Engineering Co9S8/WS2 array films as bifunctional electrocatalysts for efficient water splitting

Abstract

An elaborate design of highly active, low-cost and durable bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in water splitting is undoubtedly vital but challenging to develop the hydrogen economy. Herein, we report a novel kind of three-dimensional Co₉S₈/WS₂ electrocatalyst with array structures as efficient bifunctional electrocatalysts for overall water splitting. The resulting hierarchically Co₉S₈/WS₂, as a robust integrated 3D hydrogen-evolving electrode, can deliver a current density of 10 mA cm_{geometric area}⁻² at an overpotential of 138 mV in alkaline media, together with high stability. Combined with density functional theory calculations, the superior electrocatalytic activity is attributed to the unique structures and synergistic effect of chemical and electronic couplings between Co₉S₈ and WS₂. Furthermore, this bifunctional electrode enables a high-performance alkaline water electrolyzer with 10 mA cm⁻² at a cell voltage of 1.65 V. Therefore, this unique 3D architecture opens an exciting new avenue to explore the use of composite sulfides toward full water splitting.