Unveiling two electron-transport modes in oxygen-deficient TiO₂ nanowires and their influence on photoelectrochemical operation

Introducing oxygen vacancies (V_O) 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 V _O-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 V_O-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 V_O-TiO ₂ NWs, a trap-free transport mode at the core, and a trap-limited transport mode near the surface. The considerably higher diffusion coefficient (D_n) of the trap-free transport mode grants a more rapid electron flow in V_O-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.