This work deals with nickel electronucleation
and growth processes
onto a glassy carbon electrode from NiCl2·6H2O dissolved in ethylene glycol (EG) solutions with and without 250
mM NaCl as a supporting electrolyte. The physicochemical properties
of EG solutions, namely, viscosity and conductivity, were determined
for different Ni(II) concentrations. From cyclic voltammetry, it was
found that in the absence of the supporting electrolyte, the cathodic
efficiency of Ni electrodeposition is about 88%; however, in the presence
of the supporting electrolyte, the cathodic efficiency was reduced
to 26% due to water (added along the supporting electrolyte) reduction
on the growing surfaces of Ni nuclei. This side reaction produced
both H2(g) and OH– ions. Part of the
former was occluded in Ni, and the latter reacted with Ni(II) ions
in EG forming passivation products such as Ni(OH)2(s).
Moreover, it was shown that metallic Ni did not catalyze the EG reduction
in this system. From chronoamperometry, it was shown that in the absence
of the supporting electrolyte, the amount of Ni electrodeposits, for
the same overpotential and time, was higher than in the presence of
the supporting electrolyte. The j–t plots recorded in the latter system, for different Ni(II)
concentrations, were analyzed using a model which involves a contribution
due to multiple 3D nucleation and diffusion-controlled growth and
another related to the simultaneous reduction of water on the Ni nuclei
growing surfaces. This model allows not only the quantification of
the Ni nucleation kinetic parameters but also the effective deconvolution
of the individual contributions to the total current; thus, from the
integration of the j–t plots
of these contributions, it was 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 of pure
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 by
the magnetic measurement performed in a physical property measurement
system.