SURFACE INTERACTION OF BENZOIC-ACID WITH A COPPER ELECTRODE

Adsorption of benzoic acid at copper electrodes, obtained by electropl ating copper on gold, has been studied in 0.1 M HClO4 using a radiotra cer technique and cyclic voltammetry. Impedance spectroscopy has been applied to verify the real surface area of copper electrodes also dete rmined from voltammetric data in the double-layer region. Radiotracer measurements of adsorption have indicated that benzoic acid is surface active on copper in the entire range of potentials available to elect rochemical investigation in the perchloric acid solution, ie, from -0. 30 to 0.30 V (vs. rhe). Adsorption increases with the increase in the electrode potential and bulk concentration of benzoic acid, and reache s saturation at the surface coverage not exceeding 0.30. Exchange of t he adsorbate with the bulk benzoic acid molecules is slow but is consi derable enough to confirm reversibility of the surface process. Princi pal thermodynamic parameters of adsorption have been calculated from t he experimental surface concentration data using the Frumkin isotherm, found applicable in this case. Benzoic acid molecules are most likely oriented parallel to the surface, with radiotracer data providing no indication of change of that orientation at any potential used in this work. Despite apparent lack of reorientation, benzoic acid adsorption on copper is similar to that on polycrystalline gold, particularly if the rates of the surface process, the Gibbs energies of adsorption an d the degrees of the surface/bulk exchange are compared for both syste ms.