Ionic conductivity of alkali-metal salts in sub- and supercritical carbon dioxide+methanol mixtures

Ionic conductivity of lithium, sodium, and potassium perfluoroacetate salts and lithium acetate in sub- and supercritical carbon dioxide+methanol mixtures is reported as a function of CO2 pressure and temperature. Although the mole fraction of salts was low (10−4–10−2), the ionic conductivity was large (∼10−5–10−4 S cm−1) compared with pure CO2 (below measurement capabilities) and CO2+methanol (∼10−7–10−8 S cm−1). In the sub-critical two-phase region, the ionic conductivity in the CO2-rich phase increased with pressure, but the conductivity decreased in the supercritical region with CO2 pressure. Solvent viscosity and ion diffusivity in the single-phase region predominantly influence conductivity, whereas it is affected by salt solubility in the two-phase region.