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

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.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

Hydrogen evolution on plasma carburised nickel and effect of iron deposition from electrolyte in alkaline water electrolysis

Presence of carbon in electrodeposited nanocrystalline Ni-Fe-C cathodes renders a high electroactivity for hydrogen evolution reaction (HER) in hot alkaline solutions. In the present work carbon was introduced into nickel cathodes by plasma treatment in CH4 + H2 gas mixture at 47 0 C. Electrochemical measurements were carried out in the solution of 25 wt.% KO H (reagent p.a.) at 80 C. In some measurements the solution wa s pre-electrolysed to remove heavy metals. Carburisation resulted in a significant enhancement of catalytic activity of nickel for HER during short cathodic polarisation. Later, differences between the materials almost disappeared, evidently due to deposition of iron and of other heavy metals from the solution. Cathodes with iron deposits underwent an activation following anodic polarisation. It wa s proposed that the activating effect of iron can be associated with the formation of highly reactive iron during cathodic reduction of oxide species (probably Fe(OH)4 2 ). The activating effect of prior anodic polarisation can be due to the formation of large amounts of oxide species which can undergo the reduction to reactive iron