Insights into Chemical Changes Causing Transient Potential Patterns during Cobalt Electrodeposition: An Operando SHINERS Investigation

Abstract

Transient potential oscillations in a self-organized system involve a sequence of mass-transfer-limited chemical reactions. Often, these oscillations determine the microstructure of the electrodeposited metallic films. In this study, two distinct potential oscillations have been observed during galvanostatic deposition of cobalt in the presence of butynediol. Understanding the underlying chemical reactions in these potential oscillations is essential for designing efficient electrodeposition systems. Operando shell-isolated nanoparticle-enhanced Raman spectroscopy is deployed to record these chemical changes, and we present direct spectroscopic evidence of adsorbed hydrogen scavenging by butynediol, Co(OH)2 formation, and removal limited by mass transfer of butynediol and protons. The potential oscillatory patterns have four distinguishable segments associated with mass-transfer limitation of either proton or butynediol. These observations improve our understanding of the oscillatory behavior in metal electrodeposition.

Potential Oscillations During Cobalt–Nickel Electrodeposition in the Presence of Butynediol

“…For the sake of clarity, a single potential oscillation is considered (Figure A). The single oscillation can be segmented into four regions, as observed in our previous operando SHINERS study of cobalt electrodeposition with butynediol A n –B n region: Proton reduction to adsorbed hydrogen takes place on CoNi by the following Volmer step. CoNi + H false( aq false) + + e − → CoNi − H ad goodbreak0em1em⁣ ( Volmer ‐ step ) The Heyrovsky step is not possible at low overpotentials as the M–H bond (where M = Co, Ni) is very stable.…”

“…Our study revealed that the strongly adsorbed intermediate, viz., Co–H, during the electrodeposition of cobalt led to the suppression of current, resulting in the NDR, where the adsorbed hydrogen can be scavenged by butynediol as a result of its hydrogenation, leading to electrochemical potential oscillation . Our operando SHINERS-Raman investigation provided insights regarding the involvement of cobalt hydroxide formation/dissolution for the observation of oscillation in addition to adsorbed hydrogen formation/removal …”

“…Thus, it is envisaged that their codeposited CoNi surface adsorbed with hydrogen might also exhibit a chemical catalytic behavior similar to/better than the individual metals toward the hydrogenation of butynediol. As the surface concentration of the protons and butynediol might affect the course of the interfacial processes during the electrodeposition of CoNi, just like cobalt electrodeposition, we studied the galvanostatic electrodeposition of CoNi under quiescent and hydrodynamic conditions by varying the current densities as well as butynediol concentrations. Several critical factors involved in the potential oscillations were identified by means of chronopotentiometric studies under quiescent and hydrodynamic conditions, and we attempted to explain the mechanism of the observed electrochemical potential oscillation during the electrodeposition of CoNi based on the phenomena that take place at the interface.…”