Manipulated Reaction Route for Oxyhydroxides toward Top‐Performing Water Oxidation via e_g Electron Filling State

Abstract Oxygen evolution reaction (OER) activity on transition metal (TM) catalysts is governed by OER mechanism, yet discovering a controllable parameter to custom‐tailor OER mechanism remains a challenge. Here, the study highlights an e_g electron‐filling state in octahedral TM‐catalysts, achieved by the modulation of splitting energy (Δ) via different anions (R) (Cl⁻, PO₄³⁻, NO₃⁻, F⁻, SO₄²⁻, CO₃²⁻). The e_g‐ electron filling state customization predominantly arises from the adjustment of Co‐d_z² orbital energy, which can tailor the bandgap between Co‐d_z² and O‐p orbits (Δε_d‐p), thus customizing lattice‐oxygen (O_L) activities and the OER mechanism. Combining the experimental measurements with DFT calculations, it is concluded that increased e_g electron in TM‐catalysts brings decreased Δε_d‐p, which can manageably strengthen lattice‐oxygen reactivity. Consequently, the OER mechanism on TM catalyst is transformed from adsorbate precipitation mechanism (AEM) to lattice oxygen oxidation mechanism (LOM) and customized OER pathways with different lattice‐oxygen activities. The screened PO₄^3‐_TM, with the optimal O_L activity in LOM path, possesses excellent activity and stability, achieving a current density of 10 mA cm⁻² at 236 mV overpotential and maintaining stable operation for 300 h with inapparent degradation at 10 mA cm⁻².