Synergistically enhanced corrosion resistance, electrical conductivity and interface adhesion of TiONx/TiN coatings through in-situ anodizing and plasma nitriding of Ti BPs for PEMWE cells

High corrosion resistance, high electrical conductivity and strong interface adhesion on Ti substrate are fundamental requirements for the coatings on bipolar plates (BPs) of proton exchange membrane water electrolysis (PEMWE). In this work, TiON_x/TiN composite coatings on Ti BPs with a small lattice mismatch of only 1.37% are prepared through anodizing and then in-situ plasma nitriding for TiON_x and magnetron sputtering for TiN. The lattice mismatch is remarkably smaller than that between TiO₂ and TiN (8.88%). The small lattice mismatch and the in-situ grown on Ti BPs could ensure the strong interface adhesion strength of the TiON_x/TiN coating at level 0 (ISO 2409:2007). Moreover, commonly, TiON_x exhibits good corrosion resistance, while TiN displays high electrical conductivity. Accordingly, the composite coatings exhibit enhanced corrosion resistance (0.17 μA·cm^-2) and high electrical conductivity (6.75 mΩ·cm² at 1.5 MPa). After 300 h of potentiostatic test at 2 V, the TiON_x/TiN coating maintains a low corrosion current density of 4.6 μA·cm^-2 and interface contact resistance (ICR) of 23.64 mΩ·cm². In cell assembly test, the TiON_x/TiN-coated BP exhibits lower ICR and higher electrolysis efficiency (77.89%) than uncoated BPs (64.35%). Overall, the TiON_x/TiN coating prepared through anodizing and then in-situ plasma nitriding might be potential candidates for protecting Ti BPs of PEMWE.