Semi-integrative Voltammetry as an Efficient Tool To Study Simple Electrochemical Systems in Deep Eutectic Solvents

The utilization of deep eutectic solvents (DESs) in electrochemical studies has grown in recent years due to their low cost and environmental friendliness compared to traditional ionic liquids. However, the determination of diffusion coefficient (D) and heterogeneous constant rate (k⁰) using the traditional electrochemical approach may mask some concerns because of the high viscosity and limited conductivity in these media. In this work, it is shown that the determinations of D and k⁰ in glyceline DES by voltammetric studies using the Nicholson approach is problematic. Furthermore, the semi-integrative approach is evaluated which reveals that it is an efficient tool to determine such parameters that have a significant influence of the electrolyte viscosity and conductivity. The D values are 2.8 × 10^-8 and 4.2 × 10^-8 cm² s^-1 for Nicholson and semi-integrative approaches, respectively, using 0.05 M FeCl₃ in glyceline at 30 °C, which indicates an underestimation of D by employing the Nicholson equations. Also, k⁰ is obtained using Saveant's methodology which cannot be obtained by the typical evaluation of ΔE_p (Nicholson's approach) when ΔE_p > 200 mV as it occurs in the case of concentrations ≥ 0.25 M FeCl₃, depending on the potential scan rate.