JPS60189870A - Operation of fuel cell - Google Patents

Abstract

PURPOSE:To prevent performance drop of a cell by adding electrolyte required to supplement electrolyte lost by scattering from a cell, in mist form in fuel gas of phosphoric acid type fuel cell. CONSTITUTION:Carbon base plate having a porosity of 63% is coated with carbon powder catalyst containing 15wt% of platinum to make an electrode. Electrolyte paste comprising phosphoric acid, silicon carbide, and zirconium phosphate is spreaded between two electrodes, then an electrode 1 with which air 2 is brought into contact and an electrode 3 with which hydrogen 4 is brought into contact are arranged to form a phosphoric acid type fuel cell. Phosphoric acid 8 comprising 85% H3PO4 and 15% H2O is supplied to a mist generator 6. Phosphoric acid mist and steam generated at 200 deg.C and they are added to hydrogen 4 to operate the cell. Therefore, electrolyte which is lost by scattering is effectively supplemented to keep a specified amout of electrolyte. This prevents performance drop of the cell.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of operating a fuel cell, and in particular a method for replenishing electrolytes such as phosphoric acid that are scattered and lost from the battery and maintaining the amount of electrolyte in the battery at a predetermined level. The present invention relates to a fuel cell operating method for preventing deterioration of cell performance.

[Background of the invention]

Roughly speaking, there are two reasons why the performance of fuel cells, such as phosphoric acid fuel cells, deteriorates. 1
One is the agglomeration of platinum, which is mainly used as an electrode catalyst.
One is a decrease in the active surface area due to dissolution, poisoning, etc., and the other is the disappearance of phosphoric acid used as an electrolyte from the battery body. For the former, measures have been taken, such as adding a second component to platinum to stabilize it, or pre-treating carbon powder as a carrier to stabilize it, and these measures have been found to be effective. However, no effective measures have been taken to prevent the latter loss of phosphoric acid. The battery is constructed by sandwiching phosphoric acid between an oxygen electrode where oxygen is reduced and an oxygen electrode where hydrogen is oxidized. Since this phosphoric acid is a liquid, it is used by kneading it with a fine powder matrix that is non-conductive and has low reactivity with phosphoric acid to form a paste and applying it between the two electrodes. This phosphoric acid is said to scatter and disappear from the oxygen electrode side as water is generated when oxygen is reduced at the oxygen electrode. In order to replenish this disappearing phosphoric acid, a method has been adopted in which phosphoric acid is stored in advance in a porous carbon substrate (for example, JP-A-53-32352, JP-A-53-323).
(See Publication No. 53). However, when attempting to increase the storage amount, the pores in the substrate become blocked, making it impossible for reactive gases such as oxygen and hydrogen to diffuse through the electrode. In other words, there is a limit to the amount of phosphoric acid that can be stored. In addition, a method has been proposed in which a phosphoric acid replenishment hole is provided in the electrode and phosphoric acid is supplied from the outside, but when stacking many batteries to increase their size, it is necessary to Many issues remain, including how to uniformly distribute acid inside the electrode.

Even when an electrolyte other than phosphoric acid, such as sulfuric acid, is used, the problem of deterioration of battery performance due to electrolyte scattering and disappearance occurs.

However, in fuel cells using fuel gas, no effective means have been taken to replenish electrolyte.

[Purpose of investigation]

An object of the present invention is to provide a fuel cell operating method that can replenish electrolytes such as phosphoric acid that scatter and disappear from the battery, maintain the amount of electrolyte in the battery at a predetermined level, and prevent deterioration of battery performance. .

[Summary of the invention]

The present invention adds an amount of electrolyte necessary to replenish the electrolyte that scatters and disappears from inside the battery in the form of a mist together with water vapor into the fuel gas and supplies it into the battery to maintain the amount of electrolyte inside the battery at a predetermined amount. This is how it was done.

In the present invention, the electrolyte is not limited to phosphoric acid, but may also be sulfuric acid or the like. The electrolyte layer may be formed by each of the above-mentioned liquids alone, or may be formed by kneading each of the above-mentioned liquids with a non-conductive fine powder (matrix) that has low reactivity with each of these liquids to form a paste, or an electrolyte layer. An ion exchange membrane may be provided between the two. In addition to hydrogen, fuel gas also includes
Includes reformed gas, etc.

Below, we will explain the example of a phosphoric acid fuel cell in particular. In order to make phosphoric acid into a mist, 100% H3PO4 (P
100 using phosphoric acid below 72.4% as 2O3)
Heat above ℃.

Phosphoric acid containing 100% H3PO4 or less contains free water, and this water turns into steam at a temperature of 100°C or higher, and when it scatters from the phosphoric acid, it entrains phosphoric acid.
Turn into mist. According to the experimental data of the present inventors, a temperature of 150° C. or higher is desirable in order to supply phosphoric acid at the required rate. Specific methods for making a mist include supplying phosphoric acid directly into the flow of gas containing hydrogen, or setting up a heating tank for making mist and supplying it into the gas containing hydrogen after making it into a mist. This method is effective. The phosphoric acid mist added in this manner reaches the hydrogen electrode (fuel electrode) and further moves into the matrix, where it effectively functions as an electrolyte. However, when phosphoric acid containing 100 wt% or more of H3PO4 is used, there is a shortage of free water, which not only slows down the rate of formation of mist, but also condenses phosphoric acid in the matrix, lowering electrical conductivity and lowering battery performance. . In this way, water vapor is an essential component for making phosphoric acid work as an electrolytic agent.

[Embodiments of the invention]

Example 1 A carbon powder catalyst containing 15 wt% platinum was coated on a carbon substrate with a thickness of 0.5 mm, a width of 60 cm, a porosity of 63%, and an average pore radius of 20 μm, and two electrodes with a platinum content of 0.5 mg/cm2 were coated. A sheet was prepared. Between these electrodes, 50 wt% phosphoric acid, 30 wt% silicon carbide, 20 wt% zirconium phosphate,
A battery as shown in FIG. 1 was constructed by applying 300 g of the paste consisting of wt%. Air 2 to electrode 1 at 50Nl/
hydrogen 4 was applied to the electrode 3 at a rate of 20Nl/mi.
Contact was made at n. At this time, the mist generator 6 contains H3PO4.
20 by supplying 85% phosphoric acid and 15% H2O.
Phosphoric acid mist and water vapor were generated at 0° C. and added to hydrogen 4. When a power generation test was conducted in this way, the initial voltage was 0.61V at a current density of 220mA/cm2,
0.60V after 1000h, 0.5 after 3000h
It was 8V. In addition, after the test, the amount of phosphoric acid in the battery (inside the matrix and electrodes) was analyzed.
After 3000 hours, the weight was 155 g (calculated value).

Comparative Example A power generation test was conducted under the same conditions as in the example except that phosphoric acid mist and water vapor were not added to hydrogen 4.
．． It was 62V, but after 1000 hours it was 0.48V, 20
After 00h, the voltage was 0.21V.

In addition, the amount of phosphoric acid in the battery after the test was 96g and 54g.
had disappeared.

〔Effect of the invention〕

As described above, according to the present invention, the mist-like electrolyte entrained in the fuel gas is supplied to the electrolyte from the electrode through the fuel chamber, and the amount of electrolyte in the battery can be maintained at a predetermined amount. Therefore, deterioration in battery performance due to electrolyte scattering and loss can be prevented.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus for actually measuring the operating method of the present invention. 1...electrode, 2...air, 3...electrode, 4...hydrogen, 5...electrolyte paste, 6...mist, generator, 7...pump, 8...phosphoric acid. Continuation of page 1 [Phase] Inventor 1) Takeshi Murahiro Hitachi City, Saiwai-cho 3-chome, 1-1, Hitachi, Ltd. Hitachi Research

Claims (6)

[Claims] 1. A porous card-shaped oxidizing agent electrode and an oxidizing agent chamber are arranged on one surface of the electrolyte layer, and a porous fuel electrode supporting the catalytically active component on the other surface of the electrolyte layer. A method of operating a fuel cell in which a fuel chamber to which fuel gas is supplied includes supplying a mist of the electrolyte and water vapor to the fuel gas supplied to the fuel chamber according to the amount of electrolyte in the cell. Characteristic fuel cell operation method. 2. The method of operating a fuel cell according to claim 1, wherein the electrolyte is phosphoric acid. 3. In claim 1, the fuel gas is
A method of operating a fuel cell characterized by using hydrogen gas. 4. The method of operating a fuel cell according to claim 1, wherein the oxidizing agent is oxygen. 5. In claim 1, the electrolyte layer comprises:
A method of operating a battery characterized by being formed into a paste by kneading phosphoric acid with a matrix. 6. Claim 2, wherein the phosphoric acid mist contains an acid containing 100 wt% or less of H3PO4 at 100°C.
A method of operating a fuel cell obtained by heating above.