Manipulated Reaction Route for Oxyhydroxides toward Top‐Performing Water Oxidation via eg 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 − , PO 4 3− , NO 3 − , F − , SO 4 2− , CO 3 2− ). The e g ‐ electron filling state customization predominantly arises from the adjustment of Co‐ d z 2 orbital energy, which can tailor the bandgap between Co‐ d z 2 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 PO 4 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 .