Electrodeposited Nickel-Cobalt-Sulfide Catalyst for the Hydrogen Evolution Reaction

A novel Ni-Co-S-based material prepared by the potentiodynamic deposition from an aqueous solution containing Ni2+, Co2+, and thiotirea is studied as an electrocatalyst for the hydrogen evolution reaction (HER) in a neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by Varying the ratio of the concentrations of Ni2+ and Co2+ ions in the electrolytes. Under optimized deposition conditions, the bimetallic Ni-Co-S exhibits higher electro-catalytic activity than its monometallic counterparts. The Ni-Co-S catalyst requires an overpotential of 150 mV for the HER onset, and 10 mA cm(-2) current density is obtained at 280 mV overpotential. The catalyst exhibits two different Tafel slopes (93 and 70 inV dec(-1)) indicating two dissimilar mechanisms. It is proposed that the catalyst comprises two types of catalytic active sites, and they contribute selectively toward HER in different potential regions.