Preparation of Cu2O/TiO2 nanotube arrays heterojunction and their photoelectrochemical response in visible light

Abstract

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 unmodified 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 (Voc) of Cu2O/TiO2NTs-30 was -0.629 V and reduced 0.046 V, the short-circuit current density (Isc) enhanced 4.5 times, indicating that there were many more photoelectrons accumulated on the surface of the Cu2O/TiO2 nanotube arrays heterojunction. The improved Isc 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. © 2013 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.