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

Abstract Ti-N layer with a thickness about 1 ∼ 2.2 μm was formed on titanium alloys through plasma nitriding at 750 °C in NH 3 and a mixture of NH 3 and N 2 (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 μA to 0.86 μA. Under a pressure of 140 N cm −2 , the interfacial contact resistance of the untreated sample increased from 22.1 mΩ cm 2 before corrosion testing to 40.5 mΩ cm 2 after corrosion at cathodic conditions. The nitrided sample, on the other hand, saw its contact resistance rise from 4.5 mΩ cm 2 before corrosion to 7.3 mΩ cm 2 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.