JPH0624123B2 - Method for manufacturing molten carbonate fuel cell - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a molten carbonate fuel cell, which is capable of easily producing a unit cell having excellent characteristics and capable of achieving a large output.

[Technical background of the invention and its problems]

Conventionally, a fuel cell is widely known as a highly efficient energy conversion device. Fuel cells are classified into phosphoric acid type, molten carbonate type, and solid electrolyte type depending on the electrolyte used. Among them, the molten carbonate fuel cell has major characteristics such that the electrode reaction is likely to occur because the operating temperature is high, an expensive noble metal catalyst is not required, and the heat generation efficiency is high.

A molten carbonate fuel cell is a unit cell composed of a pair of porous electrode plates arranged opposite to each other, that is, an oxidizer electrode and a fuel electrode, and an electrolyte layer having an alkali carbonate as an electrolyte interposed between these electrodes. Is usually laminated by a plurality of interconnectors. Then, during operation, the alkali carbonate is brought into a molten state at a high temperature of 500 to 750 ° C., and the carbonate is reacted with the oxidant gas and the fuel gas diffused in each electrode plate to produce an electrochemical reaction. The direct current output is obtained by a dynamic process.

The electrolyte layer of such a molten carbonate fuel cell needs to satisfy the following conditions. That is, not only the ability to retain molten carbonate is sufficient, but also the operating temperature has sufficient mechanical strength, especially compressive strength, and gas cross-mixing due to cracking of the electrolyte layer does not occur in the fuel cell. In order to reduce the internal resistance per unit cell, it should be as thin as possible, and it should be possible to make sufficient contact with each electrode, and it should be possible to increase the size to increase the output per unit cell. It has high productivity so that it can respond to the increase in scale.

By the way, in a conventional molten carbonate fuel cell, an electrolyte retaining material and a carbonate are mixed exclusively as an electrolyte layer,
A plate-like body called a so-called electrolyte tile obtained by hot pressing at 0 to 500 ° C. and 200 to 500 kg / cm ² is used.

However, although the electrolyte layer formed as described above has a sufficient function of retaining molten carbonate, it is inferior in mechanical strength, and if the size of the electrolyte tile is 50 cm square or more, it can be easily handled by ordinary handling. There is a problem in that it is damaged and requires careful attention to be incorporated into the battery, and even after the incorporation, cross-mixing of gas easily occurs due to cracking of the electrolyte layer due to thermal cycle of the battery. Therefore, there is a limit to thinning and increasing the size of the electrolyte layer, and the thickness is 1
The limit was about mm.

Even if the electrolyte layer can be made thinner by some method, the fuel cell having the conventional structure has the following problems. That is, the oxidant gas and the fuel gas during fuel cell operation are usually separated by a layer of molten carbonate.
Therefore, the thinner this layer is, the lower the ability to withstand the gas pressure is, the molten carbonate is pushed out to the gas downstream side, and there is a problem that gas cross-mixing eventually occurs.

Furthermore, when forming the electrolyte layer by hot pressing as described above, it is necessary to use a high pressing pressure per unit area, and therefore a large-sized press device must be used, which requires a large equipment cost. There was a problem. Moreover, in such a manufacturing method, since it is necessary to pressurize the mixture of the holding material and the carbonate at a high temperature, it takes time to heat the mixture, and moreover, a sudden mechanical impact is generated during the press working. Since it is not given, it is difficult to keep the production rate per sheet within 10 minutes, resulting in a problem of extremely poor productivity. Therefore, there has been a problem that a large cost is required to manufacture a large-sized fuel cell by such a manufacturing method.

[Object of the Invention]

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a molten carbonate fuel cell capable of manufacturing a unit cell capable of improving energy efficiency and high output with high productivity. It is to provide a manufacturing method.

[Outline of Invention]

A method for manufacturing a molten carbonate fuel cell according to the present invention, in manufacturing a unit cell, comprises a mixture of a fine powder material and an organic binder on one surface of a first porous electrode plate to form a thin fine powder layer. To form an electrolyte layer by coating a mixture of a mixed carbonate, a carbonate holding material and an organic binder on the upper surface of the fine powder layer, and then from the fine powder material and the organic binder on the electrolyte layer. The second porous electrode plate is laminated via the thin fine powder layer.

〔The invention's effect〕

According to the manufacturing method of the present invention, a method of forming a fine powder layer and an electrolyte layer on a porous electrode plate having high mechanical strength is adopted. Therefore, even if the electrolyte layer is formed to be extremely thin, the electrode plate serving as the base has high mechanical strength, so that the electrolyte layer does not crack during handling during manufacturing. Moreover, since the electrolyte layer is extremely flexible including the organic binder, the electrolyte layer is also a layer which is not easily broken. Moreover, since the fine powder layer is provided between each porous electrode plate and the electrolyte layer, it becomes possible to increase the hydrodynamic resistance between the electrode and the electrolyte layer by this fine powder layer. It is possible to prevent the molten carbonate from moving due to the gas pressure. Therefore, the thinning of the electrolyte layer and the prevention of gas cross-mixing can be achieved at the same time. Therefore, according to the manufacturing method of the present invention, it is possible to reduce the thickness and size of the electrolyte layer, and eventually it is possible to manufacture a high-power fuel cell.

In addition, unlike the conventional hot pressing method, such a method can form the electrolyte layer at room temperature, and
Since the method of simply applying the slurry-like material onto the upper surface of the fine powder layer formed on the electrode plate is employed, the effect of extremely high productivity is achieved. Therefore, it is possible to mass-produce a large fuel cell.

Example of Invention

Hereinafter, a molten carbonate fuel cell manufactured by employing the manufacturing method of the present invention will be described with reference to the drawings.

In FIG. 1, X is a fuel cell main body mounted in a manifold (not shown). The fuel cell main body X is configured by alternately stacking unit cells 1 and interconnectors 2.

The unit cell 1 includes a pair of porous electrode plates, that is, a fuel electrode 3
And an oxidizer electrode 4, an electrolyte layer 7 is formed via fine powder layers 5 and 6 to form a five-layer structure. Fuel electrode 3
For example, a powder of Ni-Cr alloy, Co-Cr alloy, or the like is sintered to form a porous sintered body having a desired porosity. The oxidizer electrode 4 is formed of, for example, a porous sintered body of Ni, Ni-based alloy. The fine powder layers 5 and 6 are formed by kneading a fine ceramic powder such as LiAlO ₂ , an organic binder and a non-aqueous solvent, and coating the mixture on the fuel electrode 3 and the oxidant electrode 4. The electrolyte layer is formed by kneading a mixed carbonate, a carbonate retaining material such as LiAlO ₂ , an organic binder, and a non-aqueous solvent, and coating the mixture on the fine powder layer 5 or 6.

The interconnector 2 is, for example, a plate-shaped body made of stainless steel having a plurality of grooves formed on both surfaces and extending in directions orthogonal to each other. The groove formed on one surface is used as a gas passage 8 for an oxidant gas, The groove formed on the other surface is used as the gas passage 9 for the fuel gas.

Then, when operating the fuel cell thus configured, the temperature of the fuel cell main body X is raised to 500 to 750 ° C. During this temperature rising process, the electrolyte layer 7 and the fine powder layers 5, 6 are
At the same time as the organic binder therein is volatilized, a part of the fine powder is fused. Thereafter, the oxidant gas is caused to flow through the gas passage 8 of the interconnector 2 in the direction indicated by the arrow P in the figure, and the fuel gas is caused to flow through the gas passage 9 in the direction indicated by the arrow Q. This causes an electrode reaction to generate a DC voltage between the electrodes.

Next, a specific example of the method of manufacturing such a fuel cell and the experimental results thereof will be described.

A Ni sintered body with a porosity of 75% was used with an oxidizer electrode 4 and a porosity of 65%
The Ni-Cr sintered body was used as the fuel electrode 3, and a slurry containing 20 m ² / g of fine powder of LiAlO ₂ (lithium aluminate) and 3% by weight of polyvinyl butyral was spray-coated on each of the above electrodes, and the back surface of the electrodes was also coated. Then, the fine powder layers 5 and 6 having a thickness of 0.05 mm as shown in FIG. After drying this fine powder layer, 60 g of mixed carbonate
₂ g of γ-LiAlO ₂ and ₂ g of polyvinyl butyral well kneaded in isopropyl alcohol were applied to the upper surface of the fine powder layer 6 formed on the oxidizer electrode 4 and shown in FIG. 2 (b). An electrolyte layer 7 having such a thickness of 1 mm was formed.
The electrolyte layer 7 was dried and then pressurized at 100 kg / cm ² to be integrated. Further, the fuel electrode 3 on which the fine powder layer 5 previously manufactured is formed is laminated on the upper surface of the electrolyte layer 7, and the second
A unit battery 1 having a five-layer structure as shown in FIG.

The unit battery 1 is heated to a temperature between 350 ° C. and 550 ° C. to melt the carbonate and volatilize the organic binder.
The temperature was raised to 50 ° C. to cause an electromotive reaction.

The current-voltage characteristics of this unit battery 1 were measured and found to be 3
The results shown in Figure A were obtained. For comparison, the current-voltage characteristics of a unit cell using a 2 mm-thick electrolyte layer obtained by the conventional hot pressing method are shown in FIG. As is clear from this figure, the unit cell manufactured by the method of this example was able to obtain a higher output voltage than the conventional one. This is because the thickness of the electrolyte layer 7 can be reduced.

In addition, the unit battery 1 obtained by the method of this embodiment is
It was confirmed that the bubble generation pressure at the battery operating temperature was increased by 50% as compared with the conventional one, and the gas cross-mixing was small. This is because the fine powder layers 5 and 6 formed on both sides of the electrolyte layer 7 prevent migration of the molten carbonate due to gas pressure.

Then, in this case, it was confirmed that the electrolyte layer could be formed within 1 minute per sheet, and the productivity was extremely good, so that the productivity of the fuel cell was also high.

As described above, according to the manufacturing method of the present embodiment, the above-described effects can be sufficiently exhibited.

In addition, as another example, a three-layer structure was formed by forming an electrolyte layer of 1 mm square and a thickness of 0.6 mm on the electrode via a fine powder layer. Holding both ends of this three-layer structure,
It wasn't destroyed by its own weight.

Further, a unit powder was formed by further adding a fine powder layer and electrodes to the three-layer structure, and a plurality of unit batteries were laminated and the whole was fastened at a pressure of 1 kg / cm ² . As a result, it was confirmed that about 10% of the thickness of the electrolyte layer bites into one electrode, and the familiarity between the electrolyte layer and the electrode is improved as compared with the conventional one.

Furthermore, 2 using the electrolyte layer by the conventional hot pressing
When 0 layer laminated battery was tightened with a pressure of ² kg / cm ² ,
While cracks occurred in the three electrolyte layers, no cracks occurred in this example.

As described above, according to this example, it was confirmed that the above-described effects were sufficiently exhibited.

The present invention is not limited to the above embodiment.
For example, the carbonate holding material is lithium aluminate (LiAlO ₂ )
However, it may be strontium titanate (SrTiO ₃ ) or cerium oxide (CeO ₂ ). In addition, the fine powder layer 5,
As the fine powder used for 6, nickel powder or nickel alloy powder may be used. Both of the fine powder layers do not have to be formed on the electrode plate in advance. For example, the electrode plate, the fine powder layer, the electrolyte layer, the fine powder layer, and the electrode plate may be laminated in this order. . The organic binder may be polytetrafluoroethylene, polyethylene glycol, polymethylmethacrylate, or the like, and the non-aqueous solvent may be an alcohol having C2 to C6, toluene,
It may be acetone or the like.

Further, although the mixed carbonate was not described in detail in the above embodiment, the following combinations can be adopted.

Li ₂ CO ₃ / K ₂ CO ₃ , Li ₂ CO ₃ / K ₂ CO ₃ / Na ₂ CO ₃ , Na ₂ CO ₃ / K ₂ CO ₃ , Li ₂ CO ₃ / K ₂ CO ₃ / SrCO ₃ , Li ₂ CO ₃ / K ₂ CO ₃ / CaCO ₃ .

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a main part of a molten carbonate fuel cell assembled by using a unit cell manufactured by the manufacturing method according to the present invention, and FIGS. 2 (a) to 2 (c) are the same. FIG. 3 is a diagram for explaining the manufacturing process of the fuel cell, and FIG. 3 is a diagram for explaining the cell characteristics of the fuel cell in comparison with a conventional example. 1 ... Unit battery, 2 ... Interconnector, 3 ... Fuel electrode, 4 ... Oxidizer electrode, 5,6 ... Fine powder layer, 7 ... Electrolyte layer, 8, 9 ... Gas passage, A ... ... Characteristics of Example, B ...
... Characteristics of Comparative Example.

Claims (1)

[Claims] 1. A mixture obtained by mixing a molten carbonate-resistant fine powder material and an organic binder on one surface of a first porous electrode plate in manufacturing a unit cell of a molten carbonate fuel cell. To form a thin fine powder layer, and a mixture of a mixed carbonate, a carbonate holding material and an organic binder is applied to the fine powder layer obtained in this step to form an electrolyte layer. And a step of laminating the second porous electrode plate on the electrolyte layer obtained in this step through a thin fine powder layer made of a molten carbonate resistant fine powder material and an organic binder. A method for producing a molten carbonate fuel cell, which comprises: