Surface-reduced Si-doped TiO2 nanotubes for high-efficiency photoelectrochemical water splitting

TiO2 is a promising photocatalyst in the reaction of water splitting for hydrogen. Here, we used NaBH4 reduction reaction to introduce Ti3+/V-O defect states into Si-doped TiO2 nanotubes and investigated the photoelectrochemical water splitting properties. It was found that the photocatalytic activity was improved through NaBH4 reduction because of the existence of Ti3+/V-O. The defect states (Ti3+/V-O) could play a role of capture trap and accelerate the separation of photogenerated electrons and holes. The photocurrent density of the Si-doped TiO2 nanotubes reduced for 3 h was 1.5 mA/cm(2) compared to 0.7 mA/cm(2) of the unreduced nanotubes. The conversion efficiency was 0.7%, which was almost 4 times than that of pure TiO2. On the other hand, reduction for a long time would generate excess defect states and thus cause the decrease of photocurrent density. Excess defect states could act as the recombination centers of photogenerated electrons and holes.