Nickel electrodeposition from an aqueous solution of ammonium chloride onto a Highly CONTENIDO Oriented Pyrolytic Graphite (HOPG) electrode: A kinetic and morphological study

In this study, an electrochemical investigation was conducted on the electrodeposition of nickel onto a Highly Oriented Pyrolytic Graphite (HOPG) electrode from an ammoniacal solution containing 0.01 M NiCl(2 )and 0.1 M NH4Cl. The potential range in which nickel can be electrodeposited was determined by a cyclic voltammetric study, which also made it possible to assess the charge transfer coefficients related to the reduction and oxidation processes. A kinetic analysis of the nucleation and growth of nickel was also carried out using chronoamperometry. The current density transients (CDTs) derived from this technique were modeled through a kinetic mechanism involving three distinct contributions: (a) two-dimensional instantaneous nucleation, (b)three-dimensional nucleation limited by mass transfer, and (c) a proton reduction process. Nonlinear fitting of the CDTs indicated that both the nucleation rate (A) and the number of active nucleation sites (N-0) increased with the applied potential. Furthermore, the analysis of the contributions to the CDTs showed that, on average, 7.9% of the applied electric charge is consumed by the nucleation and growth process, while the remainder is used for proton reduction. The average Gibbs free energy (triangle G) calculated for the formation of a stable nucleus was 1.2x10(-20)J nucleus(-1). Additionally, Scanning Electron Microscopy (SEM) analysis revealed the presence of spherical nickel particles dispersed on the surface, with diameters ranging from 60 nm to 235 nm.