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Multicomponent nanoparticle exsolution has emerged as a promising process for obtaining highly active catalysts supported on perovskite oxides. For instance, FeCoNi alloys can be exsolved from Sr2FeCo0.2Ni0.2Mn0.1Mo0.5O6−δ, boosting the electrocatalytic properties of these electrodes. However, due to differences in cation diffusion properties, the composition of the nanoparticles is uneven and strongly affected by process conditions such as temperature. An additional key feature of exsolution is its reversibility, which could help in catalyst regeneration if poisoned. Nevertheless, there is little knowledge on the reversibility mechanisms of multicomponent exsolved alloys. For that purpose, a combination of synchrotron-based in situ X-ray Diffraction (XRD) and Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) was employed in this work to uncover these missing aspects of multicomponent alloyed exsolution. These techniques allowed determination of the crystallographic and surface-related phenomena occurring during reversible exsolution both to the nanoparticles and the perovskite oxide support. This enabled the identification of the exsolution onset temperature and the range at which the double perovskite to Ruddlesden–Popper transition occurred, a process that has notable implications for the electrocatalytic performance. Finally, in combination with microscopy analyses, it was possible to reveal the morphological and compositional changes that the exsolved nanoparticles experienced upon reduction–oxidation cycles. This resulted in a re-arrangement of the surface species and a variation in the composition (Fe enrichment) of the regenerated ternary alloyed exsolved nanoparticles. These results indicate that reversible exsolution might alter the catalytic properties of the exsolved nanoparticles, with profound implications in the performance of (electro)catalytic processes. [ABSTRACT FROM AUTHOR]

Mo/TiO2 catalysts with atomic dispersion of molybdenum appear active and stable in the gas-phase hydrogenation of CO2. A comparison between various titania materials shows a crucial effect of the support surface structure on the methanol yield. Molybdenum supported at low coverage on rutile titania nanorods is the most active and methanol-selective system. From catalyst characterization by aberration-corrected scanning transmission electron microscopy, near-ambient pressure X-ray photoelectron spectroscopy, diffuse reflectance UV-vis spectroscopy, and temperature-programmed techniques, we suggest that the most active catalysts for methanol production involve ultradispersed molybdate species with high reducibility and strong interaction with the rutile support. [ABSTRACT FROM AUTHOR]

SnS and SnS2 are earth abundant layered semiconductors that owing to their optoelectronic properties have been proposed as materials for different photovoltaic, photosensing and photocatalytic applications. The intrinsic efficiency of these materials for such applications is driven by their charge transfer dynamics, which in turn depend on their electronic structure and the interaction of the molecular orbitals involved in the charge transfer process. In this publication, we provide a step-by-step description of the use of the core hole clock method to obtain orbital dependent charge transfer times for SnS2 and SnS down to the attosecond time scale. We use both S 1s and Sn 3d core holes, with natural core hole lifetimes of 1.3 fs and 300 as, as time references to obtain a complete picture of electron delocalisation times across the conduction band of both materials. Ultrafast electron delocalisation times, lower than 5 femtoseconds and as low as tens of attoseconds, are measured for electrons excited to the unoccupied molecular orbitals of both materials. SnS delocalisation times are found to be shorter than those for SnS2 for all probed molecular orbitals, with delocalisation times being more than an order of magnitude shorter for higher lying molecular orbitals. DFT calculations show that charge transfer dynamics are strongly influenced by the interlayer interaction within these materials. The slower delocalisation of electrons in SnS2 can be linked to the restricted out of plane spatial dispersion of the molecular orbitals in the conduction band and consequent limitation of the electron delocalisation pathways. The results presented in this paper highlight the high potential of combining the core hole clock method with high-level DFT calculations to study orbital dependent charge transfer in semiconductor materials for optoelectronic applications down to the attosecond scale. [ABSTRACT FROM AUTHOR]

The atomic contributions to valence electronic structure for 37 ionic liquids (ILs) are identified using a combination of variable photon energy XPS, resonant Auger electron spectroscopy (RAES) and a subtraction method. The ILs studied include a diverse range of cationic and anionic structural moieties. We introduce a new parameter for ILs, the energy difference between the energies of the cationic and anionic highest occupied fragment orbitals (HOFOs), which we use to identify the highest occupied molecular orbital (HOMO). The anion gave rise to the HOMO for 25 of the 37 ILs studied here. For 10 of the ILs, the energies of the cationic and anionic HOFOs were the same (within experimental error); therefore, it could not be determined whether the HOMO was from the cation or the anion. For two of the ILs, the HOMO was from the cation and not from the anion; consequently it is energetically more favourable to remove an electron from the cation than the anion for these two ILs. In addition, we used a combination of area normalisation and subtraction of XP spectra to produce what are effectively XP spectra for individual ions; this was achieved for 10 cations and 14 anions. [ABSTRACT FROM AUTHOR]

The structures of mixtures of ionic liquids (ILs) featuring a common 1-butyl-3-methylimidazolium ([C4C1im]+) cation but different anions have been investigated both experimentally and computationally. 1H and 13C NMR of the ILs and their mixtures has been performed both on the undiluted liquids and those diluted by CD2Cl2. These experiments have been complemented by quantum chemical density functional theory calculations and molecular dynamics simulations. These techniques have identified the formation of preferential interactions between H2 of the imidazolium cation and the most strongly hydrogen bond (H-bond) accepting anion. In addition, a preference for the more weakly H-bond accepting anion to interact above the imidazolium ring through anion–π+ interactions has been identified. The modelling of these data has identified that the magnitude of these preferences are small, of the order of only a few kJ mol−1, for all IL mixtures. No clustering of the anions around a specific cation could be observed, indicating that these interactions arise from the reorientation of the cation within a randomly assigned network of anions. π+–π+ stacking of the imidazolium cations was also studied and found to be promoted by ILs with a strong H-bond accepting anion. Stacking interactions are easily disrupted by the introduction of small proportions (＜50 mol%) of a weakly coordinating anion due to their propensity to form anion–π+ interactions. These results suggest that the formation of IL mixtures with different anions leads to subtle structural changes of much lower energy than the Coulombic ordering of ions, accounting for why most IL mixtures exhibit ideal, or nearly ideal, behaviour. [ABSTRACT FROM AUTHOR]

Ionic liquid–vacuum outer atomic surfaces can be created that are remarkably different from the bulk composition. In this communication we demonstrate, using low-energy ion scattering (LEIS), that for ionic liquid mixtures the outer atomic surface shows significantly more atoms from anions with weaker cation–anion interactions (and vice versa). [ABSTRACT FROM AUTHOR]

Single crystalline pyrochlore Bi2Ti2O7 films have been grown in three different orientations on yttria-stabilised zirconia at temperatures as low as 600 °C, by using a simple wet chemistry method based on the spin-coating technique. Contrary to free-standing powders and polycrystalline films, epitaxial single crystalline Bi2Ti2O7 is stable relative to other bismuth titanate compounds at temperatures up to 900 °C. A study of core X-ray photoelectron spectra shows Bi2Ti2O7 films contain an oxygen deficiency whose concentration depends on the annealing temperature. Based on low-energy ion scattering spectroscopy, it was determined that crystalline surfaces terminate in BiOx-like structures. [ABSTRACT FROM AUTHOR]

Simple ionic liquids have long been held to be designer solvents, based upon the ability to independently vary their cations and anions. The formation of mixtures of ionic liquids increases this synthetic flexibility. We review the available literature of these ionic liquid mixtures to identify how their properties change and the possibility for their application. [ABSTRACT FROM AUTHOR]

Ionic liquid surfaces can become electrically charged during X-ray photoelectron spectroscopy experiments, due to the flux of photoelectrons leaving the surface. This causes a shift in the measured binding energies of X-ray photoelectron peaks that depends on the magnitude of the surface charging. Consequently, a charge correction method is required for ionic liquids. Here we demonstrate the nature and extent of surface charging in ionic liquids and model it using chronopotentiometry. We report the X-ray photoelectron spectra for a range of imidazolium based ionic liquids and investigate the use of long alkyl chains (CnH2n+1, n≥ 8) and the imidazolium nitrogen, both of which are part of the ionic liquid chemical structure, as internal references for charge correction. Accurate and reproducible binding energies are obtained which allow comparisons to be made across ionic liquid-based systems. [ABSTRACT FROM AUTHOR]

A range of chloroindate(iii) ionic liquid systems was prepared by mixing of 1-alkyl-3-methylimidazolium chloride with indium(iii) chloride in various ratios, expressed as the mol fraction of indium(iii) chloride, χInCl3. For χInCl3≤ 0.50, the products were liquids, whereas for χInCl3> 0.50, the products were biphasic (suspensions of a solid in an ionic liquid). Speciation of these chloroindate(iii) systems was carried out using a wide range of techniques: differential scanning calorimetry (DSC), polarised optical microscopy (POM), liquid-state and solid-state 115In NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). Ionic liquids prepared using an excess of the organic chloride (χInCl3 0.5) contained indium(iii) chloride powder suspended in a neutral tetrachloroindate ionic liquid. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of FeIIIto FeIIin the ionic liquid (IL) mixture of 1-ethyl-3-methylimidazolium ethylsulfate, [C2C1Im][EtOSO3], and 1-butyl-3-methylimidazolium tetrachloroferrate (iii), [C4C1Im][FeIIICl4], was monitored in situby X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

A range of chloroindate(iii) ionic liquid systems was prepared by mixing of 1-alkyl-3-methylimidazolium chloride with indium(iii) chloride in various ratios, expressed as the mol fraction of indium(iii) chloride, chi(InCl(3)). For chi(InCl(3)) 0.50, the products were biphasic (suspensions of a solid in an ionic liquid). Speciation of these chloroindate(iii) systems was carried out using a wide range of techniques: differential scanning calorimetry (DSC), polarised optical microscopy (POM), liquid-state and solid-state (115)In NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). Ionic liquids prepared using an excess of the organic chloride (chi(InCl(3)) < 0.5) contained [InCl(6)](3-), [InCl(5)](2-) and [InCl(4)](-) anions, in proportions dependent on the chi(InCl(3)) value. Equimolar mixtures yielded single compounds: 1-alkyl-3-methylimidazolium tetrachloroindates(iii). Systems containing an excess of indium(iii) chloride (chi(InCl(3)) > 0.5) contained indium(iii) chloride powder suspended in a neutral tetrachloroindate ionic liquid.

Ultra high vacuum-spectroelectrochemistry was used to investigate the electrochemically generated Cu species in the ionic liquid (N-methylacetate)-4-picolinium bis(trisfluoromethylsulfonyl)imide, [MAP][Tf(2)N]. The diffusion of Cu(+) across the surface of the ionic liquid was monitored in situ by X-ray photoelectron spectroscopy (XPS). A numerical procedure was developed to simulate the surface process from which, the apparent diffusion coefficient of Cu(+) across the surface is estimated to be 3.5 x 10(-5) cm(2) s(-1). Bulk diffusion process of Cu(+) in [MAP][Tf(2)N] was investigated ex situ for comparison with the surface process.

We report the enthalpies of vaporisation (measured using temperature programmed desorption by mass spectrometry) of twelve ionic liquids (ILs), covering four imidazolium, [C(m)C(n)Im]+, five pyrrolidinium, [C(n)C(m)Pyrr]+, two pyridinium, [C(n)Py]+, and a dication, [C3(C1Im)2]2+ based IL. These cations were paired with a range of anions: [BF4]-, [FeCl4]-, [N(CN)2]-, [PF3(C2F5)3]- ([FAP]-), [(CF3SO2)2N]- ([Tf2N]-) and [SCN]-. Using these results, plus those for a further eight imidazolium based ILs published earlier (which include the anions [CF3SO3]- ([TfO]-), [PF6]- and [EtSO4]-), we show that the enthalpies of vaporisation can be decomposed into three components. The first component is the Coulombic interaction between the ions, DeltaU(Cou,R), which is a function of the IL molar volume, V(m), and a parameter R(r) which quantifies the relative change in anion-cation distance on evaporation from the liquid phase to the ion pair in the gas phase. The second and third components are the van der Waals contributions from the anion, DeltaH(vdw,A), and the cation, DeltaH(vdw,C). We derive a universal value for R(r), and individual values of DeltaH(vdw,A) and DeltaH(vdw,C) for each of the anions and cations considered in this study. Given the molar volume, it is possible to estimate the enthalpies of vaporisation of ILs composed of any combination of the ions considered here; values for fourteen ILs which have not yet been studied experimentally are given.

The presence of water can have a significant influence upon both the physical and dielectric properties of ionic liquids and consequently their ability to interact with microwaves. Herein we show that complex permittivity initially decreases as low concentrations of water are added to the system, the continued addition of water gives rise to an inversion in this trend. We propose that this minimum point may be used to identify water dimer formation.

Monolayer adsorption of water onto an ionic liquid in ultra-high vacuum has been demonstrated, revealing a heat of adsorption which exceeds the heat of absorption into the bulk liquid by approximately 40 kJ mol(-1).

Eight common imidazolium based ionic liquids have been successfully evaporated in ultra-high vacuum, their vapours analysed by line of sight mass spectrometry and their heats (enthalpy) of vapourisation determined. They were found to evaporate as ion pairs, with heats of vapourisation which depend primarily on the coulombic interactions within the liquid phase and the gas phase ion pair. An electrostatic model is presented relating the heats of vapourisation to the molar volumes of the ionic liquids.