Electronic Structure Engineering of Highly‐Scalable Earth‐Abundant Multi‐Synergized Electrocatalyst for Exceptional Overall Water Splitting in Neutral Medium

Efficient neutral water splitting may represent in future a sustainable solution to unconstrained energy requirements, but yet necessitates the development of innovative avenues for achieving the currently unmet required performances. Herein, a novel paradigm based on the combination of electronic structure engineering and surface morphology tuning of earth‐abundant 3D‐hierarchical binder‐free electrocatalysts is demonstrated, via a scalable single‐step thermal transformation of nickel substrates under sulfur environment. A temporal‐evolution of the resulting 3D‐nanostructured substrates is performed for the intentional enhancement of non‐abundant highly‐catalytic Ni(3+) and pS(n) (2−) species on the catalyst surface, concomitantly accompanied with densification of the hierarchical catalyst morphology. Remarkably, the finely engineered NiS (x) catalyst synthesized via thermal‐evolution for 24 h (NiS (x) ‐24 h) exhibits an exceptionally low cell voltage of 1.59 V (lower than Pt/C‐IrO(2) catalytic couple) for neutral water splitting, which represents the lowest value ever reported. The enhanced performance of NiS (x) ‐24 h is a multi‐synergized consequence of the simultaneous enrichment of oxygen and hydrogen evolution reaction catalyzing species, accompanied by an optimum electrocatalytic surface area and intrinsic high conductivity. Overall, this innovative work opens a route to engineering the active material's electronic structure/morphology, demonstrating novel Ni(3+)/pS(n) (2−)‐enriched NiS (x) catalysts which surpass state‐of‐the‐art materials for neutral water splitting.