ZnO nanowire arrays appear as one of the most promising building blocks for photoelectrochemical devices. ZnO can be
efficiently sensitized to solar light absorption by lining its surface with a solar light absorber or by doping with metal
transition impurities. The particular morphology of ZnO nanowires may induce light scattering, increasing solar light
absorption in the sensitizer. The electrodeposition of ZnO nanowire arrays from oxygen reduction was investigated in
this work using Zn2+ precursor salts such as ZnSO4 and Zn(CH3COO)2 instead of the most frequently used ZnCl2.
Important differences in the dimensions of the obtained nanowires were observed. The influence of the adsorbing
behavior of Cl-, SO4- and CH3COO- anions on the growth mechanism was discussed depending of the Zn2+ precursor.
The anion concentration in solution was determined not only by the zinc precursor, but also by the supporting electrolyte
(NaCl, Na2SO4 and CH3COONa) concentrations. By using anions that exhibit different adsorbing properties on the
different ZnO crystalline faces, a new strategy was developed to tailor the dimensions of the ZnO nanowires. The effects
of nanowire length on the light scattering were investigated by optical spectroscopy. An overview of the influence of
these effects on the sensitization of ZnO nanowires to solar light was presented by using ZnO/CdSe core-shell nanowires
as an example.
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.
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