Electrochemical investigations in supercritical fluids and other non-polar media
thesisposted on 15.12.2014, 10:35 by John. Harper
This thesis describes the use of novel electrolytes in media of extremely low relative permittivity. Double layer capacitance, conductivity and voltammetric experiments are presented and attempts are made to elucidate the ionic entities in solution and at the electrode / solution interface. Charge is found to be predominantly carried by triple ions and these have a surprisingly appreciable influence on the double layer structure.;Voltammetric responses are presented in dichloroethane (DCE), anisole (Anis) and cyclohexane (cHex) and it is shown that the reversibility of a process is affected by the length of the tetraalkylammonium chain of the electrolyte. Reversible responses are only observed at very slow sweep rates, and this is a result of the slow electrode desorption kinetics of the electrolyte ions. This has profound consequences for electrochemical studies made in non-aqueous media using quaternary ammonium electrolytes.;Finally, bulk electrolysis experiments are performed in scCO2/water mixtures. It is shown that formate and hydrogen are primarily formed on a platinum surface, whereas oxalate and hydrogen are the major products on lead. This is ascribed to a change in reaction pathway compared to such studies in aqueous media. Supercritical fluids are shown to have significant advantages over liquid solvents for the electrochemical reduction of CO2.