Influence of the silver electrode surface structure on electrochemical adsorption of thiourea in perchloric acid solution

Electrosorption of thiourea (TU) on single crystal electrodes: Ag(111), Ag(100) and Ag(110) was studied using electrochemical and radiochemical methods. A radiotracer method, with TU labeled with C-14 in 0.1 M HClO4, was used to determine the surface concentration of the adsorbate. From radiometric data it follows that adsorption of TU is reversible with respect to the bulk concentration and the potential in the range of ideal polarizability of electrodes. The maximum surface concentration of TU, determined radiometrically, follows the sequence: Ag(111) > Ag(100) > Ag(110), which is in agreement with the atom surface density of the silver planes. The simple Langmuir adsorption equation describes experimental data up to 80% of surface coverage. The Gibbs energy of adsorption is similar (25.5 +/- 1 kJ/mol) for all planes studied.