Electrohydrodynamic impedance investigation of silver electrode position in a thiosulphate ligand system

Abstract

Mass transfer-limited silver plating from a thiosulphate solution has been studied by means of the electrohydrodynamic (EHD) impedance technique. The aim of the investigation was to find out how the surface topography determines the measurements and through this information possibly detect the decomplexation reaction preceding the charge transfer. To that end, the rapid reduction reaction of ferricyanide to ferrocyanide in 1 M KCl was used to compare its EHD frequency response on a smooth platinum electrode and on rough Pt-modified silver electrodes, prepared by depositing a thin Pt film on silver platings obtained after different electrolysis times. Through this method, the predominating influence of the surface roughness was elucidated, even of crystallites with a characteristic diameter of 1–3 μm. In the latter case, the EHD behaviour was similar to that of a flat, partially blocked electrode, and allowed an in situ evaluation of the average active site dimension. Also, the diffusion coefficient of Ag(S 2O 3) 3− 2 has been determined by both a dc method and from EHD data in the low frequency range. As to ac impedance measurements of the electrocrystallization process, the EHD measurements presented can support the analysis of the former in the corresponding frequency domain.