Self-organized highly oriented TiO₂ nanotube arrays have been obtained by anodization of a Ti sheet in fluoride-containing electrolytes.Cu₂O/TiO₂ nanotube arrays heterojunction have been fabricated by electrochemical methods. The content of Cu₂O loaded on the arrays was controlled by varying the electrodeposition time. The samples have been characterized by scanning electron microscopy (SEM) and UV-vis absorption spectrum. In addition, visible photoelectric conversion and photocatalytic water splitting performance of composite electrode materials were characterized under visible light with the measured density of 100 mV·cm^-2. The results demonstrated that all Cu₂O/TiO₂ nanotube arrays heterojunction had a strong absorption in the visible region which suggested that the composite Cu₂O/TiO₂ nanotubes could make more efficient use of visible light compared with the unmodi?ed TiO₂ nanotubes. Simultaneously, p-n heterojunction was formed between Cu₂O and TiO₂ and the p-n junction was equivalent to a single directional conductive diode that allows electrons to flow from the n-type to the p-type, but the backward flow was prohibited. They could enhance the charges transport and reduce the recombination rate of electrons and holes effectively. Separating the electron-hole pairs in different semiconductors could induce a potential difference at the heterojunction interface. Moreover when the electrodeposition time was 30 min, Cu₂O particles were uniform and almost covered the surface of TiO₂ nanotubes. Comparing with the composite Cu₂O/TiO₂ nanotubes prepared by other electrodeposition time, Cu₂O/TiO₂ nanotube arrays heterojunction fabricated by electroplating for 30 min, noted by Cu₂O/TiO₂NTs-30, had better performance of photoelectrochemical response in visible light, the visible photoelectric conversion and photocatalytic water splitting efficiency were both the highest. Compared with TiO₂ nanotube arrays, though the open-circuit voltage (V_oc) of Cu₂O/TiO₂NTs-30 was -0.629 V and reduced 0.046 V, the short-circuit current density (I_sc) enhanced 4.5 times, indicating that there were many more photoelectrons accumulated on the surface of the Cu₂O/TiO₂ nanotube arrays heterojunction. The improved I_sc was also reflected in the increased incident monochromatic photo-to-current conversion efficiency (IPCE), the IPCE response at the maximum absorption wavelength was enhanced almost 6 times.

Key words: TiO₂ nanotube arrays, Cu₂O, visible light, photo-splitting water, photoelectric conversion