ELECTROHYDRODYNAMIC IMPEDANCE INVESTIGATION OF SILVER ELECTRODEPOSITION IN A THIOSULFATE LIGAND SYSTEM

Mass transfer-limited silver plating from a thiosulphate solution has been studied by means of the electrohydrodynamic (EHD) impedance techn ique. The aim of the investigation was to find out how the surface top ography determines the measurements and through this information possi bly detect the decomplexation reaction preceding the charge transfer. To that end, the rapid reduction reaction of ferricyanide to ferrocyan ide in 1 M KCl was used to compare its EHD frequency response on a smo oth platinum electrode and on rough Pt-modified silver electrodes, pre pared by depositing a thin Pt film on silver platings obtained after d ifferent electrolysis times. Through this method, the predominating in fluence of the surface roughness was elucidated, even of crystallites with a characteristic diameter of 1-3 mum. 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 dimensio n. Also, the diffusion coefficient of Ag(S2O3)2(3-) has been determine d by both a dc method and from EHD data in the low frequency range. As to ac impedance measurements of the electrocrystallization process, t he EHD measurements presented can support the analysis of the former i n the corresponding frequency domain.