Effects of CrN/Cr coating layer on durability of metal bipolar plates under a fuel recirculation system of direct methanol fuel cells

Effects of a CrN/Cr coating layer on the durability of metal bipolar plates (stainless steel (STS) 430) are investigated in direct methanol fuel cells (DMFCs) with a fuel recirculation system, since under fuel recirculation the metal bipolar plates can be faced with a tougher corrosion environment. Before the fuel recirculation, the performance losses of the cells consisting of metal bipolar plates are ascribed to cathode degradation, due to a high corrosion level of the cathode side. However, after fuel recirculation, corrosion of the anode metal bipolar plate by pH decrease and overpotential increase brings about severe anode degradation. It is found that damage by corrosion of the cathode metal bipolar plate is limited to degradation of the cathode catalyst, whereas corrosion of the anode metal bipolar plate deteriorates not only the catalysts but also the electrolyte membrane. These durability tests show that the CrN/Cr coatings deposited on the STS 430 improve the corrosion resistance of the metal substrate and lead to low performance degradation.