Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1998-11-25
2001-07-17
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06261710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bipolar separator plate for use in polymer electrolyte membrane (PEM) fuel cells. More particularly, this invention relates to a liquid cooled, bipolar sheet metal separator plate for use in polymer electrolyte membrane fuel cells. Although the concept of this invention may be applied to bipolar separator plates for a variety of fuel cell designs, it is particularly suitable for use in polymer electrolyte membrane fuel cell stacks in which the fuel and oxidant are provided to each of the fuel cell units comprising the fuel cell stack through internal manifolds.
2. Description of Prior Art
There are a number of fuel cell systems currently in existence and/or under development which have been designed and are proposed for use in a variety of applications including power generation, automobiles, and other applications where environmental pollution is to be avoided. These include molten carbonate fuel cells, solid oxide fuel cells, phosphoric acid fuel cells, and polymer electrolyte membrane fuel cells. One issue associated with successful operation of each of these fuel cell types is the control of fuel cell temperature and the removal of products generated by the electrochemical reactions from within the fuel cell.
Polymer electrolyte membrane fuel cells are particularly advantageous because they are capable of providing potentially high energy output while possessing both low weight and low volume. Polymer electrolyte membrane fuel cells are well known in the art. Each such fuel cell comprises a “membrane-electrode-assembly” comprising a thin, proton-conductive, polymer membrane-electrolyte having an anode electrode film formed on one face thereof and a cathode electrode film formed on the opposite face thereof. In general, such membrane-electrolytes are made from ion exchange resins, and typically comprise a perflourinated sulfonic acid polymer such as NAFION™ available from E.I. DuPont DeNemours & Co. The anode and cathode films typically comprise finely divided carbon particles, very finely divided catalytic particles supported on the internal and external surfaces of the carbon particles, and proton-conductive material intermingled with the catalytic and carbon particles, or catalytic particles dispersed throughout a polytetrafluoroethylene (PTFE) binder.
The membrane-electrode-assembly for each fuel cell is sandwiched between a pair of electrically conductive elements which serve as current collectors for the anode/cathode and frequently contain an array of grooves in the faces thereof for distributing the fuel cell gaseous reactants over the surfaces of the respective anode and cathode.
Commercially viable fuel cell stacks may contain up to about 600 individual fuel cells (or fuel cell units), each having a planar area up to several square feet. In a fuel cell stack, a plurality of fuel cell units are stacked together in electrical series, separated between the anode electrode of one fuel cell unit and the cathode electrode of an adjacent fuel cell unit by an impermeable, electrically conductive, bipolar separator plate which provides reactant gas distribution on both external faces thereof, which conducts electrical current between the anode of one cell and the cathode of the adjacent cell in the stack, and which, in most cases, includes the internal passages therein which are defined by internal heat exchange faces and through which coolant flows to remove heat from the stack. Such a bipolar separator plate is taught, for example, by U.S. Pat. No. 5,776,624. In such fuel cell stacks, the fuel is introduced between one face of the separator plate and the anode side of the electrolyte and oxidant is introduced between the other face of the separator plate and the cathode side of a second electrolyte.
Cell stacks containing 600 cells can be up to several feet tall, presenting serious problems with respect to maintaining cell integrity during heat-up and operation of the fuel cell stack. Due to thermal gradients between the cell assembly and cell operating conditions, differential thermal expansions, and the necessary strength of materials required for the various components, close tolerances and very difficult engineering problems are presented. In this regard, cell temperature control is highly significant and, if it is not accomplished with a minimum temperature gradient, uniform current density will not be maintainable, and degradation of the cell will occur.
In addition to temperature considerations, fuel cell stack integrity is also a function of the physical dimensions of the stack. The larger the fuel cell stack, the more difficult it becomes to maintain stack integrity and operation. Accordingly, in addition to temperature control, for a given electrical output which is a function of the number of fuel cell units comprising the fuel cell stack, it is desirable that the fuel cell stack dimensions, in particular, the fuel cell stack height be as small as possible for a given electrical output.
SUMMARY OF THE INVENTION
Accordingly, it is one object of this invention to provide a polymer electrolyte membrane fuel cell stack having a compact design such that the number of fuel cell units per inch of fuel cell stack height for a given electrical output is increased over conventional polymer electrolyte membrane fuel cell stacks.
It is another object of this invention to provide a compact, water cooled bipolar separator plate for use in polymer electrolyte membrane fuel cell stacks.
These and other objects of this invention are achieved by a polymer electrolyte membrane fuel cell stack comprising a plurality of polymer electrolyte membrane fuel cell units, each of which comprises a membrane-electrode-assembly comprising a thin, proton conductive, polymer membrane electrolyte having an anode electrode film on one face thereof and a cathode electrode film on an opposite face thereof, an anode current collector on said anode electrode film side of said membrane-electrode-assembly and a cathode current collector on said cathode electrode film side of said membrane-electrode-assembly. Disposed between the anode electrode film side of the membrane-electrode assembly of one fuel cell unit and the cathode electrode film side of the membrane-electrode-assembly of an adjacent fuel cell unit is a separator plate having guide means for distributing fuel and oxidant gases to the anode electrode and the cathode electrode, respectively. The separator plate is constructed of at least two coextensive sheet metal elements having substantially identically shaped guide means, which coextensive sheet metal elements are nestled together and form a coolant flow space therebetween.
In accordance with one preferred embodiment of this invention, the guide means comprise a plurality of corrugations formed in the two sheet metal elements. In accordance with another preferred embodiment of this invention, the guide means comprise a plurality of dimples formed in the two sheet metal elements. Although nestled together, the two coextensive sheet metal elements are maintained at a small distance from one another, thereby forming the coolant flow space therebetween. The distance between the nestled coextensive sheet metal elements is maintained by separation means such as a plurality of nodules or bumps disposed on the face of at least one of the coextensive sheet metal elements facing another of said coextensive sheet metal elements or other means for maintaining the separation between the coextensive sheet metal elements while still providing good electrical conductivity between the coextensive sheet metal elements.
REFERENCES:
patent: 4175165 (1979-11-01), Adlhart
patent: 4678724 (1987-07-01), McElroy
patent: 4963442 (1990-10-01), Marianowski et al.
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patent: 5077148 (1991-12-01), Schora et al.
patent: 5227256 (1993-07-01), Marianowski et al.
patent: 5342706 (1994-08-01), Marianowski et al.
patent: 5470679 (1995-11-01), Lund et al.
patent: 5482792 (1996-01-01), Faita et al.
Brouillette Gabrielle
Dove Tracy
Institute of Gas Technology
Pauley Petersen Kinne & Fejer
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