Differential capacitance studies of the specific adsorption of thiosulfateon silver

The differential capacitance of a polycrystalline Ag electrode was measured in a NaClO4 electrolyte containing Na2S2O3 at concentrations ranging from 0.1 to 20 mM and at electrode potentials ranging from -0.9 to -0.3 V vs SCE . The differential capacitance measurements were analysed to obtain the sur face coverage of specifically adsorbed thiosulfate (S2O32-) as a function o f both electrode potential and bulk concentration. The various forms for th e adsorption isotherm at an electrochemical interface which are commonly em ployed are reviewed and discussed. The adsorption behaviour is best explain ed by the formation of image dipoles by the specifically adsorbed ions, who se energetic interactions are then dominated by repulsion of like dipoles. The adsorption data is quantitatively fit to an adsorption isotherm for int eracting dipoles, yielding an effective dipole moment of 0.72 D for the sys tem S2OS32-/Ag.