Steady-state macroscale voltammetry in a supercritical carbon dioxide medium

Abstract

The electrochemical oxidation and reduction of decamethylferrocene is demonstrated in supercritical carbon dioxide at a macro gold disc electrode at 100 bar and 313 K. Fast mass transport effects were exhibited and the corresponding steady-state voltammetry was observed at high scan rates. A highly lipophilic room temperature ionic liquid that readily dissolved in supercritical CO 2 with acetonitrile as a co-solvent was used as an electrolyte, allowing for a conducting supercritical single phase. Experimental observations along with simulation results confirmed the hypothesis that a thin layer of liquid-like phase of co-solvent is formed at the electrode surface and is restricted by a more supercritical phase of high natural convection and bulk concentration.

Electrochemical studies of decamethylferrocene in supercritical carbon dioxide mixtures

“…Recently Toghill et al 7 suggested, based on their experimental data for the voltammetry of DMFc in scCO 2 /MeCN, that a 60 mm thick liquid layer formed at the working electrode surface and that all of the voltammetry occurred within this layer. This conclusion was based on the results of voltammetry at macrodiscs at scan rates of 25-1000 mV s À1 .…”

Electrochemistry in supercritical fluids: A mini review

“…This was particularly noted in a recent publication by Toghill et al [21] in which macroscale voltammetry of decamethylferrocene (DMFc) was undertaken in a scCO 2 /acetonitrile medium. At moderately fast scan rates the DMFc voltammetric signal transitioned from macroscale peak shape to a steady state profile (Fig.…”

“…An alternative strategy proposed to enhance the ionic conductivity of the scCO 2 is to add a highly polar and miscible co-solvent. To-date methanol [18,19], dimethylformamide [20] or acetonitrile [18,21] has been employed. Organic co-solvents form a single phase with scCO 2 and considerably improve the solubility of ionic species.…”

Measurements of the double layer capacitance for electrodes in supercritical CO2/acetonitrile electrolytes

“…Addition of acetonitrile (CH 3 CN) as a polar co-solvent increases the effective dielectric constant for the fluid and hence the solubility of electrolytes and the solution conductivity [20]. Supercritical CO 2 /CH 3 CN has been used in our group for the electrodeposition of both copper [14] and silver [15] and Toghill et al [21] synthesised and purified as described elsewhere [13,20]. Carbon dioxide (99.999 % SCF grade, BOC) was used without further purification.…”