title: Enhanced Photoelectrochemical Activity of ZnO-Coated TiO2 Nanotubes and Its Dependence on ZnO Coating Thickness.
abstract: One-dimensional heterogeneous nanostructures in the form of ZnO-coated TiO2 nanotubes (ZnO/TiO2 NTs) were fabricated by atomic layer deposition of an ultrathin ZnO coating on electrochemical anodization-formed TiO2 nanotubes (NTs) with the thickness of ZnO coating being precisely controlled at atomic scale, and the photoelectrochemical activity of the fabricated ZnO/TiO2 NTs and the influence of ZnO coating and its thickness were studied. The structures of TiO2 NTs and ZnO coatings were characterized by X-ray diffraction, Raman backscattering spectroscopy, and transmission electron microscopy. The photoelectrochemical activity was studied through the measurements of electrochemical impendence, flat-band potential, and transient photocurrent density. The TiO2 NTs exhibit anatase structure, and the ZnO coatings are structured with hexagonal wurtzite. The photoelectrochemical activity of the ZnO/TiO2 NTs is strongly dependent on the thickness of ZnO coating. ZnO/TiO2 NTs with a thinner rather than a thicker ZnO coating exhibit better photoelectrochemical activity with reduced charge transfer resistance, increased negative flat-band potentials, and enhanced photocurrent densities. Under visible illumination, an increase of about 60 % in the photoelectrochemical activity is obtained for ZnO/TiO2 NTs with an about 2-nm-thick ZnO coating.
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Cai
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Peipei
authors.initials: P
authors.lastname: Liang
authors.affiliation: Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, 200241, China.
authors.forename: Zhigao
authors.initials: Z
authors.lastname: Hu
authors.affiliation: Institute of Modern Physics, Fudan University, Shanghai, 200433, China.
authors.forename: Liqun
authors.initials: L
authors.lastname: Shi
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Xu
authors.affiliation: Department of Optical Science and Engineering, Fudan University, Shanghai, 200433, China. jdwu@fudan.edu.cn.
authors.forename: Jiada
authors.initials: J
authors.lastname: Wu
keywords: Heterogeneous nanostructure; Photoelectrochemical activity; TiO2; ZnO; ZnO-coated TiO2 nanotube