Electrochemical Performance Testing and Characterization of Silver-Plated and Graphite-Coated 316L Stainless Steel Bipolar Plates

Abstract

316L stainless steels are the most promising materials for use as bipolar plates in proton exchange membrane fuel cells (PEMFC) because of their low cost,light weight,convenience of machining,ease of shaping into thin sheets,excellent electrical conductivity,and their heat exchange properties.However,the interfacial contact resistance (ICR) between carbon paper and stainless steel was found to increase because of passive film formation in a PEMFC cathodic environment.Additionally,the catalyst was poisoned by the corrosion products of the bipolar plate in the PEMFC anodic environment and the output power of the cell decreased.We added a conductive graphite coating onto the surface of 316L stainless steel and found the ICR of the sample reached 80.6 mΩ·cm2.The ICR was only 19.8 mΩ·cm2 when a thin layer of silver was present between the 316L stainless steel and the graphite layer.Various electrochemical tests,such as Tafel curves and oxidation curves using steady potential,were used to study the corrosion behavior of the three samples (316L stainless steel,silver-plated 316L stainless steel,silver-plated and graphite-coated 316L stainless steel) in PEMFC environments.Results showed that compared to 316L stainless steel,the corrosion potential of the silver-plated and graphite-coated 316L stainless steel increased by 0.49 and 0.35 V,respectively and the corrosion current density decreased to 10-6-10-7 A·cm-2.The silver-plated sample was easily damaged as small holes in the silver-layer allowed parts of the stainless steel substrate to be exposed.