Excess Activity Tuned by Distorted Tetrahedron in CoMoO₄ for Oxygen Evolution

Oxygen vacancies enable modulating surface reconstruction of transition metal oxides containing metal–oxygen polyhedrons into metallic oxyhydroxide for oxygen evolution reaction (OER), while revealing reconstructing mechanism is stuck by the requirement to precisely control exact sites of these vacancies. Herein, oxygen vacancies are localized only within MoO₄ tetrahedrons rather than CoO₆ octahedrons in CoMoO₄ catalyst, guaranteeing coherent reconstruction of CoO₆ octahedrons into pure CoOOH with tunable activities for OER. Meanwhile, distorted tetrahedron accelerates the dissolution of Mo atoms into alkaline electrolyte, triggering spontaneous transition of partial CoMoO₄ into Co(OH)₂. CoO₆ octahedrons in both CoMoO₄ and Co(OH)₂ can transform pure CoOOH completely at lower potential, resulting in excess intrinsic activity whose summit is identified by overpotential at 10 mA cm⁻² with 22.9% reduction and Tafel slope with 65.3% reduction. Well-defined manipulation over the distorted polyhedrons offers one versatile knob to precisely modulate electronic structure of oxide catalysts with outstanding OER performance.