Electrodeposition of arrays of ZnO nanostructures and application to photoelectrochemical devices

ZnO nano/microstructures offer the opportunity to design new types of photoelectrochemical devices. Arrays of single crystal ZnO nanowires present very interesting properties to enhance the performance in these devices. A systematic study of the deposition of single crystal ZnO nanowire arrays from the oxygen electroreduction method is reported in order to gain a further insight into the nanowire growth mechanisms and to develop an efficient electrochemical method which allows tailoring the nanowire dimensions. The influence of deposition parameters such as zinc precursor and supporting electrolyte concentrations on the formation of a polycrystalline compact ZnO layer or a ZnO nanowire array, as well as on the dimensions of the single crystal nanowires is analyzed. The effect of the polycrystalline compact ZnO buffer layer on the nanowire nucleation process and therefore on the nanowire diameter and density is also discussed. The results show that electrodeposition is a versatile and cost-effective technique which allows growing ZnO single crystal nanowire arrays with tailored dimensions. The structural and optical properties of electrodeposited nanowire arrays are discussed. ZnO nanowires can be sensitized by the coating of a thin layer of CdSe. The ZnO/CdSe photoanode exhibits excellent photoelectrochemical properties and external quantum efficiency larger than 70 % are observed in ferri/ferrocyanide solutions.