Electrodeposited Ni–Mo–Cr–P coatings for AISI 1020 steel bipolar plates

Abstract

Metallic bipolar plates (BPPs) are potential candidates to replace the conventional graphite BPPs in polymer electrolyte membrane fuel cells (PEMFCs) because they are cost-effective and easy to manufacture. In this present work, we report on the development of Ni–Mo–Cr–P electroplated AISI 1020 steel bipolar plates as a BPP material. The microstructure and composition of the Ni–Mo–Cr–P coatings were optimized varying pH of the electrolyte bath and deposition current. Compared to bare AISI 1020 steel, the coating electroplated at pH 5.5 and a pulse-current density of 0.075 A/cm2 showed an improvement in corrosion resistance by three orders of magnitude. The corrosion current densities of bare and Ni–Mo–Cr–P electroplated AISI 1020 steel in the simulated anodic environment is 1.05 × 10−2 and 4.95 × 10−5 A/cm2, respectively, while that in the simulated cathodic environment it is 3.7 × 10−2 and 4.58 × 10−5 A/cm2, respectively. The enhancement of corrosion resistance is due to the formation of a Mo and Cr based passive oxide layer. The interfacial contact resistance (ICR) of bare and Ni–Mo–Cr–P electroplated AISI 1020 steel is 53.2 and 40.06 mΩ, respectively. ICR of Ni–Mo–Cr–P is lower than the bare AISI 1020 because of the semiconducting nature of the two-layered Mo-based passive oxides. Additionally, Ni–Mo–Cr–P coated AISI 1020 steel shows a higher water contact angle than bare AISI 1020 carbon steel. A single-cell PEMFC stack with Ni–Mo–Cr–P coated AISI 1020 steel BPP shows similar polarization behavior as graphite BPP. However, the performance of Ni–Mo–Cr–P coated AISI 1020 steel BPP lacks durability, and further improvement is necessary before it can be commercially implemented.