Unveiling Two Electron-Transport Modes in Oxygen-Deficient TiO2 Nanowires and Their Influence on Photoelectrochemical Operation

Introducing oxygen vacancies (VO) into TiO2 materials is one of the most promising ways to significantly enhance light-harvesting and photocatalytic efficiencies of photoelectrochemical (PEC) cells for water splitting among others. However, the nature of electron transport in VO-TiO2 nanostructures is not well understood, especially in an operating device. In this work, we use the intensity-modulated photocurrent spectroscopy technique to study the electron-transport property of VO-TiO2 nanowires (NWs). It is found that the electron transport in pristine TiO2 NWs displays a single trap-limited mode, whereas two electron-transport modes were detected in VO-TiO2 NWs, a trap-free transport mode at the core, and a trap-limited transport mode near the surface. The considerably higher diffusion coefficient (Dn) of the trap-free transport mode grants a more rapid electron flow in VO-TiO2 NWs than that in pristine TiO2 NWs. This electron-transport feature is expected to be common in other oxygen-deficient metal oxides, lending a general strategy for promoting the PEC device performance.