Publications

The purpose of this systematic study was to investigate the effects of specific substrates and potential conditions applied while tailoring the morphology and chemical composition of nanostructured Co films. In particular, Co electrodeposition in sustainable choline chloride-urea deep eutectic solvent was assessed, using glassy carbon and two metals widely employed in electrocatalysis and biocompatible purposes, Pt and Au, as substrates for modification with Co. Various in situ electrochemical techniques were combined with a broad range of ex-situ characterization and chemical-composition techniques for a detailed analysis of the prepared Co films. Among the results, nanostructured Co films with high extended active surface areas and variable composition of oxo and hydroxyl species could be tuned by simply modulating the applied potential limits, and without using additives or surfactant agents. The study highlights the effectiveness of using deep eutectic solvent as suitable electrolyte for surface modification by controlled deposition of nanostructured Co films with further application in electrocatalysis.

JTD Keywords: Cobalt electrodeposition, Deep eutectic solvent, First growth stages, Substrate influence

The first steps of nickel electrodeposition in a deep eutectic solvent (DES) are analyzed in detail. Several substrates from glassy carbon to Pt(111) were investigated pointing out the surface sensitivity of the nucleation and growth mechanism. For that, cyclic voltammetry and chronoamperometry, in combination with scanning electron microscopy (SEM), were employed. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to more deeply analyze the Ni deposition on Pt substrates. In a 0.1 M NiCl2 + DES solution (at 70 °C), the nickel deposition on glassy carbon takes place within the potential limits of the electrode in the blank solution. Although, the electrochemical window of Pt|DES is considerably shorter than on glassy carbon|DES, it was still sufficient for the nickel deposition. On the Pt electrode, the negative potential limit was enlarged while the nickel deposit grew, likely because of the lower catalytic activity of the nickel toward the reduction of the DES. At lower overpotentials, different hydrogenated Ni structures were favored, most likely because of the DES co-reduction on the Pt substrate. Nanometric metallic nickel grains of rounded shape were obtained on any substrate, as evidenced by the FE-SEM. Passivation phenomena, related to the formation of Ni oxide and Ni hydroxylated species, were observed at high applied overpotentials. At low deposited charge, on Pt(111) the AFM measurements showed the formation of rounded nanometric particles of Ni, which rearranged and formed small triangular arrays at sufficiently low applied overpotential. This particle pattern was induced by the (111) orientation and related to surface sensitivity of the nickel deposition in DES. The present work provides deep insights into the Ni electrodeposition mechanism in the selected deep eutectic solvent.

JTD Keywords: AFM, Deep eutectic solvent, Glassy carbon, Nanostructures, Nickel electrodeposition, Platinum electrode, Pt(111), SEM, Surface sensitive