Effect of Annealing Temperature on the Hydrogen Production of TiO2 Nanotube Arrays in a Two-Compartment Photoelectrochemical Cell

Due to the energy crisis, it is necessary to develop clean and renewable energy sources. In this study, we report an efficient and economical technology to produce hydrogen from solar energy by splitting water in a two-compartment photoelectrochemical (PEC) cell without any external applied voltage. To enhance the solar conversion efficiency, highly ordered TiO2 nanotube arrays with 4 mu m in length were synthesized by a rapid anodization process in ethylene glycol electrolyte. Crystal phase and morphology of the TiO2 nanotubes (NTs) samples annealed at various temperatures were characterized by XRD and FESEM. Transient photocurrent response and linear sweep voltammetry curves were measured using electrochemical working station under solar light illumination. The photocatalytic activity was evaluated by the hydrogen production in the PEC cell. The results indicated that the crystal phase and morphology of TiO2 NTs had no great changes at low annealing temperatures. Anatase phase and tubular structure of TiO2 NTs were stable up to 450 degrees C. With further increase in temperature, the crystallization transformation from anatase to rutile phase appeared, accompanied by the destruction of tubular structures. Due to the excellent crystallization and the maintenance of tubular structures, TiO2 NTs annealed at 450 degrees C exhibited the highest photoconversion efficiency of 4.49% and maximum hydrogen production rate of 122 mu mol/(h.cm(2)), which is superior to most of those reported so far.