Interaction of the ionic liquid [BMP][TFSA] with rutile TiO₂(110) and coadsorbed lithium

Abstract

Aiming at a fundamental understanding of the processes at the electrode|ionic liquid interface in Li ion batteries, we investigated the interaction of the ionic liquid n-butyl-n-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMP][TFSA] and of Li with a reduced rutile TiO2(110) (1 × 1) surface as well as the interaction between [BMP][TFSA] and Li on the TiO2(110) surface under ultrahigh vacuum (UHV) conditions by X-ray photoelectron spectroscopy and scanning tunnelling microscopy. Between 80 K and 340 K [BMP][TFSA] adsorbs molecularly on the surface and at higher temperatures decomposition is observed, resulting in products such as Sad, Fad and TiNx. The decomposition pattern is compared to proposals based on theory. Small amounts of Li intercalate even at 80 K into TiO2(110), forming Li(+) and Ti(3+) species. The stoichiometry in the near surface region corresponds to Li7Ti5O12. For higher coverages in the range of several monolayers part of the Li remains on the surface, forming a Li2O cover layer. At 300 K, Ti(3+) species become sufficiently mobile to diffuse into the bulk. Li post-deposition on a [BMP][TFSA] covered TiO2(110) surface at 80 K results in two competing reactions, Li intercalation and reaction with the IL, resulting in the decomposition of the IL. Upon warming up, the Ti(3+) formed at low T is consumed by reaction with the IL adlayer and intermediate decomposition products. Post-deposition of [BMP][TFSA] (300 K) on a surface pre-covered with a Li2O/Li7Ti5O12 layer results in the partial reaction of [BMP][TFSA] with the Li(+) and Ti(3+) species, which gets completed at higher temperatures.

Ionic Liquid Ordering at an Oxide Surface

“…who claimed it resulted from the alkyl chain moving from a geometry where it lies parallel to the surface to one in which it is perpendicular to the surface. Such orientations have been seen before, for various ionic liquids on other surfaces, using scanning tunneling microscopy . Here we do not observe a shift in binding energy of the C4 peak, suggesting that it does not change conformation in the film thicknesses studies.…”

“…Such orientations have been seen before,f or various ionic liquids on other surfaces, using scanning tunneling microscopy. [16,18,21,22,24,27] Here we do not observe as hift in binding energy of the C4 peak, suggesting that it does not change conformation in the film thicknesses studies. NEXAFS data discussed below suggest the imidazolium ring lies perpendicular to the surfacei nt he 4 film, which is consistent with the lower binding energies of C1, C2 and C3 in the 4 film.…”

“…The (101) surface is the most thermodynamically stable anatase surface and is therefore the dominant surface exposed in nanoparticulate TiO 2 . Although there is a growing body of work on the surface chemistry of bulk ILs and thin films of ILs on metal surfaces studied by photoelectron spectroscopy, their interaction with metal oxide solid surfaces is less well studied . In this work we employ a combination of X‐ray photoelectron spectroscopy (XPS) and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy to shed light onto the interaction of 1‐butyl‐3‐methylimidazolium tetrafuloroborate ([C 4 C 1 Im][BF 4 ]) with the anatase TiO 2 (101) surface.…”

“…[14] Although there is agrowing body of work on the surface chemistry of bulk ILs and thin films of ILs on metal surfaces studied by photoelectrons pectroscopy, [15][16][17][18][19][20][21][22][23][24][25][26][27] their interaction withm etal oxide solid surfaces is less well studied. [15][16][17][18]28] In this work we employacombination of X-ray photoelectrons pectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to shed light onto the interaction of 1-butyl-3-methylimidazolium tetrafuloroborate ([C 4 C 1 Im][BF 4 ]) with the anataseT iO 2 (101) surface. Figure 2s hows C1s, N1s, F1sa nd B1sp hotoelectron spectra for the 30 4 ]w ith anatase TiO 2 ,amodel photoanode material, has been studied using ac ombination of synchrotron radiation photoelectron spectroscopya nd near-edge X-ray absorption fine structure spectroscopy.…”

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.…”