JPH03285268A - High temperature type fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the leakage of a gas between a solid electrolytic plate and an interconnector and fix both of them to each other by applying a material never plastically deformed at the operation temperature of a cell between the surface of the solid electrolytic plate having electrodes formed thereon and the interconnector. CONSTITUTION:Solid electrolytic plates 21 are covered with porous materials forming a positive electrode 22 and a negative electrode 23, and laminated through an interconnector 24, and end plates 25, 26 for taking out electricity to the outside are provided on both the ends. The interconnector is provided with a gas passage 27 for oxidizing agent such as oxygen or air and a gas passage 28 for fuel gas such as hydrogen, and the end plates 25, 26 are similarly provided with gas passages 29, 30. Onto the peripheral parts 31 of the electrolytic plate surfaces having the electrodes formed thereon, a material softened at a temperature of 1050 deg.C-1350 deg.C higher than the operation temperature of the cell to deform the softening material into sealing form followed by temperature lowering and never plastically deformed at a temperature not higher than the operation temperature 1000 deg.C is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to fuel cells, and more particularly to a method for sealing a fuel cell using a solid oxide electrolyte.

[Prior art] Fuel cells are capable of converting chemical energy directly into electrical energy with high efficiency, so they are being developed as a power generation method to replace the current power generation method using steam generated from the combustion of fossil fuels. There is.

Although fuel cells can be operated using a variety of fuels, the focus of development is on cells that use hydrogen as fuel, where the only product of the cell reaction is water.

Fuel cells that use hydrogen as fuel, which is becoming increasingly popular, are classified into alkaline type, phosphoric acid type, molten carbonate type, and solid electrolyte type, depending on the type of electrolyte in which the cell reaction occurs.

The alkaline type is characterized by a low operating temperature, but since fuel mixed with carbon dioxide reacts with the potassium hydroxide electrolyte, such fuel cannot be used in the alkaline type.

In addition, phosphoric acid fuel cells are being developed as fuel cells for the electric power industry because they can use hydrogen gas containing carbon dioxide obtained by reforming natural gas and naphtha without any problems. In addition to using a platinum group metal, there is a problem in that the catalyst used is poisoned by trace amounts of carbon monoxide contained in the raw material gas.

Molten carbonate, which is being developed for use in relatively large-scale power generation facilities, does not require expensive catalysts such as platinum group metals because it operates at high temperatures, and the waste heat generated by batteries can be used to generate steam. This type of fuel cell can be used without any problems even if the hydrogen raw material contains carbon monoxide. However, in molten carbonate fuel cells, since carbonate ions are involved in the fuel cell reaction, carbon dioxide gas is essential for the reaction, so it is necessary to mix carbon dioxide with air, which is an oxidizing agent. Therefore, processing equipment for raw materials and exhaust gas becomes complicated.

In response to these, fuel cells that do not contain gaseous or molten electrolytes and use solid electrolytes that operate as electrolytes at high temperatures, such as the above-mentioned fuel cells, are being developed as third-generation fuel cells.

Solid electrolyte fuel cells use zirconium oxide, which acts as an oxygen ion conductive electrolyte at high temperatures, stabilized by adding yttrium oxide or lucium oxide. Various fuels such as hydrogen, carbon oxide, and hydrocarbons can be used, and since the electrolyte is solid, evaporation of the electrolyte and corrosion caused by the electrolyte are unavoidable in fuel cells using liquids or molten salts. There are no problems, and the structure of the fuel cell is simple.

In addition, because the operating temperature is high, expensive catalysts such as platinum group metals are not required, and the exhaust heat is also high temperature, so the exhaust heat can be effectively used for gas turbine power generation or steam generation. It has extremely high energy efficiency and is expected to be the most superior fuel cell.

Solid electrolyte fuel cells can be broadly classified into the following three types of methods for forming electrodes on the electrolyte, depending on the manufacturing method and structure.

(b) One electrode is formed on a porous ceramic substrate with high mechanical strength such as alumina, and a zirconium oxide layer is created on top of it by a method such as thermal spraying so that there are no gas leak holes, and then a zirconium oxide layer is formed. This method forms the other electrode on top of the layer, and is used in the manufacture of cylindrical fuel cells.

(b) A method in which a material that will become an electrode is applied by sintering onto a sheet of raw zirconium oxide to form an electrode at the same time as the zirconium oxide is sintered, and is used in the production of monolithic fuel cells. It's being used.

(c) A method in which electrodes are formed on a sintered zirconium oxide electrolyte by coating or printing, and is used in fuel cells in which flat plate battery units are stacked.

However, in the production of solid electrolyte batteries, the method (c) above, in which electrodes are formed on a zirconium oxide solid electrolyte that has been sintered in advance, cannot produce zirconium oxide electrolytes and electrodes with stable quality because of the flat plate shape. Although it is suitable for manufacturing large-scale fuel cells, the voltage generated by a fuel cell composed of a pair of positive and negative electrodes is approximately 1.2 volts when open, and the output current is also limited by the efficiency of the battery. Therefore, in order to use fuel cells for power generation, a large number of unit fuel cells are electrically connected in series and parallel.

Figure 2 is a diagram showing the stacking style of a flat plate fuel cell. In the figure, 1 is a solid electrolyte plate made of stabilized or partially stabilized zirconia, and a positive electrode 2 and a negative electrode 3 are formed on the solid electrolyte plate. Covering a porous material. The solid electrolyte plates covering the electrodes are laminated with an interconnector 4 interposed therebetween.

The interconnector also includes a gas passage 7 for an oxidizing agent such as air or oxygen, and a gas passage 8 for a fuel gas such as hydrogen.
It acts to supply gas to the electrodes and to electrically connect adjacent unit fuel cells. End plates 5 and 6 are provided at both ends for extracting electricity to the outside. End plates 5 and 6 are likewise provided with gas passages 9 and 10.

The interconnector also includes a gas passage 7 for an oxidizing agent such as air or oxygen, and a gas passage 8 for a fuel gas such as hydrogen.
It acts to supply gas to the electrodes and to electrically connect adjacent unit fuel cells. End plates 5 and 6 are provided at both ends for extracting electricity to the outside. End plates 5 and 6 are likewise provided with gas passages 9 and 10. Although this figure shows only two sets of unit fuel cells, it is of course possible to obtain a fuel cell that provides a desired output voltage by stacking a large number of unit fuel cells.

In a fuel cell having such a configuration, oxygen or air is supplied to the gas passages 7 and 9, hydrogen or other fuel gas is supplied to the gas passages 8 and 10, and an external circuit (not shown) is connected to both end plates. 850℃, which is the operating temperature of
When maintained at ~1000°C, ionized oxygen flows to the positive electrode 2.
It passes through the solid electrolyte plate 1 from the side and reacts with the fuel gas at the negative electrode 3.

As a result, current flows through the external circuit.

The chemical formula for using hydrogen as a fuel gas is:
It will look like this:

Positive electrode: 1/202+ 2 e-<02-negative electrode'
H2+0z-=H20+2 In the entire e-battery, a water production reaction is occurring by oxidizing hydrogen as shown by 1/20□+H2→H20.

As shown in FIG. 3, the stacked fuel cell stack 11 may be provided within a pressure vessel 12 with manifolds for supplying and discharging oxidizer and fuel (not shown).
Alternatively, by sealing the contact point between the wall surface of the pressure vessel and the fuel cell, a space formed between the fuel cell stack and the pressure vessel is used as a gas passage, and a hydrogen supply port 13 is installed at the bottom of the pressure vessel. , exhaust port 1 for gas containing unreacted hydrogen
4. An oxygen supply port 15 and a gas discharge port 16 containing unreacted oxygen may be provided to supply and discharge gas to the fuel cell.

Also, terminals 17 and 1 supply generated power to an external circuit.
8 and an external circuit to supply power to the outside.

[Problems to be Solved by the Invention] In order to connect flat unit fuel cells in series, a large number of unit fuel cells are stacked via conductive interconnectors, but the interconnectors are exposed to high temperature oxygen and Materials that are resistant to corrosion in a hydrogen atmosphere and have good electrical conductivity, conductive ceramics such as silicon carbide, molybdenum silicide, chromium silicide, and lanthanum chromite, or alloys containing nickel, chromium, cobalt, etc., are used. However, interconnectors using these materials have a coefficient of thermal expansion of 1011 compared to stabilized zirconia solid electrolyte plates.
There is a difference of 0-61/'C. If there is such a large difference, the operating temperature of a solid electrolyte fuel cell is 850℃~10℃.
At 00"C, a gap will occur between the electrode surface of the solid electrolyte plate and the interconnector, and if oxygen and fuel gas leak, they will not be used for the cell reaction, resulting in a decrease in the fuel utilization rate and the mixing of oxygen and fuel gas. It is also dangerous if this happens.

In fuel cells operating at temperatures on the order of 200 to 600°C, such as phosphoric acid and molten carbonate fuel cells, it is relatively easy to prevent gas leakage and mixing with liquid and molten electrolytes and gaskets. However, no effective sealing method has been proposed at high operating temperatures of 850° C. to 1000° C., and this has been one of the reasons for delaying the development of flat plate solid oxide fuel cells.

[Means for Solving the Problem] The present inventors have diligently studied a sealing method for a solid electrolyte fuel cell, alleviated the difference in thermal expansion between a solid electrolyte plate and an interconnector, and 10 higher than the operating temperature of
It has a softening point between 50℃ and 1350℃, and has a softening point between 850℃ and 10℃.
They discovered a method for reliably sealing by using a sealing material that does not undergo plastic deformation at an operating temperature of 00°C.

That is, FIG. 1 is a diagram showing the configuration of a solid oxide fuel cell according to the present invention, and is an exploded view of an electrolytic cell stack in which flat unit fuel cells are stacked in three stages. In the figure, 21 is a solid electrolyte plate made of stabilized or partially stabilized zirconia, and the solid electrolyte plate is coated with a porous material that forms a positive electrode 22 and a negative electrode 23. Adjacent unit fuel cells are stacked via interconnectors 24 that electrically connect them, and end plates 25 and 26 are provided at both ends for taking out electricity to the outside. Further, the interconnector is provided with a gas passage 27 for an oxidizing agent such as oxygen or air, and a gas passage 28 for a fuel gas such as hydrogen, and the end plates 25 and 26 are similarly provided with gas passages 29 and 30. The peripheral edge 31 of the electrolyte plate surface on which the electrodes are formed is heated to
Softens from 50℃ to 1350℃, and the softened product is 102 to 10
It has a viscosity of 7 voids, is deformed into a sealed shape, cooled,
It uses a material that does not undergo plastic deformation at an operating temperature of 1000°C or less, and after heating to a temperature at which the glass paste softens, the glass paste is solidified in the process of lowering the temperature to the operating temperature, thereby creating a gap between the electrolyte plate and the interconnector. This is to seal and mechanically fix the two.

Glass pastes that can be used for this purpose include high softening point aluminosilicate glass, high silicate glass, crystallized glass, Li2O°5i02 type, β-spodumene solid solution (E cordierite type glass, etc.) can be given.

Or, like crystallized glass, from 1050℃ to 135℃
After it is softened at 0° C. and formed into a sealed shape, it may be maintained at this temperature to precipitate a crystalline phase from the glass phase to prevent plastic deformation and be fixed by sealing or the like. If the glass paste coating width is too large, the area of the part that functions as a fuel cell will be reduced, and if it is too small, there is a possibility of leakage, so it is preferably about 2 to 8 mm, and the coating thickness is 0.1 to 0.0 mm. Approximately 5 mm is preferable.

In addition, instead of applying glass paste, we sandwich and stack glass plates made of the same glass components as the glass paste, heat the glass to its softening temperature, and then harden the temperature and solidify it for sealing and fixing. Alternatively, at least one surface of the solid electrolyte plate on which electrodes are formed and the interconnector is coated with a glass paste in which glass that does not deform plastically at the operating temperature of the battery is dispersed in an organic substance. Sealing and fixing may be performed by sandwiching and stacking glass plates made of the same components as the components, heating the glass to a softening temperature, and then lowering the temperature to solidify it.

[Function] In a flat plate solid electrolyte fuel cell, there is a gap between the surface of the solid electrolyte plate on which electrodes are formed and the interconnector.
By applying a material that softens between 050° C. and 1350° C. and does not undergo plastic deformation at the operating temperature of the battery, it is possible to prevent gas leakage between the solid electrolyte plate and the interconnector and to fix the two.

[Example] A fuel cell stack was manufactured according to the first stacking method. A solid electrolyte plate of partially stabilized zirconia with a size of 50×50III11 to which 3 mol % of yttrium oxide was added was used. And on the oxygen passage side of the solid electrolyte, L a @, gs r I! , )MnO3 powder (average particle size of about 5 μm) was applied to a thickness of 0.3 mm by brush coating to form a positive electrode. Further, on the hydrogen passage side, a cermet mixed powder of nickel/zirconium dioxide (weight ratio: 9:1) was applied to a thickness of 0.2 mm by brush coating in the same manner as the positive electrode to form a negative electrode.

Nichrome is used for the interconnector, and the solid electrolyte plate 2
Li20.5i0 with a softening point of 1200°C is placed around the periphery of 1.
A paste of 2-series crystallized glass was applied to a thickness of 0.2 fins.

The fuel cell stack stacked in three layers in this way was mounted in a pressure vessel and heated. Heating is from room temperature to 150℃
From 150°C to 300°C, heat at 5°C per minute to evaporate the glass paste solvent.
At temperatures above 300°C, nitrogen was flowed on the hydrogen path side to prevent oxidation of the electrode, and the temperature was increased to 1200°C at a rate of 5°C per minute to melt it and held at the same temperature for 10 minutes.

After that, when the temperature was lowered to 1000℃ and power generation was started by supplying oxygen to the positive electrode side and hydrogen to the negative electrode side, the open circuit voltage was 3.7 volts. Estimating from the value of the electrochemical potential according to Nernst's equation, gas leakage occurred. In addition, the solid electrolyte plate and interconnector were sufficiently mechanically fixed.

[Effect of the invention] In a solid electrolyte fuel cell having a flat electrolyte plate, the peripheral edge of the electrolyte plate softens at 1050°C to 1350°C and does not undergo plastic deformation at the cell operating temperature of 850°C to 1000°C. Glass was applied to seal the space between the interconnector and the solid electrolyte plate, reducing the possibility of gas leakage, and since both were fixed, safe operation was possible without shifting due to vibration.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a solid oxide fuel cell manufactured by the method of the present invention, FIG. 2 is a diagram showing the configuration of the solid oxide fuel cell, and FIG. 3 is a diagram illustrating an example of how the fuel cell stack is installed. It is. Solid electrolyte...2 Positive electrode...2 Negative electrode...2 Interconnector...2 Glass paste application area...3

Claims (8)

[Claims] (1) A high-temperature fuel cell characterized in that a sealing material that does not undergo plastic deformation at the operating temperature of the cell is interposed between a solid electrolyte plate forming an electrode and an interconnector. (2) Claim 1, wherein the operating temperature is 850°C to 1000°C.
High temperature fuel cell described. (3) The high temperature fuel cell according to claim 1 or 2, wherein the sealing material is glass having a softening temperature between 1050°C and 1350°C. (4) The high-temperature fuel cell according to any one of claims 1 to 3, wherein the sealing material is crystallized glass that forms a crystalline phase at the operating temperature. (5) A high-temperature type characterized by laminating a solid electrolyte plate on which electrodes are formed and at least one surface of the interconnector by applying a glass paste in which glass that does not deform plastically at the operating temperature of the battery is dispersed in an organic substance. Method of manufacturing fuel cells. (6) A method for manufacturing a high-temperature fuel cell, which comprises sandwiching and stacking glass that does not undergo plastic deformation at the operating temperature of the cell between a solid electrolyte plate on which electrodes are formed and an interconnector. (7) A glass paste in which glass that does not deform plastically at the operating temperature of the battery is dispersed in an organic substance is applied to at least one surface of the solid electrolyte plate on which the electrode is formed and the interconnector. A method for manufacturing a high temperature fuel cell. (8) The method for manufacturing a high-temperature fuel cell according to any one of claims 5 to 7, characterized in that the glass is heated to 1050°C to 1350°C to soften and seal the glass.