Investigation of the local photothermal effects by fabricating a CQDs/Au/TiO2 photoelectrode in a PEC water splitting system

Abstract

The high efficiency of the photoanode material is of great significance for photoelectrochemical (PEC) water splitting. Herein, a CQDs/Au/TiO₂ nanorod array composite photoanode was constructed with special attention to local photothermal effects. The intensity and characteristics of the local thermal effect generated by the photothermal conversion of plasmonic Au nanoparticles (Au NPs) and carbon quantum dots (CQDs) are accurately represented by an equivalent simplified temperature field model constructed innovatively. Further studies demonstrated that the local thermal effect not only stimulates the activity of the small polaron semiconductor TiO₂, but also accelerates the charge transfer and surface dynamic reaction from the aspects of kinetics and thermodynamics. Simulation and experimental results also showed that the surface plasmon resonance (SPR) effect of Au NPs and the up-conversion fluorescence characteristics of CQDs can cooperate to improve the carrier concentration. Meanwhile, the formation of a Schottky heterojunction between Au and TiO₂, and CQDs as hole collectors synergistically promoted the bulk charge separation. Therefore, the CQDs/Au/TiO₂ photoanode achieved a remarkable H₂ evolution rate of 641.9 μL h⁻¹ cm⁻² under AM 1.5 illumination, five times higher than that of the pure TiO₂ photoanode.