Interfaces of ionic liquids and transition metal surfaces—adsorption, growth, and thermal reactions of ultrathin [C1C1Im][Tf2N] films on metallic and oxidised Ni(111) surfaces

Abstract

Ultrathin films of the ionic liquid 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([C(1)C(1)Im][Tf(2)N]) were deposited on differently terminated Ni(111) single crystal surfaces. The initial wetting behaviour, the growth characteristics, the molecular arrangement at the interface, and thermal reactivity were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS). On clean Ni(111), the initial growth occurs in a layer-by-layer mode. At submonolayer coverages up to at least 0.40 ML, a preferential arrangement of the IL ions in a bilayer structure, with the imidazolium cations in contact with the Ni surface atoms and the anions on top of the cation, is deduced. For higher coverages, a transition to a checkerboard-type arrangement occurs, which is most likely due to repulsive dipole-dipole interactions in the first layer. An overall preference for a checkerboard-type adsorption behaviour, i.e., anions and cations adsorbing next to each other, is found on the oxygen-precovered O(√3×√3)R30° Ni(111) surface. The thermal stability of adsorbed IL layers on Ni(111) and on a fully oxidised Ni(111) surface was studied by heating the layers to elevated temperatures. For clean Ni(111) reversible adsorption takes place. For the oxidised surface, however, only cation-related moieties desorb, starting at ~450 K, while anion-related signals remain on the surface up to much higher temperatures.

Ionic Liquids in Catalysis

“…7b. Starting at 0.55 monolayers, a transition to a checkerboard-type ''sandwich'' structure is found, with alternating orientations of neighboring sandwiches [156]; see Fig. 7c.…”

“…PVD and ESID preparation methods enable the application of UHV-based analysis techniques now also for studying the IL/support interface under well-defined conditions, which is of highest relevance of SCILL applications. The first studies by AR-XPS demonstrated that the adsorption and wetting behaviour strongly depend on the particular combination of IL and support, with a strong influence of contaminations [150,156,192]. Furthermore, it was demonstrated that XPS can be also used to study reactions in ILs or at ILsubstrate or IL-electrode interfaces in situ, as a function of time or temperature [148,161,162,173,[193][194][195][196][197][198][199][200].…”

“…For such films, the interface is not accessible by XPS, due to damping of the interface signals by the IL film. (2) For ILs that can be evaporated intact (that is as neutral ion pairs [216]), the preparation of ultrathin IL films by physical vapour deposition under well-controlled and clean UHV conditions is possible [150,156,192]. A second promising concept is electrospray ionization deposition (ESID), which enables even the deposition of less stable ILs onto solid surfaces [164].…”

“…In the following, several examples will be discussed in order to demonstrate, how sensitive the observed behaviour depends on the specific combination of IL and substrate. Specifically, we address [C n C 1 Im][Tf 2 N] layers (n = 1, 8) on Au(111) [192] and Ni(111) [156]. We first discuss the behaviour of the IL in the first layer, i.e., the initial stages of film formation.…”

Perspective: Chemical reactions in ionic liquids monitored through the gas (vacuum)/liquid interface

“…[67][68][69][70][71][72] We also exclude studies where the reaction was not carried out in situ, that is, spectra were not recorded while the reaction proceeded, or the sample was moved to a different site in the XPS setup or was even removed from the XPS setup in order to carry out the reaction. [73][74][75][76][77] We also do not address studies that incorporate electrochemical sample manipulation, 66,67,[69][70][71][78][79][80][81][82][83][84][85][86] electrodeposition of metal or organic layers from ILs, [87][88][89][90][91] and IL decomposition 84,[92][93][94][95][96][97][98][99][100][101][102] or nanoparticle formation in ILs. 62,75,103 Each of these topics was studied extensively and would justify a separate review.…”