Application of the ac admittance technique to double-layer studies on polycrystalline gold electrodes

Abstract A detailed examination of the dependence of the ac admittance of a cell containing a polycrystalline gold electrode has been made in the double-layer region as a function of dc potential, ac frequency and electrode history. It is shown that the interfacial impedance of a gold electrode with a carefully prepared surface can be treated under these circumstances as a constant phase element when it is in contact with an aqueous solution containing 0.05 M KClO 4 . Analysis of the frequency dependence of the cell impedance gives the surface inhomogeneity parameter n which turns out to be very close to unity. Although the electrode surface is only slightly inhomogeneous on a microscopic scale, a very large frequency dispersion of the impedance is observed experimentally. A method of estimating the true specific capacity of the electrode is presented, and conditions for carrying out the experiments in a reproducible manner are discussed.