JPH0799695B2 - 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 has excellent characteristics, can be made large in size, and has excellent manufacturability.

[Technical background of the invention and its problems]

Molten carbonate fuel cells, which are under development in recent years,
Electrolytic reaction of carbonates in an molten state at high temperature to cause electrode reaction. Electrode reaction is more likely to occur compared to other fuel cells such as phosphoric acid type and solid electrolyte type, high heat generation efficiency, and expensive precious metal. It has features such as no need for a catalyst.

By the way, in such a molten carbonate fuel cell, the electromotive force obtained by one fuel cell is as low as 1 V. Therefore, in order to construct a high output power plant, a plurality of unit cells are stacked in series to form a fuel cell. The main body must be configured to obtain the added output of each unit battery. Therefore, this type of fuel cell is configured as follows.

That is, each unit cell is composed of a pair of gas diffusion electrode plates, that is, a fuel electrode and an oxidizer electrode, and an electrolyte layer made of an alkali carbonate interposed therebetween. Each of these unit batteries is laminated via a separator that has both an electrical connection function between the unit batteries and a function of forming a passage of a reaction gas to each electrode plate.

A manifold having a function of distributing and collecting a reaction gas is applied to four side surfaces of the fuel cell main body, and an oxidant gas is supplied to one of the manifolds and a fuel gas is supplied to an adjacent manifold, Both gases are caused to flow on both sides of the unit cell so as to cross each other, for example. Then, a reaction of H ₂ + CO ₃ ^2- → H ₂ O + CO ₂ + 2e ⁻ occurs at the fuel electrode and a reaction of 1 / 2O ₂ + CO ₂ + 2e ⁻ → CO ₃ ²⁻ occurs at the oxidizer electrode, and the DC output is generated. Then, the gas is exhausted from each of the opposing manifolds.

By the way, from the viewpoint of preventing cross-mixing of the reaction gases flowing on both sides of the electrolyte layer, it is desirable that the electrolyte layer is a dense thin plate. This is because, if a large number of pores are included, the reaction gas will cross through the pores. From such a point, conventionally, a so-called electrolyte tile obtained by mixing an aggregate for retaining an electrolyte and a carbonate as an electrolyte layer and hot-pressing under the conditions of 400 ° C to 500 ° C and 200 to 500 kg / cm ² is used. It was called a dense plate-like body. Since this electrolyte layer has an extremely low porosity of 5 vol% or less, the reaction gas can be completely separated by the molten carbonate, and cross-mixing of the reaction gas can be prevented.

However, the electrolyte layer formed as described above is inferior in mechanical strength, and when the size of the electrolyte layer is several tens of cm square or more,
Cracks easily occur in the electrolyte layer due to slight strain generated during assembly, and cracks may occur in the electrolyte layer even after assembly due to the thermal cycle of the battery, which eventually prevents cross-mixing of reaction gases. There was a problem I could not do. Further, in order to mold the electrolyte layer by hot pressing, it is necessary to increase the applied pressure per unit volume, so a large-sized pressing device must be used, and an increase in equipment cost cannot be avoided. Moreover, in the case of hot pressing, it takes time to heat the mixture of the aggregate and the carbonate, and it is difficult to increase the production speed per sheet because a rapid mechanical impact cannot be applied during the pressing. Yes,
There was a problem of extremely poor productivity.

However, if the electrolyte layer is formed at low temperature and low pressure, as described above, the electrolyte layer will contain many pores of, for example, 10 vol% to 50 vol%, and cross-mixing of the reaction gases will occur, resulting in good characteristics. I can't.

[Object of the Invention]

The present invention has been made based on the above circumstances, and even if cracks occur in the electrolyte layer due to slight distortion at the time of assembly or thermal cycle after assembly, the reaction gas crosses. Provided is a method for producing a molten carbonate fuel cell, which can contribute to prevention of mixing, and which does not cause any deterioration in cell performance even if an electrolyte layer produced at low temperature and low pressure, which is an advantageous method for production, is used. Is intended.

[Outline of Invention]

In the method for producing a molten carbonate fuel cell according to the present invention, a step of forming an electrolyte layer having a porosity of 10 to 50 Vol% using an organic binder containing mixed carbonate, ceramic fine powder, and fibers as main components, and porosity. A step of forming a two-layered fuel gas diffusion electrode by forming a fine pore layer having an average pore diameter of 1 μm or less on one surface portion of a substrate formed of a porous body; Applying a mixed carbonate to the surface of the microporous layer and then heating it to impregnate the mixed carbonate into the microporous layer; and contacting the microporous layer on one surface of the electrolyte layer with the fuel And arranging a gas diffusion electrode and arranging an oxidant gas diffusion electrode in contact with the other surface of the electrolyte layer to assemble a unit cell.

〔The invention's effect〕

According to the manufacturing method of the present invention, a microporous layer having an average pore diameter of 1 μm or less is formed on one surface of a substrate formed of a porous body to obtain a fuel gas diffusion electrode having a two-layer structure, The mixed carbonate is applied to the surface of the microporous layer and heated to impregnate the microcarbon layer with the mixed carbonate. In this case, it is extremely easy to confirm whether or not the mixed carbonate is impregnated into the microporous layer surely and uniformly, and it is also easy to create the condition for uniform impregnation. Then, the fuel gas diffusion electrode is incorporated so that the microporous layer impregnated with the mixed carbonate contacts one surface of the electrolyte layer. Therefore,
A uniform mixed carbonate layer can be reliably formed in the microporous layer due to the surface tension, and this microporous layer acts as a reaction gas permeation preventive layer. Even if cracks occur in the electrolyte layer due to the cycle, cross-mixing of the reaction gas hardly occurs without being affected by the cracks, and the battery performance becomes good.

With such a manufacturing method, the electrolyte layer does not have to have a particularly dense structure, and thus it is not necessary to form the electrolyte layer by hot pressing. Therefore, it is possible to use an organic binder in the electrolyte layer, which allows the mixed carbonate electrolyte to bind to the ceramic fine powder and fibers. In this case, unlike the bonding by hot pressing, the electrolyte layer can be formed at a low temperature and low pressure of 200 ° C. or lower. Therefore, the processing speed of one electrolyte layer can be increased.

Example of Invention

<Example> 35 g of β-lithium aluminate powder having a specific surface area of 29 m ² / g
And 60 g of mixed carbonate with a ball mill using acetone as a solvent, and then 5 g of lithium aluminate fiber
Was added and mixed for an additional 1 hour. Next, 20 g of polyethylene, which is an organic binder, was added and mixed for 1 hour. Then, acetone was removed to prepare an electrolyte mixture. This electrolyte mixture was filled in a mold and molded under low temperature and low pressure conditions of 160 ° C. and 100 kg to obtain a thin plate-like electrolyte layer. The porosity of the obtained electrolyte layer was 35%.

Next, a fuel electrode (fuel gas diffusion electrode) was formed as follows. That is, a nickel-10w% Cr powder porous body having a porosity of 65% and an average pore diameter of 4.5 µm was used as a substrate, and fine nickel powder having an average particle diameter of 0.8 µm was suction-coated onto the porous body.
Sintering treatment was performed in a hydrogen stream at 20 ° C. for 1 hour to form a fine pore layer having an average pore diameter of 0.8 μm. 1% mixed carbonate (Li ₂ CO ₃ (62mol%)-K ₂ CO ₃ (38mol%)) was added to this porous body.
A weight of 55 mg per cm ^{2 was} applied, and the temperature was raised to 600 ° C. to impregnate the porous body. The impregnation was performed in a carbon dioxide atmosphere.

Further, a nickel porous body having a porosity of 70% and an average pore diameter of 13 μm was prepared as an oxidant electrode (oxidant gas diffusion electrode).

Then, as shown in FIG. 1, the fuel electrode 2 and the oxidant electrode 3 were arranged on both surfaces of the electrolyte layer 1 to form a single cell. In the figure, 4 indicates a fuel electrode substrate, and 5 indicates a microporous layer 5 formed on the upper surface thereof.

When the cell voltage of the single cell thus obtained at 150 mA / cm ² was examined, the results shown in FIG. 2 were obtained. In Fig. 2, a1 is the cell voltage at open circuit and a2 is 150mA /
It is the cell voltage under flowing cm ² . For comparison, b1 and b2 in the figure are cell voltages under the same conditions as above when a conventional fuel electrode is used. As is clear from this figure, it was confirmed that the single cell of the present example obtained a higher output voltage than the conventional one and the time-dependent characteristics thereof were also favorable.

Further, the change over time in the cross-mixing amount (the amount of hydrogen contained in the oxidant electrode side outlet gas) of the reaction gas of the fuel cell according to this example and the fuel cell of the conventional example was examined, and the results shown in FIG. 3 were obtained. Got As is clear from this figure, in the single cell according to the present embodiment, the cross mixing amount is also much smaller than that of the conventional cell. This is because the microporous layer is formed on the surface of the substrate in this example and contains the carbonate,
This is because carbonate is retained in the fine pores and this serves as a reaction gas permeation preventive layer.

As described above, after the fine gas layer having an average pore diameter of 1 μm or less is formed on one surface of the substrate formed of a porous body to obtain a fuel gas diffusion electrode having a two-layer structure, the surface of the fine hole layer is formed. The mixed carbonate is applied to and heated to impregnate the microporous layer with the mixed carbonate. Then, the fuel gas diffusion electrode is incorporated so that the microporous layer impregnated with the mixed carbonate contacts one surface of the electrolyte layer. Therefore, a uniform mixed carbonate layer can be reliably formed in the fine pore layer by the surface tension, and a reaction gas permeation preventive layer can be formed by the impregnated mixed carbonate layer. Even if a crack is generated in the electrolyte layer due to the subsequent heat cycle, cross-mixing of the reaction gas can be prevented without being affected by the crack.
Further, since the electrolyte layer formed under the low temperature and low pressure condition is used, a fuel cell having excellent workability and excellent characteristics can be obtained.

The present invention is not limited to the above embodiment.

That is, although the pore diameter of the fine pore layer is 0.8 μm in the above-mentioned embodiment, the pore diameter is not limited to this.
However, when the pore diameter exceeds 1 μm, the foam output indicating the cross-mixing amount becomes small, so 1 μm or less is desirable.
Further, when impregnating the molten carbonate into the microporous layer, pressure may be applied to prevent warping of the fuel electrode.

Further, in the above-mentioned examples, the mixed carbonate was set to 55 mg per cm ² , but the impregnation amount may be at least the weight that fills the fine pore layer of the fuel electrode. This amount is 5% of the total pore volume of the fuel electrode
A minimum carbonate weight satisfying the above will be required.

In addition, although the mixture of nickel and chromium is used as the fuel electrode in the above-described embodiment, nickel-cobalt alloy, copper, or the like may be used.

Further, the fine ceramic powder and fibers used for the electrolyte layer are not particularly limited to lithium aluminate, for example, as ceramic fibers zirconia, alumina, lithium zirconate, lithium titanate, boron nitride, etc., and ceramics. You may use strontium titanate, cesium oxide, etc. as a fine powder. Also,
As the organic binder, ponyvinyl butyral, polyethylene, silicone rubber, polyethylene glycol, polymethyl methacrylate, etc. may be used, and as the non-aqueous solvent, C ₂
Alcohol up -C _6, toluene, or the like may be used acetone.

As the mixed carbonate used, those shown below can be used.

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 As described above, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of a unit cell of a molten carbonate fuel cell according to an embodiment of the present invention, and FIG. 2 compares the time-dependent characteristics of the cell voltage of the unit cell with those of a conventional one. FIG. 3 is a characteristic diagram showing the change over time in the concentration of hydrogen contained in the oxidant electrode outlet gas in comparison with the conventional one. 1 ... Electrolyte layer, 2 ... Fuel electrode, 3 ... Oxidizer electrode, 4 ...
... fuel electrode substrate, 5 ... microporous layer, a, a1, a2 ... characteristics of one embodiment of the present invention, b, b1, b2 ... characteristics of a comparative example.

Claims (1)

[Claims] 1. A porosity of 10-50 using an organic binder containing mixed carbonate, ceramic fine powder and fibers as main components.
A step of forming a vol% electrolyte layer, and a step of forming a microporous layer having an average pore diameter of 1 μm or less on one surface of a substrate formed of a porous body to obtain a fuel gas diffusion electrode having a two-layer structure. A step of applying a mixed carbonate to the surface of the fine pore layer of the fuel gas diffusion electrode obtained by this step and then heating the mixed carbonate to impregnate the fine pore layer with the mixed carbonate, and one of the electrolyte layers Assembling the unit cell by contacting the surface of the microporous layer with the fuel gas diffusion electrode and arranging the other surface of the electrolyte layer with the oxidant gas diffusion electrode. A method for producing a molten carbonate fuel cell, which is characterized.