Operando Identification of <i>h</i> ‐CoSe@Co Self‐Reconstruction into a CoOOH Heterointerface as the Active Site for Alkaline Hydrogen Evolution

ABSTRACT Understanding the dynamic surface evolution of electrocatalysts under working conditions is essential for the rational design of efficient water‐splitting systems. Herein, the self‐induced surface reconstruction of a superstructural electrocatalyst composed of metallic cobalt/hexagonal cobalt selenide nanoparticles confined within an N‐doped carbon nanocage ( h ‐CoSe@Co) during the alkaline hydrogen evolution reaction (HER) is investigated. Upon surface reconstruction, h ‐CoSe@Co evolves into an h ‐CoSe/CoOOH heterointerface that serves as the catalytically active site, promoting water adsorption and facilitating water dissociation. In situ Raman spectroscopy enables direct observation of the surface reconstruction and interfacial water capture. Complementary density functional theory (DFT) calculations further demonstrate that the h ‐CoSe/CoOOH heterostructure exhibits redistributed electronic states near the Fermi level and a near‐thermoneutral Gibbs free energy of hydrogen adsorption. Due to the synergistic effects of surface reconstruction and intrinsic properties, h ‐CoSe@Co delivers enhanced HER performance relative to o ‐CoSe 2 and c‐ CoSe 2 . This proof‐of‐concept study provides deep insight into the structure–activity relationship of a cobalt‐based chalcogenide electrocatalyst through a self‐induced surface reconstruction strategy for tuning adsorption energetics, thereby advancing efficient hydrogen energy technologies.