JPH04137469A - Fused carbonate fuel cell - Google Patents

Abstract

PURPOSE:To maintain excellent power generation characteristic for a long time by using LiAlO2, on whose surface zirconia is partially made, as holding material. CONSTITUTION:An electrolyte layer for a fused carbonate fuel cell is formed of LiAlO2, on whose surface zirconia is partially made, being used as holding material, and porous matrix being made by mixing LiAlO2 or ZrO2 and being impregnated with fused alkali carbonate which is to be electrolyte, being used as reinforcing material. And it is desirable for LiAlO2 to have specific surface of 8m<2>/g or more at the state before its surface is treated. On the other hand it is desirable for the reinforcing material to be mixed at a rate of 40% or less against the holding material. Thereby it is possible to obtain excellent power generation characteristic for a long hour.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to a molten carbonate fuel cell, and particularly relates to a molten carbonate fuel cell in which the material of the electrolyte plate is improved (conventional). Technology) Molten carbonate fuel cells, which have been under development in recent years, are
The electrolyte made of alkali 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 higher. has.

The main part of this molten carbonate fuel cell is usually an electrolyte plate made of a mixture of an alkali carbonate as an electrolyte, a ceramic support material, and a reinforcing material and formed into a flat plate.
Gas diffusion electrodes (anode and cathode) such as Z-Kel alloy are brought into close contact to form a unit cell, and a plurality of these unit cells are stacked with bipolar separators interposed between them.

Here, the holding material constituting the electrolyte plate has a particle size of 0.1-0.5 μm and a specific surface area of 1°-23rr, for example. /
The γ phase of g is the main constituent phase, and the α phase is a few percent as an impurity phase.
containing LiAlO. is used. This L i A
I O2 is a relatively stable compound in molten carbonate, but if it coexists with molten carbonate for a long time, grain growth occurs, the specific surface area decreases significantly, and the porous structure that forms the skeleton Since the pore size of the matrix becomes coarse, electrolyte retention deteriorates.

In particular, when the specific surface area of the holding material decreases and becomes 5 d/g or more, the electrolyte holding property deteriorates rapidly, causing leakage and volatilization of the electrolyte 1, which increases the internal resistance and causes local dissipation of the electrolyte. This also causes cross-oh-nos caused by the oxidation, and significantly deteriorates the power generation characteristics, resulting in problem 2.

On the other hand, Zr is a relatively stable substance against molten carbonate.
O2 or partially stabilized Zr02 (stabilized with a small amount of intrium, calcia, magnesia, etc.) is known, and its long-term stability against molten carbonate salts has been proven.

However, since ZrO2 and partially stabilized ZrO2 have poor wettability with respect to molten carbonate, they still have poor electrolyte retention properties and cannot be used alone as a retention material.

(Problems to be Solved by the Invention) The present invention has been made to solve the above problems, and uses a retaining material that suppresses a decrease in specific surface area and does not deteriorate electrolyte retention properties, and can be used for a long time. An object of the present invention is to provide an electrolyte plate for a molten carbonate fuel cell that can maintain good power generation characteristics.

[Structure of the Invention (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention takes a measure of using LiAIoz whose surface is partially made into zirconia as a holding material. Here, to partially zirconia the surface of Li A I O2 means that Z on the surface of LiAlO□
This means that rO2 or Li2ZrOs phase is partially generated. This partial zirconia formation is achieved by coating the holding material by dipping it in a solution of zirconium metal, such as an alkoxide or basic solution, followed by heat treatment, and adding Zr to the surface of Li A 102 as ZrO2 or Li2Zr0. This can be done by depositing about 10% by weight in the form of.

Therefore, the electrolyte layer for a molten carbonate fuel cell according to the present invention is made of L having a partially zirconia surface as a holding material.
iAlO2 and LiAlO2 or Zr as a reinforcing material
It is formed by melting and impregnating an alkali carbonate serving as an electrolyte into a porous matrix mixed with O2.

LiAlO2 constituting the holding material of the present invention has a specific surface area of 8 m 2 / g before the above surface treatment.
or more (preferably 20 m2/g or less, more preferably 9
As a result of reaction tests with molten carbonate, etc., it was found that a range of -9-1 l/H) is preferable. That is, 8m
2/g or less, the retention during reaction is poor;
When the specific surface area is as high as /g or more, it becomes extremely difficult to form a porous body. Moreover, LiAlO2 is ideally γ-L
Although iAlO2 alone is preferred, a small amount of α-LiAlO2 usually exists as an impurity phase. This α-
When the content of LiAlO□ is 0.5% by weight or more, phase transformation to α-LiAlO2 is easily caused by reaction with molten carbonate, and grain growth is significantly accelerated.

On the other hand, the reinforcing material is 4096 or less (usually 20-
30%) is preferable.

That is, if it exceeds 40%, the electrolyte retention will be insufficient due to the low retaining material content ratio. In addition, as the reinforcing material particles, L i A I which is stable against molten salt in terms of material is used.
O2, ZrO2, L L2 ZrOs are preferable, and the average particle size is usually 10μ from the viewpoint of heat cycle resistance.
m or more and 50 μm or less is better; if it is smaller than 10 μm, the effect of preventing crack propagation is insufficient;
If it exceeds m, there is a risk that the foreign matter may become a starting point for cracks during molding.

In this way, the specific surface area is 8 m2/g or more, and the content α-L I
A l 02.0. Even when 5% by weight or less of LiAlO2 is used as a retaining material and LiAlO2 with an average particle size of 20 μm is used as a reinforcing material, the retaining material undergoes grain growth in about 2000 to 3000 hours due to reaction with molten carbonate, and the electrolyte retention is impaired. Function deteriorates. This grain growth may occur between the retaining materials or as a result of cannibalism between the retaining material and the reinforcing material.In particular, if the retaining material and the reinforcing material are made of the same material, the process of dissolution and reprecipitation will be accelerated. Since the grain growth between the retaining material and the grain growth between the retaining material and the reinforcing material occur simultaneously, the specific surface area decreases in a relatively short period of time, and the electrolyte retention function decreases.

Therefore, the holding material of the present invention contains α-Li as an impurity component.
Zr, 02 or LiAlO2 phase is partially generated on LiA 102 by coating the surface of LiAlO□ with an AIO2 content of 0.5% or less with Zr metal alkoxide or basic solution and heat-treating it. It is characterized by causing

By applying such surface treatment, the areas where LiAlO2 dissolves or re-precipitates are reduced, suppressing grain growth between the retaining materials, and at the same time suppressing the meshing between the retaining materials and reinforcing materials, increasing the specific surface area. The decline is suppressed. In particular, by adding ZrO2 to L i A I O2 as a reinforcing material, grain growth due to interlocking between the retaining material and the reinforcing material is significantly suppressed.

(Function) Li whose surface is partially zirconiaized as described above
If a porous body using A102 as a retaining material and LiAl0□ or ZrO2 as a reinforcing material is used as an electrolyte matrix, the electrolyte retaining property will be maintained for a long time, and the molten carbonate will have less deterioration in power generation characteristics. An electrolyte plate for a salt fuel cell can be provided.

(Example) The present invention will be explained in detail below.

Example 1 Specific surface area 10 m”/g, a-LiAIO□ content 0.2
% LiAlO2 was immersed in a zirconium alkoxide solution, dried, and then heat-treated at 900° C. in the air to synthesize a holding material whose surface was partially zirconia-ized. Note that there was no decrease in specific surface area before and after synthesis. On the other hand, 55 each of LiAlO2 and ZrO2 with an average particle size of 20 μm were used as reinforcing materials.
A mixed powder of 0.096 and 0.096 was used.

70 g of this holding material and 30 g of reinforcing material were mixed together with 30 g of a molding binder in 100 g of an organic solvent using a ball mill, and the slurry taken out was defoamed and spread on a film to form a crack-free sheet. When the obtained green sheet was degreased and its porosity and average pore diameter were measured, it was found that a porous matrix sheet with a porosity of 53% and an average pore diameter of 0.23 μm was obtained.

Example 2 LiAl0.1 with a specific surface area of 10rrf/g and a-L i A 102 content of 0.1%. was heat-treated in the same manner as in Example 1 to synthesize a retaining material whose surface was partially zirconia-ized. Furthermore, it was made into a sheet using the same method to obtain a good green sheet (porous matrix sheet) with no cracks.

Example 3 Specific surface area 9rrr/g, a-L iA 102 content o
.

2% Li A 102 was heat treated in the same manner as in Example 1 to synthesize a retaining material whose surface was partially zirconia. Furthermore, a good green sheet with no cracks was obtained by forming it into a sheet using the same method.

Example 4 Li A 102 with a specific surface area of 10 g/g and an α-Li A I O2 content of 0.2% was heat treated in the same manner as in Example 1, and the surface was partially zirconiaized. The materials were synthesized. Further, 60 g of this holding material and 40 g of reinforcing material were mixed together with 30 g of a molding binder in 100 g of an organic solvent using a ball mill, and the mixed slurry was defoamed and spread on a film to form a crack-free sheet. .

Example 5 Specific surface area 11rrf/g, a-L i AIO□
LiAlO2 having a content of 0.2% was heat treated in the same manner as in Example 1 to synthesize a holding material whose surface was partially zirconia. Furthermore, the green sheet was formed into a sheet in the same manner as in Example 1, and a good green sheet without cracks was obtained.

Example 6 Specific surface area 10rr”/g, a-L i AIO
□L i A 102 with a content of 0.2% was heat treated in the same manner as in Example 1 to synthesize a holding material whose surface was partially zirconia-ized. Furthermore, 80g of holding material and 20g of reinforcing material
The slurry was mixed with 30 g of a molding binder in 100 g of an organic solvent using a ball mill, and the resulting slurry was defoamed and spread on a film to form a crack-free sheet.

Comparative Example 1 LiA 102 with a specific surface area of 7g/g and an α-LiAlO□ content of 0°2% was heat treated in the same manner as in Example 1,
A holding material with a partially zirconia surface was synthesized. Furthermore, a good green sheet with no cracks was obtained by forming it into a sheet using the same method.

Comparative Example 2 Specific surface area 10rrIt/g, a-LLA102 content 0
．． 2% LiAlO2 was heat treated in the same manner as in Example 1 to synthesize a retaining material whose surface was partially zirconia. Further, 50 g of the retaining material and 50 g of the reinforcing material were mixed together with 30 g of a molding binder in 100 g of an organic solvent using a ball mill, and the slurry taken out was defoamed and spread on a film to form a crack-free sheet.

Comparative Example 3 Specific surface el 0rrf/g, a-L i A l 0
2 content of 0.6% was heat-treated in the same manner as in Example 1 to synthesize a holding material whose surface was partially zirconia-formed. Furthermore, a good green sheet with no cracks was obtained by forming it into a sheet using the same method.

Comparative Example 4 Specific surface area 10g/g, α-LLA 102 content 0
．． 10270 g of 2% L i A and 30 g of reinforcing material were mixed together with 30 g of molding binder in 100 g of organic solvent using a ball mill, and the slurry was defoamed and spread on a film to form a crack-free sheet. Molded.

The crack-free green sheet obtained on each side was cut into 4 (1) squares, and this was coated with L i 2 COs / 2 C05
(62/38 mol) of eutectic salt was melted and impregnated to prepare an electrolyte plate for stability evaluation. Stability test is air/co2-70
/30% by volume in a cathode atmosphere of 1 atm in a furnace at 650°C. Further, carbonate was removed from the electrolyte plate after 5000 hours by pickling, and the specific surface area after testing by BET method and the average pore diameter of the matrix were measured by mercury porosimetry.

The test results are shown in Table 1.

As is clear from Table 1 above, the specific surface area of the holding material is 500
All of them decreased after 0 hours of reaction with molten carbonate, but it was confirmed by SEM observation that this was the result of grain growth of the primary particles of the holding material. The surface is treated with zirconia, the α amount is 0°5% or less, and the specific surface area is 9rr.
The samples of Examples 1-6 with r/g or more and retaining material blending ratio of 60% or more have a specific surface area of 5 rf/g or more after the test, and an average pore diameter of 0.5 μm or less after electrolyte removal. It was found that it had sufficient retention. Furthermore, the tendency of grain growth tends to be suppressed as the amount of α is smaller (Example 2) and the blending ratio of the retaining material is higher (Example 6). On the other hand, comparative example 1 has a low initial specific surface area of 7r+f/g or less.
, Comparative Example 2 where the holding material blending ratio is low at 50% or less, α amount is 0
．． In Comparative Example 3, which has a large amount of 6% or more, and Comparative Example 4, in which the surface is not treated with zirconia, the specific surface area after the test decreases to 5 rf/g or less, and the average pore diameter also becomes 0.5 μm or more, which is sufficient. It was found that it had no retention properties.

Results of thermal cycling and stability evaluation of surface electrolyte plate [Effects of the invention] As detailed above, according to the present invention, grain growth and reduction in specific surface area of the retaining material in the electrolyte plate are suppressed, and electrolyte retention is Since a holding material whose properties do not deteriorate is used, it is possible to provide an electrolyte plate for a molten carbonate battery that can obtain good power generation properties over a long period of time.

Claims (1)

[Claims] (1) A molten carbonate fuel cell comprising a cathode and an anode made of a porous molded body, and an electrolyte plate disposed between the cathode and the anode and containing an electrolyte, a holding material, and a reinforcing material, the holding material Li with a partially zirconia surface
A molten carbonate fuel cell characterized by using AlO_2.