Adsorption of Thiourea on Copper Electrodes Monitored by In Situ Infrared Spectroscopy

Abstract

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.