Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1998-11-20
2004-05-11
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C029S623400
Reexamination Certificate
active
06733916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing fuel cells by fixing a polymer electrolyte film to a frame. The present invention also pertains to fuel cells manufactured according to this method.
2. Description of the Related Art
The fuel cells convert the chemical energy of a fuel directly to electrical energy. In a general configuration of the fuel cell, a pair of electrodes are arranged across an electrolyte layer. A supply of gaseous fuel containing hydrogen is fed to one electrode, that is, the anode, whereas a supply of oxidizing gas containing oxygen is fed to the other electrode, that is, the cathode. The fuel cells of this structure generate an electromotive force through the electrochemical reactions proceeding on the anode and the cathode. One major problem of the fuel cells is that the mixture of the gaseous fuel and the oxidizing gas fed to the respective electrodes lowers the efficiency of power generation. In the fuel cells, it is accordingly required to prevent the flow of gaseous fuel from being mixed with the flow of oxidizing gas.
Polymer electrolyte fuel cells have a polymer electrolyte film as the electrolyte layer. The polymer electrolyte fuel cells are generally manufactured by laying a large number of unit cells one upon another to form a stuck structure. In each unit cell, a polymer electrolyte film (hereinafter may be simply referred to as electrolyte film) is interposed between a pair of gas diffusion electrodes to form a sandwich-like structure. A pair of gas-impermeable separators are further disposed across the sandwich-like structure. The electrolyte layer separates the flow of gaseous fuel from the flow of oxidizing gas. The separator prevents the flow of gaseous fuel and the flow of oxidizing gas from being mixed with each other in the adjoining unit cells. In the polymer electrolyte fuel cell, in order to prevent the flow of gaseous fuel from being mixed with the flow of oxidizing gas, the electrolyte film is bonded to the separators with an adhesive in each unit cell to ensure the gas sealing property of the electrodes.
Even when an appropriate adhesive is selected by taking into account the materials of the electrolyte film and the separator, the fuel cell manufactured according to the prior art technique may have the insufficient adhesive strength between the polymer electrolyte film and the separator. The insufficient adhesive strength may result in damaging the gas sealing property of the electrodes. This causes the fuel cell manufactured to have the poor reliability for the gas sealing property of the electrodes.
SUMMARY OF THE INVENTION
The object of the present invention is thus to enhance the adhesive strength of a polymer electrolyte film via an adhesive and thereby manufacture a fuel cell having the high reliability for the gas sealing property.
At least part of the above and the other related objects is realized by a first method of manufacturing a fuel cell by fixing a polymer electrolyte film to a frame. The first method includes the steps of: causing the polymer electrolyte film to have a water content of not greater than 4, which is expressed as a molar fraction of H
2
O; and bonding the polymer electrolyte film to the frame with an adhesive.
In the first method of the present invention, the polymer electrolyte film treated to have the water content (expressed as the molar fraction of H
2
O) of not greater than 4 is bonded to the frame with the adhesive. As is known, the water content of the polymer electrolyte film varies with a variation in humidity of the atmosphere. The water content of the polymer electrolyte film may abruptly increase according to the relative humidity. In the case where the polymer electrolyte film has a large water content during manufacture of the fuel cell, a large quantity of water molecules are adsorbed by the functional groups in the polymer electrolyte film. This undesirably lowers the adhesive strength of the polymer electrolyte film via the adhesive. The first method of the present invention causes the polymer electrolyte film to have the water content (expressed as the molar fraction of H
2
O) of not greater than 4. This effectively prevents a large quantity of water molecules from being adsorbed by the functional groups and thereby ensures the sufficient adhesive strength of the polymer electrolyte film via the adhesive.
The first method of the present invention does not lower the adhesive strength of the polymer electrolyte film via the adhesive even when the atmosphere has a high humidity during manufacture. The fuel cell manufactured according to the first method of the present invention has the high reliability for the gas sealing property between the polymer electrolyte film and the frame.
The present invention also provides a second method of manufacturing a fuel cell by fixing a polymer electrolyte film to a frame. The second method includes the steps of: providing an adhesive having a modulus of elasticity of not greater than 10 MPa after cure; and bonding the polymer electrolyte film to the frame with the adhesive.
In the second method of the present invention, the polymer electrolyte film is bonded to the frame with the adhesive having the modulus of elasticity of not greater than 10 MPa after cure. This arrangement enables the adhesive layer between the polymer electrolyte film and the frame to be readily expanded and contracted in the fuel cell thus manufactured. In this fuel cell, even when the polymer electrolyte film is expanded or contracted with a variation in humidity of the atmosphere after the cure of the adhesive, the adhesive layer can follow the expansion or the contraction. This effectively prevents the polymer electrolyte film from being hardened or broken and protects the adhesive layer from the damage.
The fuel cell manufactured according to the second method of the present invention has the high reliability for the gas sealing property between the polymer electrolyte film and the frame even in the service environment of a remarkable humidity change.
The present invention further provides a third method of manufacturing a fuel cell by fixing a polymer electrolyte film to a frame. The third method includes the steps of: providing an adhesive having a durometer A hardness of not greater than 90 after cure; and bonding the polymer electrolyte film to the frame with the adhesive.
In the third method of the present invention, the polymer electrolyte film is bonded to the frame with the adhesive having the durometer A hardness of not greater than 90 after cure. This arrangement enables the adhesive layer between the polymer electrolyte film and the frame to be in a relatively soft state in the fuel cell thus manufactured. In this fuel cell, even when the polymer electrolyte film is expanded or contracted with a variation in humidity of the atmosphere, the adhesive layer can follow the expansion or the contraction. This effectively prevents the polymer electrolyte film from being hardened or broken and protects the adhesive layer from the damage.
Like the second method of the present invention, the fuel cell manufactured according to the third method of the present invention has the high reliability for the gas sealing property between the polymer electrolyte film and the frame even in the service environment of a remarkable humidity change.
In the first method of the present invention, it is preferable that the step of bonding the polymer electrolyte film comprises placing the adhesive having a modulus of elasticity of not greater than 10 MPa after cure and/or a durometer A hardness of not greater than 90 after cure.
Even in the case where the atmosphere has a high humidity during manufacture or in the case where there is a large variation in humidity in the service environment, this configuration ensures the high reliability for the gas sealing property between the polymer electrolyte film and the frame of the fuel cell.
In the second method of the present invention, it is preferable that the step of provi
Bell Bruce F.
Crepeau Jonathan
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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