Ultrathin ionic liquid films on metal surfaces: adsorption, growth, stability and exchange phenomena

Abstract

The interface of ionic liquids (ILs) with solid surfaces is of pivotal interest for many applications, ranging from sensors, lubrication, separation technology, and electronics to electrochemistry and catalysis. We present a short review on ultrathin layers of ionic liquids on metal surfaces using a surface science approach. We mainly focus on specific examples of imidazolium-based ionic liquids on Ag(111) and Au(111) studied by angle-resolved X-ray photoelectron spectroscopy, and relate the obtained results to existing literature. We address a variety of phenomena on the molecular level, namely, (i) the adsorption, growth and wetting behavior of ILs, (ii) the thermal stability and desorption of ILs, (iii) exchange processes of anions and cations at the IL/solid interface, and (iv) the replacement of ILs from the IL/solid interface by porphyrins.

Time- and Temperature-Dependent Growth Behavior of Ionic Liquids on Au(111) Studied by Atomic Force Microscopy in Ultrahigh Vacuum

“…As experimental methods, until recently only angle-resolved X-ray photoelectron spectroscopy (ARXPS) and UV-photoelectron spectroscopy (UPS) were applied. 17 , 27 − 31 Only very recently, the first UHV-based atomic force microscopy (AFM) studies addressing IL growth have been published. 32 , 33 Notably, scanning tunneling microscopy (STM) is not suited to study IL growth behavior, due to too strong tip effects, which occur for layers on top of the first wetting layer.…”

Enrichment effects of ionic liquid mixtures at polarized electrode interfaces monitored by potential screening

“…A very powerful method in this context is ultra-high vacuum (UHV)-based angle-resolved XPS, which however can be applied only for ultrathin IL films, due to the limited escape depth of the emitted photoelectrons on the order of a few nm. 41 Using this method, the composition of the wetting layer in direct contact with the surface and the growth of successive layers have been studied in great detail. 42 Very recently, also ultrathin layers of IL mixtures have been investigated using this approach.…”

Emerging Applications of Solid Catalysts with Ionic Liquid Layer Concept in Electrocatalysis

“…[ 61 ] Most recently, they drew the same conclusion on Ag(111) surface, showing that cation is adsorbed with cation lying flat on the metal surface at low IL coverages (<0.5 monolayer) regardless of the cationic chain length, while further increasing the IL coverage favors detachment of the long cationic chain from the Ag(111) surface, as shown in Figure a. [ 62,63 ] Behm et al. characterized 1‐Butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C 4 C 1 Pyrr][NTf 2 ] on Au(111) using STM and XPS and observed alternating cations and anions on Au surfaces and orientation of the C 4 chains pointing toward the vacuum.…”

“…Reproduced under the terms of the Creative Commons Attribution License 4.0. [ 62 ] Copyright 2020, The Author(s), Published by Informa UK Limited, trading as Taylor & Francis Group. b) Schemes for Pt and Pd nanoparticles supported on Al 2 O 3 /NiAl(110) surfaces in presence of IL [C 4 C 1 im][NTf 2 ] and adsorbed CO molecules.…”

“…with cation lying flat on the metal surface at low IL coverages (<0.5 monolayer) regardless of the cationic chain length, while further increasing the IL coverage favors detachment of the long cationic chain from the Ag(111) surface, as shown in Figure 3a. [62,63] Behm et al characterized 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C 4 C 1 Pyrr][NTf 2 ] on Au(111) using STM and XPS and observed alternating cations and anions on Au surfaces and orientation of the C 4 chains pointing toward the vacuum. [64] Vibrational spectroscopic techniques have also been intensively applied in understanding the interfacial structure of IL at solid surfaces, and many inspiring conclusions have been drawn.…”