Electrochemical Synthesis of Co-Nd Films in Urea and Choline Chloride Deep Eutectic Solvents

Cobalt chloride and neodymium chloride were dissolved in the urea and choline chloride deep eutectic solvents (DESs), and the electrochemical mechanisms of Co-Nd alloy codeposition were investigated under ambient conditions. Results from cyclic voltammetry indicated that the deposition of metallic Co on the tungsten electrode proceeds by an apparent two-electron transfer irreversible process at − 1.02 V (vs Ag). It is impossible to deposit pure Nd in urea and choline chloride DESs, whereas Co-Nd alloys can be codeposited from electrolytes with both Co(II) and Nd(III) ions. Furthermore, chronoamperometric experiments demonstrated that the electrochemical deposition of metallic Co can be considered as a three-dimensional (3-D) progressive nucleation process, while Co-Nd alloys were formed by instantaneous nucleation with diffusion-controlled growth. The average value of the diffusion coefficient of Co(II) ions in the urea and choline chloride DESs containing 3.8 × 10⁻⁵ mol/cm³ CoCl₂ at 373 K was calculated to be 1.98 × 10⁻⁷ cm²/s. Moreover, analysis by scanning electron microscopy and energy dispersive X-ray spectroscopy suggested that a flat and uniform film consisting of Co (96.26 wt pct) and Nd (3.74 wt pct) was prepared by electrodeposition on a Cu substrate.