Mn-Doping-Induced Co₃O₄ Structural Distortion and Facet Change for Enhanced Electro-Activation of O₂ toward Pollutants Removal

Oxygen is a green oxidant for the oxidative removal of environmental pollutants. In this work, we employed Mn-doped Co3O4 for electrocatalytic activation of O2 and investigated the effects of structure and facet on catalysis. Co3+ substitution by Mn3+/Mn4+ leads to Co3O4 structural distortion and a shift of preferentially exposed (311) to a more catalytically active (220) plane. Meanwhile, more vacancies are created due to the structural defects and charge imbalance between Co3+ and Mn4+. Experimental and theoretical investigations suggest that Mn-doping facilitates adsorption of O2 on the deficient (220) plane of Co3O4 by triggering a thermodynamically more stable Mn0.65Co2.35O4-[O2]* intermediate. Mn0.65Co2.35O4 gives a turnover frequency value 9.5 times higher than that for pure Co3O4. The electrocatalytic wet air oxidation process with Mn0.65Co2.35O4 shows a great energy-saving merit with specific energy consumptions as low as 2.2–5.0 kW h kg-TOC–1 in mineralizing phenolic compounds. This work opens up new opportunities for advancing air oxidation technology into more competitive processes.