JP2936001B2 - High temperature fuel cell and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel cell, and more particularly, to a method for sealing a fuel cell using a solid oxide electrolyte.

[Prior Art] A fuel cell is capable of directly converting chemical energy into electric energy with high efficiency, and is being developed as a power generation method that replaces the current power generation method using steam generated by fossil fuel combustion. .

Fuel cells operate on various types of fuels, and the main focus of development is fuel cells using hydrogen, which is the only product of the cell reaction, water.

Fuel cells using hydrogen as a fuel, which are being put to practical use, 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 alkali type has a feature that the operating temperature is low, but the fuel mixed with carbon dioxide reacts with the potassium hydroxide of the electrolyte, so that such a fuel cannot be used in the alkali type.

Phosphoric acid fuel cells are also being developed as fuel cells for the electric business because hydrogen gas containing carbon dioxide obtained by reforming natural gas and naphtha can be used without any problem. In addition, there is a problem in that a platinum group metal is used, and the catalyst used is poisoned by a trace amount of carbon monoxide contained in the raw material gas.

Molten carbonates that can be used for steam generation without using expensive catalysts such as platinum group metals to operate at high temperatures, which are under development for relatively large-scale power generation facilities. Type fuel cell can be used without any problem even if carbon monoxide is contained in the raw material hydrogen. However, in a molten carbonate fuel cell, since carbon dioxide is involved in the fuel cell reaction, carbon dioxide is indispensable for the reaction, so it is necessary to mix carbon dioxide with air, which is an oxidant. Therefore, the equipment for processing the raw material and the exhaust gas becomes complicated.

On the other hand, a fuel cell using a solid electrolyte which does not contain a gaseous or molten electrolyte and operates as an electrolyte at a high temperature, such as the above-described fuel cell, is being developed as a third-generation fuel cell.

The solid oxide fuel cell uses a stabilized zirconium oxide, which is added with yttrium oxide or calcium oxide, and operates as an oxygen ion conductive electrolyte at a high temperature. Various fuels such as hydrogen, carbon monoxide, and hydrocarbons can be used, and because the electrolyte is solid, the evaporation of the electrolyte and corrosion by the electrolyte cannot be avoided in a fuel cell using a liquid or molten salt. And the structure of the fuel cell is simple.

And since the operating temperature is high, expensive catalysts such as platinum group metals are not required, and the exhaust heat is high, so that the exhaust heat can be effectively used for gas turbine power generation or steam generation. Extremely energy efficient
It is expected as the best fuel cell.

Solid electrolyte fuel cells are roughly classified into the following three types of methods of forming electrodes on the electrolyte depending on the manufacturing method and the structure.

(A) One electrode is formed on a porous ceramic substrate having high mechanical strength such as alumina, and a zirconium oxide layer is formed thereon by a method such as thermal spraying without gas leak holes. This is a method of forming the other electrode on the layer, and is used in manufacturing a cylindrical fuel cell.

(B) A method of applying a material to be an electrode by sintering on a sheet of raw zirconium oxide before sintering, and simultaneously forming the electrode at the time of sintering of zirconium oxide. This is a method of manufacturing a monolithic fuel cell. It's being used.

(C) A method in which an electrode is formed on a sintered zirconium oxide electrolyte by coating or printing, and is used in a fuel cell in which flat cell units are stacked.

However, in the method of (c), in which an electrode is formed on a zirconium oxide solid electrolyte previously sintered in the production of a solid electrolyte battery, the zirconium oxide electrolyte and the electrode having stable quality can be produced because of the flat shape. Suitable for the manufacture of large fuel cells, but the generated voltage of a fuel cell consisting of a pair of positive and negative electrodes is about 1.2 volts when open, and the output current is also limited in terms of cell efficiency, so To use a fuel cell for power generation, a number of unit fuel cells are electrically connected in series and in parallel.
FIG. 2 is a view showing a stacking mode of a flat type fuel cell. In the figure, reference numeral 1 denotes 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. It is coated with a porous material. The solid electrolyte plates covering the electrodes are laminated via an interconnector 4.

In the interconnector, a gas passage 7 for an oxidant such as air or oxygen and a gas passage 8 for a fuel gas such as hydrogen are formed to supply gas to the electrodes and electrically connect adjacent unit fuel cells. Works. End plates 5 and 6 for extracting electricity to the outside are provided at both ends.
Gas passages 9 and 10 are provided in the end plates 5 and 6 as well.

In the interconnector, a gas passage 7 for an oxidant such as air or oxygen and a gas passage 8 for a fuel gas such as hydrogen are formed to supply gas to the electrodes and electrically connect adjacent unit fuel cells. Works. End plates 5 and 6 for extracting electricity to the outside are provided at both ends.
Gas passages 9 and 10 are provided in the end plates 5 and 6 as well. In this figure, there are only two unit fuel cells, but it is of course possible to obtain a fuel cell having a desired output voltage by stacking a large number of unit fuel cells.

In the fuel cell having such a configuration, oxygen or air flows through the gas passages 7 and 9, hydrogen or other fuel gas flows through the gas passages 8 and 10, and an external circuit (not shown) is connected to both end plates. The operating temperature of 850 ℃ ~ 100
When the temperature is maintained at 0 ° C., the ionized oxygen permeates the solid electrolyte plate 1 from the positive electrode 2 side and reacts with the fuel gas at the negative electrode 3.
As a result, a current flows through the external circuit.

The case where hydrogen is used as a fuel gas is represented by the following chemical formula.

Positive ^{_{electrode: 1 / 2O 2 + 2e -}} → O 2- ^{_{anode: H 2 + O 2 - →}} H 2 O + 2e - 1 / 2O 2 + H 2 → H generation reaction of water by oxidation of hydrogen represented by ₂ O is happening in the whole cell ing.

As shown in FIG. 3, the stacked fuel cell stack 11 is provided in a pressure vessel 12 and a manifold for supplying and discharging the oxidant and the fuel is attached (not shown).
Alternatively, a space formed between the fuel cell stack and the pressure vessel by sealing the contact point between the wall surface in the pressure vessel and the fuel cell as a gas passage, and a hydrogen supply port 13 on the bottom surface of the pressure vessel, A gas discharge port 14 containing unreacted hydrogen, an oxygen supply port 15 and a gas discharge port 16 containing unreacted oxygen can be provided to supply and discharge gas to the fuel cell.

Also, terminals 17 and 18 for supplying generated power to an external circuit
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, many unit fuel cells are stacked via a conductive interconnector. Materials that are resistant to corrosion and have good electrical conductivity in a hydrogen atmosphere, conductive ceramics such as silicon carbide, molybdenum silicide, chromium silicide, lanthanum chromite, or nickel,
An alloy containing chromium, cobalt, or the like is used. However, the interconnector using these materials is different from the stabilized zirconia solid electrolyte plate in terms of thermal expansion coefficient by 10 * 10
There is a difference of ^-6 1 / ℃. If there is such a large difference, a gap occurs between the electrode surface of the solid electrolyte plate and the interconnector at the operating temperature of the solid electrolyte fuel cell of 850 ° C. to 1000 ° C., and when oxygen and fuel gas leak, the cell reaction occurs. It is also dangerous if the fuel utilization rate decreases and the mixing of oxygen and fuel gas occurs.

For fuel cells that operate at temperatures around 200-600 ° 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 a high operating temperature of 850 ° C. to 1000 ° C., and this has been one of the causes of delay in the development of a flat solid electrolyte fuel cell.

Means for Solving the Problems The present inventors diligently studied a sealing method for a solid electrolyte type fuel cell, reduced the difference in thermal expansion between the solid electrolyte plate and the interconnector, and provided a fuel cell. 10 higher than the operating temperature of
They have found a method of reliably sealing by using a sealing material that has a softening point between 50 ° C and 1350 ° C and does not plastically deform at an operating temperature of 850 ° C to 1000 ° C.

That is, FIG. 1 is a view showing a configuration of a solid oxide fuel cell according to the present invention, in which an electrolytic cell stack in which three flat unit fuel cells are stacked is shown in an expanded manner. In the figure, reference numeral 21 denotes a solid electrolyte plate made of stabilized or partially stabilized zirconia, and the solid electrolyte plate is coated with a porous material forming a positive electrode 22 and a negative electrode 23, and together with a current collecting function forming a gas passage. Adjacent unit fuel cells are stacked via an interconnector 24 for electrical connection, and end plates 25 and 26 are provided at both ends for extracting electricity to the outside. Further, the interconnector is provided with a gas passage 27 for an oxidant such as oxygen or air and a gas passage 28 for a fuel gas such as hydrogen,
Similarly, gas passages 29 and 30 are provided in the end plates 25 and 26, and the periphery 31 of the surface of the electrolyte plate on which the electrodes are formed is softened at 1050 ° C. to 1350 ° C., which is higher than the operating temperature of the battery. The material has a viscosity of 10 ² to 10 ⁷ poise, deforms into a sealed shape, cools down, and uses a material that does not plastically deform at an operating temperature of 1000 ° C. or less, after heating to a temperature at which the glass paste softens, In the process of lowering the temperature to the operating temperature, the glass paste is solidified to seal the gap between the electrolyte plate and the interconnector and to mechanically fix both.

Among the glass pastes that can be used for such purposes, among softening point aluminosilicate glass, high silicate glass, and crystallized glass, Li ₂ O.SiO ₂ system, β-spodumene solid solution, cordierite glass Etc. can be given.

Alternatively, after being softened at 1050 ° C to 1350 ° C as in crystallized glass to form a sealed shape, by maintaining this temperature, a crystalline phase is precipitated from the glass phase to prevent plastic deformation and sealing and fixing May be performed. If the application width of the glass paste is large, the area of the portion acting as a fuel cell will be reduced, and if it is small, there is a possibility of leakage, so it is preferably about 2 to 8 mm, and the applied thickness is 0.1 to 0.5 m
m is preferred.

Also, instead of applying the glass paste, after sandwiching and laminating a glass plate made of the same component as the glass component of the glass paste, the glass is heated to a softening temperature, then the temperature is hardened and solidified to seal and fix. May be done,
A solid electrolyte plate on which electrodes are formed, a glass paste in which glass that does not plastically deform at the operating temperature of the battery is dispersed in an organic substance is applied to at least one surface of the interconnector, and the glass paste is made of the same components as the glass components of the glass paste. After sealing and laminating the glass plates and heating the glass to the softening temperature, the temperature may be lowered and solidified to perform sealing and fixing.

[Operation] In a flat plate type solid electrolyte fuel cell, between the surface of the solid electrolyte plate on which electrodes are formed and the interconnector
By applying a material that softens between 1050 ° C. and 1350 ° C. and does not plastically deform 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 both.

Example A fuel cell stack was manufactured according to the stacking method shown in FIG. A 50 × 50 mm solid electrolyte plate of partially stabilized zirconia to which 3 mol% of yttrium oxide was added was used. La _0.9 Sr _0.1 Mn is _placed on the oxygen electrolyte side of the solid electrolyte.
O ₃ powder thickness 0.3mm by (average particle size of about 5 [mu] m) brushing the
To form a positive electrode. In addition, nickel /
A cermet mixed powder of zirconium dioxide (9: 1 by weight) was applied to a thickness of 0.2 mm by a brush coating method in the same manner as the positive electrode to obtain a negative electrode.

Nichrome is used for the interconnect, and the solid electrolyte plate
The periphery of 21 was coated with a paste of Li ₂ O.SiO ₂ -based crystallized glass having a softening point of 1200 ° C. with a thickness of 0.2 mm.

The fuel cell stack thus stacked in three stages was mounted in a pressure vessel and heated. Heating from room temperature to 150 ° C
Until 1 minute at 1 ° C. to evaporate the solvent of the glass paste. 5 ℃ / 300 ℃ per minute from 150 ℃ to 300 ℃
In the above, nitrogen was allowed to flow to the hydrogen passage side to prevent oxidation of the electrode, and the temperature was raised to 1200 ° C. at 5 ° C. per minute to melt and maintain the same temperature for 10 minutes.

After that, the temperature was lowered to 1000 ° C and oxygen was supplied to the positive electrode side and hydrogen was supplied to the negative electrode side, and when power generation was started, the open circuit voltage was 3.7 volts.Estimation from the electrochemical potential value according to the Nernst equation showed that almost no gas leakage However, the solid electrolyte plate and the interconnector were sufficiently mechanically fixed.

[Effects of the Invention] In a solid electrolyte fuel cell having a flat electrolyte plate, the periphery of the electrolyte plate softens at 1050 ° C to 1350,
At the operating temperature of the battery, 850 ° C to 1000 ° C, glass that does not deform plastically is applied to seal the gap between the interconnector and the solid electrolyte plate, reducing the possibility of gas leakage and fixing both, so vibration occurs Safe operation is possible without deviation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a solid oxide fuel cell manufactured by the method of the present invention, FIG. 2 is a diagram showing a configuration of a solid oxide fuel cell, and FIG. 3 is a diagram showing an example of mounting a fuel cell stack. . Solid electrolyte ... 21 Positive electrode ... 22 Negative electrode ... 23 Interconnector ... 24 Glass paste application area ... 31

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-178454 (JP, A) JP-A-3-101858 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (6)

(57) [Claims] A high-temperature fuel comprising a sealing material that does not plastically deform at a battery operating temperature of 850 ° C. to 1000 ° C. between a solid electrolyte plate on which electrodes are formed and an interconnector. battery. 2. The high-temperature fuel cell according to claim 1, wherein the sealing material is glass having a softening temperature between 1050 ° C. and 1350 ° C. 3. The high-temperature fuel cell according to claim 1, wherein the sealing material is a crystallized glass that forms a crystal phase at an operating temperature. 4. A solid electrolyte plate on which electrodes are formed and a glass paste obtained by dispersing glass which does not undergo plastic deformation at an operating temperature of a battery in an organic substance is applied to at least one surface of the interconnector and laminated. A method for manufacturing a high-temperature fuel cell. 5. A method for manufacturing a high-temperature fuel cell, comprising sandwiching and laminating 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. 6. The method for producing a high temperature fuel cell according to claim 4, wherein the glass is heated to 1050 ° C. to 1350 ° C. to soften and seal the glass.