Potential Screening at Electrode/Ionic Liquid Interfaces from In Situ X-ray Photoelectron Spectroscopy.

A new approach to investigate potential screening at the interface of ionic liquids (ILs) and charged electrodes in a two-electrode electrochemical cell by in situ X-ray photoelectron spectroscopy has been introduced. Using identical electrodes, we deduce the potential screening at the working and the counter electrodes as a function of applied voltage from the potential change of the bulk IL, as derived from corresponding core level binding energy shifts for different IL/electrode combinations. For imidazolium-based ILs and Pt electrodes, we find a significantly larger potential screening at the anode than at the cathode, which we attribute to strong attractive interactions between the imidazolium cation and Pt.

Temperature-Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non-Fluorinated Ionic Liquids.

Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF ] anion but two different cations, namely 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF ], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C C Im][PF ], with 10, 25, 50 and 75 mol % content of [PFBMIm][PF ]. We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF ].

Few layer 2D pnictogens catalyze the alkylation of soft nucleophiles with esters.

Group 15 elements in zero oxidation state (P, As, Sb and Bi), also called pnictogens, are rarely used in catalysis due to the difficulties associated in preparing well-structured and stable materials. Here, we report on the synthesis of highly exfoliated, few layer 2D phosphorene and antimonene in zero oxidation state, suspended in an ionic liquid, with the native atoms ready to interact with external reagents while avoiding aerobic or aqueous decomposition pathways, and on their use as efficient catalysts for the alkylation of nucleophiles with esters. The few layer pnictogen material circumvents the extremely harsh reaction conditions associated to previous superacid-catalyzed alkylations, by enabling an alternative mechanism on surface, protected from the water and air by the ionic liquid.

Cation Exchange at the Interfaces of Ultrathin Films of Fluorous Ionic Liquids on Ag(111).

In the context of applications with thin ionic liquid (IL) films on solid supports, we studied the ion distribution within mixed thin IL films by angle-resolved X-ray photoelectron spectroscopy. After the deposition of 1-methyl-3-octylimidazolium hexafluorophosphate, [CCIm][PF], on top of a wetting layer (WL) of 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF], on Ag(111) at room temperature (RT), we find a preferential enrichment of the [PFBMIm] cation at the IL/vacuum interface. In a similar deposition experiment at 82 K, this cation exchange at the IL/solid interface does not occur.

Anion Exchange at the Liquid/Solid Interface of Ultrathin Ionic Liquid Films on Ag(111).

Thin ionic liquid (IL) films play an important role in many applications. To obtain a better understanding of the ion distribution within IL mixture films, we sequentially deposited ultrathin layers of two ILs with the same cation but different anions onto Ag(111), and monitored their dynamic behaviour by angle-resolved X-ray photoelectron spectroscopy. Upon depositing [C C Im][PF ] on top of a wetting layer of [C C Im][Tf N] at room temperature (RT), we found a pronounced enrichment of the [Tf N] anions at the IL/vacuum interface, due to a rapid anion exchange at the IL/solid interface.

Time-dependent changes in the growth of ultrathin ionic liquid films on Ag(111).

Various amounts of the ionic liquids (ILs) [C1C1Im][Tf2N] and [C8C1Im][Tf2N] were deposited in vacuo by physical vapour deposition (PVD) on single crystalline Ag(111) at room temperature and subsequently monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS) as a function of time. For very low coverages of up to one closed molecular layer, an initial wetting layer was rapidly formed for both ILs. Deposition of higher amounts of [C1C1Im][Tf2N] revealed an initial three-dimensional film morphology.

Surface Enrichment in Equimolar Mixtures of Non-Functionalized and Functionalized Imidazolium-Based Ionic Liquids.

For equimolar mixtures of ionic liquids with imidazolium-based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle-resolved X-ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1-methyl-3-octylimidazolium hexafluorophosphate+1,3-di(methoxy)imidazolium hexafluorophosphate ([C C Im][PF ]+[(MeO) Im][PF ]), we find a strong enrichment of the octyl chain-containing [C C Im] cation and a corresponding depletion of the [(MeO) Im] cation in the topmost layer. For a mixture with different cations and anions, that is, [C C Im][Tf N]+[(MeO) Im][PF ], we find both surface enrichment of the [C C Im] cation and the [Tf N] (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO) Im] and [PF ] are depleted from the surface.

Probing the Surface Tension of Ionic Liquids Using the Langmuir Principle.

At 298 K, the surface tension of ionic liquids (ILs) of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series, [C CIm][NTf], ranges from around 35 mN·m for [CCIm][NTf] to just below 30 mN·m for [CCIm][NTf]. However, the decrease rate along the series is not constant: a large decrease from [CCIm][NTf] to [CCIm][NTf] is followed by almost constant values from [CCIm][NTf] to [CCIm][NTf]. Such behavior is hard to interpret from a molecular point of view without suitable information about the free-surface structure of the different ILs.