JPH0412460A - High-temperature fuel cell - Google Patents

Abstract

PURPOSE:To unify the temperature distribution of a fuel cell by providing a gas feed path at the center section of a flat solid electrolyte plate forming an electrode, providing a dispersing means of gas from the feed path to the electrode, and controlling the temperature of the fed gas. CONSTITUTION:An oxidizer gas feed pipe 7 and a fuel gas feed pipe 8 are provided at the center section of a solid electrolyte plate 1 made of a flat plate of partially stabilized zirconia added with yttrium oxide, a positive electrode 2 is formed except a seal section 9, and a negative electrode is formed on the back face. The pipes 7, 8 are formed at the center section of an inter- connector 31 made of nichrome and electrically connecting unit fuel cells like for the plate 1, and oxidizer gas and fuel gas are fed to the electrodes through grooves 32, 33 for gas dispersion. They are stacked in three layers and heat- treated, then it is held at 1000 deg.C, and oxygen is fed to the positive electrode side and hydrogen is fed to the negative electrode side for power generation. The temperature of the fed gas is adjusted, and the temperature distribution of the fuel cell can be unified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to fuel cells, and more particularly to fuel cells using a flat 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. .

Fuel cells operate using various types of fuel, but the focus of development is on cells that use hydrogen as fuel, where the only product of the cell reaction is water.
Depending on the type of electrolyte used, there are alkaline type, phosphoric acid type,
Classified into molten carbonate type and solid electrolyte type.

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

In addition, phosphoric acid fuel cells are being developed as fuel cells for electric utilities because they can use hydrogen gas containing carbon dioxide obtained by reforming natural gas and naphtha without any problems. There is a problem in that a platinum group metal is used as a catalyst, and 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. 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 stabilized or partially stabilized zirconia, which is stabilized or partially stabilized by adding yttrium oxide or calcium oxide to zirconium oxide, which acts as an oxygen ion conductive electrolyte at high temperatures. There is. 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.

Depending on the manufacturing method and structure of solid electrolyte fuel cells, methods for forming electrodes during electrolysis can be roughly divided into the following three types.

(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 an electrode material 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.

It is used in fuel cells that consist of stacked flat battery units.

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. Suitable for manufacturing large fuel cells.

The voltage generated by a fuel cell consisting of a pair of positive and negative electrodes is about 1 to 2 volts when open, and the output current is also limited by the efficiency of the cell. unit fuel cells must be electrically connected in series and parallel, but with flat plate fuel cells, it is possible to increase the energy density per unit volume by reducing the thickness of each stage. Suitable for manufacturing large fuel cells in which many unit fuel cells are stacked.

FIG. 2 is a diagram showing the stacking style of a flat plate fuel cell. In the figure, 11 is a solid electrolyte plate made of stabilized or partially stabilized zirconia, and a positive electrode 12 and a negative electrode 13 are formed on the solid electrolyte plate. Covering a porous material. The solid electrolyte plates covering the electrodes are laminated via an interconnector 14.

In addition, a gas passage 17 for an oxidizing agent such as air or oxygen and a gas passage 18 for a fuel gas such as hydrogen are formed in the interconnector to supply gas to the electrodes and to electrically connect adjacent unit fuel cells. act. End plates 15 and 16 are provided at both ends for extracting electricity to the outside. End plates 15 and 16 are similarly provided with gas passages 19 and 20.

In addition, a gas passage 17 for an oxidizing agent such as air or oxygen and a gas passage 18 for a fuel gas such as hydrogen are formed in the interconnector to supply gas to the electrodes and to electrically connect adjacent unit fuel cells. act. End plates 15 and 16 are provided at both ends for extracting electricity to the outside. End plates 15 and 16 are similarly provided with gas passages 19 and 20. In this figure, the unit fuel cell is 2
Of course, it is possible to obtain a fuel cell that obtains 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 17 and 19, hydrogen or other fuel gas is supplied to the gas passages 18 and 20, and an external circuit (not shown) is connected to both end plates. 8, which is the operating temperature of
When maintained at 50° C. to 1000° C., ionized oxygen permeates the solid electrolyte plate 11 from the positive electrode 12 side and reacts with the fuel gas at the negative electrode 13 . 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-102- negative electrode:
H2+02-+H3O+ 2 e- In the entire battery, a water production reaction is occurring by oxidation of hydrogen as shown by 1/202 +H2→H20.

[Problems to be Solved by the Invention] In the electromotive reaction in a fuel cell that uses hydrogen and oxygen, the reduction reaction of oxygen and the oxidation reaction of hydrogen proceed at different locations, the positive electrode and the negative electrode. The combustion energy of oxygen can be extracted not as heat but as electrical energy.

Expressing the reaction in a fuel cell thermodynamically, there is a relationship between ΔG, which is a Gibbs free energy change, and the generated electromotive force E, as follows: ΔG=nFE. Here, n is the number of electrons involved in the reaction, and F is a Faraday constant.

Further, there is a relationship between ΔG and ΔH, which is the enthalpy change of the reaction, as ΔG=ΔH−TΔS.

Here, T is the temperature and ΔG is the entropy change of the reaction. On the other hand, since the heat of combustion generated in a chemical reaction is equal to ΔH, which is the enthalpy change of the reaction, the thermal efficiency η of electricity generation by a fuel cell is the ratio of the electromotive force to the calorific value due to the chemical reaction between the fuel and the oxidizer. It is expressed as =ΔG/ΔH.

Therefore, even in the power generation of fuel cells, the generation of thermal energy corresponding to the difference between the enthalpy change of the reaction and the free energy of the cast will inevitably occur, and in addition to this theoretically unavoidable generation of thermal energy, The electrical resistance of the electrode or electrolyte and the contact resistance between the electrode and the current collector result in a loss of electromotive force in the fuel cell, which manifests itself in the generation of heat in the fuel cell.

Therefore, in order to remove the thermal energy generated by the fuel cell and maintain the operating temperature of the fuel cell, it is necessary to cool the fuel cell. Phosphoric acid fuel cells, whose operating temperature is around 200°C, are equipped with liquid or gas cooling means for every few cells in the fuel cell stack to maintain temperature and recover the generated thermal energy for effective use. Also, in the case of molten carbonate type fuel cells, cooling means are stacked on the fuel cell stack.

High-temperature fuel cells using solid electrolytes have an operating humidity of 8
Since the temperature is as high as 50° C. to 1000° C., it is not preferable to provide a cooling means in the stack to complicate the structure of the battery. In addition, since the operating temperature is high, it is possible to control the heat generated from the fuel cell by dissipating heat from the fuel cell to the surroundings, but if the heat is only radiated to the surroundings, the heat generated in the center will accumulate, so the fuel cell The temperature distribution between the surrounding area and the inside becomes larger.

[y! , Means for Solving the Problem] The present inventors have intensively studied a method for cooling a high-temperature fuel cell using a solid electrolyte, and found that when utilizing heat dissipation from a fuel cell stack to the surroundings, The center of the solid electrolyte plate of the fuel cell is used to supply fuel gas and oxidizer gas from the center of the fuel cell, and to extract gas containing unreacted components from the surrounding area, in order to equalize the temperature distribution within the fuel cell stack. A gas supply pipe is provided in the central part, and the supplied gas is passed through a gas passage provided between the solid electrolyte plate of the fuel cell and the interconnector, and the low temperature gas introduced from the center is used for the fuel cell reaction. After that, it is discharged from the surrounding area.

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 a fuel cell consisting of a set of unit fuel cells.

In the figure, 1 is a temporary solid electrolyte made of stabilized or partially stabilized zirconia.The solid electrolyte plate is coated with a porous material that forms the positive electrode 2 and the negative electrode 3, and the electric power generated from the temporary solid electrolyte electrodes is collected. In order to conduct electricity, end plates 4 and 5 are provided at both ends of the fuel cell stack, but when multiple unit fuel cells are stacked, an interconnector is provided to electrically connect adjacent unit fuel cells. Provide and laminate.

A dispersion plate 6 for dispersing gas is provided between the end plate and the solid electrolyte plate.
are installed and laminated. The dispersion plate provided on the positive electrode side has grooves or porous pipes for dispersing and supplying the oxidant gas from the supply pipe 7 provided in the center to the positive electrode, and the dispersion plate provided on the negative electrode side The distribution plate has grooves or porous pipes for dispersing and supplying fuel gas from the fuel gas supply pipe 8 to the negative electrode.

Figure 3 (A) is a plan view of one side of the interconnector providing a gas passage from the center to the periphery; Figure 3 (B) is a plan view of the other side; ) shows a sectional view of the interconnector along the line AA, and (D) shows a sectional view of the interconnector along the line BB.

The oxidant gas supply conduit 7 and the fuel gas supply conduit 8 provided in the center of the interconnector 31 are supplied to the electrodes through a groove 32 formed in the interconnector. The shape and pattern of the grooves are not limited to those shown in this figure, but any arbitrary shape such as a radial shape or an annular shape can be provided in the supply pipe.

FIG. 4 is a plan view of the solid electrolyte plate 1 viewed from the positive electrode side, in which an oxidant gas supply pipe 7 and a fuel gas supply pipe 8 are provided in the center. The positive electrode 2 is formed except for a sealing part 9 which is sealed by applying glass paste to the peripheral part.

[Since a gas supply path was provided in the center of the flat solid electrolyte plate that formed the working co-electrode, and a means for dispersing gas from the supply path to the electrode was provided, the temperature of the gas to be supplied could be controlled. The temperature distribution of the fuel cell can be made uniform.

[Example 50x50+w+ thickness 0.2 of partially stabilized zirconia with 3 mol% of yttrium oxide added as solid electrolyte]
A w+m plate was used. A fourth electrode is placed in the center of this solid electrolyte plate.
As shown in the figure, holes measuring 5 by 2 H for supplying oxidizer and fuel gases were formed using an ultrasonic machining machine. and,
On the oxygen passage side of the solid electrolyte, there are L a @ and S r L with an average particle size of 5 μm, excluding the area around the gas supply hole.
IM n O3 powder was applied by brushing to a thickness of 0. ．． 3+a+
The positive electrode was prepared by applying the same to the positive electrode. Also, on the hydrogen passage side, except for the peripheral area of the gas supply passage, a cermet mixed powder of nickel/zirconium dioxide (9:1 by weight) was applied to a thickness of 0.2 mm using the same brush coating method as on the positive electrode. It was used as a negative electrode.

Nichrome was used for the interconnector, and grooves were provided in the interconnector for gas dispersion.

Glass paste was applied to the solid electrolyte plate at the portions corresponding to the periphery of the gas supply path and the outer periphery of the interconnector to prevent gas leakage.

A notch was provided in a portion of the outer periphery of the interconnector so that a gas outlet connected to the manifold was formed in a portion of the outer periphery of the interconnector. In this way, the fuel cell stack stacked in three stages was heated. Heating is from room temperature to 15
The glass paste was heated at 1°C per minute to 0°C to evaporate the solvent of the glass paste. From 150°C to 300'C, 5°C per minute, and above 300°C, nitrogen is flowed on the hydrogen path side to prevent oxidation of the electrode, and the temperature is 1000°C at 5°C per minute.
``The temperature rose to C.

Thereafter, when the temperature was maintained at 1000° C. and oxygen was supplied to the positive electrode side and hydrogen was supplied to the negative electrode side, power generation was started, the open circuit voltage was 3.7 volts, and a maximum output of 4 W per -stage was obtained.

[Effects of the Invention] In a solid electrolyte fuel cell having a flat electrolyte plate, a conduit for supplying gas is provided in the center of the electrolytic chamber plate to supply gas to the electrodes of each fuel cell. By adjusting the temperature of the supply gas, the temperature distribution of the fuel cell can be made uniform.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a high-temperature fuel cell using the solid electrolyte of the present invention. FIG. 2 is a diagram showing the stacking style of a flat plate fuel cell. Figure 3 shows an interconnector with a gas passage from the center to the periphery. Figure 4 shows a gas supply pipe installed in the center of the solid electrolyte plate.

Claims (1)

[Claims] A high-temperature fuel cell characterized in that a gas supply path is provided in the center of a flat solid electrolyte plate on which electrodes are formed, and a means for dispersing gas from the supply path to the electrodes is provided.