Efficient H 2 production by water-splitting using indiumetin-oxide/V-doped TiO 2 multilayer thin film photocatalyst R. Dholam*, N. Patel, A. Miotello Dipartimento di Fisica, Universita ` degli Studi di Trento, I-38123 Povo (Trento), Italy article info Article history: Received 29 November 2010 Received in revised form 28 February 2011 Accepted 7 March 2011 Available online 6 April 2011 Keywords: Photocatalytic water-splitting Hydrogen generation V-doped TiO 2 RF-magnetron sputtering Visible light irradiation Multilayer Charge recombination abstract In order to sensitize TiO 2 in visible light and to reduce photo-induced charge recombination, the multilayer films of IndiumeTin 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 absorp- tion edge with increasing dopant concentration and, most importantly, the dopant energy levels are formed in the TiO 2 band gap due to V 5þ /V 4þ ions as confirmed by UVeVisible 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 mmol/h of H 2 production rate. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction It is extremely important to use clean and renewable energy sources such as solar and wind for hydrogen production which is presently produced (about 95%) from fossil fuels by procedures that lead to increase in greenhouse gases [1]. Photocatalytic water-splitting by using solar energy could contribute to the solution of environmental and energy issues related to the hydrogen production [2]. TiO 2 semiconductor provides several advantages over other materials as a photocatalyst for hydrogen production by water- splitting such as: i) high resistant to corrosion and photo- corrosion in aqueous media, ii) cheap and easily available, iii) environmentally clean, iv) energy band edges which are well- matched with the redox level of water, and v) electronic properties that can be varied by just changing the lattice defects chemistry or the oxygen stoichiometry [3]. In addition, TiO 2 is also the most desired material for self-cleaning tech- nology and in purification of toxic compounds from polluted water and air [4e6]. However, because of the wide energy band gap (w3.2 eV) of TiO 2 , only a small fraction of solar spectrum, UV light (3e5% of total), can be used for photocatalytic * Corresponding author. Tel.: þ39 3478267397. E-mail address: rupal@science.unitn.it (R. Dholam). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 6519 e6528 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.03.028