Cadmium Electrodeposition on Glassy Carbon from Ethaline Deep Eutectic Solvent: Electrochemical and Surface Analysis

This study explores the electrodeposition of cadmium (Cd) onto a glassy carbon electrode (GCE) using ethaline, a deep eutectic solvent composed of choline chloride and ethylene glycol, as the electrolyte. The mechanism and kinetics of Cd deposition were investigated at 35°C through cyclic voltammetry and potentiostatic techniques. From voltammetric analysis, the exchange current density ((7.4 ± 0.1) μA cm⁻²) were determined for the Cd(II)/Cd(0) redox couple. Analysis of current transients showed that deposition followed a multiple three-dimensional (3D) nucleation mechanism with diffusion-controlled growth, modeled using Scharifker and Mostany’s approach. Kinetic parameters such as nucleation frequency (A), number density of active sites (N₀), and diffusion coefficient (D = (4.86 ± 0.10) × 10⁻7 cm²·s⁻¹) were evaluated. The overpotential dependence of A enabled estimation of a surface energy ((6.26 ± 0.02) × 10⁻6 J cm⁻²), nucleation work (400 J mol⁻¹), and critical nucleus size (<1 atom). Scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron microscopy analyses revealed a uniform Cd distribution, with quasi-spherical and irregular structures interconnected by nanowires. Cd existed as both metallic and oxidized forms. Additionally, UV–Vis spectroscopy and Kubelka–Munk analysis yielded an optical band gap of 2.2 eV, consistent with cadmium oxide nanoparticles.