Role of Chloride Ions on Electrochemical Deposition of ZnO Nanowire Arrays from O_2 Reduction

  • Tena-Zaera R
  • Elias J
  • Wang G
 et al. 
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Abstract

A systematic study of the role of KCl on the electrodeposition of
ZnO nanowire arrays from the reduction of oxygen in ZnCl2 solutions
was performed. Besides its role as a supporting electrolyte, other
major effects were found. An increase of KCl concentration ([KCl])
considerably decreased the rate of O2 reduction. The consequent decrease
in OH- production rate resulted in an augmentation of the ZnO deposition
efficiency, from a value around 3% for [KCl] = 5 ? 10-2 M to more
than 40% for [KCl] = 3.4 M. The increase of the deposition efficiency
mainly resulted in an enhancement of the longitudinal growth rate.
However, high [KCl] (>1 M) also favored the lateral growth of the
ZnO nanowires, resulting in diameters as big as 300 nm (in comparison
to the diameter of 80 nm obtained for [KCl] < 1 M). The observed
effects were discussed in terms of Cl- ion adsorption on the cathode
surface. The possible preferential adsorption of the anion on the
(0001) ZnO surface was emphasized. Transmission electron microscopy
revealed that the ZnO nanowires were single crystals, irrespective
of [KCl] in the electrolyte. Thus, playing with the chloride content
in the solution is an interesting way to obtain ZnO single-crystal
nanowire arrays with tailored dimensions under controlled deposition
rates. The influence of the nanowire dimensions on the optical properties
was also discussed, showing the interest of this study in the frame
of nanostructured solar cells.

A systematic study of the role of KCl on the electrodeposition of
ZnO nanowire arrays from the reduction of oxygen in ZnCl2 solutions
was performed. Besides its role as a supporting electrolyte, other
major effects were found. An increase of KCl concentration ([KCl])
considerably decreased the rate of O2 reduction. The consequent decrease
in OH- production rate resulted in an augmentation of the ZnO deposition
efficiency, from a value around 3% for [KCl] = 5 ? 10-2 M to more
than 40% for [KCl] = 3.4 M. The increase of the deposition efficiency
mainly resulted in an enhancement of the longitudinal growth rate.
However, high [KCl] (>1 M) also favored the lateral growth of the
ZnO nanowires, resulting in diameters as big as 300 nm (in comparison
to the diameter of 80 nm obtained for [KCl] < 1 M). The observed
effects were discussed in terms of Cl- ion adsorption on the cathode
surface. The possible preferential adsorption of the anion on the
(0001) ZnO surface was emphasized. Transmission electron microscopy
revealed that the ZnO nanowires were single crystals, irrespective
of [KCl] in the electrolyte. Thus, playing with the chloride content
in the solution is an interesting way to obtain ZnO single-crystal
nanowire arrays with tailored dimensions under controlled deposition
rates. The influence of the nanowire dimensions on the optical properties
was also discussed, showing the interest of this study in the frame
of nanostructured solar cells.

Author-supplied keywords

  • 111
  • 16706 - 16711
  • c 2007
  • chem
  • j
  • phys

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Authors

  • Ramon Tena-Zaera

  • Jamil Elias

  • Gillaume Wang

  • Claude Lévy-Clément

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