Initial stages of silver electrodeposition on a model Pt(111) single-crystal substrate from ethaline

Deep eutectic solvents (DES) are a new class of solvents with unique properties that are very promising media for the electroplating of metals and alloys. Knowledge about the regularities of metal electrodeposition is noticeably promoted by studies on model single crystal electrodes with a known well-ordered surface structure. In this work, we investigate the regularities of under- and overpotential deposition (upd and opd, respectively) of silver from a silver chloride solution in ethaline on a Pt(111) single crystal surface. For a better understanding of the occurring processes, we employ a complex approach involving electrochemical and in situ and ex situ microscopic techniques. We show that the process of gradual surface poisoning is observed on Pt(111) in the potential range in which no massive solvent degradation is yet observed. We also observe that the extent of this process largely depends on the employed potential of contact between the electrode and the solution and the studied potential range.

The presence of Ag upd on Pt(111) in ethaline is demonstrated using voltammetric and in situ STM data. The available results and charge analysis are used to compare the Ag upd processes in ethaline and in aqueous solutions. We discuss the number of Ag adlayers on Pt(111), the effect of the potential of initial contact of the electrode with the solution and cycling history, and the possibility of anion upd and formation of coadsorbate between Ag adatoms and upd chloride anions (chlorine adatoms). We also demonstrate that upd Ag is not completely desorbed until high anodic potentials, where it seems to catalyze the solvent oxidation. Phase deposition of silver from ethaline on Pt(111) starts at almost zero overpotentials, which is probably related to the presence of the already deposited Ag adlayer. Even at very low overpotentials the deposit includes both large planar 2D crystallites and 3D crystallites formed on the surface defects and at the edges of the flat deposit islands. As the overpotential grows, the epitaxiality is gradually lost; the deposit becomes unshaped and the amount of 3D crystallites and their height increase.