Synergistic enhancement on corrosion resistance and electrical conductivity of N-doped TiO₂ coatings for bipolar plate of PEM electrolyzer

Commonly, TiO₂ passivation layer will be formed on titanium bipolar plates (BPs) in the anodic side of the proton exchange membrane (PEM) electrolyzer after long-term operation in an acid environment, which will result in high contact resistance and large energy consumption. So it is urgent to fabricate anti-corrosion but high electrical conductivity coatings on BPs. In this work, the combination process of anodizing and nitriding technologies is adopted to prepare N-doped TiO₂ coatings on Ti BPs. The interface contact resistance (ICR) and the self-corrosion current density (I_corr) of the N-doped TiO₂ coatings can be down to 1.788 mΩ∙cm²@1.5 MPa and 8.41 nA∙cm⁻², respectively, which meet the requirements of the DOE target. After the potentiostatic polarization at 2 V for 168 h, the corrosion current density of N-doped TiO₂ coatings is stabilized at around 4 μA∙cm⁻², which is 80 % lower than that of bare Ti (20 μA∙cm⁻²). It can be ascribed to the formation of Ti nitride/oxy-nitride in the anodized TiO₂ coatings upon the treatment of NH₃ plasma. Essentially, N-doping increases the electrical conductivity, simultaneously N atoms fill in the oxygen vacancies in TiO₂ coatings, which suppresses the ion dissolution and consequently improves the corrosion resistance properties. The results are of significant guidance to the design and fabrication of coatings protecting BPs.