Insights into Electronucleation and Electrodeposition of Nickel froma Non-aqueous Solvent Based on NiCl2 center dot 6H2O Dissolved in Ethylene Glycol br

This work deals with nickel electronucleation andgrowth processes onto a glassy carbon electrode from NiCl2middot6H2Odissolved in ethylene glycol (EG) solutions with and without 250mM NaCl as a supporting electrolyte. The physicochemicalproperties of EG solutions, namely, viscosity and conductivity,were determined for different Ni(II) concentrations. From cyclicvoltammetry, it was found that in the absence of the supportingelectrolyte, the cathodic efficiency of Ni electrodeposition is about88%; however, in the presence of the supporting electrolyte, thecathodic efficiency was reduced to 26% due to water (added alongthe supporting electrolyte) reduction on the growing surfaces of Ninuclei. This side reaction produced both H2(g)and OH-ions. Partof the former was occluded in Ni, and the latter reacted withNi(II) ions in EG forming passivation products such as Ni(OH)2(s). Moreover, it was shown that metallic Ni did not catalyze the EGreduction in this system. From chronoamperometry, it was shown that in the absence of the supporting electrolyte, the amount of Nielectrodeposits, for the same overpotential and time, was higher than in the presence of the supporting electrolyte. Thej-tplotsrecorded in the latter system, for different Ni(II) concentrations, were analyzed using a model which involves a contribution due tomultiple 3D nucleation and diffusion-controlled growth and another related to the simultaneous reduction of water on the Ni nucleigrowing surfaces. This model allows not only the quantification of the Ni nucleation kinetic parameters but also the effectivedeconvolution of the individual contributions to the total current; thus, from the integration of thej-tplots of these contributions, itwas demonstrated that the charge amount of each process depends on the Ni(II) concentration. Scanning electron microscopy,energy-dispersive X-ray spectroscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the presence ofpure Ni nanoparticles electrodeposited on the electrode surface. Moreover, X-ray measurements verified the formation of a high-crystallinity face-centered cubic structure with preferred orientation growth on the < 111 > direction, which were also corroborated bythe magnetic measurement performed in a physical property measurement system.