Characterization and electrochemical performance of plasma-nitrided titanium alloy for bipolar plates

Ti-N layer with a thickness about 1~2.2 μm was formed on titanium alloys through plasma nitriding at 750 °C in NH3 and a mixture of NH3 and N2 (1:2) for 4 h. SEM and XRD were employed to characterize the microstructure and phase composition of nitrided layer. Electrochemical tests evaluated the anti-corrosion properties of the samples before and after nitrided in a simulated proton exchange membrane fuel cells (PEMFC) environment. Interface contact resistance (ICR) was also measured. Results indicated that the corrosion potential in cathodic conditions was increased from -415 mV for untreated titanium to 148 mV for that nitrided in mixture gas. While, the corrosion current density was reduced from 6.64 A to 0.86A. Under a pressure of 140 N/cm², the interfacial contact resistance of the untreated sample increased from 22.1 mΩ cm2 before corrosion testing to 40.5 mΩ cm2 after corrosion at cathodic conditions. The nitrided sample, on the other hand, saw its contact resistance rise from 4.5 mΩ cm2 before corrosion to 7.3 mΩ cm2 after corrosion. The Ti-N compound layer effectively diminished the corrosion current density and sustained an exceptionally low ICR under the simulated operating conditions of a bipolar plate.