Electrocatalysis of the hydrogen evolution reaction by thermally formed sulfides on steels

The electrocatalytic activity was studied of sulfides, formed by thermal sulfidization of various com. available steels, for the cathodic evolution of H from sodium chloride. The effects of certain surface active anions on the H evolution reaction on these sulfidized steels were also studied. Sulfidization of C steels and Si steels increases their electrocatalytic activity with respect to cathodic H evolution and thereby reduces the over potential in sodium chloride solns. (typically about 100-150 mV at 0.5 A cm-2). The anomalously high Tafel slopes obsd. for H2 evolution reaction on steels during brine electrolysis is explained as due most probably to the presence of a hydride film on the steel surface at high cathodic potentials. A comparison of the H overpotentials and corrosion currents reveals that C steels - both in their plain and sulfidized forms - are better cathodes for brine electrolysis