Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-07-23
2001-06-19
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S210000
Reexamination Certificate
active
06248467
ABSTRACT:
BACKGROUND OF THE INVENTION
In an exemplary application, polymer electrolyte fuel cells (PEFCs) are currently under development to produce electrical power for a variety of stationary and transportation applications. To produce useful currents and voltages, individual fuel cells are connected in series to form stacks of cells. Adjacent cells in a stack are typically separated by bipolar plates, which serve as the anode for one fuel cell and the cathode for the adjacent cell. Thus the bipolar plate must function as a current collector as well as an impermeable barrier between the gases on either side of the plate. In addition, many stack designs incorporate gas flow channels into the bipolar plate. These flow fields ideally provide equal distribution of reactant gases over the entire area of a catalyzed proton exchange membrane. Flow fields are commonly molded or machined into both sides of a bipolar plate, with an anode flow field on one side and a cathode flow field on the other side.
To date, the bipolar plate remains the most problematic and costly component of PEFC stacks, as well as other electrochemical cells, such as alkaline fuel cells, zinc-air batteries, and the like. The most commonly used material for single cell testing is machined graphite, which is expensive and costly to machine. The brittle nature of graphite also prevents the use of thin components for reducing stack size and weight, which is particularly important for transportation applications. Other stack designs consider the use of metal hardware such as stainless steel. But a number of disadvantages are associated with stainless steel, including high density, high cost of machining, and possible corrosion in the fuel cell environment. Still other designs use graphite/poly(vinylidene fluoride) composites, which can be relatively brittle and expensive and require long process cycle times. Attributes of a suitable material include:
i) high electronic conductivity;
ii) low weight;
iii) low permeability;
iv) physical and chemical stability under fuel cell operating conditions
v) low cost of mass production.
RELATED ART
Thermoplastic composite materials for use in fuel cell bipolar plates are described in U.S. Pat. No. 4,214,969 (Lawrance) and U.S. Pat. No. 4,339,322 (Balko et al.). The '969 patent describes a molded graphite/poly(vinylidene fluoride) material, and the '322 patent claims improvements in the mechanical properties of the same with the addition of carbon fibers. However, thermosetting resins tend to offer the important advantage of shorter process cycle times over thermoplastics. Bipolar plate materials comprising graphite in thermosetting resin matrices are described in U.S. Pat. No. 4,301,222 (Emanuelson et al.), U.S. Pat. No. 4,265,727 (Beckley), U.S. Pat. No. 4,670,300 (Stewart), U.S. Pat. No. 4,737,421 (Uemura et al.) and U.S. Pat. No. 4,197,178 (Pellegri et al.). The '222 patent describes graphite/phenolic composites, but due to porosity and corrosion issues other resins are currently preferred over phenolics. The '727 patent describes thermosetting resin composites filled with a combination of graphite fibers and graphite powders of specific dimensions. The advantage of rapid cure cycles for thermosetting resins is diminished if additional process steps (such as coatings or heat treatments) are required. The '300 and '421 patents describe composite plates formed by carbonizing or graphitizing precursor sheets of cellulose fibers and a thermosetting resin. The '178 patent describes materials comprising molded aggregates of an electrically conductive powdered material and a thermosetting resin, preferably epoxy, which are coated with a layer of a chemically resistant, nonconducting thermosetting resin.
Various attributes, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the apparatus of this invention may comprise a bipolar plate for use in an electrochemical cell, said plate being formed from a thermosetting vinyl ester resin having a conductive powder embedded therein in an amount sufficient to impart a desired level of electrical conductivity to said plate. In preferred embodiments of the invention, said conductive powder is graphite with particle sizes predominantly in the range of 80 to 325 mesh. The bipolar plate may further include short fiber reinforcements such as glass, polymer, graphite/carbon, and cotton.
REFERENCES:
patent: 4197178 (1980-04-01), Pellegri et al.
patent: 4214969 (1980-07-01), Lawrance
patent: 4265727 (1981-05-01), Beckley
patent: 4301222 (1981-11-01), Emanuelson et al.
patent: 4339322 (1982-07-01), Balko
patent: 4374906 (1983-02-01), Breault
patent: 4426340 (1984-01-01), Goller et al.
patent: 4670300 (1987-06-01), Stewart, Jr.
patent: 4737421 (1988-04-01), Uemura et al.
patent: 4759989 (1988-07-01), Abe et al.
patent: 4830938 (1989-05-01), McCullough et al.
patent: 4851304 (1989-07-01), Miwa et al.
patent: 4938942 (1990-07-01), Gorman et al.
patent: 5532083 (1996-07-01), McCullough
patent: 5589053 (1996-12-01), Moran et al.
Busick Deanna N.
Wilson Mahlon S.
The Regents of the University of California
Weiner Laura
Wilson Ray G.
LandOfFree
Composite bipolar plate for electrochemical cells does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite bipolar plate for electrochemical cells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite bipolar plate for electrochemical cells will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2531285