Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-11-26
2004-05-25
Tsang-Foster, Susy (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06740442
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a single cell of a flat plate type solid oxide fuel cell and a cell stack utilizing this single cell. More particularly, the present invention relates to improvement in the structure of a single cell.
BACKGROUND ART
A solid oxide fuel cell includes an air electrode to which air containing oxygen is supplied from the outside, a fuel electrode to which fuel gas such as hydrogen, carbon monoxide or methane is supplied from the outside, and an electrolyte through which oxygen ions can pass between these electrodes, and is constituted to generate electric power by electrochemical reaction of fuel gas and oxygen ions. At the air electrode, electrons supplied from an external circuit react with oxygen in air so that oxygen ions are produced. Then, the oxygen ions pass through the electrolyte to reach the fuel electrode. Further, at the fuel electrode, the oxygen ions having passed through the electrolyte react with fuel gas so that products are emitted and electrons are supplied to an external circuit.
As one conformation of this solid oxide fuel cell, there is conventionally a flat plate type. In the flat plate type solid oxide fuel cell, a fuel electrode film is formed on one surface (for example, a front surface) of an electrolyte plate, and an air electrode film is formed on the other surface (for example, a back surface), thereby forming a single cell. Then, a plurality of single cells are superposed each other with a separator plate having a gas flow path formed thereto being sandwiched therebetween, thereby forming a laminated body. Furthermore, when a metal manifold plate for distributing gas in accordance with each electrode is attached around the laminated body, a cell stack is formed.
In this flat plate type solid oxide fuel cell, however, since the structural strength of the cell stack is assured by the electrolyte plate and the separator plate, the extremely high accuracy of the dimension or flatness of the electrolyte plate or the separator plate is demanded in order to prevent the cell stack from being damaged due to the thermal stress generated during heating such as power generation. The processing cost of the electrolyte plate and the separator plate is therefore increased, and the quality control of these plates must be performed strictly.
Moreover, since the separator plate and the single cell are superposed as separate members, the electric resistance between these members becomes large, and large losses are generated in the electrical output from the stack.
In addition, since the separator plate has flow paths between respective electrodes by providing, e.g., ribs in order to distribute gas, the separator plate does not have enough strength and is apt to be damaged. Additionally, its processing cost is increased.
Further, since a material used for the separator plate is relatively expensive and must have an enough thickness in order to assure the strength, the material cost of the cell stack is increased.
Furthermore, since the manifold plate provided around the laminated body constituted by superposing the single cells is made of metal, the thermal expansion coefficient of the manifold plate is greatly different from that of the laminated body of the single cells. Therefore, the thermal stress is produced between the laminated body and the manifold plate during electric power generation, which can be a factor of damage to the cell and stack.
It is an object of the present invention to provide a single cell of a flat plate type solid oxide fuel cell and a cell stack utilizing this single cell which can improve the strength of the cell and/or stack and facilitate processing of components to reduce the processing cost. Moreover, it is another object of the present invention to provide a single cell of a flat plate type solid oxide fuel cell and a stack utilizing this single cell which can improve the output characteristic and reduce the material cost.
DISCLOSURE OF INVENTION
To achieve this aim, according to the present invention, there is provided a single cell of a flat plate type solid oxide fuel cell, the single cell comprising: a first electrode member consisting of a porous substrate; an electrolyte film formed on any one of a front surface and a back surface of the first electrode member; a second electrode member formed on the electrolyte film; and a separator film formed on the other surface of the first electrode member, wherein the first electrode member is one of a fuel electrode and an air electrode, and the second electrode member is the other one of the fuel electrode and the air electrode.
Therefore, since the first electrode member is formed by a porous substrate, gas can come into contact with the first electrode member while passing through the inside of the first electrode member, thereby causing a reaction. Thus, since ribs or the like for forming a gas flow paths do not have to be provided, the structure of the single cell can be simplified, and the strength can be improved. As a result, the size of the single cell can be increased, and the power generation characteristic can be hence enhanced. In addition, since the gas passes through the inside of the porous substrate, a contact area of the first electrode member with respect to air per unit capacity can be enlarged. Consequently, the power generation performance by the single cell can be improved.
Additionally, since the first electrode member is formed by the porous substrate, the first electrode member can be softer than an solid matter composed of a material forming the electrode member. Accordingly, since the thermal stress of the cell and stack obtained by superposing the single cells during the power generation operation can be absorbed and alleviated, the high flexibility of the cell stack can be obtained, thereby improving the strength. Further, since the high processing accuracy of the single cell for avoiding damage due to the thermal stress is no longer necessary, the production cost can be reduced, and the quality control can be facilitated.
Furthermore, since a separator film is directly formed to the first electrode member consisting of the porous substrate, the separator film enters multiple minute holes on the surface of the first electrode member, and contact areas between the first electrode member and the separator film can be thereby increased. As a result, the contact resistance (electrical resistance at contact parts) between the first electrode member and the separator can be greatly reduced, thereby improving the power generation performance.
In addition, since both the separator and the electrolyte are films, for example, thin films each having a thickness of a several ten micron, the power losses caused due to the internal resistance of these films can be reduced. As a result, the power generation performance can be improved. Additionally, since the separator is formed of a film, a quantity of an expensive separator material to be used can be decreased. Consequently, the manufacturing cost of the single cell can be reduced.
Further, according to the present invention, in the single cell of the flat plate type solid oxide fuel cell, at least one of a part of the electrolyte film and a part of the separator film is a seal portion which covers all or a part of side surfaces of the first electrode member and functions as a gas seal film.
Therefore, since the inside and the outside of the first electrode member are shielded by the electrolyte film and the separator film, and the seal portion, the air or the fuel gas can pass through the inside of the first electrode member without wastefully leaking it out of the first electrode member.
Furthermore, according to the present invention, in the single cell of the flat plate type solid oxide fuel cell, the seal portion includes: a side film portion which covers each entire area of one of two pairs of opposed side surfaces of the first electrode member and seals that pair of side surfaces to prevent the gas from escaping; and a corner film portion which covers both end porti
Central Research Institute of Electric Power Industry
Notaro & Michalos P.C.
Tsang-Foster Susy
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