Plasma carburizing for improvement of Ni-Fe cathodes for alkaline water electrolysis

Electrodeposited Ni-Fe-C alloys have high electroactivity for hydrogen evolution reaction (HER) in alkaline water electrolysis. In the present work carbon was introduced into Ni and Ni–Fe alloys by plasma treatment in CH4+H2 gas mixture at 470 oC. Despite of a very low solubility of carbon in nickel, carbon entered into nickel to the depth of about 0.5 µm, formed about 2-µm thick carbide layer in high-Fe alloys, and increased hardness. Electrochemical measurements in 25 wt.% KOH at 80 oC showed that carburization resulted in an improvement of catalytic activity toward HER, especially of Ni and 1Ni-Fe. Carburization also increased the resistance to corrosion during cathodic polarisation and under open-circuit conditions. XPS surface analysis showed that after corrosion the oxide content was on carburized materials significantly lower than that on untreated materials. It is suggested that the enhanced electroactivity of plasma carburized cathodes is due mainly to the enlargement of the surface area of disintegrated material. A catalytic affect might also be exerted by carbon-metal particles.