Role of Chloride Ions on Electrochemical Deposition of ZnO Nanowire Arrays from O₂ Reduction

Abstract

A systematic study of the role of KCl on the electrodeposition of ZnO nanowire arrays from the reduction of oxygen in ZnCl 2 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 O 2 reduction. The consequent decrease in OHproduction 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 Clion 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.

TEMPLATE ASSISTED ELECTRODEPOSITION OF HIGHLY ORIENTED ZnO NANOWIRE ARRAYS AND THEIR INTEGRATION IN DYE SENSITIZED SOLAR CELLS

“…However, both experimental procedures only differ in that in our case we have not employed KCl as supporting electrolyte. Therefore, chloride concentration plays an important role in the electrochemical ZnO nanowires nucleation-growth mechanism, results which are aligned with those reported in aqueous solution 43 . In current paper highly oriented ZnO nanowires were prepared by TAED on the pores of alumina membranes deposited on ITO (Indium Tin Oxide) substrates from dimethylsulfoxide solutions containing ZnCl 2 and O 2 as precursors.…”

Localized versus delocalized states: Photoluminescence from electrochemically synthesized ZnO nanowires

“…The electrochemical deposition ͑ECD͒ of ZnO at temperatures below 100°C, based on the reduction of dissolved molecular oxygen in aqueous solutions containing Zn 2+ ions, 5 has recently shown promising results in obtaining arrays of single crystalline ZnO nanowires with tailored dimensions. [6][7][8][9] Because of the aqueous environment, the limited purity of the involved chemicals and the low growth temperatures ͑especially when compared to typical growth temperatures used for vapor-phase epitaxial methods͒ is not a priori clear how the nanowire material compares to that of nanowires synthesized by, e.g., high-temperature vaporliquid-solid processes. 10 However, a detailed knowledge of the microscopic processes governing the optical and electronic properties of chemically synthesized nanowires is mandatory to understand, tailor, and optimize any optoelectronic device based on such nanowires.…”

EFFECT OF CHLORIDE IONS ON THE STRUCTURAL, OPTICAL, MORPHOLOGICAL, AND ELECTROCHEMICAL PROPERTIES OF Cu2O FILMS ELECTRODEPOSITED ON FLUORINE-DOPED TIN OXIDE SUBSTRATE FROM A DMSO SOLUTION

“…Therefore, in aqueous solutions, the longitudinal growth of hexagonal ZnO nanowires is favored over the lateral one, due to the reaction of Zn 2+ with hydroxyl ions adsorbed on the top of the nanowire (polar face (0001), which hinders the lateral growth 30 . However, if the chloride ion concentration is increased, these ions will be adsorbed on the top, and will not hinder the lateral growth [31][32] . As a result, hexagonal nanowires with different diameters can be performed by controlling the solution composition during the electrodeposition process.…”