Analyzing HER catalytic sites of nickel sulphides, a DFT computational study

Abstract

Intermittent energy storage using hydrogen gas, produced by electrochemical water splitting, could prove to be invaluable as we move towards greener energy solutions. Conventional electrocatalysts are typically platinum-based but due to its scarcity this material is unsuitable to be deployed on a larger scale. The past decade much research has been done on finding other materials suitable for electrocatalysis that are cheaper and more efficient than platinum. Materials like transition metal oxides, metal sulphides, and phosphides have amassed a significant amount of interest. Among the metal sulphides, nickel sulphides have been shown to have a relatively low overpotential, making them excellent candidates as electrocatalysts. Nickel sulphides have been studied for their catalytic efficiency in the Hydrogen Evolution Reaction (HER), both theoretically and experimentally, but few studies have analysed the individual catalytic sites involved and their efficiency. In this study Density Functional theorem (DFT) modelling is used to analyse α-NiS, β-NiS, NiS2, and Ni3S2. The electronic structure, adsorption energies, dissociative adsorption energies, hybridization, charge density difference, and electronic charge of all surfaces, sites, and adsorbents involved are determined and analysed. With ΔGH* values of 0.10 and 0.05 eV the Ni3S2 surface of miller index (101), Ni/S-terminated, presents the most promising sites for performing the Volmer step in HER of the nickel sulphides studied.