Efficient H 2 production by water-splitting using indium–tin-oxide/V-doped TiO 2 multilayer thin film photocatalyst

Abstract

In order to sensitize TiO 2 in visible light and to reduce photo-induced charge recombination, the multilayer films of Indium–Tin Oxide (ITO)/V-doped TiO 2 were synthesized by radio-frequency magnetron sputtering. V-doped TiO 2 thin films showed red shift in TiO 2 absorption edge with increasing dopant concentration and, most importantly, the dopant energy levels are formed in the TiO 2 band gap due to V 5+/V 4+ ions as confirmed by UV–Visible and XPS spectra. Multilayer films with different numbers of ITO/V-doped TiO 2 (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 TiO 2 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 TiO 2. The measured enhanced photocurrent is attributed to: 1) ability of V-doped TiO 2 to absorb visible light, 2) number of space-charge layers in form of ITO/TiO 2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the space-charge layer by decreasing the V-doped TiO 2 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 H 2 production rate.