JPS62128457A - Molten carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To achieve the long time performance of electrical energy generating ability and anti-heat cycle resistance, by providing an electrolytic plate which is formed by hot-compression molding the mixture of the main holding material of electrolyte and lithium aluminate powder and the reinforcing material of potassium titanate fiber. CONSTITUTION:Lithium aluminate powder is used for a main holding material, the potassium titanate fiber of relatively small quantity, namely 5-30 weight portions against the main holding material of 50 weight portions is added to the main holding material as a reinforcing material, and powdery substance in which the electrolytic powder of the mixture of lithium carbonate and potassium carbonate, the lithium aluminate powder and the potassium titanate fiber are mixed and dispersed is hot- compression molded with using a hot press so as to form an electrolytic plate. The electrolytic plate in which the carbonate powder of the mixture of lithium carbonate and potassium carbonate, the lithium aluminate powder and the potassium titanate fiber are mixed in a prescribed blending ratio is molded and processed by the way of hot press under the conditions of the molding temperature of about 480 deg.C and the pressure of about 200-600kg/cm<2>. Thus, anti-heat cycle resistance can be improved, and electrical energy generating ability can be maintained stably for long time.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a molten carbonate using an alkali carbonate (hereinafter abbreviated as carbonate) such as potassium carbonate (KxCOs) or lithium carbonate (Li, CO3) as an electrolyte. type fuel cells, in particular electrolyte plates containing carbonates.

[Prior art and its problems]

A molten carbonate fuel cell uses carbonate (600
The fuel gas is contained in a reaction gas chamber defined by a current collector plate that also serves as a spacing piece and a pair of end plates on the surfaces of a cathode electrode and an anode electrode arranged on both sides of an electrolyte plate that maintains a temperature of about By flowing an oxidizing gas and an oxidizing gas, electricity is generated through an electrochemical reaction that occurs between both pairs of electrodes. As mentioned above, since the operating temperature is as high as about 600°C, there is no need for a noble metal catalyst in the electrode pair to promote the reaction, and the exhaust heat generated by power generation can be used over a wide range of areas, resulting in high overall efficiency. , the fuel gas can contain carbon monoxide (CO) and carbon dioxide (COz), and therefore, it is possible to convert from a large-scale power generation plant combined with a coal gasification plant to a decentralized one using natural gas, etc. It is attracting attention as a next-generation fuel cell that can be applied to small-cap power generation devices.

By the way, the electrolyte plate used in large-capacity fuel cells is a thin plate with a thickness of about 1 m and a side length of nearly 1 m, and the conductivity of the electrolyte made of carbonate, which becomes molten at the operating temperature. It is required to be a flat thin plate without any unevenness or curvature in order to be able to prevent runoff without interfering with the flow and to improve adhesion with the electrode. Therefore, the electrolyte plate is made of a porous structural material that is thermally stable at high temperatures of around 600°C, is not attacked by molten carbonate, and retains a large amount of electrolyte through capillary action to prevent leakage and maintain conductivity. I need. As this type of structural material, materials made by mixing and sintering refractory powders such as magnesia, alumina, and zirconia are known, but due to problems with the flatness of the thin plates, lithium aluminate (Li kto2) is used.
A mixture of powder and carbonate powder that is heated and compressed is now being used. The structural material formed in this manner has excellent carbonate resistance, and because the mixing ratio of lithium aluminate and carbonate can be freely adjusted during manufacturing, it is highly porous and has excellent carbonate retention. Since the flatness is good and the adhesion with the electrode pair is good, an electrolyte plate with excellent power generation performance can be obtained.

However, when the carbonate solidifies below the operating temperature, it is mechanically brittle and easily damaged during transportation of the electrolyte plate and assembly of the fuel cell, and temperature cycles associated with the operation and shutdown of the fuel cell are disadvantageous. (heat cycle) and the resulting thermal stress can cause cracks. In particular, if the electrolyte plate cracks due to heat cycle, the fuel gas and oxidant gas may come into direct contact, resulting in an explosion, etc. Since there is a risk of serious accidents, improving this problem is even more important than damage during assembly.

Measures to improve mechanical strength and heat cycle resistance include embedding carbonate-resistant Kanthal alloy wire mesh in the electrolyte plate, and mixing and dispersing ceramic fibers such as alumina fibers, lithium aluminate fibers, and zirconia fibers. etc. are being attempted. However, Kanthal alloy nets corrode during long-term use and their reinforcing effect decreases, alumina fibers react with carbonates and lose their form as fibers and their reinforcing effects decrease, and lithium aluminate fibers It is difficult to mass produce and has a low carbonate retention capacity due to its small specific surface area, and zirconia fibers do not react with carbonates and have good long-term stability, but are expensive and somewhat hinder power generation performance. There are shortcomings and further improvements are required.

[Purpose of the invention]

The present invention was made in view of the above-mentioned situation, and an object of the present invention is to provide a molten carbonate fuel cell equipped with an electrolyte plate that can maintain carbonate retention power, power generation performance, and heat cycle resistance for a long period of time. With the goal.

Summary of the Invention The present invention provides potassium titanate (Kz T ia Ot,
) fJ! Focusing on the fact that the fiber has excellent resistance to molten carbonate, has a specific surface area comparable to that of lithium aluminate, and is also inexpensive, we mainly used lithium aluminate powder, which has been used as a structural material for electrolyte plates. As a holding material, a relatively small amount of potassium titanate fiber of 5 to 30 parts by weight is added as a reinforcing material to 50 parts by weight of the main holding material, and electrolyte powder consisting of a mixture of lithium carbonate and potassium carbonate, lithium aluminate powder. , the electrolyte plate was formed by heat compression molding a powder in which potassium titanate fibers were mixed and dispersed using a hot press. It is possible to obtain an electrode plate that is capable of stably retaining the weight part of electrolyte for a long period of time to perform stable power generation, and that is resistant to cracking during a heat cycle that simulates the start and stop of a fuel cell. It is.

[Examples of the Invention] The present invention will be described below based on Examples. Potassium titanate (general formula r<, o-nTi 02) is produced by mixing and reacting potassium carbonate (K!COs) and titanium oxide (TiO2) in a predetermined ratio. By increasing the blending amount and increasing the n number, fibrous potassium titanate can be obtained, for example, 6
With potassium titanate (KI TI60+s), potassium titanate fibers with a diameter of about 1 μm and a length of 50 μm or more can be obtained, and the potassium titanate fibers formed in this way have a surface area of about 1 g (referred to as specific surface area). ) is approximately 10 n//g, which is almost comparable to that of lithium aluminate powder, which is the main holding material.

The electrolyte plate of the present invention comprises the above-mentioned lithium aluminate powder,
Potassium titanate fibers and carbonate powder made of a mixture of lithium carbonate and potassium carbonate are mixed at a predetermined blending ratio,
A predetermined amount of the evenly dispersed powder is placed in a press mold with an even thickness, and the molding temperature is approximately 480℃ and the pressure is 200~600#/
The potassium titanate fibers in the electrolyte plate do not react further with the potassium carbonate (K, CO3) in the electrolyte, and the potassium titanate fibers in the electrolyte plate do not react with the potassium carbonate (K, CO3) in the electrolyte. It has been confirmed that the reaction of Li, C08) does not proceed at an operating temperature of around 600°C, and therefore power generation performance and its stability, which are influenced by electrolyte retention and adhesion with electrode pairs, as well as heat Practicality can be verified by confirming the improvement in mechanical stability against cycles.

Table 1 is a characteristic table showing the compounding ratio and heat cycle test results in Examples of the present invention, including lithium aluminate and carbonate (L 1203 10 KxCOs).

Contains potassium titanate fiber! The heat cycle resistance of the electrolyte plates of Examples 1 to 4 in which the (parts by weight) was changed in four steps is shown in comparison with that of Comparative Example 1 which does not contain potassium titanate fibers. The test electrolyte plate was made by molding a mixed powder obtained by thoroughly mixing and dispersing the powders in the respective amounts using the hot pressing method described above, and forming a sheet with a thickness of 1.8 m.
, a rectangular electrolyte plate with a side length of 18411111+ was manufactured, and the test electrolyte plate thus formed was hung in a heat cycle tester and heated to room temperature and 650°C at a rate of 1°C per minute.
The figure shows the number of cycles in which the electrolyte plate does not crack when heat cycles are repeatedly applied to increase and decrease the temperature between ℃ and ℃.

Table 1 In Table 1, test electrolyte plates 1 to 4 as examples
The amount of lithium aluminate powder as the main support was kept constant at 50 parts by weight, and the amount of potassium titanate fiber as a reinforcing material was changed to 5.10.20.30 parts by weight. As a result of changing the blending amount from 55 parts by weight to 1,80 parts by weight in proportion to the increase in the amount of reinforcing material, 5 parts each of lithium aluminate and carbonate were added.
Compared to the number of heat cycles of Comparative Example 1, which contained 0 parts by weight, the number of heat cycles of 3 to 2
5 times and was able to improve in proportion to the amount of potassium cum titanate blended. In addition, the mechanical retention of the electrolyte plates of Examples 4 to 4 at room temperature also increased as the amount of potassium titanate added increased.

Figure 1 is a characteristic diagram comparing the terminal voltage vs. current density characteristics with that of Comparative Example 1, showing the results of a single cell test using an electrolyte plate with the above-mentioned Example 3 (potassium titanate fiber blend [20%)]. , effective electrode area 200 d, operating temperature 65
0℃, fuel gas H3/CO! (ratio 80/20, oxidizing gas 0) A i r /Cot ratio 70/30. In the figure, the characteristic curve 30 of Example 3 after 500 hours of power generation shows almost the same performance as the initial characteristic curve 10 of Comparative Example 1, and the electrolyte plate of Example 3 has almost no loss of electrolyte, and the electrode This shows that it maintains stable adhesion. Further, a similar test was conducted for Example 4, and although no significant deterioration in power generation performance was observed, oozing of electrolyte was observed as a result of disassembly and inspection.

In the above-mentioned Examples to 4, the mixing ratio of the electrolyte and the structural material (stium aluminate + potassium titanate fiber) in the electrolyte plate was 1:1 (50% by weight: 50% by weight).
By increasing the blending ratio of potassium titanate fibers in the structural material, the heat cycle resistance of the electrolyte plate is improved as shown in Table 1.
[The above test results show that when the proportion of IJ tium powder decreases below a specified amount, the electrolyte retention strength tends to decrease, and the heat cycle resistance and mechanical strength of the electrolyte plate and electrolyte retention tend to decrease. It can be said that the balance between power and power generation performance depends on the blending ratio of powder and fiber in the structural material. In addition, the balance conditions for the above performance are
Based on the above-mentioned study results, if the composition ratio is set to a range in which there is no tS quality oozing to the extent that it affects performance and improvement in heat cycle resistance is observed, lithium aluminate: potassium titanate fiber: carbonate The upper limit of the mixing ratio of salt is about 50:30:80 (wt%) in terms of parts by weight, and 31:x9:50 (wt%) in terms of weight ratio in the electrolyte plate.
), and it is considered appropriate to set the lower limit of the blending ratio to about 5o:5:55 (parts by weight) or about 45:5:50 (i% by weight), which is effective for heat cycle resistance.

Note that the method for manufacturing the electrolyte plate is not limited to the hot pressing method, and it goes without saying that a different molding method such as a tape casting method may be used.

〔Effect of the invention〕

As described above, the present invention is configured to use a mixture of 50 parts by weight of lithium aluminate powder and 5 to 30 parts by weight of potassium titanate fibers as the structural material of the electrolyte plate. As a result, due to the mechanical reinforcing effect of potassium titanate fibers, the heat cycle resistance of the electrolyte plate can be improved several times compared to that of conventional technology using a structural material made only of lithium aluminate powder. It is possible to eliminate the risk of cracking of electrode plates due to heat cycles and the resulting direct contact between fuel gas and oxidant gas, which has been a problem in the technology, and it is possible to provide a highly reliable molten carbonate fuel cell. Furthermore, the excellent electrolyte holding power of the lithium aluminate powder can prevent the electrolyte from oozing out or flowing out, making it possible to provide a molten carbonate fuel cell that can maintain stable power generation performance for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the results of a single cell test in an example of the present invention. 10: Initial characteristic curve in Comparative Example, 3o: Characteristic curve after 500 hours of power generation in Example 3. Den 5 Brahma Za (Ge A /cq♂) Sai1c21

Claims (1)

[Scope of Claims] 1) A main holder comprising an electrolyte plate formed by heating and compression molding a mixture of an electrolyte made of an alkali carbonate, a main holding material made of lithium aluminate powder, and a reinforcing material made of potassium titanate fiber. 5 to 30 parts by weight of reinforcing material per 50 parts by weight of material
A molten carbonate fuel cell comprising parts by weight. 2) The molten carbonate fuel cell according to claim 1, wherein the potassium titanate fiber has a specific surface area in the range of 1 to 10 m^2/g. 3) A molten carbonate fuel cell according to claim 1 or 2, characterized in that the electrolyte content is in the range of 55 to 80 parts by weight.