Adsorption of thiourea on copper electrodes monitored by in situ infrared spectroscopy

In situ infrared (IR) spectroscopy was used to monitor the adsorption of thiourea onto copper electrodes in 0.5 M sulfuric acid solutions sunder cathodic polarization. At potentials negative of the open-circuit potential, p-polarized IR spectra provided evidence for the partial desorption of TU. The desorption had a reversible character as indicated by the recovery of the spectra upon reestablishing open-circuit conditions. Thiourea bands appearing in s-polarized spectra at very negative potentials were attributed to deprotonation of thiourea within the thin-layer gap of the cell resulting from hydrogen ion reduction. Both the bulk, s-polarized, and surface, p-polarized, spectra showed bipolar symmetric N-C-N vibrational bands. The bands were attributed to changes in N-C-N bond order resulting from protonation of the S atom or adsorption of the thiourea via the S atom, respectively.