A STUDY OF THE HYDROGEN EVOLUTION REACTION ON A NI NIFES ELECTRODEPOSITED COATING/

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