Electrochemical study of thiourea and substituted thiourea adsorbates on polycrystalline platinum electrodes in aqueous sulfuric acid

Abstract

The electrochemical response of adsorbates produced on polycrystalline Pt from thiourea, methyl thiourea, 1,3 dimethyl thiourea and tetramethyl thiourea dissolved in aqueous 0.5 M sulfuric acid are comparatively studied using electrochemical routines. The adsorption kinetics of thioureas on Pt follows an Elovich-type equation. Their saturation coverage, measured from the decrease in the H-atom electrosorption charge after correction for molecular size for steric effects, decreases as the size of the molecule producing adsorbates increases. Adsorption data fulfill the empirical Frumkin isotherm with a repulsive adsorbate–adsorbate lateral interaction term. Adsorbate electrooxidation starts at about 0.65 V vs SHE. The deprotonation of hydrogen-containing thioureas yields soluble products, their electrochemical behaviour being to some extent similar to that of formamidine disulfide. For E > 0.65 V vs SHE, the oxidation of thioureas can be described as complex processes in which intermediates compete with oxide layer formation on platinum.