The electrodeposition of cobalt and cobalt oxides from a glyceline deep eutectic solvent is reported. Cyclic voltammetry, chronoamperometry, scanning electron microscopy, and Raman spectroscopy are employed to study the Co deposition processes. Surface analysis reveals that metallic cobalt is deposited at potentials less negative than the current peak potential whereas cobalt oxides are detected and electrochemically observed when the deposition is done at more negative potentials. i–t transients are analyzed by applying the Scharifker and Hills (SH) theoretical model. It is concluded that cobalt deposition occurs via a progressive nucleation and growth mechanism for concentrations higher than 0.05 mol L⁻¹ cobalt ions. For concentrations ≤0.025 mol L⁻¹ cobalt ions and low overpotentials, the mechanism changes to instantaneous nucleation. The i_m–t_m relationships of the SH model are used to determine the values of the kinetic parameters and the cobalt ion diffusion coefficient.

Electrochemical impedance spectroscopy (EIS), an alternated current measurement, is a powerful technique that can be used to distinguish the different charge storage mechanisms. In addition, EIS allows quantification of the electrode performance. However, the utilization of potential-dependent EIS measurements is more convenient to explore electrochemical phenomena occurring at the electrode interface. Herein, we discuss the advantages in using multiple polarized EIS for performance evaluation of three classical electrode types: capacitive, pseudocapacitive, and battery-like, employed in supercapacitor devices. The results are compared with those obtained by direct current methods displaying good agreement in the case of capacitive electrodes. On the other hand, pseudocapacitive and battery-like electrodes exhibit strong ohmic effects and non-reversible processes when the power law equation is utilized. Both of these issues can be circumvented by using potential-dependent EIS.