TiO2 electrocatalysis via three-electron oxygen reduction for highly efficient generation of hydroxyl radicals.

• H 2 O 2ad was reduced in situ to OH during ORR on the TiO 2 /C cathode. • OH was generated with a high yield (2.69 μg cm−2 min−1) and high current efficiency (92.8%). • The interaction between O 2 and TiO 2 was observed directly using in situ Raman spectroscopy. • A continuous three-electron oxygen reduction mechanism was proposed. The use of heterogeneous catalysts to improve the Electro-Fenton (EF) process has attracted significant attention. However, complex redox reactions and multiple mass transfer steps during the EF process result in limited current efficiency with only a low rate of generation of hydroxyl radicals (OH). Herein, we establish a three-electron oxygen reduction reaction (ORR) process coupling adsorbed H 2 O 2 (H 2 O 2ad) generation with an in situ EF-like reaction on TiO 2 during cathodic electrolysis. Anatase TiO 2 was composited with graphite, enabling the electrochemical reduction of Ti4+ to Ti3+. H 2 O 2ad was formed during the ORR, electrocatalyzed by TiO 2 , then the H 2 O 2ad was reduced in situ to OH without desorption. The generation and decomposition of Ti-OH during the electrochemical reduction were directly observed by in situ Raman spectroscopy. This result was further confirmed by density functional theory (DFT) calculations. Based on this three-electron ORR mechanism, the OH yield reached 2.69 μg cm−2 min−1 and the current efficiency approached 92.8% at a current density of −0.80 mA cm−2 within 2 h during ORR on the TiO 2 /graphite (TiO 2 /C) cathode. [ABSTRACT FROM AUTHOR]