Experimental performance assessment of metal-foam flow fields for proton exchange membrane fuel cells

Interest in fuel-cell technology as a clean power source has been increasing. Fuel cells are prime candidates for replacing internal combustion engines, and for use as power plants. Flow fields in bipolar plates of proton exchange membrane fuel cells distribute reactants over the reactive sites of the membrane electrode assembly. Bipolar plates are typically graphite with parallel or serpentine channels as flow fields. The efficiency of a fuel cell or a stack depends on the performance of the bipolar plates, which is contingent on the flow field design. The drawbacks of graphite include heavy weight, fabrication inaccuracy, high cost, fixed porosity, and brittleness. In this paper, open-cell metal foam is experimentally investigated as a flow field for a new bipolar plate design. The performance of the conventional bipolar plate with a serpentine flow field is directly compared to that of the metal-foam designs (with various porosities) at the same operational conditions. Results show that, in the case of the new design, the cell current, voltage and power density are improved, and temperature and pressure distributions on the membrane are more even. Metal-foam flow fields are seen to maintain safe operating temperature for the membrane (55-87 degrees C). Just as important, the conversion efficiency is 9.9% higher for the metal-foam design, and its weight is 27.8% lower compared to the graphite bipolar plate. There is a savings of 4% in hydrogen use when using the metal-foam flow fields. As such the new design is a viable replacement for the conventional graphite bipolar plate.