JPH04215257A - Molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To suppress a catalyst from being poisoned by molten carbonate and extend the life of a battery by arranging a cathode impregnated with all the carbonate required for a unit cell and an anode containing no carbonate via an electrolyte plate. CONSTITUTION:A porous anode 2 made of Ni powder containing Cr and a serrate type corrugated plate 3 made of inconel and having fuel gas passages are provided on one face of an electrolyte plate 1 mainly made of gamma-lithium aluminate, and columnar catalysts 4 carried with Ni on alumina are filled in recesses. A porous cathode 5 made of Ni powder and containing carbonate and a serrate type corrugated plate 6 are provided on the other face of the plate 1, and bipolar plates 7 made of stainless steel are arranged on back faces of the corrugated plates 3, 6. The infiltration of the required quantity or above of molten carbonate into the anode 2 is prevented while the gas permeability into the cathode 5 is maintained.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to molten carbonate fuel cells, and more particularly to direct internal reforming molten carbonate fuel cells.

0002

[Prior Art] The electrolyte of the above-mentioned molten carbonate fuel cell is a molten carbonate salt such as a eutectic salt of lithium carbonate and potassium carbonate, and an electrolyte plate made of a porous ceramic body such as lithium aluminate is used. Retained. An anode and a cathode are brought into contact with both sides of this electrolyte plate, respectively, and power is generated by supplying fuel gas to the anode side and oxidizing gas to the cathode side at a specified temperature (for example, 650° C.). The above-mentioned fuel gas is composed of, for example, hydrocarbons and water vapor, and is mainly reformed into hydrogen and carbon monoxide for use in the cell reaction.

[0003] The above-mentioned molten carbonate fuel cells are classified according to the reforming method into an external reforming type in which the fuel cell is reformed outside the stack, and an internal reforming type in which the fuel cell is reformed within the stack. The latter is
Since the structure uses the reaction heat of the battery to reform the fuel gas and supply it to the anode, it is expected that the battery will have a good cooling effect and high system efficiency. The latter type includes a direct internal reforming type in which the supplied fuel gas contacts both the anode and the catalyst, and an indirect internal reforming type in which the supplied fuel gas first contacts only the catalyst and is then supplied to the anode. There is.

Next, a method for manufacturing the above molten carbonate fuel cell will be explained. First, in the above-mentioned battery, carbonate is mixed in the electrolyte plate in advance. In other words, carbonate is added to a slurry of a ceramic material such as lithium aluminate mixed with an organic plasticizer and a binder, and this is formed into a sheet by tape casting, which makes it easy to make a large area electrolyte plate and form it into a sheet. form into a shape. Since this sheet contains an organic plasticizer and a binder and has flexibility, this sheet and a pair of electrodes constitute a unit battery. As the stack heats up, the plasticizer and binder are dispersed, creating an electrolyte plate consisting of a porous ceramic body that holds the molten carbonate. However,
Such a manufacturing method has a problem in that after the plasticizer or binder is scattered, the scattered portion becomes pores, resulting in gas crossover.

[0005] Therefore, a unit cell is constructed of an electrolyte plate sheet containing no carbonate, and an anode and a cathode impregnated with a predetermined amount of carbonate. During the heating process of this battery, pores are generated as described above, and the molten carbonate impregnated in the anode and cathode penetrates into these pores. Therefore, it is possible to suppress the occurrence of gas crossover.

[0006]

[Problems to be Solved by the Invention] However, in the direct internal reforming type molten carbonate fuel cell, since the reforming reaction and the anode electrode reaction occur close to each other, the hydrogen produced in the reforming reaction is consumed sequentially. , the modification reaction is promoted. However, if the anode is impregnated with carbonate in advance as described above, the anode will be impregnated with more than the necessary amount of molten carbonate, so a direct internal reforming type molten carbonate fuel cell in which the anode and catalyst are arranged close to each other, In this case, the catalyst is poisoned by the molten carbonate at the anode during the temperature rising process or at the beginning of operation. Therefore, there was a problem that the battery life was shortened.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide a molten carbonate fuel cell that can suppress poisoning of the catalyst by molten carbonate and extend the battery life. With the goal.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method in which a cathode impregnated with all the carbonates necessary for a unit battery and an anode containing no carbonates are connected to each other through an electrolyte plate. It is characterized by being located.

[0009]

[Operation] During the heating process of the stack, the molten carbonate impregnated in the cathode penetrates into the pores in the electrolyte plate and the pores in the anode, which are created by the scattering of the plasticizer and binder. When the anode is impregnated with molten carbonate by such a method, it is possible to prevent the anode from being impregnated with more than the required amount of molten carbonate. Therefore, it is possible to suppress the catalyst from being poisoned during the temperature rising process of the battery or during the initial stage of operation.

0010

[Embodiment] [Embodiment 1] An embodiment of the present invention will be described below based on FIGS. 1 and 2. FIG. 1 is a schematic perspective view of the main parts of the fuel cell of the present invention, in which one side of an electrolyte plate 1 (porosity: 60%, thickness: 0.6 mm) mainly composed of , an anode 2 (porosity: 60%, thickness: 1 mm) made of a porous body of chromium-containing nickel powder, and a serrated corrugate 3 made of Inconel and forming a fuel gas passage are provided in this order. In the recess of the corrugate 3, there is a cylindrical catalyst 4 in which nickel is supported on alumina.
is filled.

On the other hand, on the other side of the electrolyte plate 1, there is a cathode 5 made of a porous body of nickel powder and containing carbonate.
(Porosity: 65%) and a serrated corrugate 6 made of Inconel and forming an air passage are provided in this order. In addition, the back of both corrugates 3 and 6 is made of SUS316L.
Bipolar plates 7, 7 consisting of are arranged respectively.

[0012] Here, the electrolyte plate 1 and cathode 5 were manufactured as follows. The electrolyte plate 1 is made by first thoroughly mixing the following electrolyte plate materials in a ball mill.
Prepare slurry. γ-lithium aluminate
100 parts by weight Binder (polyvinyl butyral resin) 30 parts by weight Plasticizer (dioctyl phthalate) 20
Parts by weight Solvent (ethanol)
300 parts by weight Next, the thus obtained slurry was formed into a sheet by tape casting, and the organic matter was scattered to produce an electrolyte plate 1 having a porosity of 50% and a thickness of 0.6 mm.

On the other hand, for the cathode 5, first, nickel powder with an average particle size of 5 μm is prepared by the doctor blade method, and then this is sintered.The sintered nickel powder is then used to form a porous body (porosity: 65%). ). Next, by impregnating the above porous body with the amount of eutectic salt of lithium carbonate and potassium carbonate (Li:K=62:38 mol%) required for the unit battery, a thickness such that the impregnation rate is 85% is obtained. Cathode 5 was produced.

[0014] The battery thus produced is shown below (A
1) It is called a battery. [Example 2] A battery was produced in the same manner as in Example 1 above, except that the cathode 5 had a thickness such that the eutectic salt impregnation rate was 62%. The battery thus produced is hereinafter referred to as the (A2) battery.

[Comparative Example] A battery was produced in the same manner as in Example 1, except that not only the cathode 5 but also the anode 2 was impregnated with the eutectic salt. The battery thus produced is hereinafter referred to as the (X) battery. [Experiment] The (A1) battery of the present invention, the (A2) battery, and the (X) battery of the comparative example were used to generate electricity, and the changes in battery voltage over time were investigated. The results are shown in FIG. 2. The experimental conditions were a current density of 150 mA/cm2, a battery operating temperature of 650°C, and a ratio of water vapor to methane in the fuel gas of 3:1.
I went there.

As is clear from FIG. 2, (A1
) battery, (A2) battery, the initial voltage is approximately 1300
It was observed that the battery (X) of Comparative Example was maintained for only about 700 hours. This is because in the (A1) battery and (A2) battery of the present invention, the proportion of catalyst that is poisoned at the beginning of operation is small, so the proportion of active catalyst increases in subsequent operation. On the other hand, in the battery (X) of Comparative Example, the proportion of the catalyst that is poisoned is high in the initial stage of operation, so it is thought that this is because the proportion of active catalyst decreases in the subsequent operation.

[Other matters] ■Although not shown in FIG. 2 above, the same method as above was performed using a cathode with a thickness such that the eutectic salt impregnation rate is 54% and a cathode with a thickness such that the impregnation rate of the eutectic salt is 94%. We conducted an experiment. As a result, when the impregnation rate was 54%, the above (A1) battery, (A2)
) It was observed that the voltage was 0.1 V lower than that of the battery. This is thought to be due to the increased thickness of the cathode, which resulted in poor gas diffusion.

On the other hand, when the impregnation rate of the eutectic salt was 94%, the voltage was further reduced. This is considered to be due to one of the following reasons. (1) Since this battery has a high impregnation rate of eutectic salt, gas does not diffuse sufficiently during oxidation of the nickel in the cathode, and the nickel is sintered as it is and then oxidized. This is why the pore diameter and porosity decrease.

(2) Due to insufficient gas diffusion on the cathode side, the organic matter in the electrolyte plate is not dispersed smoothly and is carbonized and remains. However, this battery and the above (
When the power generation of the X) battery was completed after 300 hours and the amount of poisoning of the catalyst was investigated, the amount of poisoning of this battery was 11 compared to the (X) battery.
It was observed that the value had decreased to /2. Therefore, it can be seen that the effect of the present invention of reducing the amount of poisoning has been achieved.

From the above results, the impregnation rate of the eutectic salt into the cathode is preferably 60% or more and 90% or less. That is, if the impregnation rate of the eutectic salt into the cathode is set to 60% or more, it is possible to suppress the increase in the thickness of the cathode and to minimize the increase in gas diffusion resistance during operation, while it is set to 90% or less. This allows the heating process of the battery to be carried out without impairing the gas permeability into the cathode, which is necessary for the oxidation process of nickel in the cathode and the process of scattering organic matter in the electrolyte plate, which are carried out during heating up to operating temperature. Also, poisoning of the catalyst at the initial stage of operation can be prevented.

[0021] The plasticizer is not limited to the above-mentioned dioctyl phthalate, but may also be polyethylene glycol, and the solvent is not limited to ethanol, but may be, for example, P-xylene. . ■The cathode material is not limited to the above-mentioned nickel, and may be, for example, nickel oxide, and the anode material is not limited to the above-mentioned chromium-containing nickel, but may be, for example, aluminum or cobalt-containing nickel. Good too.

[0022]

As explained above, according to the present invention, it is possible to prevent the anode from being impregnated with more than the required amount of molten carbonate while maintaining gas permeability into the cathode. As a result, it is possible to prevent the catalyst from being poisoned during the temperature rising process of the battery or in the early stages of operation, resulting in the effect that the battery life of the molten carbonate fuel cell is dramatically extended.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of the main parts of a molten carbonate fuel cell according to the present invention.

FIG. 2 is a graph showing changes in battery voltage over time in the (A1) battery of the present invention, the (A2) battery, and the (X) battery of the comparative example.

[Explanation of symbols]

1 Electrolyte plate 2 Anode 4 Catalyst 5 Cathode

Claims (1)

[Claims] 1. A molten carbonate fuel cell characterized in that a cathode impregnated with all the carbonates necessary for a unit cell and an anode containing no carbonate are arranged with an electrolyte plate interposed therebetween.