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 (Icorr) of the N-doped TiO2 coatings can be down to 1.788 m Omega center dot cm2@1.5 MPa and 8.41 nA center dot 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 mu A center dot cm- 2, which is 80 % lower than that of bare Ti (20 mu A center dot 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.