Corrosion behavior of Ti-Nb-Ni foil as bipolar plates substrate in simulated PEMFC solution: Effects of fluoride concentration and temperature

In this work, corrosion behavior of Ti-Nb-Ni foil in 0.5 M H2SO4 solution containing different fluoride concentrations at various temperatures was investigated by electrochemical measurements, X-ray photoelectron spectroscopy and scanning electron microscopy. Corrosion resistance of specimens degraded with temperature and fluoride concentration increasing judged by more negative open circuit potential, larger corrosion current density as well as reducing polarization resistance. The critical fluoride concentrations were in the range of 100 similar to 200 ppm for 20celcius and 50 similar to 100 ppm for 40celcius to 80celcius, above which passive film was destroyed causing contact between substrate and solution. While in the cases of fluoride concentrations lower than critical value, passivation of foil was retained. Furthermore, a nickel-rich layer was found via X-ray photoelectron spectroscopy analyses and thickness of the layer descended with fluoride concentration and temperature increasing. Interfacial contact resistance of the foils after being potentiostatically polarized at 0.6 V for 6 h at 80celcius were lower than 10 m omega center dot cm(-2), meeting the requirement of Department of Energy (DOE) and interfacial contact resistance increased by different degrees with fluoride concentrations.