Honeycomb-like nanocomposite Ti-Ag-N films prepared by pulsed bias arc ion plating on titanium as bipolar plates for unitized regenerative fuel cells

Honeycomb-like nanocomposite Ti-Ag-N films are prepared by pulsed bias arc ion plating, and for the first time served as surface modification layer on TA1 titanium as bipolar plates for unitized regenerative fuel cells (URFCs). Phase structure and surface morphology of the coated samples are investigated by XRD and SEM. Corrosion resistance of bare Ti plates and Ti-Ag-N coated samples is evaluated in simulated URFC conditions, and the interface contact resistance (ICR) between bipolar plates and carbon papers is measured before and after potentiostatic polarization tests. Ti2N phase with a preferred orientation of (1 1 0) plane is observed in the Ti-Ag-N film. SEM observation indicates that the film appears honeycomb-like and forms a nanocomposite microstructure with Ag nanoparticles embedded in Ti2N matrix. Compared to bare titanium plates, the coated sample shows improved corrosion resistance and ultra-low ICR (2 mΩ cm2 under a compaction pressure of 1.4 MPa). The superior conductivity of the coated sample is attributed to nanocomposite microstructure containing highly conductive Ag nanoparticles, and honeycomb-like rough surface obtained in this study. Nanocomposite Ti-Ag-N coated titanium bipolar plate exhibits prominent interfacial conductivity and excellent corrosion resistance at high potential, being a promising candidate as bipolar plate for applications in URFCs.

► The employment of nanocomposite Ti-Ag-N film as surface modification layer on TA1 titanium as bipolar plates for URFCs to improve their performances in URFC operating conditions.
► The design and synthesis by pulsed bias arc ion plating of nanocomposite Ti-Ag-N films with Ag nanoparticles evenly embedded in dense Ti2N matrix.
► Additionally, the film appears honeycomb-like.
► These features facilitate the coated samples to perform well as BPPs in URFCs, i.e. to maintain good conductivity and corrosion resistance in URFC corrosive media.
► TA1 titanium plates present superior corrosion resistance and maintain excellent conductivity (ICR <10 mΩ cm2 under 1.4 MPa before or after corrosion tests) in URFC working conditions by coating such a nanocomposite Ti-Ag-N film designed and purposed in this study.