Bi(III) Ion Electroreduction in the Presence of Ethanol and Sodium 1-Octanesulfonate at a Thin-Layer Amalgam Electrode (Renewable Liquid Silver Amalgam Film Electrode); Kinetic and Thermodynamic Aspects.

This study investigates the Bi(III) ions electroreduction in aqueous chlorate(VII) and aqueous-ethanolic chlorate(VII)-supporting electrolytes (SE) in the presence of the anionic surfactant sodium 1-octanesulfonate (1OSASS) over a range of temperatures. Electrochemical techniques, including direct current (DC) polarography, cyclic voltammetry (CV), and square-wave voltammetry (SWV), were used to evaluate both kinetic and thermodynamic parameters. Increasing ethanol concentration led to a decrease in the standard heterogeneous electron transfer rate constant (ks), despite an increase in the diffusion coefficient of the oxidised species (Dox). Rising temperature and surfactant concentration caused a shift in the formal potential (Ef 0) and an increase in redox peak separation (ΔE), indicating reduced process reversibility. Activation parameters, including activation energy (Ea), enthalpy (ΔH0), entropy (ΔS0), and Gibbs free energy (ΔG0), were determined using the Arrhenius and Eyring equations. The results confirm that 1OSASS exhibits a 'cap-pair' effect, likely due to competitive adsorption and complexation, significantly affecting redox kinetics. Overall, the study highlights the complex influence of the solvent-surfactant system on the structure of the electrical double layer (EDL) and on the kinetics and mechanism of the Bi(III) ions electroreduction process.