Efficient H2 production by water-splitting using indium–tin-oxide/V-doped TiO2 multilayer thin film photocatalyst

In order to sensitize TiO2 in visible light and to reduce photo-induced charge recombination, the multilayer films of Indium–Tin Oxide (ITO)/V-doped TiO2 were synthesized by radio-frequency magnetron sputtering. V-doped TiO2 thin films showed red shift in TiO2 absorption edge with increasing dopant concentration and, most importantly, the dopant energy levels are formed in the TiO2 band gap due to V5+/V4+ ions as confirmed by UV–Visible and XPS spectra. Multilayer films with different numbers of ITO/V-doped TiO2 (6 at.%) bilayers (namely, 2-, 3-, 4-, 5-, 6- and 7-bilayers) were deposited, in order to reduce the charge recombination rate, by keeping the total thickness of TiO2 constant in each multilayer film. In multilayer films, when exposed to visible light the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/V-doped TiO2. The measured enhanced photocurrent is attributed to: 1) ability of V-doped TiO2 to absorb visible light, 2) number of space-charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the space-charge layer by decreasing the V-doped TiO2 layer thickness. The reduced charge recombination rate in multilayer films was also confirmed by the photocurrent kinetic curves. The superior photocatalytic efficiency of the 6-bilayers film is also reflected in hydrogen production rate through water-splitting: we obtained indeed 31.2 μmol/h of H2 production rate.