Modulating the electronic structure of Mn promotes singlet oxygen generation from electrochemical oxidation of H₂O via O-O coupling

Abstract

Selectively catalytic conversion H₂O into singlet oxygen (¹O₂) without additional oxidants is considered as an economic-efficient method for organic pollutants degradation. However, H₂O are more consistent with the spin state of ¹O₂ than common oxygen (O₂), retarding the kinetics of spin transition-induced reaction between O₂ and ¹O₂. Herein, we report an unprecedented ¹O₂ mediated electrocatalytic oxidation process, which allows O–O coupling for ¹O₂ evolution from H₂O over CrMn@C anode. The electron occupancy (eg) of CrMn@C (0.89) is very close to the optimal eg (0.95) of manganese-based materials reported in the literature, which facilitates the activation of H₂O on surface. Mn(Mn0.193Cr1.808)O₄-Mn in CrMn@C electrode significantly promotes the activation of H₂O to produce *O, followed by coupling of *O at adjacent sites to produce *OO, which further spontaneously forms ¹O₂. And H₂¹⁸O isotope experiments provide direct evidence for the production of ¹O₂ directly from H₂O. Consequently, the production of ¹O₂ is enhanced with the yield of 785.6 μmol·L⁻¹. Such ¹O₂-dominated electrocatalytic oxidation system can achieve efficient removal of electron-rich pollutant (bisphenol A) and improve the biodegradability of pharmaceutical wastewater (from 0.17 to 0.39).