Fe-based layered double hydroxides carbon cathode modulates oxygen reduction pathways and HO formation mechanism in electro-peroxone system

Abstract

Electro-peroxone (EP) is an emerging technology that combines electrochemistry and O₃ to remove contaminants. However, conventional carbon cathodes primarily contribute to the synthesis of H₂O₂ in the system, which may scavenge HO. Herein, a series of Fe-based layered double hydroxides (LDH) was loaded onto graphite felt cathodes to strengthen the removal of organic contaminants. The EP system with CuFe-LDH/GF cathode (EP-CuFe-LDH/GF) demonstrated the highest removal rate (91.2 % within 20 min) of oxalic acid (OA), a typical ozone-resistance substance, approximately twice that of the EP-GF system. HO was identified the main reactive species. A new pathway for O₂ reduction and the generation of HO was found. The loading of CuFe-LDH altered the reduction pathway of O₂ on the GF cathode from 2e⁻ to 1e⁻ or 4e⁻ process. As a result, HO was produced by the combination of O₃ and O₂⁻ instead of O₃ and H₂O₂, which avoided the quenching of HO by H₂O₂ and enhanced the removal of OA. Moreover, the breaking complexation by O₃, cathodic O₃ reduction and metal-OH catalyzed O₃ processes also contributed to the HO formation. Furthermore, the system could efficiently remove OA across a broad pH range of 3.0 to 9.0, addressing the poor performance of conventional EP systems under acidic conditions. Overall, the finding of this significant mechanism advances the understanding of organic pollutants removal and broadens the potential applications of EP system.