Exploring the Heterostructure Engineering of SnS/NiCo₂O₄ for Overall Water Splitting

Abstract

A bifunctional electrocatalyst with a low overpotential is a prerequisite for realizing efficient overall water splitting. In this scenario, the search for low-cost and non-precious electrocatalysts in electrolysis research leads to the employment of spinel oxides and chalcogenides. Herein, a heterostructure bifunctional electrocatalyst consisting of tin sulfide (SnS) nanosheets engrafted onto nickel cobalt oxide (NiCo2O4) nanoneedles suspended on nickel foam was prepared using the conventional hydrothermal method. The interface of SnS/NiCo2O4 was found to contain half-metallic Sn–O bonds as evident from density functional theory calculations and X-ray photoelectron spectroscopy. Furthermore, SnS growth on NiCo2O4 triggers new crystalline (0 2 1) planes and the vertical orientation of nanosheets enhancing the catalytic kinetics by exposing more surface S atoms, which provide a lower adsorption energy for hydrogen/oxygen moieties. The SnS/NiCo2O4 catalyst on Ni foam exhibits overpotentials of 302 mV (at a current density of 20 mA cm–2) and 154 mV (at a current density of 20 mA cm–2) for oxygen and hydrogen evolution reactions, respectively, in a 1.0 M potassium hydroxide electrolyte. Furthermore, a potential of 1.57 V was required to attain a current density of 10 mA cm–2 in the overall water-splitting process. Apart from this bifunctional ability, the catalyst shows good stability (>25 h) in the electrolyte. The growth of chalcogenides on spinel oxides paves a new way to realize efficient electrocatalysts with reduced adsorption energies.