Interfacial charge density modulation by coupling CeO2 with dual-phase NiS/Ni3S2 to accelerate alkaline water splitting

To improve the catalytic kinetics for water electrolysis, it is essential to apply oxygen vacancies and heterojunction engineering simultaneously to electrocatalysts and enhance the ad/desorption process of intermediate substances (H*, OH*, O*, OOH*). Nevertheless, the synergistic effect of these two strategies in eutectic nickel sulfide composite materials has not received systematic investigation. In this study, a self-supported NiS/Ni3S2/CeO2 composite heterostructure comprising NiS/Ni3S2 nanosheets and CeO2 nanoparticles as a dual-functional electrocatalyst was proposed. NiS/Ni3S2/CeO2 exhibits remarkable catalytic activity with an ultra-low overpotential of 85 mV at 10 mA cm−2 for HER and 300 mV at 50 mA cm−2 for OER. As a dual-function electrode, NiS/Ni3S2/CeO2 electrocatalysts require only 1.52 V battery potential to deliver 10 mA cm−2, outperforming Pt-based/RuO2-based metal catalysts. DFT calculations reveal that the interface coupled with CeO2 undergoes rapid charge recombination, leading to the introduction of many oxygen vacancies that can effectively adjust the electron density of neighboring Ni sites and optimize the H* adsorption binding force, thereby accelerating the overall kinetic process of water electrolysis. This work provides a reliable electronic structure adjustment strategy to fabricate highly cost-effective and durable electrocatalysts for overall water splitting.