Navigating Covalency of Cobalt Oxides for Enhanced Oxygen Evolution

Abstract Understanding the metal–oxygen covalency in transition metal oxides lays the groundwork for fine‐tuning their activity toward oxygen evolution reaction (OER). Herein, a large‐scale synthesis of cobalt oxide heterostructure nanowires encapsulated in nitrogen‐doped carbon (CoO/Co ₃ O ₄ @NC) is reported and reveals the correlation of Co–O covalency with OER activity. Operando characterizations reveal that the surfacial Co species are partially oxidized to higher‐valence CoO ₂ , which serve as the active sites for OER. Theoretical calculations further disclose the charge redistribution at CoO/Co ₃ O ₄ interface, effectively enhancing electrochemical conductivity and OER kinetics. Additionally, moderate Co–O covalency is found to promote stronger interaction with reaction intermediates, reducing the energy barrier and improving OER activity. Consequently, CoO/Co ₃ O ₄ @NC heterostructure nanowires achieve superior OER activity with an overpotential of 263 mV at 10 mA cm ⁻² . Moreover, the electrocatalyst preparation could be easily scaled up to gram‐level per batch. This work deepens the fundamental understanding about the role of Co–O covalency in OER, and demonstrates a cost‐effective electrocatalyst for larger‐scale practical applications.