Use of CO as a Cleaning Tool of Highly Active Surfaces in Contact with Ionic Liquids: Ni Deposition on Pt(111) Surfaces in IL

Abstract

This work proposes a pretreatment strategy of a flame-annealed Pt(111) single crystal ensuring surface ordering and avoiding water surface contamination for experiments in ionic liquid (IL) media. A room temperature ionic liquid (RTIL) and a deep eutectic solvent (DES) representative of two families of ionic liquids were selected as test electrolytes: The RTIL used was the 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethyl)sulfonylimide ([Emmim][Tf2N]), and the DES was based on the eutectic mixture of choline chloride (ChCl) and urea (1ChCl:2urea molar ratio). The electrode was flame-annealed and, instead of the water quenching step, it was cooled down in CO atmosphere until the surface was fully covered by a protective carbon monoxide (CO) layer. Prior to experiments, the removal of CO from the surface was performed by electrochemical oxidation. The CO reactivity on Pt(111) was different depending on the IL nature. While CO is easily oxidized to CO2 in [Emmim][Tf2N], in DES, CO remains adsorbed on the substrate and restructures undergoing an order–disorder transition. For both liquids, the proposed method allows for obtaining neat blank cyclic voltammograms, demonstrating that the adsorption of CO is a useful tool to protect the high catalytic surfaces, such as Pt in contact with ILs. To illustrate the feasibility of the CO treatment in electrochemical work with ILs, the general trends for the modification of Pt(111) single crystal surface with metallic nickel nanostructures on both types of IL was investigated. Nickel electrodeposition on the Pt(111) substrate was explored in both [Emmim][Tf2N] and DES by using classical electrochemical techniques, such as cyclic voltammetry and chronoamperometry, while the deposits were characterized by FE-SEM, EDS, and XPS.