A study of the hydrogen evolution reaction on a Ni/NiFeS electrodeposited coating

Composite cathode materials based on nickel, such as NiFe, NiMo, NiMoCd, NiS, and NiMoS2, are of considerable practical interest as possible electrocatalysts for hydrogen production in alkaline water electrolyzers. This work describes the development of a new composite material of Ni and FeS (referred to as Ni/NiFeS) that shows a high electrocatalytic activity toward the hydrogen evolution reaction. Ni/NiFeS coatings were obtained by codeposition of Ni and FeS particles on Ni previously electrodeposited on a mild steel substrate. The evaluation of this material as H-2-evolving cathodes was done in alkaline solution through steady-state techniques. The polarization behavior of the material shows two distinct regions exhibiting different Tafel slopes over the temperature range 273 to 353 K. A detailed mechanistic study of the hydrogen evolution reaction on Ni/NiFeS was carried out by ac impedance techniques. The rate constants for the elementary steps were obtained and suggest a mechanism that involves an electron transfer followed by an electrochemical desorption step. The consistency of the analysis was confirmed by establishing that the apparent activation energy calculated from the dependence of the rate constant of the rate-determining step with T-1 has the same value as that found for the overall reaction.