Black Ni/Si-doped TiO2 nanostructures were successfully fabricated through electrochemical anodization of Ti-1Ni-55i alloy and Sn-reduction treatment. After Sn-reduction treatment, the band gap of Ni/Si-doped TiO(2 )became much smaller compared to other samples, which can be attributed to the synergetic effect of Ni/Si doping and the large quantity of Ti3+/Voxygen vacancy species induced by Sn-reduction treatment. The black Ni/Si-doped TiO2 nanostructures exhibited a remarkable enhancement in the photoelectrochemical (PEC) water splitting in comparison with the pure TiO2 and Ni/Si-doped TiO2. The highest photocurrent reached 2.15 mA/cm(2) (at 0 V versus Ag/AgCl), corresponding to a conversion efficiency (similar to 1.10%) which was 5.8 times that of the pure TiO(2 )nanotubes. The first-principles calculations using density-functional theory (DFT) showed that ion doping and self-doped Ti(3+ )defect levels in the forbidden gap induced through Snreduction treatment could improve the mobility of photogenerated carriers and suppress charge recombination, which was in well agreement with the experimental results. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.