Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-07-23
2004-07-13
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06761990
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polymer electrolyte fuel cell, particularly to a separator therefor.
BACKGROUND ART
A polymer electrolyte hydrogen-oxygen fuel cell is excellent in its output characteristics, whereby its application to e.g. automobiles, is expected. For practical application of the above fuel cell, it is required to develop a fuel cell which provides a high output density and a high energy efficiency constantly over a long period of time even under such an operational condition that the utilization ratios of a fuel and air are high.
The polymer electrolyte fuel cell usually has a construction such that a pair of power generation electrodes (a fuel electrode and an air electrode) face each other via a polymer electrolyte, and the pair of electrodes and the electrolyte are bonded to form a membrane electrode assembly. A plurality of such assemblies are laminated via separators, and the entire assembly is clamped to be integral (stacked).
Here, the separator has channels for supplying a fuel gas and an oxidant gas (such as air) to the electrodes, and it serves as a partition plate between the adjacent two units. Accordingly, the separator is required to have characteristics such that the gas permeability is low, it is light in weight, it is excellent in corrosion resistance and oxidation resistance when exposed to a steam atmosphere at a temperature of from room temperature to a vicinity of 150° C. as the operational temperature of the fuel cell, it has good electrical conductivity for a long period of time, and it can be mechanically processable. Further, the separator is required to be a good conductor for electricity and heat in order to efficiently remove electricity and heat generated by a reaction of the cell out of the cell system.
As conventional separator materials, carbon type bulk materials such as artificial graphite and glassy carbon, are known. However, the carbon type materials are poor in toughness and brittle, whereby the following problems are likely to occur when it is used as a separator under such a condition that a stress other than a compression stress, or a mechanical shock, is likely to be exerted. Namely, the problems are such that the separator itself is broken, whereby the shape can not be maintained, cracking is likely to form, whereby air tightness can not be maintained, mechanical forming or processing is difficult, whereby the processing cost tends to be high, and recycling is difficult.
As a means to solve the above problems, it has been proposed to use as a separator a molded product obtained by subjecting flat graphite powder particles so called expanded graphite (such as Grafoil, tradename, manufactured by UCAR Co.) to dispersion treatment by e.g. an acid and adding a binder, followed by molding. This molded product is a flexible material which can be mechanically processable by e.g. pressing, whereby the problems relating to the toughness and the mechanical shock resistance, are overcome. However, such a molded product has a problem such that the mechanical strength is low, and the shape can hardly be maintained when made thin, or it is susceptible to deforming even when a small stress is applied thereto.
Further, the fuel cell is required to be small in size and light in weight and to provide a high output especially when it is used as a power source for an automobile, and it is necessary to increase a power per unit volume and to cool a heat generated by conducting electricity and by a reaction of the cell with a compact structure. Especially when a fluorine-containing polymer electrolyte having a high electrical conductivity, is used, this cooling will be essential, since the heat resistant temperature of the electrolyte is usually not so high. Cooling can be accomplished with the most compact structure when a fluid is permitted to flow at a high flow rate through a narrow and long channel formed in a separator, specifically, when water is permitted to flow under a high pressure. However, when the above-mentioned expanded graphite is used as the separator material, if the separator is maintained in the presence of water at a high temperature, the water is likely to penetrate into laminated particles of graphite, whereby the shape can not be maintained, thus leading to a problem that a long term reliability can not be attained.
As a means to solve the above-mentioned problems of the separator made of a carbon material, an attempt has been made to use a metal such as a surface-treated stainless steel, titanium or aluminum as the separator material (e.g. EP0780916). When a metal is employed, the mechanical processing will be easy, the strength will be high even thin, the toughness, the mechanical shock resistance, the fluid shielding property, and thermal and electrical conductivity will be excellent. However, the metal material has problems such that the specific gravity is large (for example, 8.0 with stainless steel, 4.5 with titanium and 2.7 with aluminum), whereby the output per unit mass of the fuel cell tends to be low.
Therefore, the present invention has an object to provide a polymer electrolyte fuel cell having a separator which is made of a material which can easily be formed and processed, whereby the shape and air tightness can be maintained even when a stress other than a compression stress, a mechanical shock, vibration, etc., are exerted, and the initial good electrical conductivity can be maintained over a long period of time even when exposed to a steam atmosphere from room temperature to the vicinity of 150° C. as the operational temperature of the fuel cell, and which is light in weight and industrially practical.
DISCLOSURE OF THE INVENTION
The present invention provides a polymer electrolyte fuel cell comprising a plurality of membrane electrode assemblies laminated via separators, each assembly comprising a membrane-form polymer electrolyte and a pair of a fuel electrode and an air electrode facing each other via the electrolyte, wherein the separator has a fuel gas channel for supplying a fuel gas to the fuel electrode, an oxidant channel for supplying an oxidant to the air electrode and a fluid channel for removing a heat generated by a reaction out of the cell system, and the separator is made of a metal
on-metal composite material which has faces made of non-metal which are in contact with the membrane electrode assemblies and side walls of the fluid channel which are made of metal.
In the present invention, the separator has a role to provide a fuel gas and an oxidant to the fuel electrode and the air electrode, respectively, and a role to circulate a fluid for cooling to remove a heat generated by conduction of electricity and by a reaction of the cell out of the cell system. Here, air is used mainly as the oxidant, and accordingly, the electrode to which the oxidant is supplied, will be referred to as an air electrode in this specification. As the fluid for cooling, water is preferred, since the heat can thereby be efficiently removed. Further, the separator has a role to shield a gas or moisture to prevent permeation of the gas or moisture between the adjacent two membrane electrode assemblies and a role to transmit the generated electric current.
The fuel gas channel and the oxidant channel usually consist of grooves formed by ribs formed on the surface of the separator. Such a gas channel may consist of a plurality of linear or curved grooves, but a meandering groove may be formed over the entire surface of the separator so that it has only one inlet and one outlet for a gas.
In the present invention, the separator is made of a metal
on-metal composite material, and at least side walls of the fluid channel for cooling are made of metal. Accordingly, even when the above side walls are exposed to water as the fluid for cooling at a temperature of up to about 150° C. as the operational temperature of the fuel cell, the water for cooling will not penetrate into the interior of the separator, and the shape of the separator can be maintained.
Further, in the separator in the pre
Endoh Eiji
Kunisa Yasuhiro
Yanagisawa Eiji
Yoshitake Masaru
Asahi Glass Company Limited
Bell Bruce F.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wills M.
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