Graphene-wrapped TiO2nanofibers with effective interfacial coupling as ultrafast electron transfer bridges in novel photoanodes

Abstract

For TiO2-based photoanodes, the interfacial coupling between TiO2 and conductive materials (e.g., carbon) plays a vital role in determining the electron transfer efficiency and thus photoelectrical performance. In this paper, we describe a facile approach to effectively engineering the interfacial coupling between reduced graphene oxide (RGO) and TiO2 in well-designed one-dimensional (1D) RGO-wrapped TiO2 nanofibers, which act as ultrafast electron transfer bridges when implanted in photoanodes. The 3–5 nm RGO nanoshells were hybridized with TiO2 nanofibers as an electron donor component via d–π electron orbital overlap between C and Ti atoms, by adopting a thermal reduction at 450 °C. Remarkable photoelectric improvement, in terms of high photocurrent density by 2.2-fold and ultralow charge transfer resistance (Rct) by 0.2-fold, is ascribed to the interfacial charge transfer. Completely reduced RGO in RGO/TiO2 nanofibers was not necessary at the expense of their hydrophilicity, as it led to unexpected isolation in the photoanodes. The thermal reduction temperature of RGO/TiO2 nanofibers was found to be critical, and a maximal photocurrent density could be achieved by 2.7-fold at 530 °C. An excess of RGO/TiO2 nanofibers of more than 5 wt% had a degrading effect on the photoelectrical activity, largely due to the light-block effect and isolation in the matrix. This strategy provides new insight for tuning the intrinsic chemical and/or physical properties of well-designed semiconductor nanostructures with promising photoactivities in highly efficient photovoltaic devices.