Photoelectrocatalytic Activation of C─H Bond in Toluene by Titanium Dioxide-Supported Subnanometric PtO_x Clusters

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 subnanometric PtO_x cluster-loaded TiO₂ (PtO_x/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 PtO_x/TiO₂ photoanode follow an electrophilic hydroxyl species (OH*)-mediated pathway, which can suppress the over-oxidation of BA. Moreover, we reveal that subnanometric PtO_x clusters promote toluene adsorption and OH* species generation, leading to the high efficiency of toluene oxidation. This work is expected to broaden the avenue toward the activation of C(sp³)─H bond under mild conditions in aqueous solution via a sustainable way.