Simultaneous characterisation of electrode kinetics and electrolyte properties in ionic liquids using a rotating disc electrode

In this work, simultaneous characterisation of conductivity, viscosity and heterogeneous kinetics is demonstrated in a deep eutectic solvent based on choline chloride and ethylene glycol, using concurrent steady state voltammetric and impedance measurements at a rotating disc electrode. A theoretical treatment based on post-experimental correction of ohmic losses is shown to be reliable. The parameters determined at 25 °C are: standard rate constant of electron transfer k0 = 10 ± 1 × 10−4 cm s−1, charge transfer coefficient α = 0.39 ± 0.03, formal potential E0′ = 0.430 ± 0.005 V vs. Ag/AgCl, conductivity κ = 10.1 ± 0.3 mS cm−1, dynamic viscosity η = 37 ± 3 mPa s, diffusion coefficient of Cu2+DO = 1.32 ± 0.5 × 10−7 cm2 s−1 and Stokes radius of the Cu2+ complex RH = 0.33 nm.Conventional conductivity and rheometric measurements were also performed. The electrolyte conductivity and dynamic viscosity were 8.0 ± 0.3 mS cm−1 and 41 ± 3 mPa s respectively at 25 °C. These values compare well with the values determined using electrochemical methods. The deep eutectic solvent used has been shown to exhibit conductivity and viscosity comparable to modern ionic liquids based on discrete anions. The Stokes radius of the [CuCl4]2− complex formed confirms the similarity of these deep eutectic solvents to basic chloroaluminate ionic liquids.

► EIS at the RDE is performed in a deep eutectic solvent (DES). ► Gives electrode kinetics, mass transport, conductivity and viscosity of the DES. ► DES similar to room temperature ionic liquid (RTIL). ► Chlorocomplex formation confirmed. ► Facile measurement and analysis.