Protective Ti sub-oxide coatings on proton exchange water electrolysis prepared by HiPIMS technology

Electrolysis, the process of splitting water into hydrogen and oxygen using electrical current, stands as a pivotal technology in the current hydrogen economy. Among various electrolyser technologies, proton exchange membrane water electrolysers (PEMWEs) are favored for their high efficiency, durability, and suitability for commercial applications. However, the cost of PEMWE systems, particularly the bipolar plates (BPs), which account for ∼25 % of system costs, remains a critical challenge. Stainless steel BPs has been explored as a cost-effective alternative to titanium BPs, but they require protective coatings to prevent corrosion under PEMWE conditions. This study focuses on developing titanium suboxide (Ti sub-oxide) coatings for stainless steel BPs to enhance corrosion resistance, maintaining a moderate contact resistance. Ti sub-oxide coatings were deposited using High-Power Impulse Magnetron Sputtering (HiPIMS), a technique enabling high-density and homogeneous material deposition. Key strategies to increase coating compactness, including substrate polarization and cyclic ion bombardment during deposition, were investigated. Morphological and compositional analyses were conducted, along with evaluations of corrosion resistance and electrical performance. The results demonstrate that Ti sub-oxide coatings developed with the selected approaches, exhibit improved compactness, which could potentially limit electrolyte infiltration, enhancing the durability and performance of stainless steel substrates. These findings highlight the promising behavior of Ti sub-oxide coatings under harsh PEMWE conditions. While further studies are needed in actual PEM electrolyzers, they suggest a cost-effective solution for advancing PEMWE technology and green hydrogen scalability toward Net Zero goals. • Ti sub-oxide coatings were deposited on stainless steel using the HiPIMS technique. • Substrate polarization and ion bombardment enhanced coating compaction effectively. • Corrosion tests were conducted for 24 h under PEMWE working conditions. • Increased bombardment cycles yielded coatings with higher corrosion resistance. • A higher protection was achieved for Ti sub-oxide coatings with more cycles.