Carolin Barth, Stefan Saager, Ludwig Decker, Bert Scheffel, Fraunhofer Institute for Electron Beam and Plasma Technology FEP; Dresden, Germany
Background: Titanium-based thin films on graphite-filled composite bipolar plates (CBPs) are of high interest for PEM electrolysis due to corrosion resistance and electrical performance. Plasma-activated electron-beam PVD (PA-EB-PVD) enables high deposition rates while limiting the temperature of heat-sensitive CBP substrates, revealing a clear techno-economic advantage. The approach yields dense coatings on substrates with polymer skins and laser-structured surfaces.
Methods: A PA-EB-PVD process based on the principle of spotless arc-activated deposition (SAD) was employed to deposit titanium coatings on CBPs. The investigated substrates include polymer-skinned, machined, and laser-structured CBPs. A matrix of substrate pretreatments (Ar/O₂ ion bombardment, hollow cathode etching, CO₂ snow-stripping) has been evaluated and the dependency of the coating properties on the degree of plasma activation has been analyzed. Through-plane sheet resistance (R_TP) and corrosion resistance (i_Corr) have been measured. FEM simulations of substrate heating have been validated against experimental data. The study also analyzes coating density and adhesion, corrosion behavior, and the influence of substrate chemistry on R_TP and i_Corr.
Results: Plasma activation of EB-PVD by SAD markedly improves coating density and adhesion while enabling coverage on CBPs with substrate temperatures near the limit (T_sub ≤ 130°C). Laser-structured CBPs subjected to PA-EB-PVD with higher SAD arc currents deliver the best electrical performance. Substrate type governs RTP and corrosion response, machined substrates showing higher RTP and higher corrosion resistance, and laser-structured substrates providing superior durability when optimized. FEM simulations reasonably reproduce static heating but require refinement to capture dynamic plasma interactions and substrate motion. Overall, the results define a scalable pathway for high-rate Ti-based coatings on CBPs, quantify thermo-kinetic corrosion interdependencies, and provide actionable insights for deployment in industrial settings.