Photoelectrocatalytic activation of C–H bond in toluene by titanium dioxide-supported sub-nanometric PtO x clusters

Abstract

Selective oxidation of C(sp3)–H bonds via photoelectrocatalytic (PEC) strategy provides a promising approach to synthesize valuable oxygenates, but the efficiency of this process is still unsatisfactory due to the stable nature of hydrocarbon molecules. Herein, we report the PEC oxidation of toluene to benzaldehyde (BA) over a sub-nanometric PtOx cluster-loaded TiO2 (PtOx/TiO2) photoanode, achieving BA production rate of 1.75 μmol cm‒2 h‒1 with selectivity of 83.5% in aqueous medium, which is 4.4-fold higher than that of pristine TiO2. The strategy is also effective for the selective oxidation of toluene derivatives. As a proof-of-concept, we fabricate a self-powered PEC tandem device with S-shaped flow channels for the oxidation of toluene, producing BA with a productivity of ~170 μmol under light irradiation. Experimental studies combined with density functional theory (DFT) results demonstrate that the toluene oxidation over PtOx/TiO2 photoanode follow an electrophilic hydroxyl species (OH*)-mediated pathway, which can suppress the over-oxidation of BA. Moreover, we reveal that sub-nanometric PtOx clusters promote toluene adsorption and OH* species generation, leading to the high efficiency of toluene oxidation. This work is expected to broaden the avenue towards the activation of C(sp3)–H bond under mild conditions in aqueous solution via a sustainable way.