Research on VNbMoTaW-C high entropy alloy carbide films on 316L stainless steel as bipolar plates in proton exchange membrane fuel cells environment

In this paper, VNbMoTaW high entropy alloy (HEA) carbide films with various VNbMoTaW contents are obtained on stainless steel 316L (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs) by closed field unbalanced magnetron sputter ion plating (CFUBMSIP). According to the results of the scanning electron microscope (SEM), VNbMoTaW-C films are dense and compact. The results of X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) indicate that the outermost layer of VNbMoTaW-C film is mainly composed of a large amount of amorphous carbon (a-C) (composed of C-sp2 and C-sp3), along with a small amount of metallic carbide and high entropy alloy BCC phase. Interfacial contact resistance (ICR) results show that VNbMoTaW-C-0.5A has a value of 5.73 mS2 cm2 at 1.4 MPa, which satisfies the Department of Energy's (DOE) 2020 technical targets. The potentiodynamic polarization test is performed in a simulated PEMFCs environment, indicating that all the films could improve the corrosion resistance of the SS316L substrate. In the simulated PEMFCs cathode environment, the corrosion current densities of VNbMoTaW-C-0.3A, VNbMoTaW-C0.5A, VNbMoTaW-C-0.8A and VNbMoTaW-C-1A are 0.186 mu A cm- 2, 0.077 mu A cm- 2, 0.380 mu A cm-2 and 0.234 mu A cm- 2, respectively, which are much lower than the DOE technical target.