Stainless steel as a bipolar plate material for solid polymer fuel cells

Stainless steel bipolar plates for the Solid Polymer Fuel Cell (SPFC) offer many advantages over conventional graphitic materials. These include relative low cost, high strength, ease of manufacture and as they can be shaped into thin sheets, significant improvement in the power/volume ratio. However, interfacial ohmic losses across the metallic bipolar plate and the Membrane Electrode Assembly (MEA), reduce the overall power output from a SPFC. Despite a large range of commercially available alloys, 316 stainless steel has traditionally been the alloy of choice for bipolar plates. A number of alternative grades of stainless steel have been evaluated in terms of the electrical resistance of their surface oxide film. This showed that ohmic losses exhibited in fuel cell performance varied depending on the elemental composition of the stainless steel alloy. Three stainless steel alloys, 310, 316 and 904L, were chosen as candidate bipolar plate materials. Increased polarisation was observed in the order 904L < 310 < 316. This was maintained throughout an ongoing endurance test, where these cells have been run for over 3000 h without significant performance degradation. This difference in polarisation behaviour was attributed to variation in thickness of the oxide film. Analysis has shown no deleterious effect on the surface of the bipolar plate and no evidence of corrosion. (C) 2000 Elsevier Science S.A. All rights reserved.