Modulating interfacial charge redistribution of Ni2P/CuCo2S4 p-n nano-heterojunctions for efficient electrocatalytic overall water splitting

Fabricating effective yet inexpensive catalysts is an important target in the research of water electrolysis and clean energy generation. Key challenges still remaining in this area are the rich density of surface-active sites, efficient interfacial charge transfer and improved reaction kinetics. Herein, Ni2P/CuCo2S4 p-n junctions are constructed via an in situ hydrothermal growth of Ni2P nanoparticles on CuCo2S4 nanosheets. Extensive X-ray photoelectron, optical absorption and electrochemical spectroscopy studies coupled with density functional theory calculations provide a mechanistic understanding of the electrochemical behaviour of these catalysts. The integrated Ni2P/CuCo2S4 p-n junctions, owing to the intimate interfacial interactions, offer interesting possibilities to purposively modulate the electronic structure of active sites at the interface, and thus to improve the hydrogen adsorption energetics and electrochemical reaction kinetics. As a result, the catalyst with 30 wt% Ni2P content displays high intrinsic electrocatalytic activity, requiring overpotentials of 183 and 360 mV to deliver 10 mA cm−2 for HER and 40 mA cm−2 for OER in alkaline media, respectively, far lower than those of individual Ni2P (400 and 520 mV) and CuCo2S4 (348 and 380 mV), further showing remarkable durability for 30 h. In addition, an alkaline two-electrode water electrolyzer assembled by Ni2P/CuCo2S4 nano-heterojunctions exhibits a relatively low cell potential of 1.67 V at 10 mA cm−2. These Ni2P-modified CuCo2S4 heterostructures demonstrate great potential for renewable hydrogen production technologies, including water electrolysis.