In this paper in situ visible electroreflectance measurements have been carried out in order to extract new electrochemical
information from the dependence of ΔR/R on the frequency of potential modulation. The behaviour of some
typical components of a Au electrodeposition bath has been investigated: a metal salt (KAu(CN)2), a supporting electrolyte
(NaClO4), a metal cation complexing agent (KCN). The voltammetric behaviour of the relevant systems has been investigated
by means of Cyclic Voltammetry (CV) and Electrochemical Impedance Spectrometry (EIS). The optical and
current density dynamics have been compared applying a potential square-wave modulation with frequencies in the range
1÷300 Hz and have been found to exhibit clearly different time-constants. Sensitivity to the electrolyte chemistry and radiation-
wavelength have been proved for optical impedance.