CHANGES OF THE SPECIFIC SURFACE-ENERGY OF GOLD DUE TO THE CHEMISORPTION OF SULFATE

Changes of the specific surface energy of sputtered gold films on an oscillating quartz plate were measured by Koesters laser interferometry as functions of the electrode potential and of the concentration of sulphate in aqueous solutions of different pH simultaneously with changes of mass and current density. Impedance spectra were obtained under the same conditions. Equilibrium with respect to adsorbed mass was attained much faster than equilibrium with respect to electrode deformation. The potential of zero charge was independent of pH in the concentration range investigated. Capacitances derived from specific surface energies agreed well with those obtained from impedance spectra. The time dependence of the surface energy corresponds to a frequency dependence of the double-layer capacitance. The frequency dependence of the double-layer capacitance was characterized by a constant-phase element (CPE) with impedance Z(CPE) = (1/B)(j omega)(-alpha). The parameters B and alpha were independent of frequency, but depended on the electrode potential. It was concluded that the CPE behaviour is probably due to energy dissipation in the solid during potential perturbation.