Fuel cell collector plate and method of fabrication

Details Fuel cell collector plate and method of fabrication Fuel cell collector plate and method of fabrication

1998-11-18

2001-01-30

Nuzzolillo, Maria (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000

Reexamination Certificate

active

06180275

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to compositions and methods for fabricating electrically-conductive polymer composite structures and coatings, and more particularly to a highly-conductive graphite composite particularly suited for net shape molding a current collector plate for a fuel cell.
BACKGROUND OF THE INVENTION
Solid polymer electrolyte membrane (PEM) type electrochemical fuel cells are well known. Generally, PEM fuel cells comprise a membrane electrode assembly (MEA) and diffusion backing structure interposed between electrically conductive graphite current collector plates. In operation, multiple individual cells are arranged to form a fuel cell stack. When the individual cells are arranged in series to form a fuel cell stack, the current collector plates are referred to as bipolar collector plates. The collector plates perform multiple functions, including: (1) providing structural support; (2) providing electrical connection between cells; (3) directing fuel and oxidant reactants and/or coolant to individual cells; (4) distributing reactant streams and/or coolant within individual cells; (5) removing byproduct from individual cells; and (6) separating fuel and oxidant gas streams between electrically connected cells, In addition to being electrically conductive, collector plates must have good mechanical strength, high thermal stability, high resistance to degradation caused by chemical attack and/or hydrolysis, and low permeability to hydrogen gas.
Typically, collector plates have intricate patterns formed on their major surfaces. For instance, integral channels may be provided for directing fuel, oxidant and/or byproduct through the fuel cell. Historically, graphite structures have been machined to a desired configuration from graphite composite blanks. Due in part to the expense and time consuming nature of machining, more recent efforts in the fuel cell manufacturing industry have focused on the development of compositions and methods for producing net shape molded fuel cell structures, such as bipolar collector plates, using compression molding and injection molding techniques. These efforts, which have had limited success, have concentrated primarily on molding compositions incorporating fluoropolymer binder materials. For example, bipolar collector plates molded from thermoplastic fluoropolymers, such as vinylidene fluoride, are disclosed in U.S. Pat. Nos. 3,801,374, 4,214,969, and 4,988,583.
Compared to other polymeric materials, fluoropolymers have relatively high viscosities. Significantly, the relatively high viscosity associated with fluoropolymers limits their effectiveness as binder materials in molding and coating compositions.
In an effort to maximize the electrical conductivity of current collector plates for fuel cells, it is desirable to maximize electrically-conductive filler loading levels. Generally, as the percentage of filler particles in a given polymer composition is increased, there is a corresponding increase in the viscosity of the composition. Consequently, regardless of the polymer binder material chosen, the addition of electrically conductive filler must be limited to ensure some minimum degree of flow during processing. Such viscosity limitations are particularly pronounced in injection molding applications, where the viscosity of the polymer composition must be maintained at a low enough level to allow the composition to travel through intricate mold features such as channels and gates. In the case of fluoropolymer compositions, the high initial viscosity level associated with the fluoropolymer binder restricts the quantity of filler that can be loaded into the binder prior to processing. Consequently, the electrical conductivity of fuel cell collector plates fabricated using fluoropolymer binders is correspondingly limited.
For these and other reasons, there is a well-established need for improved compositions and methods for processing highly conductive composite structures for electronic, thermoelectric and electrochemical device applications.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a composition for fabricating thermally- and electrically-conductive polymer composite structures and coatings for use in highly-corrosive environments, wherein the electrical conductivity of the resulting structure or coating is improved as a result of enhanced filler loading capacity of the composition.
It is another object of this invention to provide a composition, and a method for processing said composition, to form a thermally- and electrically-conductive polymer composite structure or coating for use in electronic, thermoelectric and electrochemical devices.
It is another object of this invention to provide a non-fluorinated composition for rapidly net shape molding a current collector plate for a polymer electrolyte membrane (PEM) fuel cell, wherein improved filler loading results in a current collector plate having a higher bulk electrical conductivity then conventional current collector plates fabricated from fluoropolymer-based compositions.
These and other objects of the invention are achieved with the novel compositions and methods of the present invention. Novel polymer compositions are provided for producing highly-conductive coatings and net shape molded structures for a variety of applications, including: corrosion-resistant electrical and thermal conductors and contacts; battery and capacitor electrodes; electrodes for electrochemical coating and synthesis of materials; and electrochemical device components, such as current collector plates for polymer electrolyte membrane (PEM) fuel cells.
Briefly, according to the invention, a highly-loaded polymer composition is provided for fabricating a structure or coating generally suitable for use in electronic, thermoelectric and electrochemical devices. In the preferred embodiment of the invention, the composition is particularly suited for compression molding and/or injection molding a current collector plate for a PEM fuel cell. The composition is comprised of a low viscosity polymer loaded with a chemically-inert, thermally and electrically conductive filler.
The polymer is chosen from the group of polymers having a melt viscosity of less than 1,000 Newton-seconds per square meter (N*s/m
2
) over a shear rate range of 1,000 to 10,000 sec
−1
. Furthermore, it is preferred that the polymer has material properties and characteristics as summarized in Table 2 (below). Suitable families of polymers include: polyphenylene sulfide (PPS); modified polyphenylene oxide (PPO); liquid crystal polymer (LCP); polyamide; polyimide; polyester; phenolic; epoxy-containing resin and vinyl ester.
The polymer composition is loaded with highly-conductive filler. In the preferred embodiment of the invention, the filler comprises carbon and/or graphite particles having an average particle size ranging from approximately 0.1 to 200 microns, and preferably in the range of about 23 to 26 microns. The filler particles have a surface area ranging from approximately 1 to 100 m
2
/g, and preferably in the range of 7 to 10 m
2
/g (as measured by BET testing standards). The composition may include additional components, including: carbon and/or graphite nanofibers; carbon and/or graphite fibers; metal fibers such as stainless steel or nickel; and metal-coated carbon and/or graphite fiber concentrates having thermoplastic or thermoset sizing chosen from the aforementioned group of potential polymers.
The composition is subsequently formed into a desired shape by compression molding, injection molding, or a combination thereof. Alternatively, the composition can be used in cladding or costing operations.
BRIEF DESCRIPTION OF THE DRAWINGS
(None)


REFERENCES:
patent: 3801374 (1974-04-01), Dews et al.
patent: 4197178 (1980-04-01), Pellegri et al.
patent: 4214969 (1980-07-01), Lawrance
patent: 4414142 (1983-11-01), Vogel et al.
patent: 4704231 (1987-11-01), Chung
patent: 4851304 (1989-07-01), Miwa et al.
patent: 4988583 (1991-01-01), Watkins et al.
patent: 579818

Affiliated with

Also associated with

Rating

Fuel cell collector plate and method of fabrication does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fuel cell collector plate and method of fabrication, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel cell collector plate and method of fabrication will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2552494