Role of Transition Metal Substitution on Nickel Sulfide toward Electrocatalytic Water Splitting

Nickel sulfide has been extensively studied as an electrocatalyst for water-splitting applications due to its low cost, high activity, unique surface electrical state, and high stability in alkaline medium. In this study, the effect of transition metal cation substitution on nickel sulfide (NixSy) toward the electrochemical water-splitting performance is investigated. Different transition metal substitutions on nickel sulfide, such as iron, cobalt, and manganese, are carried out during hydrothermal synthesis. The transition-metal-substituted NixSy is obtained by low-temperature hydrothermal sulfurization of nickel foam using sodium thiosulfate. The hydrothermal sulfurization using sodium thiosulfate results in mixed-phase nickel sulfide, along with a nanostructure morphology. Fe-substituted NixSy exhibits better oxygen evolution reaction (OER) characteristics with overpotentials of 193.1 and 226.3 mV vs RHE at 10 and 100 mA/cm2, respectively. Co-NixSy showed better hydrogen evolution reaction (HER) characteristics with 124 and 223.4 mV vs RHE at 10 and 100 mA/cm2, respectively. The overall water-splitting studies show that Co-NixSy||Fe-NixSy exhibits a cell voltage of 1.58 V at 20 mA/cm2. The stability of the electrocatalysts is verified by chronopotentiometry for 30 h duration.