Effect of pH on the electrochemical corrosion and surface conductivity of a new high-Cr ferritic stainless steel in simulated PEMFC environments

Abstract

The corrosion behavior and surface conductivity of high-Cr ferritic stainless steels 32Cr1Mo and 27Cr4Mo were comparatively investigated in the simulated proton exchange membrane fuel cell (PEMFC) cathode and anode environments under pH = 0 to 4 conditions at 80 °C by using electrochemical measurements, interfacial contact resistance (ICR), and surface analyses such as X-ray photoelectron spectroscopy (XPS). Both stainless steels show spontaneous passivation in the simulated cathode environments, but are in an active corrosion state in the anode environments. As pH ≥ 3, they can almost spontaneously passivate in the anode environments with the active peak current densities less than 1 µA cm⁻². After 5 h of polarization at the typical working potentials, the ICR change rates of both stainless steels enlarge with the increase of pH in the cathode and anode environments, but their ICR values are lower than about 17 and 11 mΩ cm² at 140 N cm⁻², respectively. Compared to 27Cr4Mo, 32Cr1Mo shows lower passive current densities and slightly higher surface conductivity, resulted from the formation of relatively thinner passive films with more Cr-oxides and less oxides of Fe and Mo. It is promising for 32Cr1Mo to be applied to the high-performance metallic bipolar plates.