| dc.description.abstract | Organic sulfides with imidazole functional groups have been extensively studied as corrosion inhibitors and biosensors. However, their adsorption behavior at the electrochemical interface remains insufficiently explored. In this study, the adsorption behavior of imidazolethiol and benzimidazolethiol molecules, such as 2-mercapto-1-methylimidazole (MMI), 1-methyl-1H-benzimidazole-2-thiol (MBIT), and 2-Mercapto-5-methylbenzimidazole (MMBI), on a Au(111) electrode was investigated using cyclic voltammetry (CV) and scanning tunneling microscopy (STM). The relationship between the adsorption behavior and factors such as potential, pH, and anions was examined.
The results elucidated that the adsorbed MMI and MBIT molecule assumed the unprotonated form, allowing its S- and N-ends to bind with the Au electrode at a positive potential, resulting in ordered array structures and a unique honeycomb structure, respectively, as observed through Molecular resolution STM imaging. At negative potentials, the N-Au bond broke, leading to disorder in the MMI adsorption layer. In contrast, MBIT and MMBI closely packed through π-π interactions, resulting in a similar ordered line structure. This restructuring event was coupled with the protonation of the imidazole functional group. At more negative potentials, the S−Au bond broke, causing the molecules to desorb from the Au electrode. The observation of pitted surface morphology on the Au (111) electrode surface indicated that the molecules adsorbed in a typical S-Au-S motif, forming ordered structures. MBIT possibly formed a unique honeycomb structure as Au(MBIT)3. Additionally, the coadsorption of MBIT and MMBI with anions indeed affected their ordered adsorption structures.
The second part of this study focused on the nucleation and growth process of Ni on the Au electrode and the influence of thiol molecules on Ni deposition. Protracted STM scanning could enable Ni adatoms penetrating the uppermost layer of Au electrode, yielding a Ni-Au mixed surface. Further Ni deposition on the Au(111) domains leads to multilayered moiré patterns. The MMI additive causes uniform Ni nucleation on the Au(111) electrode at a more positive potential than that observed without MMI, forming a smooth Ni adlayer on the Au electrode. Meanwhile, MMI molecules adsorb to the Ni deposit with their –S and –N ends. Bulk Ni deposition with MMI is 3D, resulting in a rolling hill morphology. CV results showed that the addition of MMI significantly accelerated nickel deposition, leading to increased deposition quantity and efficiency. It was speculated that MMI molecules formed Ni(MMI)x2+ complexes, effectively transferred to the Au electrode, and facilitated Ni deposition. In contrast, due to the contribution of the benzene ring, MBIT and MMBI formed hydrophobic barrier layers that hindered the approach of Ni(H2O)62+ to the Au electrode surface, thus suppressing Ni electrodeposition.
This study provided insights into the adsorption states of imidazolethiol molecules on a Au (111) electrode and their role in the Ni electrodeposition process. It contributes to a better understanding of the adsorption behavior of organic sulfides at the electrochemical interface and can aid in the development of novel electroplating agents. | en_US |