TiO2 nanotube arrays can be synthesized by several experimental procedures. Here we construct the first theoretical model of the array. Based on the density functional theory calculations, the formation energy of the TiO2 nanotube array is nearly the same as that of rutile TiO2 (1 1 0) surface. Moreover the electronic properties of TiO2 nanotube arrays have been analyzed. The thermodynamic properties of H2O splitting on the TiO2 nanotube and nanotube arrays have been discussed using the density functional theory calculations and Gibbs free energy diagrams. The overpotential of H2O splitting is 0.51 and 1.0 eV on the outside and inside of nanotube and 1.13 eV on the inside TiO2 nanotube of an array. (c) 2010 Elsevier B.V. All rights reserved.