The reduction of l-cystine hydrochloride at stationary and rotating disc mercury electrodes

Ralph, T.R., Hitchman, M.L., Millington, J.P. and Walsh, F.C. (2005) The reduction of l-cystine hydrochloride at stationary and rotating disc mercury electrodes. Electrochimica Acta, 51 (1), 133-145. (doi:10.1016/j.electacta.2005.04.012).

Abstract

The kinetics of l-cystine hydrochloride reduction have been studied at a mercury-plated copper rotating disc electrode (RDE) and at a stationary mercury disc electrode (SMDE) in 0.1 mol dm?3 HCl at 298 K. The reduction of the disulphide is irreversible and hydrogen evolution is the major side reaction. In contrast to steady state electrode kinetic studies at a mercury drop electrode (which shows a well-defined limiting current), the mercury-plated Cu RDE shows overlap between disulphide reduction and hydrogen evolution. These effects are attributable to strong reactant adsorption with a calculated surface coverage close to 100%. A Tafel slope of ?185 mV per decade is found with a cathodic transfer coefficient of 0.32 and a formal rate constant of 6.7 × 10?9 m s?1. The relative merits of steady state voltammetry at a mercury-plated copper RDE and linear sweep voltammetry at the SMDE are discussed, as is the mechanism of l-cysteine hydrochloride formation.

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