Interaction of Ester‐Functionalized Ionic Liquids with Atomically‐Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability

Abstract

Hybrid materials consisting of ionic liquid (ILs) films on supported oxides hold a great potential for applications in electronic and energy materials. In this work, we have performed surface science model studies scrutinizing the interaction of ester-functionalized ILs with atomically defined Co O (111) and CoO(100) surfaces. Both supports are prepared under ultra-high vacuum (UHV) conditions in form of thin films on Ir(100) single crystals. Subsequently, thin films of three ILs, 3-butyl-1-methyl imidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf ]), 3-(4-methoxyl-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([MBMIM][NTf ]), and 3-(4-isopropoxy-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([IPBMIM][NTf ]), were deposited on these surfaces by physical vapor deposition (PVD). Time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) were applied to monitor in situ the adsorption, film growth, and thermally induced desorption. By TP-IRAS, we determined the multilayer desorption temperature of [BMIM][NTf ] (360±5 K), [MBMIM][NTf ] (380 K) and [IPBMIM][NTf ] (380 K). Upon deposition below the multilayer desorption temperature, all three ILs physisorb on both cobalt oxide surfaces. However, strong orientation effects are observed in the first monolayer, where the [NTf ] ion interacts with the surface through the SO groups and the CF groups point towards the vacuum. For the two functionalized ILs, the [MBMIM] and [IPBMIM] interact with the surface Co ions of both surfaces via the CO group of their ester function. A very different behavior is found, if the ILs are deposited above the multilayer desorption temperature (400 K). While for [BMIM][NTf ] and [MBMIM][NTf ] a molecularly adsorbed monolayer film is formed, [IPBMIM][NTf ] undergoes a chemical transformation on the CoO(100) surface. Here, the ester group is cleaved and the cation is chemically linked to the surface by formation of a surface carboxylate. The IL-derived species in the monolayer desorb at temperatures around 500 to 550 K.

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

“…This geometry was observed previously for several ILs with [Tf 2 N]as anion by ARXPS on Au(111) [71,73] and by STM on Ag(111) [94,119], Au (111) [73,94,119], and other surfaces [75,76,[121][122][123][124]. Notably, is was found at RT [71,73,76,80,81,121,123,124] and also at temperatures around 100 K [71,73,81,94,122]. Preferential orientation of the anion at the IL/metal interface was also reported by in situ IR spectroscopy for [C 2 C 1 Im][TfO] on Pd(111) [125][126][127] and on Co-covered Pd(111) [128], such that the SO 3 group points towards the metal and the CF 3 group away from the surface.…”

“…Independent of the length of the alkyl substituents at the imidazolium cation, the [Tf 2 N]anion was found to adsorb on Ag(111) in a cis conformation with an upright orientation, with the oxygen atoms pointing towards the metal and the CF 3 groups away from the surface [80,81]. This geometry was observed previously for several ILs with [Tf 2 N]as anion by ARXPS on Au(111) [71,73] and by STM on Ag(111) [94,119], Au (111) [73,94,119], and other surfaces [75,76,[121][122][123][124]. Notably, is was found at RT [71,73,76,80,81,121,123,124] and also at temperatures around 100 K [71,73,81,94,122].…”

Adsorption Motifs and Molecular Orientation at the Ionic Liquid/Noble Metal Interface: [C2C1Im][NTf2] on Pt(111)

“…This implies that the IL can be tuned to the desired characteristics by combining the respective ions. For this reason, ILs are often denoted as “designer solvents”. − ,, Further modification of the ions by introducing functional groups offers additional flexibility. ,,− In order to adjust the properties of the IL to a specific process, however, it is essential to understand in detail the interaction of the IL with the catalytically active component of the support. Here, many questions are still open such as the wetting behavior, the film growth, and the interaction of IL ions with the active sites at molecular scale.…”

“…Here, many questions are still open such as the wetting behavior, the film growth, and the interaction of IL ions with the active sites at molecular scale. Such insight is available from surface science studies, and in the last years several groups have addressed these questions following a surface science approach. ,− …”

Structure formation and surface chemistry of ionic liquids on model electrode surfaces—Model studies for the electrode | electrolyte interface in Li-ion batteries

“…[TFSI] --based ILs with different cations with single crystalline surfaces has been investigated (ex situ) under UHV conditions [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] and in-situ in an electrochemical environment. [32][33][34][50][51][52][53][54][55] For example, employing angle-resolved X-ray photoelectron spectroscopy (ARXPS), Cremer ("checkerboard") arrangement on Au(111), with both anions and cations bound directly to the surface.…”