Optimisation of pack chromised stainless steel for proton exchange membrane fuel cells bipolar plates using response surface methodology

Stainless steels, as low cost materials, are attractive for proton exchange membrane fuel cells (PEMFC) bipolar plates. However, these metallic alloys require surface coatings or treatments to enhance its corrosion resistance and surface conductivity in PEMFC environments. In this study, response surface methodology based on Box–Behnken design was employed to investigate the influence of time, activator content and temperature on corrosion current density of pack chromised 304 stainless steel in simulated PEMFC environment of aerated 0.5 M H₂SO₄ + 2 ppm HF at 70 °C. These process parameters were optimised and the performance of the optimised coatings in simulated and real PEMFC environments was investigated. The results indicated that temperature
had the most significant influence on the performance of chromised coatings in the selected PEMFC environment. The optimised coating produced at 1040 °C for 3 hours with powder containing 6.84 wt% activator content exhibited better corrosion resistance than the substrate in typical PEMFC cathode and anode environments respectively as well as about six fold decrease in the contact resistance of the substrate at 150 N/cm². Hence, the single fuel cell assembled with the bipolar plate coated with the optimised process parameters exhibited a two-fold increase in the maximum power density of the cell with the uncoated bipolar plates.