IMPEDANCE ASPECTS OF ANION ADSORPTION ON GOLD SINGLE-CRYSTAL ELECTRODES

In order to explore the origins of the capacitance dispersion observed for single crystal electrodes, voltammetric and impedance measurement s on Au(111) and Au(100), in the absence and the presence of specifica lly adsorbed anions, mostly Br-, have been carried out. Interfacial ca pacitances and rate coefficients characterizing the kinetics of adsorp tion have been evaluated from the impedance spectra. We present eviden ce that the double layer behaves as an ideal capacitance in the absenc e of specific adsorption. The approximation with a constant phase elem ent yields an exponent larger than 0.99. The ''capacitance dispersion' ' observed in the presence of specific adsorption is either assigned t o a slow diffusion or adsorption process, or to transformations within the adlayer or the substrate surface.