Tuning the oxygen reduction pathway in a flow-through electrocatalytic system to enable the in-situ production of hydroxyl radical and singlet oxygen for robust wastewater treatmen

Abstract

The development of electrocatalytic systems with tandem hydroxyl radical (•OH)- and singlet oxygen (1O2)-mediated pollutant degradation routes broadens the application scenarios for electrochemical water treatment technology. Nonetheless, the precise tuning of the electrocatalytic O2 reduction reaction (ORR) to achieve synchronous synthesis of •OH and 1O2 is still challenging in electro-Fenton (EF)-like systems. Herein, an FeTiO3-based flow-through electrochemical cell is proposed for highly efficient and selective ORR to yield both •OH and 1O2, which is achieved by regulating the adsorption/desorption of key intermediates (*OOH, *O2•− and *H2O2). The accumulated concentrations of •OH and 1O2 in the FeTiO3-based system reach 83 and 31 μmol L−1 after 120 min, respectively, outperforming the TiO2 counterpart. Such an advanced system demonstrates outstanding performance for the degradation of electron-rich contaminants, even in complex wastewater matrices. The mechanistic insights reveal an enhanced *O2 adsorption, leading to highly selective *O2-to-*O2•−-to-1O2 and *O2-to-*H2O2-to-•OH pathways at Fe-O-Ti sites. Therefore, this work provides a new flow-through system for simultaneous •OH and 1O2 production, significantly expanding the potential applicability of electrocatalytic processes.