Charge interaction and local structure induced abundant sulfur vacancies and lattice strain in NiS/NiS₂ heterojunction for efficient overall water splitting

Highly efficient and long-lasting non-precious metal-based electrocatalysts for overall electrolysers of freshwater and seawater for hydrogen production are still a great challenge in the hydrogen economy. Herein, a durable Cr_0.50-NiS/NiS₂ heterojunction designed to control charge interactions and local structure environment is introduced here to efficiently promote overall water splitting (OWS) for both alkaline freshwater and seawater. Charge redistribution and tailored local environments in the Cr_0.50-NiS/NiS₂ enable water molecule activation and efficiently optimize hydrogen adsorption during hydrogen evolution reaction (HER). Meanwhile, the former triggers self-induced electrochemical phase transition to a highly active phase for oxygen evolution reaction (OER), achieving remarkable performance and stability for OWS in both freshwater and seawater electrolytes. To deliver a current density of 10 mA·cm⁻², the as-synthesized Cr_0.50-NiS/NiS₂ catalyst exhibited excellent activity in alkaline electrolyte, requiring overpotentials of 158 mV (freshwater) and 155 mV (seawater) for OER, 110 mV (freshwater) and 128 mV (seawater) for HER. In a home-assembled electrolyzer for alkaline water splitting, the Cr_0.50-NiS/NiS₂ electrodes operated at relatively low applied potential 1.48 V (freshwater) and 1.45 V (seawater) to deliver 10 mA·cm⁻². Finally, a two-electrode seawater electrolysis system with Cr_0.50-NiS/NiS₂ as both cathode and anode demonstrated excellent stability over 500 h of seawater electrolysis without significant degradation, underscoring its potential as a cost-effective catalyst for sustainable hydrogen production.