Dynamic active site reconstruction dictates the oxygen evolution reaction performance of cobalt-based...

Cost-effective and facile synthetic routes that afford materials with optimized surface architectures and high intrinsic chemical reactivities are crucial for scalable electrocatalyst development. Heteroatomic substitution of cobalt oxides is a key strategy for improving oxygen evolution reaction (OER) performance, yet the role of electrochemical activation across different compositions remains unclear. This study systematically examines how changes in structural and electronic properties, alongside dynamic active site reconstruction during catalyst activation affects OER performances. In this work, defect-rich M_xCo_1-x oxides (M = Fe, Mn, Ni, Cu; x = 0.1) with interstitial porosity and pseudo-amorphous interfaces were synthesized via a mechanochemical NaCl solid solution route. Among these catalysts, Fe/CoO/Co₃O₄ exhibited superior OER activity, achieving 220 mV overpotential at 10 mA cm^-2 in 1 M KOH. Unlike other systems, Fe/CoO/Co₃O₄ showed minimal redox potential shift during activation but a significant current density increase, attributed to dynamic reconstruction that stabilizes Fe sites on the Co matrix. High-resolution TEM confirmed partial amorphization after 30 CV cycles, while Raman spectroscopy revealed CoO vibration changes and CoOOH formation. Density functional theory (DFT) calculations indicate Fe or Mn doping modifies Co₃O₄ electronic structure by increasing the density of states (DOS) above the Fermi level (∼2 eV), primarily driven by Co 3d-O 2p hybridization and stronger metal-oxygen covalency. Additionally, Fe/CoO/Co₃O₄ exhibits a high Co³⁺/Co²⁺ ratio and oxygen vacancy (OV) concentration, boosting OER efficiency. However, excessive Fe doping reduces performance, underscoring the need for optimal substitution. This work identifies active site reconstruction and metal-oxygen bond covalency as critical descriptors for designing high-performance alkaline OER electrocatalysts.