Bridging Surface Science and Electrochemistry: A “Model Electrocatalysis” Study of Oxidation-Gradient-Triggered Ni-Based Water Oxidation Electrocatalysis

Oxygen evolution reaction (OER) is the rate-determining process in hydrogen production by full water electrolysis. While nickel-based oxides are known to undergo surface reconstruction to form the catalytically active nickel oxyhydroxide (NiOOH) phase under alkaline conditions, the intrinsic correlation between the initial atomic structure of the pre-catalyst and the properties of the in situ - formed active phase remains elusive, hindered by the uncontrollable catalyst surface. Here, benefiting from surface-science techniques, we develop a vacuum-interconnected “model electrocatalysis” strategy to advance fundamental studies on the four-electron OER process from catalyst preparation to catalysis evaluation under contamination-free conditions, where nickel-oxide model pre-catalysts with varied oxidation gradients are synthesized on Ni single crystals to investigate the evolution of key surface oxygen-related intermediate species and their effect on OER performance. We demonstrate that the pre-catalyst’s oxidation gradient acts as a critical structural driving force that determines the efficiency of surface reconstruction into the catalytically active NiOOH phase. Multimodal spectroscopy and microscopy characterizations, electrochemical measurements, and density functional theory (DFT) calculations collectively reveal a volcano-type OER behavior governed by the pre-catalyst’s oxidation gradient. More specifically, an increase in oxidation gradients downshifts the Ni d-band center, narrows its energy level difference with the *OH highest occupied state of adsorbed *OH, reduces antibonding orbital occupancy, and strengthens *OH binding. A moderate oxidation gradient (O/Ni = 0.6) optimizes the hydroxyl binding energy (OHBE) and facilitates the kinetic transformation into NiOOH by balancing *OH stabilization and interfacial charge transport. Over-oxidation, in contrast, leads to *OH overbinding and sluggish OER kinetics (*OH → *O → *OOH conversion), hindering the structural evolution into the catalytically active NiOOH phase. This study demonstrates the feasibility of the “model electrocatalysis” concept in elucidating how pre-catalyst atomic structures govern the generation and properties of the real active phases in electrochemical energy conversion.