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 di ssolved in aqueous 0.5 M sulphuric acid on polycrystalline platinum electro des is investigated at 298 K, using voltammetry and rotating ring-disk elec trode techniques. The electro-oxidation of thiourea on platinum involves tw o stages occurring in different potential windows. The first thiourea elect ro-oxidation stage for E < 0.7 V (vs. SCE), yielding soluble formamidine di sulphide as the main product, behaves as an electrochemical process under i ntermediate kinetics. Kinetic parameters for the electro-oxidation of thiou rea are estimated. The voltammetric electroreduction of formamidine disulph ide 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 adsor bed residues competing with the oxide monolayer formation on platinum. (C) 1999 Elsevier Science S.A. All rights reserved.