Corrosion-Resistant and Conductive a-C/Ta/Cu-Coated Magnesium as Bipolar Plates for Ultralightweight Proton Exchange Membrane Fuel Cells

In the present research, a hydrophobic amorphous carbon (a-C)/Ta/Cu coating is proposed for Mg bipolar plates (BPPs) for the ultralightweight proton exchange membrane fuel cells (PEMFCs). The microstructure, hydrophobicity, corrosion resistance, and interfacial contact resistance (ICR) of the a-C/Ta/Cu coated Mg BPPs are systemically investigated. Based on the unique coating design, the corrosion current density of the coated Mg BPPs is only 0.002 μA/cm2 during the 24 h potentiostatic polarization test at 0.6 V vs Ag/AgCl, accompanied by the interfacial contact resistance (ICR) as low as 2.6 and 3.9 mΩ cm2 before and after the electrochemical test, respectively. The anticorrosion and ICR performance both meet the requirements of the U.S. Department of Energy (DOE), exhibiting outstanding advantages over other surface-modified metal BPPs. The excellent performance is maintained even when the coating is locally damaged after the high potential corrosion test at 1.38 V vs Ag/AgCl, indicating the long-term durability of the a-C/Ta/Cu coating. The function and degradation mechanism of the multilayer coating are also discussed.