Photoelectrochemical (PEC) water splitting based on doping-modified one-dimensional (1D) TiO2 is a promising approach to sustainable hydrogen evolution. Here we successfully fabricated high-efficiency reduced Ti-Si-O nanotubes photoanode through anodizing two-phase Ti Si alloy and one step NaBH4 reduction, and investigated its PEC water splitting properties. It was found that Si-doped TiO2 nanotubes mainly grew at the alpha-Ti region of Ti-5Si alloy substrate, and they easily dissolved at the Ti5Si3 phase region of the alloy. Both Si element and Ti3+/oxygen vacancy (V-o) were successfully doped into the oxide nanotubes, resulting in enhanced optical absorption and facilitated separation of photogenerated electron-hole pairs. The reduced Ti-Si-O nanotubes photoanode with co-doped Si element and Ti3+/V-o could have a high photocurrent density of 1.39 mA/cm(2) at 0 V vs. Ag/AgCl. The solar to hydrogen efficiency could reach 0.88% and it was 4.89 times that of undoped TiO2. It demonstrated that co-doping of Si and Ti3+/V-o shows great potential in improving the PEC water splitting properties of undoped TiO2. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.