In Situ Spectroelectrochemical Investigation of Potential‐Dependent Changes in an Amphiphilic Imidazolium‐Based Ionic Liquid Film on the Au(111) Electrode Surface

Abstract

AbstractThe stability of ionic liquids (ILs) at charged interfaces makes them very attractive in electrochemical applications. In this work, a Langmuir–Blodgett transfer is used to fabricate a monolayer of an amphiphilic 1‐methyl‐3‐octadecylimidazolium perchlorate IL on the Au(111) surface. The IL monolayer immersed in an aqueous electrolyte solution is very stable over a wide potential window. Polarization modulation infrared reflection absorption spectroscopy is used to monitor structural changes in the model of the electrical double layer of the IL in aqueous solution. The imidazolium cation is in direct contact with the Au(111) surface. The imidazolium ring adopts a rigid orientation, inclined toward the metal surface, in the monolayer on the Au(111) surface. The orientation of hydrocarbon chains responds to electric potentials. At low negative surface charge densities of the Au(111) electrode, the hydrocarbon chains in the amphiphilic cation have a large average tilt versus surface normal. A negative potential shift is accompanied by a reorientation of the hydrophobic hydrocarbon chains that adopt an up‐ward orientation, making the film permeable for counter‐ and/or co‐ions. This transition leads to the formation of an ordered, single‐component monolayer of the amphiphilic cation on the electrode surface.