Electrochemical synthesis and characterization of high-purity cobalt nanostructures from CoCl 2 ·6H 2 O dissolved in ethylene glycol-based nonaqueous solutions

In this work, electrodeposition and electronucleation of cobalt on a glassy carbon electrode from CoCl 2 ·6H 2 O dissolved in ethylene glycol-based solutions (with and without NaCl as supporting electrolyte) were studied. Cyclic voltammetry and chronoamperometry have shown that cobalt can be easily electrodeposited from these nonaqueous solvents through one-step of two electrons with high cathodic efficiencies and insignificant effect of the side reaction. The analyses of current density transients were performed using the three-dimensional nucleation and diffusion-controlled growth model of Co metallic nuclei, to derive kinetic parameters such as nucleation frequency, A , density number of active sites, N 0 , and diffusion coefficient, D . Characterization methods, such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction, verified the presence of high-purity (electrodeposited) Co nanoparticles with the hexagonal close-packed structure on the electrode surfaces. It was found that the supporting electrolyte influenced the morphology and size distribution of Co nanoparticles and their preferred growth along the electrodeposition plane. Finally, linear sweep voltammetric curves indicated a strong electrocatalytic activity of cobalt electrodeposited from ethylene glycol-based solutions towards hydrogen evolution reaction in acidic and alkaline solutions, even better than platinum for the case of cobalt directly electrodeposited from ethylene glycol.