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

• FeTiO 3 -based electrocatalytic system for simultaneous conversion of O 2 to • OH and 1 O 2 • Enhanced O 2 adsorption and *OOH formation at oxygen vacancy-rich Fe-O-Ti sites • Anodic OER ensures the continuous O 2 mass transport needed for cathodic ORR • Synergistic contributions of • OH and 1 O 2 to destroy electron-rich pollutants • Removal of organic pollutants in robust flow-through system: effective in actual matrices The development of electrocatalytic systems with tandem hydroxyl radical ( • OH)- and singlet oxygen ( 1 O 2 )-mediated pollutant degradation routes broadens the application scenarios for electrochemical water treatment technology. Nonetheless, the precise tuning of the electrocatalytic O 2 reduction reaction (ORR) to achieve synchronous synthesis of • OH and 1 O 2 is still challenging in electro-Fenton (EF)-like systems. Herein, an FeTiO 3 -based flow-through electrochemical cell is proposed for highly efficient and selective ORR to yield both • OH and 1 O 2 , which is achieved by regulating the adsorption/desorption of key intermediates (*OOH, *O 2 •− and *H 2 O 2 ). The accumulated concentrations of • OH and 1 O 2 in the FeTiO 3 -based system reach 83 and 31 μmol L −1 after 120 min, respectively, outperforming the TiO 2 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 *O 2 adsorption, leading to highly selective *O 2 -to-*O 2 •− -to- 1 O 2 and *O 2 -to-*H 2 O 2 -to- • OH pathways at Fe-O-Ti sites. Therefore, this work provides a new flow-through system for simultaneous • OH and 1 O 2 production, significantly expanding the potential applicability of electrocatalytic processes.