Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2002-06-05
2004-09-21
Cantelmo, Gregg (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S247000, C429S253000, C029S623100, C524S495000, C524S496000, C442S111000
Reexamination Certificate
active
06794078
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a fuel cell, a fuel-cell separator for separating the fuel gas and oxidizer gas (air or oxygen) in a fuel cell and a method of producing the fuel-cell separator.
BACKGROUND ART
Recently, the considerably increasing consumption of fossil fuels for automobile or the like has caused various problematic environmental disruptions due to the large amounts of various waste gases generating on combustion of the fuels. As a means for solving the problem, fuel cells, being a safe and pollution-free energy generating system, have become of major interest and been actively studied and developed on the worldwide level, and some are put to practical use.
Because of their high energy efficiency, fuel cells can reduce environmental pollution and are expected to be widely used as small dynamos or the power supply for EVs. It is the principle of fuel cells to develop a potential difference by the conversion of chemical energy to electric energy through the oxidation and reduction of a fuel gas and an oxidizer gas (air or oxygen) which are allowed to flow separately over electrodes (positive electrode and negative electrode) attached on the upper and lower sides of an electrolyte layer, and the transfers of cations and electrons in the electrolyte layer. Because fuel cells are produced by piling up electrodes and electrolyte layers alternately in multi-layers, separating plates (separators) for separating the fuel gas from the oxidizer gas are interposed between positive electrodes and negative electrodes which are placed one on the other. To secure gas feed paths, separators generally have ribs (projecting parts; adjoining ribs form a groove therebetween which works as a path for a gas, such as hydrogen or oxygen, or product water). Charge collector plates surrounding the multi-layered electric cells collect the potential difference developed in each electric cell.
Among the members constructing a fuel cell that are important and occupy a majority are the separators, which perform important tasks influencing the characteristics of fuel cells, for example, stable supply of gases (oxygen, hydrogen or the like) to catalysts and electrolyte layers and immediate discharge of the product water out of the system. Separators, therefore, require various properties, including 1) separation of fuel gases from oxidizer gases (gas non-permeability), 2) electric conductivity and 3) resistance to swelling with water produced on negative electrodes or with electrolytic solutions.
Separators have generally been produced by mechanically grooving a graphite block or glassy carbon to form ribs, thereby providing feed paths for fuel gases and oxidizer gases. An alternative is high pressure molding of an expanded-graphite or an expanded-graphite sheet produced by treating a flaky natural graphite with acid and then with heat, or by impregnating the molded expanded-graphite with a liquid thermosetting resin and curing to prevent swelling with liquids (Japanese Patent Application Non-examined Publication Nos. 60-65781 and 60-12672).
Disclosed in the specification of International Publication No. WO97/02612 is a method wherein an expanded-graphite powder of specific particle diameters is dispersed in a thermoplastic or thermosetting resin, molded into a block and then mechanically grooved.
The methods using various machining techniques are costly because they need highly accurate cutting machines or techniques, a very long machining time or a tremendous labor, for example, impregnating the cutting-processed separators with resins by using a vacuum drier. Further, the separators cut out of graphite plates are thick, and have the defect that each separator is so heavy as to problematically increase the weight per fuel cell (generally containing several hundreds of separators). This causes energy loss when fuel cells are fabricated in cars or the like. Additional drawbacks of the separators cut out of graphite plates are hardness and fragility. When several hundreds of separators are stacked and clamped to prevent a gas leak, some are often broken under the clamping pressure. The methods using the expanded-graphite involve the problems that moldable ribs are limited in dimension, and the products apt to swell with the gas generated during molding and cannot be supplied stably.
The separator disclosed in the specification of International Publication No. WO97/02612 has the defect that because the particles of the expanded-graphite powder used for production have small diameters and are very fragile and weak, the expanded-graphite powder is crashed during mixing with resins and gives molded articles of poor strength.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the invention is to provide a fuel-cell separator which is free from problems relating to the properties of fuel-cell separators, such as electric resistance, gas permeability, swelling with liquids and mechanical strength, and is very moldable and economical.
Another object of the invention is to provide a ribbed fuel-cell separator which is further improved in that it can be made lighter because its plate part can be thinned even for high ribs.
Another object of the invention is to provide a fuel-cell separator which is further improved in dimensional accuracy.
Another object of the invention is to provide a fuel-cell separator which is further improved particularly in electrical properties and mechanical strength.
Another object of the invention is to provide a method for economically and stably producing through simple steps a fuel-cell separator which is free from problems relating to the properties of fuel-cell separators such as electric resistance, gas permeability, swelling with liquids and mechanical strength, and has good moldability.
Another object of the invention is to provide a method for producing a fuel-cell separator by using a resin which cures readily without troubles such as corrosion of molds.
Another object of the invention is to provide a further improved method for producing a fuel-cell separator which is particularly excellent in electric properties and mechanical strength.
Another object of the invention is to provide a fuel cell of high quality which contains fuel-cell separators excelling in the properties of fuel-cell separators relating to electric resistance, gas permeability, swelling with liquids and mechanical strength.
Another object of the invention is to provide a fuel cell which is further improved in stably maintaining its cell-properties during a long-term usage.
Accordingly, the invention relates to the following subjects.
(1) A fuel-cell separator comprising a resin and an electric conductor dispersed in the resin.
(2) The fuel-cell separator as described in (1), wherein the electric conductor is a powdery electric conductor having an average particle diameter of 25 &mgr;m or more.
(3) The fuel-cell separator as described in (1) or (2), wherein the electric conductor is an expanded-graphite powder.
(4) The fuel-cell separator as described in (3), wherein the expanded-graphite powder has a sulfuric acid ion (SO
4
2−
) concentration of 500 ppm or less.
(5) The fuel-cell separator as described in any one of (1) to (3), wherein the resin is a cured phenolic resin.
(6) The fuel-cell separator as described in (5), wherein the resin is a cured phenolic resin cured by ring-opening-polymerization.
(7) The fuel-cell separator as described in any one of (1) to (6), which has a shape of a ribbed-plate formed by monobloc-molding a plate and ribs.
(8) The fuel-cell separator as described in (7), wherein the ribs have a height of 0.3 mm or more.
(9) The fuel-cell separator as described in (7), wherein the ribs have a height of 0.6 mm or more.
(10) The fuel-cell separator as described in any one of (7) to (9), wherein the ratio of the height (A) of the ribs to the thickness (B) of the plate, (A/B), is 0.5 or more.
(11) The fuel-cell separator as described in any one of (7) to (10), which has the ribs on one side of the plate.
(12) The fuel-cell separator as described in any on
Fujita Atsushi
Hasuda Harufumi
Seki Tomonori
Tashiro Noriji
Antonelli Terry Stout & Kraus LLP
Cantelmo Gregg
Hitachi Chemical Company Ltd.
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