Chronoamperometric determination of diffusion coefficients of ferrocene in ionic liquids mixed with CO2 at high pressures

The diffusion coefficients (D) of ferrocene have been determined by chronoamperometry in two ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([BMIM][Tf2N]) and 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)amide ([OMIM][Tf2N]) at atmospheric pressure and mixed with CO2 at high pressures (p = 1.5, 3.0, and 4.5 MPa) at two isotherms (T = 298.15 and 313.15 K) using the high-pressure electrochemical cell developed in our laboratory. The results showed that D increased with increasing pressure in two ILs, of which the dependence was well represented by a quadratic form of pressure. More remarkable increase in D with pressure was observed at lower temperature in both ILs, due to the higher solubility of CO2 at a fixed pressure. This leads to the crossing points in the plots of Dvs. p at two different temperatures, which correspond to ∼3.1 MPa for [BMIM][Tf2N] and ∼3.5 MPa for [OMIM][Tf2N].