JPS6224566A - Molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To prevent a decrease in cell performance even when an electrolyte layer produced at low temperature and low pressure is used by forming a microporous layer on the surface, which is in contact with an electrolyte layer, of a fuel gas diffusion electrode, and filling the microporous layer with mixed carbonate. CONSTITUTION:A molten carbonate fuel cell consists of an electrolyte layer in which mixed carbonate is held in ceramic fine powder and fibers, a fuel gas diffusion electrode which is arranged on one side of the electrolyte layer, and an oxidizing gas diffusion electrode which is arranged on the other side of the electrolyte layer. In this fuel cell, a microporous layer is formed on the surface, which is in contact with the electrolyte layer, of the fuel gas diffusion electrode, and is filled with mixed carbonate. A unit cell is constituted by arranging the fuel electrode 2 and the oxidizing agent electrode 3 on each side of the electrolyte layer 1. The fuel electrode 2 consists of a fuel electrode substrate 4 and a microporous layer 5 which is formed on the substrate 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a molten carbonate fuel cell that has excellent characteristics, can be made large-sized, and is easy to manufacture.

[Technical background of the invention and its problems]

Molten carbonate fuel cells, which have been under development in recent years, are
The electrolyte made of carbonate is molten at high temperature to cause an electrode reaction.Compared to other fuel cells such as phosphoric acid type and solid electrolyte type, the electrode reaction occurs more easily and the heat generation efficiency is high, and it uses expensive precious metals. It has features such as not requiring a catalyst.

By the way, in such a molten carbonate fuel cell, the electromotive force obtained by one fuel cell is as low as IV, so in order to configure a high output power generation plant, it is necessary to stack multiple unit cells in series to form a fuel cell. The main body must be configured to obtain the summed output of each unit battery. Therefore, this type of fuel cell is constructed 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 between them. Each of these unit cells is stacked with a separator interposed therebetween, which has both the function of electrical connection between the unit cells and the function of forming a passage for reaction gas to each electrode plate.

Manifolds having reactive gas distribution and recovery functions are applied to the four sides of the fuel cell main body, and one of these manifolds is supplied with oxidizing gas, and the adjacent manifold is supplied with fuel gas, Both gases are made to flow, for example, perpendicularly to both sides of the unit cell. Then, at the fuel electrode, a reaction of H2+CO32--H20+CO2+2e- is caused, and at the oxidizer electrode, a reaction of 1/202 +CO2+2e--CO32- is caused, and after obtaining a DC output, gas is released from each opposing manifold. I'm trying to get it out.

Incidentally, from the point of view of preventing cross-mixing of the reaction gas flowing through both sides of the electrolyte layer, it is desirable that the electrolyte layer be a dense thin plate. This is because if the material contains a large number of pores, the reaction gases will cross each other through the pores. From this point of view, conventionally, the electrolyte layer is made by mixing aggregate for electrolyte retention with carbonate,
A dense plate-like body, called an electrolyte tile, obtained by hot pressing under the conditions of lld was used. 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, in order to form the electrolyte layer by hot pressing, it is necessary to apply a high pressure per unit volume, and therefore a large-sized press apparatus must be used, which inevitably increases equipment costs. Moreover, in the case of hot press,
It takes time to heat the mixture of aggregate and carbonate, and sudden mechanical shock cannot be applied during pressing, so 1.
There was a problem in that it was difficult to increase the production speed per sheet, and the productivity was extremely poor.

However, if the electrolyte layer is formed at low temperature and low pressure, as mentioned above, the electrolyte layer contains, for example, 10vol% to 50vol%.
%, and cross-mixing of the reactant gases occurs, making it impossible to obtain good properties.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and provides a molten carbonate fuel cell that does not cause any deterioration in cell performance even when using an electrolyte layer manufactured at low temperature and low pressure, which is an advantageous manufacturing method. It's about doing.

[Summary of the invention]

The present invention provides an electrolyte layer formed by holding a mixed carbonate with ceramic fine powder and fibers, a fuel gas diffusion electrode disposed on one surface of the electrolyte layer, and an electrolyte layer disposed on the other surface of the electrolyte layer. In a molten carbonate fuel cell comprising an oxidant gas diffusion electrode, a microporous layer is formed on a surface of the fuel gas diffusion electrode that contacts the electrolyte layer, and the microporous layer is formed with the mixed carbonate. It is characterized by being filled with

〔Effect of the invention〕

According to the present invention, carbonate is contained in the microporous layer formed on the fuel gas diffusion electrode, and is held within the pores of the microporous layer by surface tension. Therefore, since this acts as a permeation-preventing layer for reactive gases, cross-mixing of reactive gases hardly occurs, resulting in good battery performance.

With such a configuration, the electrolyte layer does not need to have a particularly dense structure, so there is no need to form the electrolyte layer by hot pressing. It is therefore possible to use, for example, an organic binder in the electrolyte layer, thereby binding the mixed carbonate electrolyte to the ceramic fine powder and fibers.

In this case, hot press 1. , unlike the join by
The electrolyte layer can be formed at a low temperature and pressure of 200° C. or less. Therefore, the processing speed of each electrolyte layer can be increased.

[Embodiments of the invention]

<Example> 35 g of β-lithium aluminate powder with a specific surface area of 29 yd/g and 60 g of mixed carbonate were thoroughly mixed in a ball mill using acetone as a solvent, then 5 g of lithium aluminate fiber was added and further mixed for 1 hour. did. Next, 20 g of polyethylene as an organic binder was added and mixed for 1 hour. Thereafter, acetone was removed to prepare an electrolyte mixture. This electrolyte mixture was filled into a mold and heated to 160°C.
It was molded under low temperature and low pressure conditions of 100 kg to obtain a thin plate-like electrolyte layer. The resulting electrolyte layer had a porosity of 35%.

Next, a fuel electrode (fuel gas diffusion electrode) was formed as follows. That is, a nickel-10w%Cr powder porous body with a porosity of 65% and an average pore size of 4.5p was used as a substrate, fine nickel powder with an average particle size of 0.8m was applied by suction to this, and the mixture was heated at 820°C for 1 hour. A sintering treatment was performed in a hydrogen stream to form a microporous layer with an average pore diameter of 0.8 dust. Mixed carbonate (L i2 CO3 (62 mo 1
%) - to 2 CO3 (38mo 1%)) per 11
A weight of 5η was applied, and the temperature was raised to 600°C to impregnate the porous body. Note that this impregnation was performed in a carbon dioxide atmosphere.

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

Then, as shown in FIG. 1, a fuel electrode 2 and an oxidizer electrode 3 were placed on both sides of the electrolyte layer 1 to form a single cell. In the figure, numeral 4 indicates a fuel electrode substrate, and numeral 5 indicates a microporous layer 5 formed on two sides of the fuel electrode.

When the cell voltage of the single cell thus obtained at 150771A/~ was investigated, the results shown in FIG. 2 were obtained. In Fig. 2, al is the cell voltage when open circuit, a
2 is the cell voltage under 15071LA/i current flow. For comparison, bl 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 this example can obtain a higher output voltage than the conventional one, and its aging characteristics are also good.

In addition, when we investigated the change over time in the amount of cross-mixing of reactant gases (the amount of hydrogen contained in the oxidizer electrode side outlet gas) of the fuel cell according to the present example and the fuel cell of the conventional example, the results are shown in Fig. 3. I got it. As is clear from this figure, in the single cell according to this example, the amount of cross-mixing is also very small compared to the conventional cell. This is because in this example, a microporous layer is formed on the surface of the substrate, and this layer contains carbonate.
This is because the carbonate is retained within the micropores and serves as a reaction gas permeation prevention layer.

As described above, by using an electrolyte layer formed by low-temperature, low-pressure molding and a fuel electrode in which a microporous layer is formed on a substrate and this microporous layer is impregnated with carbonate, a fuel cell with excellent processability and good characteristics can be achieved. is obtained.

Note that the present invention is not limited to the embodiments described above.

That is, in the above embodiments, the pore diameter of the microporous layer is between 0.8 and 0.8, but the pore diameter is not limited to this.

However, if the pore diameter exceeds 1p, the foam output indicating the cross-mixing amount will be small, so it is desirable that the pore diameter be 1p or less. Further, when impregnating the microporous layer with molten carbonate, pressure may be applied to prevent warping of the fuel electrode.

Further, in the above embodiment, the mixed carbonate was 5511 g per IC7j, but the amount of impregnation that fills the microporous layer of the fuel electrode may be as long as the above amount. This amount would require a minimum carbonate weight that satisfies 5% or more of the total pore volume of the fuel electrode.

In the above-described embodiments, a mixture of nickel and chromium was used as the fuel electrode, but a nickel-cobalt alloy, copper, etc. may also be used.

Furthermore, the ceramic fine powder and fibers used in the electrolyte layer are not particularly limited to lithium aluminate, but include ceramic fibers such as zirconia, alumina, lithium zirconate, lithium titanate, and boron nitride. Strontium titanate, cesium oxide, etc. may be used as 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,
Alcohols of 2 to C6, toluene, acetone, etc. may also be used.

Moreover, as the mixed carbonate to be used, those shown below can be used.

L i2 CO3/2 C03 L 12CO3/2 CO3/Na2CO3Na2C
O3/2 C03 L i2 CO3/2 CO3/S r C03L
i2 CO3/ni2 CO3/CaCO3 Thus,
The present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

Figure 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 Figure 2 compares the cell voltage characteristics over time of the same battery with a conventional one. FIG. 3 is a characteristic diagram showing a change over time in the hydrogen concentration contained in the oxidizer electrode outlet gas in comparison with a conventional one. DESCRIPTION OF SYMBOLS 1... Electrolyte layer, 2... Fuel electrode, 3... Oxidizer electrode, 4... Fuel electrode base, 5... Microporous layer, a, al,
a2...Characteristics of an embodiment of the present invention, b, bl, b2...
・Characteristics of comparative example. Applicant's agent Patent attorney Takehiko Suzue 1st drawing vJ Chiku (h) → 2nd drawing Fang 3rd drawing

Claims (4)

[Claims] (1) An electrolyte layer formed by holding a mixed carbonate with ceramic fine powder and fibers, a fuel gas diffusion electrode placed on one side of this electrolyte layer, and an oxidation layer placed on the other side of the electrolyte layer. In a molten carbonate fuel cell comprising a chemical gas diffusion electrode, a microporous layer is formed on a surface of the fuel gas diffusion electrode that contacts the electrolyte layer, and the microporous layer is formed with the mixed carbonate. A molten carbonate fuel cell characterized by: (2) The molten carbonate fuel cell according to claim 1, wherein the electrolyte layer contains an organic binder during its manufacturing process and is formed under low temperature and low pressure conditions. (3) The molten carbonate fuel cell according to claim 1, wherein the microporous layer of the fuel gas diffusion electrode has pore diameters that vary in the thickness direction. (4) The molten carbonate fuel cell according to claim 1 or 3, wherein the microporous layer of the fuel gas diffusion electrode has a pore diameter of 1 μm or less.