an effective area S1. As oxygen gas and hydrogen ion H<+> never reach the diffusion preventing part, no electrode reaction take place in the diffusion preventing part to form a part which can not be potentially defined. In the effective area S1 part of the electrode catalytic layer, oxygen gas and H<+> ion are supplied thereto, the electrode reaction uniformly takes place to reduce the electrode potential. When the effective area of the electrode catalytic layer of a fuel electrode is S2, both the effective areas satisfy the relation of S1<=S2. Thus, a local reduction of electrode reaction is prevented, a local potential rise is consequently eliminated, causing no breakage of the electrodes, and a fuel cell excellent in reliability can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell electrode, and more particularly to a fuel cell having excellent oxidant electrode stability.

[0002]

2. Description of the Related Art A fuel cell directly converts the chemical energy of a fuel into electric energy. Its structure is such that electrodes 6 as shown in FIG. 9 are arranged with an electrolyte layer 8 made of phosphoric acid interposed therebetween. , A fuel gas and an oxidant gas are supplied from an external gas supply system to each electrode, and the fuel gas or the oxidant gas is electrochemically reacted on the electrode catalyst of each electrode, and as a result, electric energy is supplied to the outside of the system. It is a type of power generation device that takes out.

The electrode 6 is constructed by adhering an electrode catalyst layer 5 on an electrode substrate 4 made of porous carbon. The electrode catalyst layer 5 is formed by binding the catalyst particles 7 supporting the noble metal fine particles 1 on the surface of the catalyst carrier 2 by the particles 3 of the fluororesin. Inside the electrode catalyst layer 5, the gas from the electrode base material side and the electrolytic solution from the electrolytic solution layer come into contact with each other, a three-phase interface is formed, and an electrochemical reaction proceeds.

At the fuel electrode, an oxidation reaction of hydrogen gas is performed, and at the oxidant electrode, a reduction reaction of oxygen gas is performed. In terms of operating efficiency, the battery is operated at a high temperature (about 200 ° C), and a theoretical voltage of about 1.1 V is generated when there is no load (when the fuel electrode side is set to 0 standard, the oxidizer electrode is +1 It shows a potential of 0.1 V), and the voltage is 0.8 V or less at the rated load.

On the fuel electrode side, the hydrogen gas serving as the fuel becomes hydrogen ions and electrons at the three-phase interface, the hydrogen ions move in the electrolyte layer 8, and the electrons pass through the external circuit and the oxidizer of the counter electrode. Reach the pole. At the oxidizer electrode, oxygen gas activated at the three-phase interface and hydrogen ions generated at the fuel electrode, which have moved through the electrolyte layer, and electrons that have passed through the external circuit electrochemically react to generate water. To generate.

[0006]

As described above, in the fuel cell, the migration of ions occurs due to the electrochemical reaction between the fuel electrode and the oxidant electrode. Therefore, if the reaction is hindered at either one of the electrodes, the movement of hydrogen ions is hindered and the counter electrode is affected.

For example, if the reaction of the oxidizer electrode is hindered,
The potential of the fuel electrode is close to that of hydrogen. Further, when the reaction of the fuel electrode is disturbed, the potential of the oxidant electrode becomes close to the potential of oxygen and approaches the potential of +1.1 V on the basis of hydrogen.

By the way, it has been known that in a phosphoric acid fuel cell with an operating temperature of 160 ° C. or higher, when the potential exceeds 0.85 V, the corrosion current of the electrode increases (see FIG. 6) and the deterioration of the cell characteristics increases. (See FIGS. 7 and 8). Therefore, in actual fuel cell operation at 200 ℃, 0.
I try not to exceed 85V. However, in an actual fuel cell, as shown in Fig. 10, when the electrode catalyst layer of the oxidizer electrode (portion where the three-phase interface can be formed) is larger than the actual reaction portion (portion where the fuel electrode contacts via the electrolyte layer). Alternatively, in the case of a battery in which the fuel electrode has a reservoir (the part that holds the electrolytic solution on the electrode substrate), the fuel electrode in the reservoir part causes diffusion inhibition of the fuel gas due to the retained electrolytic solution, Interfering with the migration of ions to the oxidant electrode of the counter electrode, a partial high potential portion exceeding 0.85 V is generated at the oxidant electrode. In such a case, there is a problem that the oxidizer electrode is destroyed due to corrosion and the performance of the battery is degraded.

The present invention has been made in view of the above points, and an object thereof is to provide a fuel cell which prevents the oxidizer electrode from partially increasing in electric potential and is free from electrode destruction due to corrosion and excellent in reliability. It is in.

[0010]

According to the present invention, the above object has an oxidizer electrode, an electrolyte solution layer, and a fuel electrode, and the electrolyte solution layer is provided between the opposing oxidizer electrode and fuel electrode. It is sandwiched to supply the electrolytic solution to both electrodes, and the oxidizer electrode and the fuel electrode each have an electrode catalyst layer on the electrode substrate that diffuses the reaction gas. the area S _1, the effective area of the electrode catalyst layer of the fuel electrode S ₁ and S ₂ when the S ₂ is achieved by a satisfies the following equation _{S 1 ≦ S 2 (I)} . Here, the reactive species refers to ions in the reaction gas or the electrolytic solution.

[0011]

When the effective area S ₁ of the electrode catalyst layer of the oxidant electrode is equal to or smaller than the effective area S ₂ of the electrode catalyst layer of the fuel electrode, partial diffusion inhibition of hydrogen ions can be suppressed.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an exploded view showing an electrode of a fuel cell according to an embodiment of the present invention. The electrode catalyst layer of the oxidant electrode is partly treated with a fluororesin to form a reactive species diffusion preventing portion. Since oxygen gas and hydrogen ions H ⁺ do not reach, no electrode reaction occurs in the diffusion prevention portion, and the portion cannot be defined in terms of potential. Oxygen gas and H in the effective area of the electrode catalyst layer
^{As +} ions are supplied, the electrode reaction occurs uniformly and lowers the electrode potential. If not treated with a fluororesin, this portion will have a high potential.

FIG. 2 is a diagram showing the cell voltage time dependency 10 of the fuel cell according to the embodiment of the present invention in comparison with the conventional one 11. The battery is highly reliable because the electrodes are not destroyed.

FIG. 3 is an exploded perspective view showing a fuel cell according to another embodiment of the present invention. A predetermined portion of the electrode base material is treated with a fluororesin. Prevents oxygen gas diffusion in the oxidizer electrode catalyst layer. When the diffusion of oxygen gas is prevented, the electrode reaction does not occur in this portion and the potential of the electrode is not raised.

4 and 5 are corresponding views showing electrodes of a fuel cell according to still another embodiment of the present invention. Both have a reservoir in the electrode. In the former, the reservoir has the same size, and in the latter, the reservoir for the oxidant electrode is made larger and arranged symmetrically. The reservoir is a storage portion for the electrolytic solution and serves as a diffusion preventing portion for the reaction gas.

[0016]

According to the present invention, it has an oxidizer electrode, an electrolyte layer, and a fuel electrode, and the electrolyte layer is sandwiched between the oxidizer electrode and the fuel electrode which are opposed to each other. The electrolytic solution is supplied, and the oxidant electrode and the fuel electrode each have an electrode catalyst layer on the electrode substrate that diffuses the reaction gas. The effective area of the electrode catalyst layer of the oxidant electrode is S ₁ , the electrode of the fuel electrode is since S ₁ and S ₂ satisfies the following equation S ₁ ≦ S ₂ (I) when the effective area of the catalyst layer and S _2, reduction of local electrode reaction can be prevented,
As a result, there is no local increase in the potential, the electrode is not damaged, and a highly reliable fuel cell can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded view showing an electrode of a fuel cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing cell voltage time dependence of a fuel cell according to an embodiment of the present invention in comparison with a conventional one.

FIG. 3 is an exploded perspective view showing a fuel cell according to another embodiment of the present invention.

FIG. 4 is an exploded view showing electrodes of a fuel cell according to still another embodiment of the present invention.

FIG. 5 is an exploded view showing electrodes of a fuel cell according to still another embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between electrode potential and temperature and corrosion current.

FIG. 7 is a diagram showing the relationship between electrode potential and cell deterioration rate.

FIG. 8 is a diagram showing the relationship between cell temperature and cell deterioration rate.

FIG. 9 is a sectional view showing a fuel cell.

FIG. 10 shows a conventional fuel cell, FIG. 10 (a) is a perspective view,
Figure 10 (b) is an exploded view showing the electrodes.

[Explanation of symbols]

1 Precious metal particles 2 Catalyst carrier 3 Fluororesin particles 4 electrode base material 5 Electrode catalyst layer 6 electrodes 7 catalyst particles 8 Electrolyte layer

Claims (4)

[Claims] 1. An oxidant electrode, an electrolytic solution layer, and a fuel electrode, wherein the electrolytic solution layer is sandwiched between the oxidant electrode and the fuel electrode facing each other, and the electrolytic solution is supplied to both electrodes. , The oxidizer electrode and the fuel electrode each have an electrode catalyst layer on the electrode substrate for diffusing the reaction gas, and the effective area of the electrode catalyst layer of the oxidizer electrode is S ₁ ,
When the effective area of the electrode catalyst layer of the fuel electrode is S ₂ , S ₁
And S ₂ satisfy the following formula S ₁ ≦ S ₂ (I). 2. The fuel cell according to claim 1, wherein the electrode has a reactive species diffusion preventing portion for determining an effective area of the electrode catalyst layer. 3. The fuel cell according to claim 2, wherein the reactive species diffusion preventing portion is a filler provided in the electrode catalyst layer. 4. The fuel cell according to claim 2, wherein the reactive species diffusion preventing portion is a reservoir provided on the electrode base material.