Electrochemical response of thiourea and formamidine disulphide on polycrystalline platinum in aqueous 0.5 M sulphuric acid

The electrochemical response of both thiourea and formamidine disulphide dissolved in aqueous 0.5 M sulphuric acid on polycrystalline platinum electrodes is investigated at 298 K, using voltammetry and rotating ring-disk electrode techniques. The electro-oxidation of thiourea on platinum involves two stages occurring in different potential windows. The first thiourea electro-oxidation stage for E < 0.7 V (vs. SCE), yielding soluble formamidine disulphide as the main product, behaves as an electrochemical process under intermediate kinetics. Kinetic parameters for the electro-oxidation of thiourea are estimated. The voltammetric electroreduction of formamidine disulphide dihydrochloride to thiourea is inhibited gradually by the adsorption of byproducts from the electrochemical reactions. The second thiourea electro-oxidation stage for E > 0.7 V involves the oxidation of thiourea and adsorbed residues competing with the oxide monolayer formation on platinum. (C) 1999 Elsevier Science S.A. All rights reserved.