Electrochemical determination of ferrocene diffusion coefficient in [C6MIM][PF6]-CO2 biphasic system

Diffusion coefficient is an important property in chemical industry and precise measurements can be achieved by electrochemical techniques. Study of ferrocene diffusion was carried out in 1-hexyl-3-methyl imidazolium hexafluorophosphate-dense CO₂ (C₆MIM]PF₆-CO₂]) biphasic system using microelectrode technique. Diffusion coefficients were determined by cyclic voltammetry and Randles-Šev?ík relationship in the temperature and pressure ranging from 303.15 to 333.15 K and 1-10 MPa, respectively. Computed phase simulations were also used. Two-phase system was determined whatever experimental conditions and composition tested. Volumes of heavy and light phase were estimated as well. Both electroanalytical and computed studies showed that C₆MIM]PF₆]-CO₂ biphasic system containing initial molar fraction of CO₂ up to 0.9 can be used without decrease in diffusion coefficient values. The order of magnitude of these diffusion coefficients of ferrocene in greener aprotic media is about 10⁻⁶ m² s⁻¹. Theoretical analysis of ferrocene mass transport was also carried out using Sutherland formula and viscosity model based on Eyring's absolute rate theory. Dramatic decrease in C₆MIM]PF₆]-CO₂ mixture viscosity with x(CO₂) was estimated by calculations.