Impurity-Driven Interfacial Reconstruction Unlocks Highly Active Sites in Ni-Fe Selenides for Water Oxidation

Understanding how surface-active sites emerge during electrochemical operation is critical for advancing oxygen evolution reaction (OER) catalysts. In this study, we investigate the dynamic reconstruction behavior of nickel (Ni)-iron (Fe) selenide systems, with a particular focus on the role of selenium (Se) in facilitating surface reorganization and activating Fe species. Through a comparative analysis of bulk-doped NiFeSe, surface-adsorbed Fe-NiSe, and sequentially modified Se1-Fe2-Ni systems, we demonstrate that catalytic performance is strongly governed by interfacial dynamics rather than bulk composition. Operando Raman spectroscopy and XPS analyses reveal that the formation of Se-Se species and Fe³⁺ in selenide environments are key signatures of active site generation. While NiFeSe follows a relatively static transformation pathway, Fe-NiSe and Se1-Fe2-Ni exhibit distinct interfacial restructuring driven by Se dissolution and impurity-stabilized readsorption. These processes lead to the formation of highly disordered but intrinsically active surface phases, resulting in enhanced OER kinetics.