Atomic scale synergistic interactions lead to breakthrough catalysts for electrocatalytic water splitting

A breakthrough catalyst for electrocatalytic water splitting, precious-metal-free equi-molar high entropy alloy H-FeCoNiCuMo, is developed through exploring and maximizing strong synergistic interactions between atomically well-mixed constituents of H-FeCoNiCuMo over atomic scales. For overall electrolytic water splitting under severe industrial operation conditions, the H-FeCoNiCuMo//H-FeCoNiCuMo couple requires only an ultralow cell voltage of 1.627 V to deliver an ultrahigh current density of 1500 mA cm−2, and remains stable after a 100-hr continuous operation, largely outperforming a precious metal-based benchmark couple, Pt/C//IrO2, 2.038 V with 55% decay in 24 hr. A new catalytic phenomenon is discovered, two different catalytic mechanisms functioning simultaneously on different constituents of H-FeCoNiCuMo, the Volmer-Heyrovsky route on Co and Cu and Volmer-Tafel route on Ni and Mo, from which a new kinetic model is formulated to predict a new theoretical lower limit of Tafel slope of 15 mV dec−1 for hydrogen evolution reactions. [Display omitted] •High entropy alloy, containing Fe, Co, Ni, Cu, and Mo, is synthesized by pulse electroplating.•H–FeCoNiCuMo present catalytic efficiency toward pH-universal water splitting.•H–FeCoNiCuMo exhibit ultra-low η10 of 7 mV and 9 mV for alkaline HER and acidic HER.•H–FeCoNiCuMo exhibit low η10 of 194 mV for alkaline OER.•Achieve an ultra-low cell voltage of 1.416 V to deliver 10 mA cm−2 in 1 M KOH.