Patent Grant
7686854
The present invention relates to fuel cells incorporating a proton exchange membrane (PEM); more particularly, to means for preventing gas leakage between plate elements of a PEM fuel cell stack; and most particularly, to a silicone seal screen-printed on bipolar plate elements to prevent leakage between membrane electrode assembly elements and bipolar plates.
Fuel cell assemblies employing proton exchange membranes are well known. Such assemblies typically comprise a stack of fuel cell modules, each module having an anode and a cathode separated by a catalytic proton exchange membrane (PEM), and the modules in the stack being connected in series electrically to provide a desired voltage output. Gaseous fuel, in the form of hydrogen or hydrogen-containing mixtures such as “reformed” hydrocarbons, flows adjacent to a first side of the membrane, and oxygen, typically in the form of air, flows adjacent to the opposite side of the membrane. Hydrogen is catalytically oxidized at the anode-membrane interface, and the resulting proton, H+, migrates through the membrane to the cathode-membrane interface where it combines with anionic oxygen, O−2, to form water. Protons migrate only in those areas of the fuel cell in which the anode and cathode are directly opposed across the membrane. Electrons flow from the anode through an external circuit to the cathode, doing electrical work in a load in the circuit.
A fuel cell assembly typically comprises a plurality of fuel cell modules connected in series to form a fuel cell stack. For convenience in manufacture, and to provide a more rugged assembly, the anode for one cell and the cathode for an adjacent cell typically are formed as rigid plates and then bonded back-to-back, forming a “bipolar plate”, as is well known in the art. A fuel cell assembly thus consists typically of a stack of alternating bipolar plates and proton exchange membranes. At the outer edges of the assembly, the plates and membranes are sealed together to contain the reactant gases and/or coolant within the assembly. Thus, an important aspect of forming a stacked fuel cell assembly is preventing leakage between the membranes and the plates.
One prior art approach has been to mold a liquid silicone rubber (LSR) gasket directly onto the bipolar plates using liquid injection molding techniques. This has proved to be difficult due to the complex shape of the seal and plate geometry, and also the very brittle nature of some composite materials typically used in forming the bipolar plates.
Another prior art approach has been to provide a die-cut or separately-molded gasket on one side of the plates, the membrane thus being sandwiched between the gasket and the adjacent bipolar plate. In some instances, an assembly may leak initially at the interface between the membrane and the non-gasketed plate surface, although the leak may self-seal when the membrane becomes hydrated in use. Initial leakage, however, is unacceptable.
Thus, sealing means on both sides of each bipolar plate is desirable because a membrane is thus sealed on both its sides against sealing material rather than against a bare bipolar plate.
It is a principal object of the present invention to economically and reliably seal a proton exchange membrane against a bipolar plate surface in a fuel cell stack, both initially and during extended operation of the stack.
Briefly described, a means for sealing a bipolar plate to a membrane in a PEM fuel cell stack includes a thin layer of a cross-linkable silicone composition between the bipolar plate and the membrane. The layer is applied as a low viscosity fluid to either the plate or the membrane and preferably is polymerized prior to assembly of the stack. A preferred means for applying the composition to the bipolar plate is screen printing. The resulting fuel cell assembly exhibits superior leak resistance. In a currently preferred embodiment, layers of the silicone composition are provided at both interfaces between a membrane and both an anode side and a cathode side of a bipolar plate.
These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:
Referring to
Referring to
A typical RTV composition is Dow Corning 3140 thinned as required using Dow Corning OS-30 methylsiloxane fluid in proportions known in the art without undue experimentations.
A preferred method for applying a thin film of the composition is screen printing, by which means complex patterns of the seal are readily provided as may be needed to accommodate complex sealing surfaces of fuel cell elements. Screen printing is well known and need not be further elaborated here. Other methods of application, for example, roller application, are of course within the scope of the invention.
Seal element 40 is preferably relatively thin, on the order of 0.005 inch or less, and preferably between about 0.001 inch and about 0.003 inch, and is readily formed in a single printing pass.
Referring to
Of course, fuel cells of either embodiments 10′, 10″ may be stacked together to form fuel cell stacks or assemblies, as known in the art.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This application is a continuation of U.S. patent application Ser. No. 10/305,612, filed on Nov. 27, 2002 now abandoned.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6451469 | Nakamura et al. | Sep 2002 | B1 |
| 20010049044 | Molter | Dec 2001 | A1 |
| 20020094464 | Wangerow | Jul 2002 | A1 |
| 20080070081 | Franklin et al. | Mar 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 1073138 | Jan 2001 | EP |
| 02093672 | Nov 2002 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20040231142 A1 | Nov 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10305612 | Nov 2002 | US |
| Child | 10877656 | US |
