Voltammetric investigation of anodic and cathodic processes at Au(hkl)|ionic liquid interfaces

Abstract

• The electrochemical behaviors of 8 ionic liquids (ILs) were studied on Au( hkl ). • Pyrrolidinium-based ILs had the widest electrical double-layer region. • The potential windows depended on Au( hkl ) and the ions comprising the ILs. • The desorption/re-adsorption of iodine for 2 iodide-based ILs depended on Au( hkl ). • In terms of the peak potential for iodine desorption: Au(100) < Au(111) < Au(110) . In this work, the effect of the crystallographic orientation of gold on the interfacial processes of six non-halide-based ionic liquids (ILs) and two iodide-based ILs was systematically investigated by linear sweep voltammetry (LSV), cyclic voltammetry (CV), and double potential step chronocoulometry (DPSCC). The cation and anion of the IL affected both the width of the electrical double-layer (EDL) region ( E dl ) and the electrochemical potential window ( E pw ) of the ILs. The shape of the CV profile in the EDL region was unique for each Au( hkl )|IL interface. The reductive desorption and re-adsorption of iodine adatoms on gold in 1-alkyl-3-methylimidazolium iodide ([C n mim][I], n = 4 or 6) were also surface-sensitive. The reduction peak current density was proportional to the scan rate, suggesting that the reaction involves adsorbed iodine. The amount of iodine adatoms desorbed during the initial cathodic scan was identical to the monolayer coverage of iodine on gold single crystal electrodes. The peak potential for reductive desorption was estimated to follow the ensuing order from negative to positive: [C 6 mim][I] < [C 4 mim][I] and Au(100) < Au(111) < Au(110) . Following reductive desorption of iodine, the cations were partly attached to the gold surface. The adsorption strength of [C n mim] + followed an identical order: Au(100) < Au(111) < Au(110) .