Relatively inexpensive, lightweight biplates for methanol fuel cells have been proposed. The reductions in weight and cost, relative to biplates now used in methanol fuel cells, would be achieved by use of a combination of modified geometry, cheaper and lighter materials, and cheaper manufacturing processes.
A typical methanol fuel cell includes a number of membrane/electrode assemblies (MEAs) stacked in alternation with biplates. Each biplate serves (1) partly as an electrical contact between the cathode of the MEA on one side and the anode of the MEA on the other side, (2) partly as a fuel-and-oxidizer-delivery manifold, (3) partly as an exhaust manifold, and (4) partly as a heat exchanger to remove waste heat. The biplate contains channels for circulating air past the cathode, plus other channels for circulating the fuel solution (methanol dissolved in water) past the anode. The flowing aqueous methanol solution, which is 97 weight percent water, can be used to remove the waste heat.
Heretofore, biplates in methanol fuel cells have been fabricated by machining them out of graphite. About one-third of the cost of a typical methanol cell is incurred in conjunction with the machined graphite biplate(s). In addition, graphite has a density of about 2.0, whereas some other materials that could be used in biplates have lower densities. Thus, if one could reduce the costs of biplates and make them of less-dense materials (plastics), one could effect significant reductions in the costs and weights of methanol fuel cells.
One reason for using graphite until now is that graphite has the required electrical conductivity. A plastic biplate by itself would not be electrically conductive, but the design could be modified to use electrically conductive pins inserted through the thickness of the biplate to provide electrical contact between the anode on one side and the cathode on the other side. The modified design would feature a "pincushion" flow-field configuration; the channels on the cathode and anode sides would be defined by the pins, which would disperse the flows of fuel and air over the electrodes (see figure).
The main body of the biplate, with its channels and holes, could be molded. To obtain the required fluid seals around the pins, the main body could be molded around the pins. A suitable material for the main body of the plate might be mineral-filled phenolic, (better known by the trade name "Bakelite"), which has a density of 1.3. While the graphite pins would increase the average density a bit, the average density would still be considerably less than that of a biplate made solely of graphite.
This work was done by Andrew Kindler of Caltech forNASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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