Facilitated photoinduced electron storage and two-electron reduction of oxygen by reduced graphene oxide in rGO/TiO₂/WO₃ composites

A triple-component composite (GTW) comprising of reduced graphene oxide (rGO), TiO₂ and WO₃ was studied for the photoinduced electron storage and release. The composite was assembled through a one-step hydrothermal method using graphene oxide (GO), TiO₂ and peroxotungstic acid as the precursors. The crystal structure and morphology of the composites were characterized by X-ray diffraction (XRD) and high resolution-transmission electron microscopy (HRTEM), respectively. Monolithic WO₃ nanoplates and mixture phase TiO₂ nanoparticles were dispersed over the surface of rGO nanosheets. The photocharge and discharge tests and the reduction of Cr(VI) and H₂O₂ by the stored electrons were carried out. Compared to the composite in the absence of rGO, the composite GTW displayed a ten times higher electron storage capacity (∼115C/g) and a much faster charging rate (8 min less charging time to reach balanced E_OC); and electrons stored in GTW achieved 17% more Cr(VI) reduction efficiency and 65% higher H₂O₂ reduction rate. Two electron reduction of oxygen by the stored photoinduced electrons was indicated by the generation of H₂O₂. The highest H₂O₂ concentration reached 39.6 μM during the oxygen reduction for the composite with rGO, while no H₂O₂ was detected for the samples in the absence of rGO. Accompanied with the enhanced electrochemical oxygen reduction reaction and chemically adsorbed O₂ on the composite, the critical roles of rGO as an electron mediator to facilitate interfacial charge transfer, as the electron container to improve electron storage capacity, and as a promoter for two-electron reduction of O₂ were established.