Urea adsorption on Pt(111) electrodes

The urea adlayers formed at the surface of Pt(111) electrodes immersed in urea-containing perchloric acid solutions have been characterized in situ by a combination of cyclic voltammetry, charge displacement and FTIRS experiments. The data obtained concern the potential-dependent changes in coverage and bonding geometry for the adsorbed urea molecules. In this respect, the infrared spectra obtained at potentials lower than 0.50 V suggest that the adsorbed urea species are bonded through only one of the nitrogen atoms. O-bonded urea molecules appear at higher potentials, being the major species at potentials around 0.70 V, for which saturation is attained. The absolute urea coverage has been estimated from the voltammetric experiments and found to be around 0.45. This value has been confirmed by a thermodynamical analysis of the charge densities involved in the formation of the urea adlayer for different potentials and urea concentrations. The charge density and coverage values are consistent with a net exchange of one electron per adsorbed urea molecule. All these data are compared with those previously reported for the Pt(100) electrode. (C) 1994 Elsevier Science S.A. All rights reserved.