Influence of pretreatment conditions on underpotential and phase deposition of silver on Pt(hkl) single crystal substrates in ethaline

Abstract

Deep eutectic solvents (DES) are a special class of solvents with specific properties that offer new possibilities for the electroplating of metals and alloys. Ethaline – a mixture of choline chloride and ethylene glycol (EG) – is one of the less viscous DES, which makes it a commonly used medium for studying electrodeposition. The understanding of the metal electrodeposition behavior is much advanced by the data on structural sensitivity obtained with the help of single crystal electrodes. This work is continuation of a previous study on Ag electrosorption and phase deposition on Pt(111) in ethaline. We extend our studies to other basal single crystal surfaces, Pt(100) and Pt(110). Also, with account for the more pronounced sensitivity of these faces to the laboratory atmosphere as compared to Pt(111) and also with regard to the previously obtained data on the possibility of spontaneous EG decomposition on Pt with formation of a CO-like adspecies, we suggest an EG–protection step in the Pt(hkl) pretreatment procedure. We compare the data on Ag electrosorption and phase deposition on the three basal single crystal surfaces pretreated by EG (EG-protected) as opposed to surfaces with no such pretreatment (unprotected). We demonstrate that the EG-protection step results in the surface poisoning by the blocking adspecies. This brings about a significant lowering of the capacitance currents and the currents related to specific adsorption of ethaline components and Ag underpotential deposition (upd) as compared to those on unprotected Pt(hkl). We also show that phase deposition of silver from ethaline on Pt(hkl) starts at almost zero overpotentials on all electrodes except for EG-protected Pt(110), which is probably related to the presence of the already deposited Ag adlayer (for unprotected electrodes) and Ag adlayer patches (for EG-protected ones). In general, Ag deposition occurs via the Stranski–Krastanov mode. Deposition on unprotected electrodes involves simultaneous 2D and 3D deposit formation, while the deposit obtained at moderate overpotentials on all EG-pretreated electrodes contains well-pronounced individual shaped crystallites.