Adsorption of thiourea on monocrystalline copper electrodes

The adsorption of thiourea on polycrystalline and monocrystalline copper el ectrodes of basal indices: (111), (100) and (110) was studied by radiometri c and electrochemical methods. The measurements were carried out in perchlo ric acid solution at ambient temperature. Thiourea labeled with C-14 was us ed in the experiments. The dependence of the surface concentration of thiou rea on the electrode potential and on the bulk concentration was determined for each studied surface. Based upon the obtained radiometric data it can be stated that adsorption of thiourea on investigated copper electrodes tak es place in the entire range of the applied potential range, The adsorption process is mainly reversible at constant potential which allowed us to det ermine adsorption isotherms and also to calculate values of the Gibbs energ y of adsorption for the copper surfaces studied. The calculated values of s urface concentration of the adsorbed species were different and dependent o n a copper plane whereas the Gibbs energy of adsorption was practically the same. This means that the energy of interaction of TU molecules with adsor ption sites on copper electrodes is similar and the differences in surface concentrations Gamma (max), are mainly due to the different number of adsor ption sites, i.e. the surface atom density of individual planes of Cu elect rodes. (C) 2001 Elsevier Science Ltd. All rights reserved.