Etching Accelerates Reconstruction and Activates Lattice Oxygen of Anion Vacancies‐Enriched Cobalt‐Iron Phosphide/(Oxy)Hydroxide Nanohybrid Frameworks for Enhanced Oxygen Evolution

Abstract Transition metal phosphides (TMPs) nanostructures are considered to be promising pre‐catalysts for electrochemical oxygen evolution reaction (OER). Nonetheless, most TMPs only experience limited surface reconstruction during OER, resulting in fewer active layer, insufficient active sites and thus unsatisfactory performance. Thereby, finely control the reconstruction level is crucial but still challenging. Here, the Co _0.7−x Fe _0.3−y P/Co _x Fe _y OOH nanohybird frameworks with numerous crystalline/amorphous interfaces are fabricated by alkali etching of hollow crystalline Co _0.7 Fe _0.3 P nanocubes, leading to in‐situ surface growth of amorphous Co _x Fe _y OOH nanosheets subunits. Such Co _0.7−x Fe _0.3−y P/Co _x Fe _y OOH nanohybrid frameworks own abundant phosphorus and oxygen vacancies, optimal interface electronic structure, and hydrophilic surface character, which manifest exceptional OER performance with the overpotential of 256 mV to reach 10 mA cm ⁻² current in alkaline media, exceeding Co _1−x P/Co _x OOH, Fe _1−y P/Fe _y OOH, Co _0.7 Fe _0.3 P, IrO ₂ , and most reported unprecious‐metal‐based catalysts. As revealed by series of ex‐situ and in‐situ spectroscopic and electrochemical analyses, the formation of anion defects and amorphous phase promote deep reconstruction of such catalyst, thus triggering lattice oxygen participation in synergy with adsorbate evolution mechanism toward OER. This work may spur the development of TMPs‐based OER catalysts by integrating structure, defect, and phase engineering via facile etching, and promote their applications in water splitting or other clean energy options.