INSITU RAMAN-SPECTROSCOPIC STUDIES ON COADSORPTION OF THIOUREA WITH ANIONS AT SILVER ELECTRODES

Thiourea (TU) adsorbed at Ag electrodes both in neutral and acidic solutions has been studied using surface enhanced Raman (SER) spectroscopy and differential capacitance measurements. The coadsorption of TU with anions may be through the NH2 group in neutral solutions, and the NH+3 group in acidic solutions respectively. Replacement of ClO-4 ions coadsorbed with TU by Cl- ions can only take place at more negative potentials as TU changes orientation at the surface. The different orientations of adsorbed TU have substantial effects on the H2 evolution at Ag electrodes. In neutral solutions the H2 evolution is catalysed by the TU adsorbed parallely to the surface, however, in acid media the H2 evolution is inhibited considerably by the TU adsorbed perpendicularly. © 1990.