High corrosion resistance and conductivity of Al2O3/CrN coating for metal bipolar plates in PEMFCs: Al2O3 hinders CrN columnar crystals growth

An excellent corrosion-resistant and good conductivity coating is desired for metal bipolar plate (BP) in proton exchange membrane fuel cell (PEMFC). In this view, a novel strategy to achieve this aim by introducing Al2O3 into CrN film. Al2O3/CrN nanocomposite coatings are first prepared by co-sputtering. Subsequently, the microstructure, electrochemical corrosion resistance, interfacial contact resistances (ICR) and contact angle are systematically investigated. As a result, Al2O3/CrN nanocomposite coating shows a low corrosion current density of 0.084 μA/cm2 in room temperature and a low corrosion current density of 0.39 μA/cm2 at 70 °C, which highly meets the requirement of U.S. DOE 2025 targets. Besides, Al2O3/CrN nanocomposite coating displays a superior durability to pure Au film. It is revealed that Al2O3 can hinder the growth of CrN columnar crystals and result in coating amorphization, which is the mechanism of Al2O3-promoted the CrN corrosion resistance. Furthermore, Al2O3/CrN coating also exhibits an excellent electrical conductivity, featuring a smaller ICR of 3.09 mΩ cm2. Inspired by these results, introducing Al2O3 into CrN coatings can provide enlightening insights to design new non-noble-metal coatings for metal BP in future PEMFC manufacturing.