Stainless steels in bipolar plates—Surface resistive properties of corrosion resistant steel grades during current loads

Instances of an increase in the contact resistance of stainless steel surfaces, resulting a decrease in the efficiency of fuel cells, were reported by automotive developers of PEM fuel cells, who had used the AISI 316L grade (EN 1.4404) in bipolar plates. To identify the reason for this, surface resistive properties were measured for a number of stainless steel grades, using cyclic current density loads. Electrochemical impedance spectroscopy (EIS) was used as a tool for these measurements of the resistive properties before and after the current density loads. In addition, a high continuous galvanostatic current density was imposed on one of the most stable and corrosion resistant stainless steel grades, 904L, to evaluate any conductive changes of the passive film due to temperature, current or a combination of the two.