Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-08-26
2001-08-28
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S010000, C429S006000, C029S623100
Reexamination Certificate
active
06280870
ABSTRACT:
BACKGROUND
The invention generally relates to the overall construction and configuration of a proton exchange membrane fuel cell, and more particularly, the invention relates to a combined fuel cell flow plate and gas diffusion layer.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions may be described by the following equations:
H
2
→2H
+
+2
e
−
at the anode of the cell, and
O
2
+4H
+
+4
e
−
→2H
2
O at the cathode of the cell.
Because a single fuel cell typically produces a relatively small voltage (around 1 volt, for example), several serially connected fuel cells may be formed out of an arrangement called a fuel cell stack to produce a higher voltage. The fuel cell stack may include different plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite material or metal and may include various channels and orifices to, as examples, route the above-described reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. In addition to the membrane, a catalyst and gas diffusion layer are sandwiched between the anode and cathode plates. The catalyst layer may be placed on the membrane or on the gas diffusion layer. The gas diffusion layer may be made out of an electrically conductive and porous diffusion material, such as a carbon cloth or paper material, for example.
Referring to
FIG. 1
, as an example, a fuel cell stack
10
may be formed out of repeating units called plate modules
12
. In this manner, each plate module
12
includes a set of plates that may form several fuel cells. For example, for the arrangement depicted in
FIG. 1
, an exemplary plate module
12
a
may be formed from a cathode cooler plate
14
, a bipolar plate
16
, a cathode cooler plate
18
, an anode cooler plate
20
, a bipolar plate
22
and an anode cooler plate
24
that are stacked from bottom to top in the listed order. The cooler plate functions as a heat exchanger by communicating a coolant through coolant flow channels that are formed in either the upper or lower surface of the cooler plate to remove heat from the plate module
12
a
. The surface of the cooler plate that is not used to route the coolant includes flow channels to route either hydrogen (for the anode cooler plates
18
and
24
) or oxygen (for the cathode cooler plates
14
and
20
) to an associated fuel cell. The bipolar plates
16
and
22
include flow channels on one surface to route hydrogen to an associated fuel cell and flow channels on the opposing surface to route oxygen to another associated fuel cell. Due to this arrangement, each fuel cell may be formed in part from one bipolar plate and one cooler plate, as an example.
For example, one fuel cell of the plate module
12
a
may include an anode-membrane-ecathode sandwich, called a membrane-electrode-assembly (MEA), that is located between the anode cooler plate
24
and the bipolar plate
22
. In this manner, the upper surface of the bipolar plate
22
includes flow channels to route oxygen near the cathode of the MEA, and the lower surface of the anode cooler plate
24
includes flow channels to route hydrogen near the anode of the MEA.
As another example, another fuel cell of the plate module
12
a
may be formed from another MEA that is located between the bipolar plate
22
and the cathode cooler plate
20
. The lower surface of the bipolar plate
22
includes flow channels to route hydrogen near the anode of the MEA, and the upper surface of the cathode cooler plate
24
includes flow channels to route oxygen near the cathode of the MEA. The other fuel cells of the plate module
12
a
may be formed in a similar manner.
In order to manufacture the fuel cell stack in a cost effective manner, the time that is required to assemble the stack needs to be minimized. One way to accomplish this is to minimize the number of components that are handled in the assembly of the stack.
SUMMARY
The components that are used to assemble a fuel cell stack may be reduced by creating flow channels in gas diffusion layers of the stack. In this manner, in an embodiment of the invention, a gas diffusion layer that is usable with a fuel cell includes a material that is adapted to permit a reactant of the fuel cell to diffuse through the material. The material includes flow channels for communicating the reactant so that at least a portion of the reactant diffuses through the material to a membrane of a fuel cell. In some embodiments, the gas diffusion layer may be received by a plate, and the plate may be stacked with other plates to form the fuel cell stack. Advantages of the present invention may include, for example, decreasing the number and cost of parts and materials required to manufacture a fuel cell stack. Other advantages may include increased structural integrity of a fuel cell stack, and increased fuel cell performance. It will be appreciated that in embodiments where a planer surface of the combined flow plate and gas diffusion layer contacts the membrane electrode assembly (as opposed to such contact being limited to contact along flow plate lands), still other advantages may include providing continuous support of the fuel cell membrane electrode assembly, homogenized diffusion, permeability, and electrical contact between the membrane electrode assembly and the combined flow plate and gas diffusion layer, and reducing the amount of stack compression needed for satisfactory electrical conductivity between the membrane electrode assembly and the combined flow plate and gas diffusion layer.
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patent: 5292600 (1994-03-01), Kaufman
patent: 5300370 (1994-04-01), Washington et al.
patent: 5523175 (1996-06-01), Beal et al.
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patent: 5736269 (1998-04-01), Okamoto et al.
patent: 5840414 (1998-11-01), Bett et al.
patent: 5853909 (1998-12-01), Reiser
patent: 6015633 (2000-01-01), Carlstrom, Jr. et al.
patent: 6127058 (2000-10-01), Pratt et al.
Carlstrom Charles M.
Eisman Glenn A.
Farkash Ron H.
Maynard William B.
Brouillette Gabrielle
Martin Angela J.
Plug Power Inc.
Trop Pruner & Hu P.C.
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