Optimizing electron density of nickel sulfide electrocatalysts through sulfur vacancy engineering for alkaline hydrogen evolution

Abstract

The development of earth-abundant Ni-compound-based electrocatalysts with high performance toward alkaline hydrogen evolution reaction (HER) is of significance for hydrogen generation. Ni₃S₂ catalysts have been widely regarded as promising candidates, but suffer from unfavorable hydrogen adsorption characteristics; hydrogen absorption on the Ni sites is not sufficiently strong. Herein, by using ab initio calculations, we have shown that hydrogen adsorption on Ni sites of Ni₃S₂ catalysts can be tuned by introducing sulfur vacancies. Inspired by this theoretical finding, we have fabricated a porous Ni₃S₂ nanosheet array catalyst grown on nickel foam that is rich in sulfur vacancies (Vs-Ni₃S₂/NF) by a plasma-assisted method. The catalyst exhibits a much improved HER activity, which only requires a low overpotential of 88 mV at a current density of 10 mA cm⁻² and a Tafel slope of 87 mV dec⁻¹ in 1 M KOH. This catalyst also shows high durability, which can sustain 15 h of high-current-density (∼100 mA cm⁻²) operation with negligible degradation. The theoretical and experimental results reveal that the increase in the electron density of Ni sites induced by sulfur vacancies plays a key role in improving its intrinsic activity. This work opens a new direction for the rational design of highly efficient transition-metal-compound electrocatalysts toward HER and beyond through defect engineering.