Kinetic and Interfacial Aspects of Bi(III) Ion Electroreduction in the Presence of Acetonitrile and 2-Thiouracil.

Both bulk solution properties and the molecular organisation of the electrode/solution interface may influence the kinetics and reversibility of an electrode process. In this study, the effects of acetonitrile (ACN) and 2-thiouracil (2-TU) in an acidic perchlorate medium on the electroreduction of Bi(III) ions were investigated. A cyclically renewable liquid silver amalgam film electrode (R-AgLAFE) was used as the working electrode as an alternative to classical mercury electrodes. Direct current polarography (DC), square-wave voltammetry (SWV), cyclic voltammetry (CV), and differential capacitance measurements were used. Increasing the ACN content from 0(v/v) to 50%(v/v) decreased the current response, Dox, and effective kinetic parameters α and ks,app while increasing ΔEp, indicating decreased apparent reversibility of the electrode process. The addition of 2-TU caused a pronounced increase in the SWV peak current and a decrease in the difference between the anodic and cathodic peak potentials. In the 50%(v/v) ACN solution, the accelerating effect was weakest at the highest 2-TU concentration. The differential capacitance measurements provided evidence consistent with significant reorganisation of the interfacial layer. Overall, the observed acceleration associated with 2-TU is consistent with adsorption-dependent interfacial effects and the possible participation of labile Bi(III)-2-TU-associated species in the near-electrode region.