Optimization of Corrosion Resistance in Magnetron-Sputtered CrAlN Coatings for Alkaline Seawater Electrolysis via Nitrogen Flow Ratio Control: Microstructural Evolution and Corrosion Mechanism

Designing materials with superior corrosion resistance is critical for seawater electrolysis systems to achieve efficient and long-term stable hydrogen production. In the current study, CrAlN coatings were deposited on TA1 titanium substrates by reactive magnetron sputtering with nitrogen flow ratios ranging from 40%–70% to investigate the effect of nitrogen stoichiometry on corrosion behavior in simulated alkaline seawater (pH ≈ 14, chloride-containing). Microstructural characterization (Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Grazing Incidence X-Ray Diffraction (GIXRD), Transmission Electron Microscopy (TEM), X-Ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM)) reveals that a 60% nitrogen ratio promotes grain refinement, improved CrN/AlN phase stoichiometry, and reduced oxygen-related defects, resulting in a dense columnar structure with minimized diffusion pathways. Electrochemical measurements show that this condition yields the lowest corrosion current density (0.297 μA·cm−2) and the highest polarization resistance (123.9 kΩ·cm2). Electrochemical impedance spectroscopy confirms enhanced charge transfer resistance and suppressed ionic transport at the coating/electrolyte interface. The results establish a clear correlation between nitrogen-controlled phase evolution, defect density, and passivation kinetics in highly alkaline chloride environments relevant to seawater electrolysis. This study targets the fabrication of protective coatings for alkaline seawater electrolysis via nitrogen flow ratio optimization. The optimized CrAlN coating achieves remarkably improved corrosion resistance compared with existing coatings, showing promising practical value for long-term stable seawater electrolysis.