Performance Enhancement of a-C:Cr Thin Films Deposited on 316L Stainless Steel as Bipolar Plates via a Thin Ti Layer by Mid-Frequency Magnetron Sputtering for PEMFC Application

Ti/a-C:Cr multilayer films were deposited on 316L stainless steel (SS316L) substrates using medium-frequency alternating current magnetron sputtering, with a single-layer a-C:Cr film also prepared on a titanium substrate. The influence of sputtering pressure on the film’s structure and properties was systematically investigated. Film morphology and microstructure were analyzed via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). At a pressure of 1.4 MPa, the interfacial contact resistance (ICR) of SS316L bipolar plates (BPPs) coated with the films reached as low as 3.30 mΩ·cm 2 , while that of titanium BPPs was 2.90 mΩ·cm 2 . Under simulated proton exchange membrane fuel cell (PEMFC) cathode conditions (70 °C, 0.6 V vs. SCE, 0.5 M H 2 SO 4 , 5 ppm HF solution), the corrosion current density, Icorr, reached optimal values of 0.69 μA·cm −2 for SS316L and 0.62 μA·cm −2 for titanium. These results demonstrate that parameter optimization enables SS316L BPPs to functionally replace titanium counterparts, offering significant cost reductions for metal BPPs and accelerating the commercialization of PEMFC technology.