Adsorption and oxidation pathways of thiourea at polycrystalline platinum electrodes

The present paper is related to study the adsorption and oxidation of thiourea (TU) on platinum electrodes in 0.1 M perchloric acid. A systematic electrochemical investigation was performed combining cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) techniques to establish the nature of the species formed during these processes. It was concluded that TU adsorbs parallel on the platinum surface in the 0.20-0.55 (I)/(RHE) potential range without faradic reaction. A dual-path reaction mechanism was evidenced in the oxidation process when TU was present in solution. The first reaction takes place from dissolved TU at E > 0.55 V-RHE to form formamidine disulphide (TU)21 which is oxidized to soluble NH2CN at E > 1.30 V-RHE. The second parallel reaction occurs from adsorbed TU at E > 0.60 V-RHE and implies the formation of adsorbed species (NH2CN, SCN and S). In a following oxidation step at E > 1.10 V-RHE, N-7, CO2, and HSO4-/SO42- were produced. All these species were characterized from the spectroscopic experiments. (c) 2005 Elsevier B.V. All rights reserved.