Highly Active and Durable Single-Atom Tungsten-Doped NiS 0.5 Se 0.5 Nanosheet @ NiS 0.5 Se 0.5 Nanorod Heterostructures for Water Splitting.

Developing robust and highly active non-precious electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is crucial for the industrialization of hydrogen energy. In this study, a highly active and durable single-atom W-doped NiS 0.5 Se 0.5 nanosheet @ NiS 0.5 Se 0.5 nanorod heterostructure (W-NiS 0.5 Se 0.5 ) electrocatalyst is prepared. W-NiS 0.5 Se 0.5 exhibits excellent catalytic activity for the HER and OER with ultralow overpotentials (39 and 106 mV for the HER and 171 and 239 mV for the OER at 10 and 100 mA cm -2 , respectively) and excellent long-term durability (500 h), outperforming commercial precious-metal catalysts and many other previously reported transition-metal-based compounds (TMCs). The introduction of single-atom W delocalizes the spin state of Ni, which results in an increase in the Ni d-electron density. This causes the optimization of the adsorption/desorption process of H and a significant reduction in the adsorption free energy of the rate-determining step (O* → OOH*), thus accelerating the thermodynamics and kinetics of the HER and OER. This work provides a rational feasible strategy to design single-atom catalysts for water splitting and to develop advanced TMC electrocatalysts by regulating delocalized spin states.