CHARACTERIZATION OF AU(111) AND AU(210) AQUEOUS-SOLUTION INTERFACES BY ELECTROCHEMICAL IMMITTANCE SPECTROSCOPY

Gold single crystals oriented to expose the (111) and (210) faces were investigated using electrochemical immittance spectroscopy (EIS) in a queous solutions of HClO4 and KF in the double layer region with the a im of identifying and explaining the frequency dispersion of interfaci al capacitance known as constant phase angle (CPA) dispersion. Au(111) and Au(210) were chosen as representing the whole range of variance o f electrochemical properties of Au(hkl) electrodes. Au(111) as the mos t uniform, microscopically smooth surface behaved with almost ideal ca pacitance in HClO4 solutions in the whole potential range and also in KF solutions, in that case with the exception of potentials well posit ive to the potential of zero charge (pzc). Au(210) being microscopical ly the most corrugated surface displayed significant CPA dispersion in both electrolytes. In HClO4, dispersion on Au(210) occurred mostly in the potential region slightly positive to the potential of zero charg e where the capacitance hump of the Helmholtz layer appeared. Analogou s dispersion occurred on Au(210) in KF solutions only at high concentr ations. The behaviour closest to ideal, dispersionless behaviour was a lways observed at sufficiently negative potentials. In KF solutions at positive potentials dispersion on both electrodes may be attributed t o the adsorption (OH-, HF). In the intermediate potential range, close to the Helmholtz capacitance hump it can be attributed to solvent-met al interactions. Dispersion was lower in well conducting (concentrated ) electrolytes and this suggests its geometrical nature is related pos sibly to the fractal pattern of the structured solvent. (C) 1998 Elsev ier Science S.A. All rights reserved.