Deciphering Interfacial Charge Transfer Phenomena at Nickel Nanocluster–Oxide Interface toward Augmented Efficacy in Electrochemical Water Splitting

The strategic engineering of heterostructure interfaces offers a promising route to surmount the activation energy barriers in water‐splitting processes, thereby enhancing overall gas evolution efficiency. In this work, a nanoheterostructure comprising nickel nanoclusters (NCs) anchored on NiO nanosheets (NS) is synthesized, and electrochemical properties are evaluated. Incorporation of Ni NCs markedly augments the hydrogen and oxygen evolution reaction activities of NiO NS, primarily due to the facilitation of charge transfer across the nanocluster/oxide interface. Under alkaline conditions, optimal water‐splitting performance is observed at NCs loadings upto 20 wt%, beyond which efficiency declined. Density functional theory calculations and X‐ray photoelectron spectroscopy analyses reveal that the enhanced catalytic activity stems from electronic interactions between Ni NCs and NiO NS, which favor the desorption of oxygen molecules. However, excessive nanocluster deposition impedes the accessibility of the nanocluster/oxide interface. Additionally, surplus NCs increase the hydrophobicity of the heterostructure, thereby hindering essential charge transfer processes. Unlike conventional metal/oxide systems dominated by polydisperse nanoparticles, this study exploits atomically precise Ni nanoclusters, enabling well‐defined interfacial sites that facilitate charge transfer and optimize *H/*OH adsorption. This atomic‐level control establishes clear structure–property correlations, offering mechanistic insight into interfacial catalysis and facilitating the deliberate development of efficient water‐splitting electrocatalysts.