Effects of fluoride ions on corrosion performance and surface properties of SS304 in simulated PEMFC cathodic environments

U.S. Department of Energy (DOE) 2025 target proposes lower cost requirements for bipolar plates. To investigate the applicability of using cost-effective 304 stainless steel (SS304) as bipolar plates in proton exchange membrane fuel cell (PEMFC) and assess its corrosion risk, this work systematically investigates the impact of fluoride ions on corrosion performance and surface properties evolution of SS304 in simulated PEMFC cathodic environments. The electrochemical tests and morphological characteristics of polarized SS304 samples (0.6 V, 5 h) reveal that an increase in F- concentration results in the inability of SS304 to passivate spontaneously and exacerbates the uniform dissolution corrosion. However, all polarized samples can be electrochemically passivated, exhibit no obvious pitting, and form bi-layer semiconductive passive films with stable current densities (0.031-0.166 & mu;A cm-2) lower than 1 & mu;A cm-2, satisfying the corrosion criterion of DOE 2025. Additionally, the ascending of F- concentration reduces surface roughness, while increasing the wettability and interfacial contact resistance (ICR) of the polarized SS304 samples. The ICR of all SS304 samples, with or without polarization test, ranges from 258 to 754 m & omega; cm2 fails to meet the relevant DOE 2025 target (<10 m & omega; cm2).