Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-08-16
2001-11-27
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000
Reexamination Certificate
active
06322919
ABSTRACT:
BACKGROUND OF THE INVENTIONS
1. Field of Inventions
The present inventions relate generally to fuel cells and, more specifically, to fuel cell bipolar plates.
2. Description of the Related Art
A fuel cell converts fuel and oxidant (collectively “reactants”) into electricity and a reaction product. Many fuel cells employ hydrogen as the fuel and oxygen as the oxidant. Here, the reaction product is water. One such fuel cell is the proton exchange membrane (PEM) fuel cell. Each individual cell in a PEM fuel cell includes an anode and a cathode separated by a thin, ionically conducting membrane, which together are often referred to as a membrane electrode assembly (MEA). The anode and cathode, on opposing faces of the tonically conducting membrane, are comprised of a thin catalyst containing film and a gas diffusion layer. Hydrogen is supplied to the anode and oxygen supplied to the cathode. The gas diffusion layer insures that hydrogen is effectively transported to the anode catalyst and that oxygen is effectively transported to the cathode catalyst. The hydrogen is electrochemically oxidized at the anode catalyst, thereby producing protons that migrate across the conducting membrane and react with the oxygen at the cathode catalyst to produce water. The individual MEAs are stacked in electrical series with impermeable electrically conductive bipolar plates therebetween that conduct current between the anode of one MEA and the cathode of the adjacent MEA. Conventional bipolar plates are flat plates that have one or more channels formed on one side for transporting fuel over one MEA and one or more channels formed on the other side for transporting oxidant over another MEA. The oxidant channels may or may not be aligned with the fuel channels.
Fuel cells are considered an attractive energy source for a variety of reasons. As compared to batteries, fuel cells are advantageous in that they can maintain a specific power output as long as fuel is continuously supplied and are not hampered by a charge/discharge cycle. Fuel cells are also relatively small and lightweight and produce virtually no environmental emissions. PEM fuel cells are particularly advantageous because they have relatively low operating temperatures and employ a non-liquid, non-corrosive electrolyte.
Despite these advantages, the inventors herein have determined that conventional fuel cells are susceptible to improvement. For example, the inventors herein have determined that it would be desirable to reduce the size and weight of conventional fuel cells. The inventors herein have further determined that such reductions in fuel cell size and weight can be realized through improvements in the design of the bipolar plates that separate adjacent MEAs.
SUMMARY OF THE INVENTIONS
Accordingly, one object of the present inventions is to provide a fuel cell that is smaller and lighter than conventional fuel cells having the same power output. Another object of the present inventions is to provide a bipolar plate that is smaller than conventional bipolar plates. Still another object of the present inventions is to provide a bipolar plate that is lighter than conventional bipolar plates.
In order to accomplish some of these and other objectives, a bipolar plate in accordance with a preferred embodiment of a present invention includes a fuel side including a series of fuel channels defining respective fuel paths and an oxidant side including a series of oxidant channels defining respective oxidant paths. At least some of the fuel channels are offset from adjacent oxidant channels in a direction transverse to the fuel and oxidant paths. A fuel cell in accordance with a present invention includes such a bipolar plate located between a pair MEAs.
The present inventions provide a number of advantages over conventional bipolar plates and fuel cells. For example, the fuel and oxidant channels in conventional bipolar plates are formed on opposing surfaces of the plate, as is illustrated in FIG.
1
. The thickness of conventional bipolar plates, as measured from the surface on the fuel side which contacts anode of one MEA to the surface on the oxidant side which contacts the cathode of another MEA, is therefore equal to the combined depths of the opposing channels and the thickness of the material that separates the channels. The thickness of the present bipolar plate is far less because the fuel and oxidant channels are not aligned. Thus, the thickness of the bipolar plate need not be equal to, and is actually less than, the combined depths of the opposing channels and the thickness of the material that separates the channels. In one preferred embodiment, the fuel and oxidant sides of the bipolar plate each include an alternating series of channels and ridges, with the ridges on the fuel side forming the oxidant channels and the ridges on the oxidant side forming the fuel channels. Here, the thickness of the bipolar plate is the sum of the depth of only one channel and the thickness of the material that forms the ridges.
This is significantly less than the thickness of a conventional bipolar plate. The result is a fuel cell with a power density (kW/L) that is approximately twice that of conventional fuel cells.
The present bipolar plate is also significantly lighter than conventional bipolar plates. Referring again to
FIG. 1
, conventional bipolar plates include a large solid area of plate material located between adjacent channels that extends from the surface on the fuel side which contacts anode of one MEA to the surface on the oxidant side which contacts the cathode of another MEA. The present bipolar plate does not include this large area because the fuel channels and oxidant channels are not aligned and, accordingly, channels are located in the area that is occupied by plate material in conventional bipolar plates. The result is a fuel cell with a specific power (kW/kg) that is two to three times that of conventional fuel cells.
The above described and many other features and attendant advantages of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.
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Rehg Timothy J.
Yang Jefferson Y. S.
Allied-Signal Inc.
Kalafut Stephen
Zak, Jr. Esq. William J.
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