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 treatment

The development of electrocatalytic systems with tandem hydroxyl radical (center dot 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 center dot 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 center dot OH and 1O2, which is achieved by regulating the adsorption/desorption of key intermediates (*OOH, *O2 center dot- and *H2O2). The accumulated concentrations of center dot OH and 1O2 in the FeTiO3-based system reach 83 and 31 mu mol 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 center dot-- to-1O2 and *O2-to-*H2O2-to-center dot OH pathways at Fe-O-Ti sites. Therefore, this work provides a new flow-through system for simultaneous center dot OH and 1O2 production, significantly expanding the potential applicability of electrocatalytic processes.