JPH0222505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a molten carbonate fuel cell in which the mechanical strength of an electrolyte layer can be improved.

[Technical background of the invention and its problems]

Conventionally, fuel cells have been widely known as a highly efficient energy conversion device. Fuel cells are classified into phosphate type, molten carbonate type, and solid electrolyte type depending on the electrolyte used. Among these, molten carbonate fuel cells have high operating temperatures, so electrode reactions occur easily, and expensive precious metal catalysts are not required.
It also has great features such as high heat generation efficiency.

A molten carbonate fuel cell is a unit cell consisting of a pair of porous electrode plates arranged opposite to each other and an electrolyte layer containing an alkali carbonate as an electrolyte interposed between the electrode plates. It is composed of layers. The electrolyte layer is formed by impregnating a porous or powdered holding material with an electrolyte in order to prevent the alkali carbonate from flowing out in a high-temperature molten state. Among such electrolyte layers, the so-called paste-type electrolyte layer uses powdered γ-lithium aluminate as the above-mentioned holding material, mixes this powder with carbonate, and molds it by molding. It has a plate-like structure called an electrolyte tile.

By the way, the performance required of the electrolyte plate is that it can sufficiently hold carbonate in a molten state.

Since the internal resistance of the battery is minimized, it can be made thinner.

In order to increase the output obtained from a unit battery, it can be made larger.

Examples include. On the other hand, conventional electrolyte plates of this type have a sufficient carbonate retention function, but have poor mechanical strength, with a bending strength of about 10 kg/mm ² at room temperature at most. Therefore, it is difficult to manufacture a thin and large electrolyte layer in terms of strength, and as a result, there is a problem that there is a limit to the output that can be obtained from a unit cell.

In addition, since the carbonate has a large volume change between the solid state and the liquid state, if the mechanical strength of the electrolyte layer is low as described above, the electrolyte may be damaged by the thermal cycle that occurs when the fuel cell starts and stops. Cracks are likely to occur in the layers. When such cracks occur, the fuel gas and oxidizing gas are mixed through the cracks, impairing the effective use of the supplied gas. Therefore, even with this method, there was a problem that high output could not be obtained.

[Purpose of the invention]

The present invention has been made based on these problems, and its purpose is to improve the mechanical strength of an electrolyte layer without affecting other properties. The object of the present invention is to provide a molten carbonate fuel cell that can be made larger, have improved heat cycle performance, and can improve the output per unit cell.

[Summary of the invention]

In the present invention, between two electrode plates arranged oppositely,
In a molten carbonate fuel cell in which a main portion is constituted by interposing an electrolyte layer mainly composed of carbonate, the present invention provides that a part of the holding material in the core of the electrolyte layer is made of carbide, nitride, The electrolyte layer is characterized in that it is composed of a woven or nonwoven fabric made of fibers of carbon, a composite compound thereof, or a mixture thereof, and that the electrolyte layer is of a paste type.

〔Effect of the invention〕

In the present invention, a part of the core holding material of a paste-type electrolyte layer is made of fibers of carbides, nitrides, carbon, composite compounds thereof, or mixtures thereof, which have excellent corrosion resistance against electrolytes made of carbonates. Composed of woven or non-woven fabrics, other properties,
For example, the bending strength at room temperature and the mechanical strength during operation cycles can be significantly improved without affecting the electrolyte layer retention function, and the initially formed internal microstructure of the electrolyte layer can be maintained over a long period of time. This makes it possible to maintain the above-mentioned strength over a long period of time. Therefore, the electrolyte layer can be made thinner, larger, have better heat cycle resistance, and have a longer lifespan, thereby contributing to the realization of a high-output fuel cell.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained based on illustrated embodiments.

Example 1 The figure shows a unit battery, and numeral 1 in the figure is an electrolyte layer. This electrolyte layer 1 is held between interconnectors 6 and 7 via porous electrode plates 2 and 4 and conductive corrugated electrode supports 3 and 5, respectively.

The electrolyte layer 1 is composed of a composite of an electrolyte 8 and a holding material 9, and the holding material 9 further includes a first holding material 9a and a second holding material 9a disposed in an intermediate portion of the electrolyte layer 1 .
and a holding material 9b.

Electrolyte 8 is specifically lithium carbonate (Li ₂ CO ₃ )
and potassium carbonate (K ₂ CO ₃ ) in a weight ratio of 7:8. Also,
The first holding material 9a constituting the holding material 9 is made of γ-lithium aluminate (γ-LiAlO ₃ ) powder that accounts for 33% of the weight of the electrolyte 8.
Further, the second holding material 9b is made of a woven fabric made of carbon fiber. This woven fabric is made by bundling and weaving approximately 3,000 carbon fibers with a diameter of 7 μm, and the weight per unit area is
It is 200g/ ^m2 .

Note that the electrolyte layer 1 was manufactured by the following steps. i.e. lithium carbonate
28g of potassium carbonate, 32g of potassium carbonate, and 20g of γ-lithium aluminate were mixed in a ball mill.
Fill a cm ² hot press mold uniformly with half of the normal molding amount, and then place a 5 x 5 mold on the top of the mixed powder.
A woven fabric serving as the second holding material 9b cut into cm ² pieces was laid down, and the remaining half of the above mixed powder was filled on the upper surface of ^this woven fabric. It was hot pressed into a plate shape of 5 x 5 cm and 2 mm thick. The relative density of the electrolyte layer thus obtained was 98%.

In the fuel cell constructed in this manner, the bending strength of a test piece cut into 20×3 mm ² from the electrolyte layer 1 was measured before assembly, and a value of 21.5 Kg/mm ² was obtained. For comparison, a similar test was conducted on the electrolyte layer without the woven fabric buried therein, and its bending strength was 8.4 Kg/mm ²
It was hot.

Further, for the fuel cell, fuel gas H ₂ +CO is supplied through the introduction hole 10 of the interconnector 6,
In addition, oxidant gas O ₂ +CO ₂ was supplied through the introduction hole 11 of the interconnector 7 to actually generate 200 mA/cm ^{2 .}
When power generation was performed and operation and stop were repeated, no destruction of the electrolyte layer 1 or deterioration of other battery characteristics was observed.

Based on the above results, by replacing part of the core holding material of the paste-type electrolyte layer with carbon fiber woven cloth, the mechanical strength of the electrolyte layer can be improved compared to conventional ones without any loss of other properties. It has been found that this can be more than doubled, making it possible to realize large-scale unit fuel cells, and exhibiting excellent heat cycle resistance.

Although carbon fiber was used for the woven fabric or non _- woven fabric in the above examples, _it is not limited to this in particular. A mixture of fibers may also be used. In short, the present invention can be modified in various ways without departing from its gist.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view of a unit cell constituting a molten carbonate fuel cell according to a first embodiment of the present invention. 1 ... Electrolyte layer, 2, 4... Electrode plate, 3, 5...
...electrode support, 6,7...interconnector, 8...
... Electrolyte, 9 ... Holding material, 10, 11 ... Introduction hole.

Claims (1)

[Claims] 1 A molten carbonate fuel cell comprising two porous electrode plates arranged opposite to each other and a paste-type electrolyte layer interposed between these electrode plates and formed by holding an electrolyte made of carbonate with a holding material. In the molten carbonic acid, the core holding material of the paste type electrolyte layer is composed of a woven fabric or a nonwoven fabric made of fibers of carbides, nitrides, carbon, composite compounds thereof, or mixtures thereof. salt fuel cell.