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

- Plasma carburized surface layers of Ni and Ni-Fe alloys contained about 80 at.% C.
- Carburized materials exhibited enhanced electroactivity toward HER, increased hardness and corrosion resistance.
- Amount of oxide corrosion products on carburized materials was much smaller than that on untreated materials.
- Enhanced electroactivity can be due to surface disintegration and catalytic effect of carbon-metal particles.

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 °C. Despite of a very low solubility of carbon in nickel, carbon entered into nickel to the depth of about 0.5 μm. In high-Fe alloys it formed a carbide layer about 2-μm thick and increased surface hardness. Electrochemical measurements in 25 wt.% KOH at 80 °C 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 on carburized materials was significantly lower than that on untreated materials. It is suggested that the enhanced electroactivity of plasma carburized cathodes was due mainly to the enlargement of the surface area of disintegrated material. Also, a catalytic effect might be exerted by carbon-metal particles.