Electrochemistry in supercritical trifluoromethane

The use of trifluoromethane (CHF3) as a solvent for electrochemical studies in supercritical conditions is analyzed. The dielectric and electrical conductivity of supercritical CHF3 was measured at 323.15 K at several densities. The solubility and electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF6) and decamethylferrocenium hexafluorophosphate (Fe(Cp*)2PF6) in supercritical CHF3 were measured at 323.15 K as a function of density. It was found that, in spite of the high ion pair formation of the TBAPF6 in the supercritical solvent, this salt is a suitable supporting electrolyte, having a conductivity much higher than that reported for other electrolytes in low dielectric constant supercritical solvents. The limiting currents measured for decamethylferrocene (Fe(Cp*)2) and decamethylferrocenium hexafluorophosphate (Fe(Cp*)2PF6) at a platinum microdisc in supercritical CHF3 at several densities and 323.15 K, show the feasibility of using the proposed supercritical system as a model for electrochemical studies in variable density media. The effect of concentration of the supporting electrolyte on the limiting current at the microelectrode is qualitatively discussed in terms of a recent theory which takes into account the ion association of the supporting and electroactive electrolytes.