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 (similar to 115C/g) and a much faster charging rate (8 min less charging time to reach balanced EOC); 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 mu M 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 O-2 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 O-2 were established. (C) 2017 Elsevier Ltd. All rights reserved.