PEM Fuel Cell Stack Development: Grafoil Bipolar Materials — A Feasibility Study

In the production of Proton Exchange Membrane Fuel Cell (PEMFC) stacks with multiple cell units, graphite has been widely used as a bipolar material. Graphite has excellent electrical conductivity, high electrochemical stability, and good machining characteristics, enabling fine and complex fuel/oxidant flow fields to be used. In spite of the above advantages, search for alternate materials is counting owing mainly to the present requirement of reduced cell volume and weight per power yield (kW) in many applications. Cost reduction for this component and volume production are other driving forces for the continuous thrust in this subject. Flexible (exfoliated) graphite is an alternate material that could meet many of the above requirements. We have made use of flexible graphite to fabricate a PEM fuel cell stack. The flow fields were introduced by stamping. An optimization study has been carried out for the width and depth of the flow field designs in terms of applied pressure to accommodate the resilience of the flexible graphite sheet. The performance of the 500 watts stack fabricated using this material compares well with that fabricated using the conventional graphite plates. However there are some technical issues still to be sorted out which will be discussed.