JPS58145067A - Fuel cell - Google Patents

Abstract

PURPOSE:To reduce electric internal resistance drop and equalize temperature, by containing wet oxidized graphite in a material component of separators of a fuel cell and obtaining the flexible separator of large electric and heat conductivity. CONSTITUTION:Wet oxidized graphite is contained in a material component of separators in a fuel cell of layer-built construction. This wet oxidized graphite can prepare a product with flexibility, elasticity and air-tightness by mechanical compression of roll molding or the like. Accordingly, use of this oxidation treated graphite or mixed material with this graphite can obtain the separator of high electric and heat conductivity at a low price. This separator, being flexible, can absorb a slight dimensional error, and a crack due to tightening at layer building of the fuel cell is not generated.

Description

[Detailed description of the invention] The present invention relates to acidic electrolyte fuel cells.

Normally, a fuel cell is constructed by stacking a plurality of fuel cells, each consisting of a fuel electrode, an air electrode, and an electrolyte layer between these two electrodes, with separators interposed in between, and tightening them together with an appropriate cooling device. ing.

Conventionally, the separator for this fuel cell has been one cut from a block of high-density graphite, or one formed by kneading graphite powder and an organic binder and press-forming the mixture.

The separator manufactured by the former method has favorable characteristics of high electrical conductivity and high thermal conductivity, but since the thin flat separator is scraped from a large graphite block, a cutting allowance greater than the thickness of the separator is required. However, it had the disadvantage of poor yield.

Unfortunately, this method required a great deal of time to process the separators with high precision, leading to high manufacturing costs.

One possible method to eliminate this drawback is to graphitize a separator formed into a shape, but this has not yet been put to practical use because the material deforms during graphitization.

The latter method, which has been put into practical use, involves kneading graphitized carbon powder and an organic binder and producing a separator using a press. .

It eliminates the need for long-term graphitization firing before and after C, and has advantages such as improved yield during separator production and shortened production time by using a mold press method instead of a mechanical cutting method.

However, this method has the drawback that the organic binder cannot be completely carbonized, resulting in slightly low electrical conductivity and thermal conductivity.Also, since the elongation of the material is low, deformation occurs during pressing or during heat treatment after pressing. Even if it's only a little,
The product of the fuel cell cannot absorb its dimensional deformation)
There was a drawback that the separator was susceptible to breakage due to the tightening pressure during fi.

The object of the present invention is to provide electrical conductivity that is easy to manufacture.

An object of the present invention is to provide a fuel cell using a flexible separator with high thermal conductivity.

Acid-treated graphite is generally produced using a combination of acids such as concentrated sulfuric acid or concentrated nitric acid and strong oxidizing agents such as potassium chlorate, potassium dichromate, or potassium permanganate to wet-process graphite with well-developed crystals. It is produced by oxidation, but unlike ordinary granular graphite, it can be mechanically compressed, making it possible to make molded products with flexibility, elasticity, and airtightness.

If this acid-treated graphite or a mixture of this material and other materials is used as a fuel cell separator, molded products with high electrical conductivity and high thermal conductivity can be made by pressing or rolling, and are movable. Because of its properties, it can absorb even slight dimensional errors and is less likely to crack due to tightening during stacking of fuel cells.

'Acid-treated graphite is resistant to acids and alkalis and is thermally stable, so separators using it can be used in phosphoric acid fuel cells, alkaline fuel cells, sulfuric acid electrolyte fuel cells that use methanol as direct fuel, It can be used in a wide range of fuel cells, including hydrazine fuel cells. Furthermore, since large-sized separators are easy to manufacture, there are great advantages to using this separator in phosphoric acid fuel cells.

The present invention will be explained in detail below.

FIG. 1 shows a phosphoric acid fuel cell having a ribbed electrode type cell structure, and numerals 1 and 2 are a fuel electrode and an air electrode made of ribbed porous graphite as a base material.

3 holds an electrolyte, such as phosphoric acid. 4 is a flat separator, and the material for this is:
A sheet extruded by a full roll of wet oxidized graphite powder is used. Because this material has elasticity, it is difficult to break mechanically even if it is thin, and is effective in saving raw materials and reducing cell height. In this structure, both the electrode and the separator are flexible, so if several hundred layers are stacked and tightened at once, the amount of deformation will accumulate, making uniform tightening difficult. Therefore, it is effective to insert a rigid clamping plate every several cells or every ten or more cells. In the case of phosphoric acid fuel cells, cooling plates are inserted every few cells, so
This cooling plate can have a tightening effect for dimensional stabilization.

Molded products made by mechanically compressing wet oxidized graphite powder are generally said to be airtight, but because they contain some pores, there is a slight amount of gas permeation, which absorbs phosphoric acid from the electrolyte layer. , there is also a risk that the ionic conductivity of the electrolyte layer will be reduced. For this reason, airtightness can be improved by impregnating a sheet-like separator with a liquid substance such as phosphoric acid in advance, or by impregnating it with a liquid binder and solidifying it by heat treatment or the like.

Wet oxidized graphite can have different υ particle shapes depending on the oxidation conditions and high-temperature rapid heating conditions after oxidation, and by combining these materials or mixing these materials with normal graphite particles, mechanical The softness of the molded product after compression can be adjusted. Therefore, it is possible to absorb the dimensional error of a hard ribbed electrode substrate with a soft separator, and it is also possible to flatten a soft ribbed electrode substrate with a hard separator.

FIG. 2 shows a phosphoric acid fuel cell having a cell structure of a ribbed separator type. Reference numerals 1 and 2 are a fuel electrode and an air electrode made of flat porous graphite as a base material. 3 is an electrolyte layer in which, for example, phosphoric acid is held. Reference numeral 4 denotes a separator with a lip, and the material used for this separator is a mixture of wet oxidized graphite material and graphite powder, which is molded by press. In this example, as wet oxidized graphite, 50% by weight of expanded graphite with a bulk specific gravity of 0.1 or less and 50% by weight of natural graphite powder with a particle size of several micrometers are mixed and pressed between flat plates at a pressure of 10~/m' or more. Then, the grooves were machined. The separator manufactured in this way uses wet oxidized graphite as a binder, so
High electrical conductivity and high thermal conductivity can be obtained without high-temperature heat treatment, and since it is more flexible than conventional methods, it is possible to absorb slight dimensional errors and has the advantage of facilitating manufacturing.

Furthermore, if a material containing wet oxidized graphite is placed between the grooved flat plates and press-molded, the manufacturing process of the grooved separator can be simplified. Furthermore, if the raw material is extruded flat or with grooves using rolls, there is no need for a high-pressure cutless, and large pressure can be applied locally with relatively small rolls, making the manufacturing equipment simpler. , continuous mass production is possible. In other words, although some deformation occurs in the roll extrusion method of continuous ribbed flat plates,
Since wet oxidized graphite has malleability, it can be put to practical use after correcting deformation.

According to the fuel cell of the present invention, since wet oxidized graphite is used as at least one of the separator material components, it has high electrical conductivity and high thermal conductivity, and is flexible without requiring high-temperature heat treatment after molding. A separator can be obtained that reduces internal resistance loss in fuel cells.

Uniform temperature 1. Effective in improving reliability of mechanical structure and reducing separator manufacturing costs.

[Brief explanation of the drawing]

1 is a perspective view showing a stacked structure of a ribbed electrode type fuel cell, and FIG. 2 is a perspective view showing a stacked structure of a ribbed separator type fuel cell.

Claims (1)

[Scope of Claims] 1. A plurality of fuel cells each consisting of a fuel electrode, an air electrode, and an electrolyte layer disposed between the two electrodes are stacked with a separator interposed therebetween, and the separator contains at least wet-oxidized graphite as a material component. A fuel cell characterized by comprising: 2. The fuel cell according to claim 1, wherein the separator is formed of a mixture of wet oxidized graphite and graphite powder.