Influence of glycine on Co electrodeposition: IR spectroscopy and near-surface pH investigations

Abstract

The influence of glycine on the mechanism of cobalt electrodeposition on Au was studied by using different experimental techniques. From cyclic voltammetry experiments, changes in deposition kinetics were observed in the presence of glycine and as a function of pH. The early stages of deposition and the morphology of the Co films were strongly influenced by the solution pH. The electroactivity of Co(gly)+ was confirmed, with slower processes related to highly coordinated cobalt ions becoming predominant with pH increase. In situ investigations were conducted at solution pH 4 and 6. The infrared spectroelectrochemical experiments showed that the concentrations of cobalt-glycine complexes increased due to changes in the interfacial pH, owing to the hydrogen evolution reaction (HER). Near-surface pH measurements during Co electrodeposition were carried out with an IrOx microelectrode, whose distance to the Au substrate was precisely controlled by using scanning electrochemical microscopy (SECM) equipment. The pH values recorded during electrodeposition were greatly influenced by the acid-base reactions of the amino acid. Although high pH values were readily reached, the accumulation of glycinate at the interface was effective at suppressing the formation of metal-hydroxide species. On the other hand, the proton-donating reactions of glycine enhanced the HER, reducing deposition efficiency.