Interaction Between Thiourea and Palladium Electrodes

Interction of thiourea (THU) with Pd electrodes (geometrical surface area 1.5 cm2,roughness factor f̵w =3-600) has been studied at 20°C. The roughness factor was measured by krypton adsorption. The interaction occurs by the following steps:(1) reversible adsorption of THU molecules on the surface of Pd electrode according to a simple Langmuir isotherm, in neutral medium and (2) surface hydrolosis of adsorbed THU molecules followed by the formation of a monolayer of strongly adsorbed sulphur on the surface of the Pd electrode in acidic or alkaline medium. The THU molecules are precursors of the adsorbed sulphur and an equivalence between their amounts has been found. The adsorbed sulphur has been determined by anodic oxidation by linear sweep voltammetry in 1 M NaOH. Brief comments on the interaction of Pd electrodes with other sulphur compounds (Na2S, H2S, CS2, cysteine and cystine) are also given.