Preparation of Cu2O/TiO2 Nanotube Arrays Heterojunction and Their Photoelectrochemical Response in Visible Light

Self-organized highly oriented TiO2 nanotube arrays have been obtained by anodization of a Ti sheet in fluoride-containing electrolytes. Cu-2O/TiO2 nanotube arrays heterojunction have been fabricated by electrochemical methods. The content of Cu-2O 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 Cu-2O/TiO2 nanotube arrays heterojunction had a strong absorption in the visible region which suggested that the composite Cu-2O/TiO2 nanotubes could make more efficient use of visible light compared with the unmodified TiO2 nanotubes. Simultaneously, p-n heterojunction was formed between Cu-2O 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, Cu-2O particles were uniform and almost covered the surface of TiO2 nanotubes. Comparing with the composite Cu-2O/TiO2 nanotubes prepared by other electrodeposition time, Cu-2O/TiO2 nanotube arrays heterojunction fabricated by electroplating for 30 min, noted by Cu-2O/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 Cu-2O/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 Cu-2O/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.