Electrochemical Characteristics with NaCl Concentrations on Stainless Steels of Metallic Bipolar Plates for PEMFCs

Stainless steel, which is used in metallic bipolar plates, is generally known to have excellent corrosion resistance, which is achieved by forming oxide films. However, localized corrosion occurs when the oxide films are destroyed by pH and chloride ions. Particularly, since the operating condition of polymer electrolyte membrane fuel cells (PEMFCs) is strongly acidic, the reduced stability of the oxide films leads to the corrosion of the stainless steel. In this research, the electrochemical characteristics of 304L and 316L stainless steels were investigated in an accelerating solution that simulated the cathode condition of PEMFCs with chloride concentrations. Results under all experimental conditions showed that the corrosion current density of 304L stainless steel was at least four times higher than that of 316L stainless steel. Maximum damage depth was measured at 6.136 μm and 9.192 μm for 304L stainless steel and 3.403 μm and 5.631 μm for 316L stainless steel for chloride concentrations of 0 and 1000 ppm, respectively. Furthermore, 304L and 316L stainless steels were found to have uniform and localized corrosion, respectively. The differences in the electrochemical characteristics of 304L and 316L stainless steel are considered to be due to the molybdenum contained in the chemical composition of 316L stainless steel.