Optimizing Corrosion Performance of WC/a-C Nanomultilayers by Tailoring Modulation Period for PEMFC Bipolar Plate Applications

WC/a-C nanomultilayers were deposited on AISI 304 stainless steel substrates to evaluate how the modulation period influences the corrosion behavior in the cathode environment of a proton exchange membrane fuel cell (PEMFC). The investigation demonstrated that a higher modulation period resulted in the expansion and densification of the columnar boundaries within the nanomultilayers, establishing more effective routes for aggressive ions to infiltrate the film layers and migrate toward the substrate material, which ultimately diminished the film's protective capabilities against corrosion. The film with a 5.8 nm modulation period showed a notable enhancement in corrosion resistance, primarily due to its elevated corrosion potential and reduced corrosion current density. With an increase in the modulation period, the film's corrosion became increasingly noticeable, particularly at a modulation period of 11.5 nm. The corrosion-induced expansion of the columnar boundaries eventually caused the film to crack and bulge due to oxidation.