In this paper, highly-ordered TiO2 nanotube (TNT) electrodes fabricated by anodization at 20 V m 0 1 M F- - based solution were annealed in O-2, N-2 and CO respectively. The surface properties of the TiO2 electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS),X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Tin+ (n =0-3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 x 10(-3) cm/s Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O-2-annealed TNT electrode. (C) 2010 Elsevier B.V. All rights reserved.