Effect of Cr content on the corrosion resistance of Ni–Cr–P coatings for PEMFC metallic bipolar plates

Abstract

In here, we report on the pulse electrodeposition of nickel–chromium–phosphorous (Ni–Cr–P) coatings on AISI 1020 low carbon steel using an aqueous electrolyte consisting of NiCl2, CrCl3, and NaH2PO2. We evaluated the effectiveness of Ni–Cr–P coatings for polymer electrolyte membrane fuel cell metallic bipolar plates. Coatings deposited at pH 3.0 and room temperature show nearly three orders improvement in corrosion resistance compared to bare AISI 1020. The corrosion current (Icorr) of Ni–Cr–P samples coated at 25 °C is 1.16 × 10−4 A/cm2, while that of bare carbon steel is 1.05 × 10−2 A/cm2. The improvement in corrosion resistance is due to the increase in Cr content in the Ni–Cr–P coatings. Cr forms a stable oxide barrier layer and inhibits pitting corrosion. The interfacial contact resistance increases with an increase in Cr content and immersion time in the corrosion media. The increase in interfacial contact resistance is also due to the formation of a stable oxide barrier.