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The Influence of Ni(II) and Co(II) Adsorptions in the Anomalous Behavior of Co‐Ni Alloys: Density Functional Theory and Experimental Studies
Author(s) -
VazquezArenas Jorge,
RamosSanchez Guadalupe,
Lara Rene H.,
RomeroIbarra Issis,
Almazan M. Eng. Francisco,
LartundoRojas Luis
Publication year - 2017
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201601957
Subject(s) - alloy , density functional theory , adsorption , substrate (aquarium) , materials science , solvation , chemical physics , plating (geology) , ion , chemistry , computational chemistry , metallurgy , organic chemistry , oceanography , geophysics , geology
The anomalous behavior arising during plating of Co‐Ni alloys has been extensively investigated, whence different qualitative proposals have been suggested to describe it, although most of them have been limited to capture underlying atomic interactions between substrate and electroactive species. This study undertakes a different approach to account such phenomenon based on density functional theory (DFT) calculations supported on experimental data. Alloys formed experimentally consistently present an anomalous behavior, except at the most cathodic current. XRD, XPS and voltammetry confirm the formation of solid solutions over alloy compositions from 40 to 90 wt% Co. SEM reveals that alloy morphology strongly depends on applied current density, which likewise affects Co content as output parameter. The effects of CoSO 4 and NiSO 4 (ion pairs) adsorptions on the anomalous behavior are explained using DFT. More favorable adsorption free energies of CoSO 4 are obtained on multiple alloy surfaces (different arrangements of 50‐50 wt% Co‐Ni) and pure metals in comparison with NiSO 4 . Additionally, rich Co sites (substrate) enhance CoSO 4 adsorption, while the specific solvation of the cation significantly contributes to the adsorption strength of the ion pairs, indicating that Co(II) reduction energetically possesses a definite advantage in alloy formation. These theoretical findings provide strong evidence to explain the anomalous behavior of Co‐Ni alloys through the NiSO 4 and CoSO 4 competitive adsorptions.