Optimization of cobalt electrodeposition from cobalt- chloride using urea and choline chloride ionic liquid

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The novel process for the electrodeposition of cobalt using the urea and the choline chloride ionic liquid (2:1 molar ratio) was studied to search the optimized parameters for the higher current efficiency. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used for the characterization of cobalt deposits after conducting experiments. The cyclic voltammetry was tested with 0.2M CoCl2 using various scan rates to determine the reduction potential in Urea/ChCl at 323K. Based on the data from cyclic voltammetry test, the transfer coefficient and the diffusion coefficient were calculated as 0.22 and 3.38×10−6cm2/s, respectively. The electrodeposition experiment was performed with the copper sheet and the graphite sheet as a working electrode and a counter electrode, respectively. The used parameters were various temperatures (323K to 383K), applied potentials (2.4V to 3.3V), and concentration of CoCl2 (0.2M to 0.5M). Current efficiency and energy consumption were calculated to find the optimal condition for the electrodeposition of cobalt. Variation of temperatures did not influence the current efficiency in range of 323K to 383K but the data at 323K showed the highest efficiency with the lowest energy consumption. Higher applied voltage caused the dendrite of cobalt deposition on the copper cathode, which reduced current efficiency. The CoCl2 concentration at 0.5M maximized cobalt deposition and resulted in more than 90 % of current efficiency (95%) by increasing the diffusion rate. SEM images showed the surface morphology of cobalt deposits on the copper cathodes according to the different parameters. As the temperature increases, the particles in the cobalt deposits grew larger without changing their shape. The higher applied voltage showed dendrites on the surface of the copper sheet at 3.3V and the measured average size of the dendrites was 156μm. Increasing the concentration of CoCl2 didn’t show the large change of the particle size except for the thicker coverage of cobalt layer. Elemental analysis was studied using XRD with two samples from the 6hour electrodeposition experiment. One was the cobalt powder from the cobalt dendrite deposit, which was easily detached, and the other was the thick cobalt layer on a copper cathode. They showed the pure cobalt peaks without any other elements.

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