Electrodeposition of Pb from PbO in urea and 1-butyl-3-methylimidazolium chloride deep eutectic solutions

- The electrochemical reduction of Pb (II) in urea-BMIC is a diffusion-controlled one-step two-electron transfer process.
- Electrodeposition of Pb in urea-BMIC involves a 3D instantaneous nucleation and diffusion-controlled growth.
- Pb was prepared from urea-BMIC-PbO with optimized current efficiency of 96.17 % and energy consumption of 0.11 kWh kg-1.
- Uniform, dense, and non-dendritic lead coating with grain size of 3 μm was prepared by potentiostatic electrolysis.

In this work, urea and 1-butyl-3-methylimidazolium chloride (urea-BMIC) deep eutectic solutions were used as electrolytes for electrodeposition of lead from lead oxide. The electrochemical behavior of Pb (II) ions was investigated by cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques at 353-373 K. Cyclic voltammograms and chronopotentiograms indicate that the reduction of Pb (II) ions to Pb is a diffusion-controlled quasi-reversible process and it proceeds via one step two-electron transfer process at −0.38 V (vs. Ag). The diffusion coefficient of Pb (II) ions increases from 3.22 × 10−8 cm2 s−1 to 1.49 × 10−7 cm2 s−1 as temperature increases from 353 K to 373 K. The activation energy for diffusion is determined to be 83.93 kJ mol−1. In addition, results from chronoamperometry show that lead deposition involves in a three-dimensional instantaneous nucleation and diffusion-controlled growth. On the other hand, the electrodeposit on a Cu substrate was pure Pb as confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Scanning electron microscopy (SEM) image indicated that a uniform, dense, and non-dendritic coating with grain size of 3 μm in diameter was prepared by potentiostatic electrolysis at −0.4 V (vs. Ag). The optimized current efficiency (96.17%) and energy consumption (0.11 kWh kg−1) was obtained by potentiostatic electrolysis at −0.4 V (vs. Ag) and 373 K from urea-BMIC deep eutectic solutions containing 0.072 mol dm−3 PbO.