Uniform Sub‑5 nm Crystalline Nickel-Based Heterojunctionsfor Overall Water Splitting Electrocatalysis

Exploring a general method for constructing uniform heterostructures with sub-5 nm crystallites and dense interfaces is crucial yet challenging for advancing water electrocatalysis. Herein, a bottom-up cocrystallization strategy, involving in situ transformation of amorphous Ni–P through gas–solid reactions, is proposed to synthesize a series of nickel-based heterojunctions on carbon cloth (CC). Thereinto, interface-wealthy NiS₂-Ni₂P/CC with densely packed 3–4 nm crystallites demonstrates superb catalytic performance for both hydrogen and oxygen evolution. The electrolyzer merely requires cell voltages of 1.79 and 1.89 V to propel overall water splitting currents of 200 and 400 mA cm^–2, respectively, outperforming the vast majority of reported nickel-based heterojunctions. Theoretical calculations reveal that charge redistribution and electronic structure modulation optimize the hydrogen and oxygen evolution pathways at the NiS₂ and Ni₂P sides of the interfaces, respectively. Moreover, uniform hybridization with densely distributed heterointerfaces offers abundant active sites for electrocatalysis, pioneering an extendable approach for constructing advanced heterojunction catalysts for green hydrogen production.