JPS6017865A - Molten salt fuel cell - Google Patents

Abstract

PURPOSE:To obtain molten salt fuel cell solid electrolyte having high electrolyte ability, high thermal and mechanical shock resistance, and good corrosion resistance by impregnating molten salt in a porous substrate prepared by press- molding the mixture of metal oxide fibers whose surfaces are covered with lithium and lithium aluminate fine powder and sintering. CONSTITUTION:Lithium aluminate fine powder is mixed with alumina fibers whose surfaces are covered with lithium and they are press-molded with a binder containing solvent. After removing solvent, the moldings is sintered at high temperature to form a porous body. The sintered porous body is impregnated with molten carbonate at high temperature to prepare an electrolyte holding body. An air electrode 4 and a fuel electrode 5 are faced with the electrolyte holding body 3 interposed. An oxidizing gas chamber 6 and a stainless steel current collector 7 are arranged on air electrode side, and a fuel gas chamber 8 and nickel current collector 9 are on fuel side. This process provides a molten salt fuel cell with high performance, long life, and low cost.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is a molten salt twisting method in which hydrogen, carbon oxide, etc. are used as the fuel, acid 2, air, carbon dioxide, etc. are used as the oxidizing agent, and molten salt is used as the electrolyte. Regarding batteries.

Conventional configurations and their problems High-temperature molten salt fuel cells attempt to obtain high current density by taking advantage of the high chemical reaction rate at high temperatures. A molten salt capable of , for example, a carbonate having a conductivity of C0j-, is used. Then, a fuel cell is constructed in which the following reaction is carried out using hydrogen as a fuel and oxygen in the air as an oxidizing agent.

As is clear from the reaction equation 2, hydrogen reacts with 003 of the electrolyte and is consumed on the fuel electrode side, producing water and carbon dioxide as reaction products. On the other hand, on the air electrode side, oxygen and carbon dioxide are consumed as electrolytes in the form of CO kidneys. Here, the carbon dioxide gas generated on the fuel electrode side is supplied to the air electrode and consumed, so the overall reaction formula is 3P2H+%02→H20, and water is intermediately formed from hydrogen and oxygen. During electrolysis a, only CO3 ions move, and carbon dioxide gas does not participate in the mass balance. Therefore, it is desirable to be able to generate electricity through the above reaction efficiently and with stable performance over a long period of time. Among the factors that influence these properties is the electrolyte holder, and it is important that it has a high electrolyte holding capacity, is stable with respect to the electrolyte, and has high thermal and mechanical strength.

Conventional electrolyte holders have been made of sintered porous materials such as fine powder of magnesium oxide (MqOL aluminum oxide).This type of sintered porous material has poor thermal shock resistance at high temperatures of 600°C or higher. , it has the disadvantage of cracking and breaking due to heat cycles at high temperatures.In order to improve this disadvantage, fibrous lithium aluminate (
An electrolyte support consisting of lithium aluminate (LIAlO2) alone or in a mixture with powdered lithium aluminate (LIAl2O2) has been proposed (U, S, RAT, 387
8296). This type of electrolyte holder-1 consists of γ-alumina fiber (A1203 fiber) and lithium carbonate (L
12 CO3) at 700℃ for 16 hours to form γ-L.
IA IO2 fiber is available. This γ-Li
A/'02 The fiber is Al2O3 fiber and has excellent monolithic properties, but has low mechanical strength and is expensive. A small Al2O3 fiber alone has a problem in terms of i=1 edibility (high reactivity with electrolyte).

Purpose of the Invention The present invention focuses on the advantages of both oxides; they are inexpensive, have high electrolyte retention, are resistant to thermal and mechanical shocks, have excellent machining properties,
The aim is to obtain a molten salt fuel cell with stable performance over a long period of time.

Structure of the Invention The present invention is based on a metal oxide (mainly Al2) whose surface is lithiated.
Fine powder of lithium aluminate (L 1A102 ) mixed with fibers (O32MqO, etc.) is pressure-coated with a binder containing a solvent, and after removing the solvent, the sintered porous substrate is impregnated with molten salt. This is a molten salt fuel cell having an electrolyte support.

Description of examples 57・.

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

An enlarged view of the metal oxide fiber used as an electrolyte holder in the molten salt fuel cell of the present invention is shown in Fig. 1, its cross section is shown in Fig. 2, and a fuel cell using this fiber as an electrolyte holder is shown in Fig. 3. Shown below. In FIG. 1 and FIG. 2, a lithiation reaction occurs on the surface of the alumina fiber (γ-A1203) 1 to form a LiAl02 layer 2. Fine powder of lithium aluminate (LiAd○2) is mixed with alumina fiber whose surface has been subjected to lithium treatment, and the mixture is pressure-molded with a binder containing a solvent. After removing the solvent,
A porous body was produced by sintering at high temperature (1,000°C or higher).

The surface lithiation reaction of alumina fibers can be achieved by setting the amount of alumina and lithium to be 60% or less of the stoichiometric amount of reaction, and also by setting the reaction time to about 1 to 2 hours. In short, the conditions were such that the lithiation reaction proceeded only at the surface.

This sintered porous body was impregnated with molten carbonate at a high temperature to form an electrolyte holder. A performance test was then conducted using the fuel cell shown in FIG. There are four air holes 4 and a fuel electrode 5 via the electrolyte holder 3 of the present invention, and an oxidant gas chamber 6 on the air electrode side.
A current collector 7 made of stainless steel is provided. On the other hand, on the fuel electrode side, there is a fuel gas chamber 8 and a current collector 9 made of nickel. be. 14 is an end plate that holds the whole.

The air electrode and the fuel electrode are all manufactured by known methods, the air electrode being a nickel sintered porous electrode doped with lithium, and the fuel electrode being a nickel sintered porous electrode doped with chromium.

Fuel cells using the electrolyte holder of the present invention (to conventional type)
B) Compare the characteristics when using alumina fiber alone and the conventional type (q... when using lithium aluminate fiber alone. Operating temperature 206
°C, fuel gas: hydrogen gas, oxidant gas: air containing 20-30% carbon dioxide, electrode size: 50 lungs x 60 cavities, thickness 20 mm for testing. 8-1. C) Ll 4Tr flow j7+ (+ degree: 100 m
A/7 n,! +) Operation test, test result Song is shown as small-, 1-
1. In this way, the initial characteristics at 60 hours are as follows:
/There is only a difference of 3 stars in the first stage, but the total is 50 including 6 stoppages.
After approximately 0 hours have elapsed, performance deterioration is seen in B and C. The cause of this is thought to be that the B-A1203 fiber reacts violently with the molten carbonate electrolyte, causing cracks, etc., and that the performance deteriorates due to partial gas mixture inside the battery and gas leaks due to deformation. It will be done. C is L i A
Although there is little reaction between the 1O2 fiber and the molten carbonate electrolyte, it itself has low mechanical strength and cannot withstand the thermal balance, causing cracks inside like B, resulting in a decrease in performance. It's happening. On the other hand, the electrolyte holder of the present invention has no cracks due to thermal balance due to the mechanical strength of the γ-A4203 fiber and suppression of reactivity with the electrolyte due to lithiation on the surface, and there are almost no cracks even after 600 hours. There is no deterioration in performance. B and C are ○ for a decrease of approximately 0.1■/cell. It has been improved by 0.01V/cell, which is less than 1.0V/cell. Furthermore, since only the surface of γ-A1203 is surrounded by the lithium compound, the material cost is less than 1% and the processing time can be shortened, making it possible to further reduce costs.

In this example, alumina (A, γ type A1203) was used as the metal oxide fiber, but other thermal oxides,
Even if it is a fiber such as Mq○, in short, if it is a fibrous ceramic with surface 1 heat resistance, the 3° dimension can be applied, but if there is a small amount of metal oxide fiber with a lithiated surface, the effect will be low, so it will not crack. Therefore, at least 2 wt % or more of the electrolyte holding body is required. On the other hand, if a large amount of fiber is added, the strength will be improved, but it will also lead to an increase in cost, so in terms of strength and performance, about 20 wt% is optimal. At that time, if the amount of lithium is stoichiometrically 100 wt% with respect to the amount of 97° Al2O3 fibers, all of the lithium will be converted to lithium and discharged, so considering the cost, it is recommended that the weight be less than 50 wt%.

As can be seen from the effects of the invention, the present invention has improved the heat resistance, corrosion resistance, and thermal equilibrium of the electrolytic holder, thereby making it possible to generate electricity with high performance and over a long period of time, and at a lower cost. A molten salt fuel cell can be obtained.

[Brief explanation of the drawing]

Figure 1 is an enlarged view of an alumina fiber with a lithium compound formed on its surface, Figure 2 is a cross-sectional view of the alumina fiber in Figure 1, and Figure 3 is a configuration diagram of a molten salt fuel cell according to an embodiment of the present invention. be. 1...Alumina fiber, 2...LiAl
02 layer, 3... Electrolyte holding body, 4... Air electrode, 6... Fuel electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure/ Figure 3 Figure 2 TI ~2;□;

Claims (3)

[Claims] (1) Lithium aluminate (LIA 1302)
A molten salt fuel cell characterized in that its constituent elements are an electrolyte holder in which a porous sintered substrate containing a mixture of fine powder and metal oxide fiber whose surface is lithiated is impregnated with molten salt. (2) The amount of the metal oxide fiber is 2 to i in the mixture of metal oxide fiber and fine powder of lithium aluminate.
2. The molten salt fuel cell according to claim 1, wherein 2 Ow is mixed within the specified range. (3) Metal oxide fiber is mainly alumina (A1203
) The molten salt fuel cell according to claim 1, wherein the molten salt fuel cell is comprised of: