Plasma-Enhanced Atomic Layer Deposition of Metallic Tantalum Protective Coatings for PEMWE Bipolar Plates

Stainless-steel bipolar plates (BPPs) are attractive for proton exchange membrane water electrolysis (PEMWE) due to their low cost and manufacturability, yet their use is limited by severe corrosion. Despite the advantages of plasma-enhanced atomic layer deposition (PEALD) in producing dense films, ion bombardment may induce surface damage and increase roughness. This paper describes a cross-flow PEALD strategy with a remote plasma source to deposit metallic tantalum (Ta) coatings on stainless steel. In a cross-flow reactor, plasma species reach the substrate primarily through diffusion across the boundary layer of the gas flow, providing a gentler plasma–surface interaction and enabling the formation of dense, smooth Ta coatings. The roughness of the Ta films is markedly reduced from 1.45 nm to 0.24 nm, which is favorable for interfacial electrical contact. The process exhibits self-limiting growth with a linear growth rate of ~0.49 Å cycle−1. In a simulated PEMWE environment, Ta-coated stainless steel shows improved corrosion resistance, with the corrosion potential increasing from −0.27 to 0.07 V vs. Ag/AgCl (pH 0.3) and the corrosion current density decreasing to 2.05 × 10−7 A cm−2. Overall, cross-flow PEALD enables high-quality metallic Ta coatings that enhance corrosion protection and interfacial electrical performance for BPPs.