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Solid-oxide fuel cells require materials that are mechanically and chemically resistant, such as doped cerium oxide or zirconium oxide1, and perovskite mixed conductors. The high working temperatures, and the intimate contact between electrolyte and electrode can bring about cation diffusion and solid-state reactions between the cell components. To investigate the local and chemical structure of the species at the interfaces, we recently employed X-ray microspectroscopy on electrode-cathode bilayers2,3. We investigated the interface between several different electrolytes, either proton conducting or oxide-ion conducting, and perovskite electrodes, after annealing at high temperatures (1100 °C for 12-72 h) to simulate the fabrication processes and prolonged operation. The interfaces were studied with space-resolved X-ray absorption spectroscopy using the focused submicrometer-sized beam available at the ID21 beamline of ESRF. We used XRF to obtain concentration maps of all elements, and collected microXANES spectra at Ca, Mn, Fe, Co and Ce absorption edges. We found that the rate of interdiffusion of the cations across the interface, and the formation of secondary phases, depends critically on the specific electrolyte/electrode pair. Moreover, microXANES spectra indicate that some cations show space-resolved changes in their oxidation and coordination state during diffusion. [1] J.W. Fergus, J. Power Sources 162 (2006), 30-40. [2] F. Giannici et al., Chem. Mater. (2015) 27 (8), 2763-2766. [3] F. Giannici, et al., ACS Appl. Mater. Interfaces 9.51 (2017), 44466-44477.

The structural and chemical compatibility between electrodes and electrolytes for use in Solid Oxide Fuel Cells (SOFCs) is a critical issue: the materials should display similar thermal expansion coefficients, and most importantly the interdiffusion of chemical species at the interface has to be minimised. Chemical compatibility is commonly investigated by means of X-ray diffraction on powder mixtures and/or scanning electron microscopy/energy-dispersive spectroscopy on cross-sections of the bilayer assembly after prolonged annealing at high temperatures, to simulate both the long-term operation of a fuel cell and the thermal treatments necessary for processing. This work reports on the application of X-ray microspectroscopy to evaluate the chemical and local structural fate of cations interdiffusing across several electrolyte/cathode bilayers. X-ray microspectroscopy combines an X-ray microprobe providing information on the spatial distribution of cations (X-ray fluorescence (XRF) maps) with chemical and structural information about the environment of atomic species, i.e. chemical and coordination state of cations, using space-resolved micro-X-ray absorption near-edge structure (microXANES). The interfaces were studied using the focused submicrometre-sized beam available at the SXM-II endstation on the ID21 beamline of ESRF. Different electrode-electrolyte couples, annealed at 1150 C for either 12 h or 72 h, were analysed with this technique. Both proton conductors such as BaCe0.9Y0.1O3 (BCY) and La0.98Ca0.02NbO4 (LNC), [1] and an oxide-ion conductor, Ce0.8Sm0.2O2 (SDC), [2] were studied in combination with common cathode materials. The effect of prolonged thermal treatment on cation diffusion, accumulation of cations at the interface and the eventual formation of secondary phases in some of the bilayers will be shown. The present results represent the first application of X-ray absorption spectroscopy to the study of materials compatibility for ceramics, specifically in materials for SOFCs. This approach can be extended to other materials or complete SOFCs: this can give insight on the mechanisms governing electrolyte-electrode compatibility and electrochemical performance in SOFCs. References. [1] F. Giannici et al., Chem. Mater. 2015, 27, 2763 [2] F. Giannici et al., ACS Appl. Mater. Interfaces 2017, 9, 44466 Acknowledgements. This work was funded through the MIUR project FIRB2012 INCYPIT, Ref. RBFR12CQP5. We acknowledge the ESRF for provision of beamtime.

This chapter is devoted to the analysis of the local atomic structure of solid oxide fuel cell (SOFC) electrolyte and electrode materials. Among the experimental techniques able to provide information about the local structure of materials, the X-ray absorption spectroscopy has the peculiarity of element selectivity, allowing to investigate the chemical environment of specific atoms embedded in a matrix. Solid oxide electrolytes allow the conduction of ionic charge carriers between the electrodes of a SOFC device; the mechanism of ion conduction depends on the type of carrier, and it is finely tuned-or even only possible-if the solid matrix is suitably tailored by insertion of doping species that modify the local structure and the dynamics of the lattice. The oxygen reduction and fuel oxidation processes are catalyzed at the respective electrodes; moreover, the cathode and anode layers must: (1) allow an efficient exchange of reactants with the environment, (2) convey the ionic species to/from the electrolyte and (3) ensure the conduction of the electrons involved in the reduction and oxidation processes. The chemical and physical stability of the interface with the electrolyte layer is another essential issue of electrode materials. The chapter begins with a section describing the basic theory underlying the X-ray absorption spectroscopy and the experimental set-ups used in fuel cell applications. The second section reports on case studies and perspectives of future development of fuel cell materials under the keynote of local structure.

Chemical and structural compatibility between materials is a critical point in all-ceramic devices working at very high temperatures: in this respect, the degradation of the cell performance is often the critical factor limiting the working life of SOFC. LaNbO4 doped with 2% Ca2+ (LNC) represents the last real breakthrough in the field of proton-conducting oxides for use as electrolytes in SOFC, showing improved stability and high conductivity with respect to perovskites [1]. To develop efficient and robust devices based on LNC, the electrical performance and chemical compatibility of various electrode materials with LNC was extensively tested in recent literature. [2] We recently applied X-ray microspectroscopy to evaluate the chemical and local structural fate of cations interdiffusing across an LNC/cathode bilayer (where the cathode is either La0.6Sr0.4MnO3, La0.6Sr0.4Co0.8Fe0.2O3, etc.) after prolonged annealing at high temperatures (1150 °C), to simulate the operating conditions of a fuel cell. The interfaces of the devices were studied with space-resolved X-ray absorption spectroscopy (XAS) using the focused submicrometer-sized beam available at the SXM-II endstation on the ID21 beamline of ESRF. We collected microXANES and microEXAFS spectra at the Nb L3, La L3, Ca K, Fe K and Mn K edges. The microXRF composition maps spectra were also collected, giving information on the distribution of cations. In general, an unexpected and impressive exsolution of the Ca2+ dopant from the LNC electrolyte towards the cathode is observed in all samples. [3] The Ca and Nb change of coordination number and geometry between the perovskite cathode and the LNC electrolyte is well supported by microXANES simulations, pinpointing the greater structural flexibility of the perovskite structure as the driving force behind the incorporation of cations from the electrolyte. Fe and Mn edge microXANES spectra also show interesting variations as a function of the distance from the interface, hinting at some kind of oxygen vacancy accumulation at the interface. At the La, Fe and Mn edges, high quality microEXAFS spectra were collected and modeled up to about 8 Å-1. The present results represent the first application of microfocus X-ray absorption spectroscopy to the study of materials compatibility in SOFC. This approach can be extended to other kinds of electrode materials, including ceramic anodes, cermets, and oxide-ion conductors, reproducing different working conditions of real devices: this is expected to give unprecedented insight on the mechanisms governing electrolyte-electrode compatibility and electrochemical performance in solid oxide fuel cells. [1] R. Haugsrud & T. Norby Nature Mater. 2006, 5, 193-196. [2] K.V. Kravchyk et al. Int. J. Hydrogen Energ. 2011, 36, 13059. [3] F. Giannici et al. Chem. Mater. 2015, in press. doi: 10.1021/acs.chemmater.5b00142

We describe the functionalization of the layered perovskite HLaNb2O7 with n-propanol, n-decanol, 3-mercaptopropyl-trimethoxysilane, imidazole, n-decylamine, and histamine. The use of sonication is found to significantly improve the reaction yield and to reduce the reaction time, compared to conventional thermal treatment under reflux. The obtained intercalates are thoroughly characterized through the use of several complementary experimental techniques (scanning electron microscopy, IR spectroscopy, X-ray diffraction, thermogravimetric analysis, magic-angle spinning NMR), clarifying their structure and chemical bonding. The implications for the design of inorganic–organic composite materials are discussed.

Dion-Jacobson phases, like MLaNb2O7, are an interesting class of ion-exchangeable layered perovskites possessing electronic and photocatalytic properties. Their protonated and organo-modified homologues, in particular, have already been indicated as promising catalysts. However, the structural analysis of these highly tailorable materials is still incomplete, and both the intercalation process and thermal stability of the included organic moieties are far from being completely understood. In this study, we present a thorough solid-state NMR characterization of HLaNb2O7·xH2O intercalated with different amounts of octylamine, or with decylamine. Samples were analyzed as prepared, and after thermal treatment at different temperatures up to 220 °C. The substitution of pristine proton ions was followed via(1)H MAS NMR spectroscopy, whereas the alkyl chains were monitored through (13)C((1)H) CP MAS experiments. The interactions in the interlayer space were explored using (13)C((1)H) 2D heteronuclear correlation experiments. We demonstrate that some of the protons are involved in the functionalization reaction, and some of them are in close proximity to the alkyl ammonium chains. Heating of the hybrid materials leads first to a rearrangement of the alkyl chains and then to their degradation. The spatial arrangement of the chains, their interactions and the thermal behavior of the materials depend on the extent of the functionalization, and on the nature of the intercalated alkyl ammonium ions.

High-energy-resolution fluorescence detection-X-ray absorption near-edge structure (HERFD-XANES) at the Au L3 edge was used to study gold catalysts supported on ceria in order to unravel the role of gold 5d orbital modifications during the activation of molecular oxygen. The variations in the HERFD-XANES resonance peak, which are directly correlated with the d-band occupancy, were monitored in situ during the redox process of the CO oxidation at room temperature under both aerobic and anaerobic conditions. Interestingly, upon the oxidation treatment and also during the aerobic CO oxidation treatment, the gold d-band fluctuates around an average value, proving that the gold clusters are partially charged. The dynamism of the gold electronic configuration was evidenced by a temporary variation of the gold d-orbital population during the oxidation reaction. The interpretation of X-ray spectroscopy data is supported by ab initio simulations performed using the FDMNES code.

A halloysite-based geopolymer filled with microwax particles was designed as a protective layer on steel substrates. Beeswax microparticles were obtained from the clay stabilized Pickering emulsions and they were homogeneously dispersed within the geopolymeric network, thus improving the coating physico-chemical properties. Specifically, this treatment changed the steel's wettability by increasing its hydrophobicity. Moreover, XRF analysis was conducted in order to have details on the chemical compositions.

Hybrid halometalates containing lead, tin, bismuth and antimony and organic cations have recently shown a bevy of interesting photophysical properties. Aiming at finding chemically stable and thermally inert species, three halobismutate species of this class, crystallized with proton sponge-derived cations (PRSH), have been isolated as microcrystalline powders by mixing 1,8-bis(dimethylamino)-naphthalene (proton sponge, or PRS) and bismuth oxide in concentrated HX acids (X ​= ​Cl, Br and I). The two isomorphous (PRSH)3Bi2X9 (X ​= ​Br, I) species, containing isolated [Bi2X9]3- anions, are triclinic at room temperature and convert upon heating into a monoclinic structure through a displacive phase transformation, fully reversible for X ​= ​I and only partially for X ​= ​Br. At variance, (PRSH)BiCl4 is polymeric, and contains extended zigzagging 1D chains formed by edge-sharing BiCl6 octahedra. These species were extensively studied by synchrotron and laboratory X-ray powder diffraction measurements, which enabled to detect the evolution toward the two high-temperature β-phases (X ​= ​Br, I), to derive the structure of five different (significantly complex) species and to assess the thermal strain tensors in the different regimes. Additional thermal, spectroscopic and computational analyses completed the characterization of these materials.

Hybrid one-dimensional lead halides, containing the protonated 1,8-bis(dimethylamino)naphthalene moiety (C14H19N2, monoprotonated "proton sponge"), were prepared by simple one-pot methods and investigated in terms of crystal structure, morphology, thermal stability and electronic properties. The as-precipitated (C14H19N2)PbBr3 and (C14H19N2)PbI3 species are isostructural and crystallize in the orthorhombic Pbca space group, resulting in 1D crystal phases with ([PbX3](-))(infinity) chains (built by face-sharing [PbX6] octahedra; X = Br, I), among which the (C14H19N2)(+) cations are inserted. The two compounds display complete miscibility in the solid state: both (C14H19N2)PbI2Br and (C14H19N2)PbIBr2 crystal phases were successfully synthetized and do not show segregation effects. TGA and DSC measurements showed that, while all these materials are stable up to 250 degrees C, the iodine-rich (C14H19N2)PbI3 and (C14H19N2)PbI2Br species undergo an irreversible phase transition around 220 degrees C to a high-temperature phase, with a smaller molar volume and an apparent symmetry lowering (to orthorhombic Pca2(1)). In these two cases, variable-temperature X-ray diffraction measurements showed a substantial crystal-to-crystal transformation, without intermediate melting or amorphization. The thermal expansion coefficients of (C14H19N2)PbI3 and (C14H19N2)PbBr3 are highly anisotropic and on the order of 10(-4) K-1 along the b crystallographic axis. Microscopic and spectroscopic measurements were performed to complement the structural analysis of the samples: band gaps in the near UV range (3.3 and 3.8 eV for (C14H19N2)PbI3 and (C14H19N2)PbBr3, respectively) were obtained.

The literature concerning protonic ceramic devices is critically reviewed focusing the reader's attention on the structure, composition, and phenomena taking place at solid-solid interfaces. These interfaces play a crucial role in the overall device performance, and the relevance of understanding the phenomena taking place at the interfaces for the further improvement of electrochemical protonic ceramic devices is therefore stressed. The grain boundaries and heterostructures in electrolytic membranes, the electrode-electrolyte contacts, and the interfaces within composite anode and cathode materials are all considered, with specific concern to advanced techniques of characterization and to computational modeling by ab initio approaches. An outlook about future developments and improvements highlights the necessity of a deeper insight into the advanced analysis of what happens at the solid-solid interfaces and of in situ/operando investigations that are presently sporadic in the literature on protonic ceramic devices.

Bilge waters are wastewaters produced on boats during navigation and usually contain hydrocarbons and oils. They cannot be directly released into the sea if not below a hydrocarbons concentration limit set by current legislation. Appropriate oil in water separator (OWS) systems can be installed on board boats to remove hydrocarbons from bilge water allowing their spillage into the sea. These systems may contain an adsorption step on a suitable adsorbent. Here, biochars produced from pyrolysis of dead Posidonia oceanica, pristine or chemically activated, have been tested as hydrocarbons adsorbents. Adsorption experiments with aqueous dispersions simulating bilge waters containing a marine gas oil (MGO) fuel for boats, a surfactant, and different NaCl concentrations were carrying out. The hydrocarbons concentrations before and after adsorption have been directly measured by using the reverse phase HPLC technique coupled with a fluorescence detector. These measurements are very fast and their reliability was verified by re-measuring the hydrocarbons concentrations of some samples with the GC–MS-MS technique, according to one of the traditional methods for hydrocarbons determination in emulsions. Different isotherm equations were used to fit the adsorption data. The biochars were characterized from the chemical-structural point of view by means of several instrumental techniques.

The recently described monodimensional hybrid pseudo-perovskite ((CH3)3SO)PbI3 exhibits complete Pb2+/Bi3+ miscibility in the B site. Heterovalent substitution imposes that charge-compensating defects are introduced in the lattice as well. This paper reports the energetics of point defects and the interaction between charge-compensating defects that occur upon Bi3+ doping in ((CH3)3SO)PbI3. Periodic DFT simulations were employed to analyze the formation energy of Pb2+ vacancies, (CH3)3SO+ vacancies, iodide vacancies, or the insertion of interstitial iodide ions. Solid solutions with a large Bi3+ content were modeled considering different charge compensation defects (Pb2+ vacancies, (CH3)3SO+ vacancies, and interstitial iodide) to consider electrical neutrality. Both the formation energy evaluation and the structural parameters after relaxation are in very good agreement with available experimental data (both X-ray diffraction and absorption spectroscopy), confirming that Pb2+ vacancies are indeed the primary ionic charge-compensation mechanism leading to solid solutions described by the formula ((CH3)3SO)3Pb3xBi2(1-x)V(1-x)I9 (0 < x < 1), where V indicates a B site vacancy. As a consequence of the complete miscibility, the defect concentration at intermediate compositions is considerable, and it is probably responsible for various peculiar structural effects observed, e.g., in ((CH3)3SO)3Pb0.99Bi1.34I9, which are related to short-range order phenomena in the chain composition. Atomistic simulations were then carried out to estimate defect-defect interactions as a function of their respective positions inside the linear PbI6/BiI6 octahedral chains. The resulting bond energies for atom pairs and triads effectively explain the relative stability of defect clusters. This approach is expected to shed light on the short-range order in this class of doped materials, but it can be extended to other structures as well. The understanding of defect structures and control of structural and electronic properties have implications for the engineering of doped materials, which find vast applications in optoelectronic devices.

Oxides with mixed protonic-electronic conductivity are relevant as oxygen electrodes for protonic ceramic fuel cells and electrolyzers. We investigate the modification of the electronic structure of (Ba,La)(Fe,Zn,Y)O3−δ when iron is partially replaced by Zn2+ or Y3+ and when it changes between 3+ and 4+ formal oxidation states. With a combination of X-ray Raman scattering (O K-edge) and X-ray absorption near edge structure (Fe, Zn, and Y K-edges) and the corresponding simulations reproducing the spectroscopic data, we quantitatively analyze the degree of covalency of the Fe-O bonds in reduced (Fe mainly 3+) and oxidized (Fe mainly 4+) materials. The simulations employ two semi-empirical parameters to account for the electronic perturbations arising from Y and Zn doping and/or a change of the iron oxidation state. In the case of large structural and electronic rearrangements, the explicit consideration of 5-fold coordinated iron proved necessary. The observed lower Fe-O bond covalence in Zn- and Y-doped samples can be related to their increased proton uptake. The results discussed and the methodology used for quantifying the covalency of the bond between transition metals and oxygen is expected to be applicable also for other perovskites. It can thus serve as a tool for further optimization of oxygen electrode materials for protonic ceramic fuel and electrolyzer cells.

The solid-state compatibility between calcium-doped lanthanum niobate and three perovskite cathode materials was investigated using two X-ray microbeam techniques, micro X-ray fluorescence and micro X-ray absorption spectroscopy. The cathode powders (lanthanum strontium ferrite, either cobalt or copper-doped, and lanthanum strontium cobaltite) in contact with the dense electrolyte pellet were annealed at 1150 degrees C for 12-144 h to simulate the effect of thermal stresses due to fabrication and long-term operation. As a result, several interdiffusion phenomena were then observed on the bilayer cross-sections: in particular, the chemical state and coordination environment of calcium, iron, niobium and lanthanum were probed with space-resolved X-ray absorption spectroscopy. The ab initio modeling of the near-edge X-ray absorption spectra reveal that the cation interdiffusion is facilitated by the structural flexibility of the perovskite structure, which is able to accommodate a variety of foreign cations in different oxidation states. Limited stability at high-temperatures was found for all candidate perovskite compositions in contact with lanthanum niobate. (C) 2021 Elsevier Ltd. All rights reserved.

In this study, the structure and morphology, as well as time, ultraviolet radiation, and humidity stability of thin films based on newly developed 1D (PRSH)PbX3 (X = Br, I) pseudo-perovskite materials, containing 1D chains of face-sharing haloplumbate octahedra, are investigated. All films are strongly crystalline already at room temperature, and annealing does not promote further crystallization or film reorganization. The film microstructure is found to be strongly influenced by the anion type and, to a lesser extent, by the DMF/DMSO solvent volume ratio used during film deposition by spin-coating. Comparison of specular X-ray diffraction and complementary grazing incidence X-ray diffraction analysis indicates that the use of DMF/DMSO mixed solvents promotes the strengthening of a dominant 100 or 210 texturing, as compared the case of pure DMF, and that the haloplumbate chains always lie in a plane parallel to the substrate. Under specific DMF/DMSO solvent volume ratios, the prepared films are found to be highly stable in time (up to seven months under fluxing N2 and in the dark) and to highly moist conditions (up to 25 days at 78% relative humidity). Furthermore, for representative (PRSH)PbX3 films, resistance against ultraviolet exposure (λ = 380 nm) is investigated, showing complete stability after irradiation for up to 15 h at a power density of 600 mW/cm2. These results make such thin films interesting for highly stable perovskite-based (opto)electronic devices.

Layered TiS2 intercalated with linear alkylamines has recently attracted significant interest as a model compound for flexible n-type thermoelectric applications, showing remarkably high power factors at room temperature. The thermal and, particularly, environmental stability of such materials is, however, a still an open challenge. In this paper, we show that amine-intercalated TiS2 prepared by a simple mechanochemical process is prone to chemical decomposition through sulfur exsolution, and that the presence of molecular oxygen is likely to mediate the decomposition reaction. Through computational analysis of the possible reaction pathways, we propose that Ti-N adducts are formed as a consequence of amine groups substituting for S vacancies on the internal surfaces of the S-Ti-S layers. These findings provide insights for possible future applications of similar hybrid compounds as devices operating in ambient conditions, and suggest isolating them from atmospheric oxygen.

International audience; This paper examines the production technology of Egyptian blue, an ancient artificial pigment, through the investigation of an unsuccessfully produced pellet derived from the Hellenistic production site of Kos (Dodecanese, Greece). This heterogeneous material was investigated by a combination of laboratory and synchrotron radiation-based (SR) techniques: scanning electron microscopy coupled with energy-dispersive Xray spectrometry, micro-Raman spectroscopy, high-resolution SR micro-X-ray fluorescence spectroscopy, and SR micro-X-ray absorption near-edge structure spectroscopy (XANES), at the ID21 beamline of the European Synchrotron Radiation Facility. Principal component analysis of a large dataset of 171 micro-XANES spectra acquired on the archaeological samples and on a series of reference copper compounds emphasizes high variations of XANES features due to different speciation and also orientation effects, as demonstrated by the simulated XANES spectra. The results indicate that, rather than inadequate firing temperatures that could have led to the reddish cuprite (Cu 2 O), unsuccessful production may occur due to the use of inappropriate starting materials, which contain an unusually high iron content. The contextual interpretation underlines the intertwined relationship between the production of Egyptian blue and metallurgy.

The structures of the disordered 1D (pseudo-)perovskites of general TMSO(Pb x Bi y )I3 formulation [TMSO = (CH3)3SO+], obtained by doping the TMSOPbI3 species with Bi3+ ions, are investigated through the formulation of a statistical model of correlated disorder, which addresses the sequences of differently occupied BI6 face-sharing octahedra (B = Pb, Bi or vacant site) within ideally infinite [(BI3)−] n chains. The x-ray diffraction patterns simulated on the basis of the model are matched to the experimental traces, which show many broad peaks with awkward (nearly trapezoidal) shapes, under the assumption that the charge balance is fully accomplished within each chain. The analysis allowed to establish a definite tendency of the metal species to cluster as pure Pb and Bi sequences. The application of the model is discussed critically, in particular as what concerns the possibility that further B-site neighbors beyond the second may influence the overall B-site occupancies.

Organic thin films based on naphthalenediimides (NDIs) bearing alkyl substituents have shown interesting properties for application in OLEDs, thermoelectrics, solar cells, sensors and organic electronics. However, the polymorphic versatility attributed to the flexibility of alkyl chains remains a challenging issue, with detrimental implications on the performances. Aryl analogues containing C6H6N2 constitutional isomers are herein investigated as one of the possible way-out strategies. The synthesis of molecular and polymeric species is described, starting from naphthaleneteracarboxyldianhydride with isomeric aromatic amines and hydrazine. The materials are fully characterized by spectroscopy, thermal and structural X-ray diffraction methods, both as bulk powders and thin films, revealing a rich structural landscape. Depending on the stereochemistry of the branching aryls, the compounds show a variety of parallel stacking of the NDI cores, and high structural stability upon heating, up to 560 °C in the polymeric form. Thin films prepared by spin coating from organic solvent solutions and studied by grazing-incidence X-ray diffraction exhibit a high degree of crystallinity indicating the intrinsic tendency of these molecules to self-assemble in an ordered fashion without the need for any post-processing technique. In line with other NDI-based diimides, UV-vis spectroscopy indicates the optical band gaps falling in the visible region (2.87-3.02 eV). DFT calculations reveal a significant lowering of the frontier orbital energies of the hydrazido derivative. Beyond solution processing, the high thermal stability and the absence of polymorphic forms of these materials suggest that sublimation-based routes for films and device preparation can also be followed. This journal is

We report on the synthesis and characterization of novel lead and bismuth hybrid (organic-inorganic) iodide and bromide pseudo-perovskites (ABX3) containing the trimethylsulfoxonium cation (CH3)3SO+ (TMSO) in the A site, Pb/Bi in the B site, and Br or I as X anions. All of these compounds are isomorphic and crystallize in the orthorhombic Pnma space group. Lead-based pseudo-perovskites consist of one-dimensional (1D) chains of face-sharing [PbX6] octahedra, while in the bismuth-based ones, the chains of [BiX6] are interrupted, with one vacancy every third site, leading to a zero-dimensional (0D) local structure based on separated [Bi2I9]3- dimers. Five solid solutions for the iodide with different Pb2+/Bi3+ ratios between (TMSO)PbI3 and (TMSO)3Bi2I9, and two for the bromide counterparts, were synthetized. Due to the charge compensation mechanism, these systems are best described by the (TMSO)3Pb3xBi2(1-x)I9 (x = 0.98, 0.92, 0.89, 0.56, and 0.33) and (TMSO)3Pb3xBi2(1-x)Br9 (x = 0.83 and 0.37) formulae. X-ray powder diffraction (XRPD) measurements were employed to determine the crystal structure of all studied species and further used to test the metal cation miscibility within monophasic samples not showing cation segregation. These systems can be described through an ionic defectivity on the pseudo-perovskite B site, where the Pb2+/Bi3+ replacement is compensated by one Pb2+ vacancy for every Bi3+ pair. This leads to a wide range of possible different (numerical and geometrical) chain configurations, leading to the unique features observed in XRPD patterns. The optical band gap of the iodide samples falls in the 2.11-2.74 eV range and decreases upon increasing the Bi3+ content. Interestingly, even a very low loading of Bi3+ (1%) is sufficient to reduce the band gap substantially from 2.74 to 2.25 eV. Periodic density functional theory (DFT) calculations were used to simulate the atomic and electronic structures of our samples, with predicted band gap trends in good agreement with the experimental ones. This work highlights the structural flexibility of such systems and accurately interprets the ionic defectivity of the different pseudo-perovskite structures.

Mixed protonic–electronic conducting oxides are key functional materials for protonic ceramic fuel cells. Here, (Ba,Sr,La)(Fe,Zn,Y)O3−δ perovskites are comprehensively investigated by X-ray spectroscopy (in oxidized and reduced states). Extended X-ray absorption fine structure shows that Zn,Y doping strongly increases the tendency for Fe–O–Fe buckling. X-ray absorption near-edge spectroscopy at the Fe K-edge and X-ray Raman scattering at the O K edge demonstrate that both iron and oxygen states are involved when the samples are oxidized, and for the Zn,Y doped materials, the hole transfer from iron to oxygen is less pronounced. This can be correlated with the observation that these materials show the highest proton uptake.

The obtainment of materials featured by high environmental compatibility is one of the main goals of modern research. On this subject, we herein report the first example of supramolecular gel in deep eutectic solvents. In particular, we prepared gels of the L-amino acids isoleucine and tryptophan in choline chloride/phenylacetic acid 1:2. All gel components are readily available and nontoxic. Gels have been fully characterized by standard gelation tests, rheology, X-ray diffraction, morphology and gelation kinetics. Data collected show that gels properties depend on the gelator nature. In particular, gel phases exhibit strong colloidal forces and, this high mechanical resistance, together with their environmental friendly nature, make them promising candidates for applications in all those fields requiring good performance and low environmental impact.

In this work we followed the formation of palladium nanoparticles, starting from palladium (II) acetate precursor, inside a poly(4-vinylpyridine-co-divinylbenzene) polymer in presence of different reducing agents. The formation and growth of palladium nanoparticles in presence of H-2 was followed as a function of temperature by simultaneous XANES-SAXS techniques, coupled with DRIFT spectroscopy in operando conditions. It was found that the pyridyl functional groups in the polymer plays a fundamental role in the stabilization of the palladium (II) acetate precursor, as well as in the stabilization of the palladium nanoparticles. The effect of a thermal treatment in alcohol (ethanol and 2-propanol) was preliminarily investigated by means of DRIFT spectroscopy in operando conditions. We found that alcohols act as reducing agents for Pd(OAc)(2). The obtained palladium nanoparticles were preliminarily characterized by means of IR spectroscopy using CO as probe molecule. (C) 2016 Elsevier B.V. All rights reserved.

The modification of metal oxide surfaces with organic moieties has been widely studied as a method of preparing organic-inorganic hybrid materials for various applications. Among the inorganic oxides, ion-exchangeable layered perovskites are particularly interesting, because of their appealing electronic and reactive properties. In particular, their protonated interlayer surface can be easily functionalized with organic groups allowing the production of stable hybrid materials. As a further step in the design of new inorganic-organic hybrid proton conductors, a combined experimental and theoretical study of two intercalated compounds (propanol and imidazole) in HLaNb2O7 is presented here. A generally very good agreement with the available experimental data is found in reproducing both structural features and C-13-NMR chemical shifts, and marked differences between the two considered intercalated compounds are evidenced, with possible important outcomes for proton conduction. Notably, the free imidazole molecules are easily protonated by the acidic protons present in the interlayer spacing, thus inhibiting an efficient charge transport mechanism. In order to overcome this problem, a model system has been considered, where the imidazoles are bound to the end of a butyl chain, the whole being intercalated between two perovskite layers. The obtained theoretical data suggest that, in such a system, proton transfer between two adjacent imidazoles is a barrierless process. These results could then open new perspectives for such hybrid proton conductors.

The stability of the electrode/electrolyte interface is a critical issue in solid-oxide cells working at high temperatures, affecting their durability. In this paper, we investigate the solid-state chemical mechanisms that occur at the interface between two electrolytes (Ce0.8Sm0.2O2, SDC, and BaCe0.9Y0.1O3, BCY) and a cathode material (La0.8Sr0.2MnO3, LSM) after prolonged thermal treatments. Following our previous work on the subject, we used X-ray microspectroscopy, a technique that probes the interface with submicrometric resolution combining microanalytical information with the chemical and structural information coming from space-resolved X-ray absorption spectroscopy. In LSM/BCY, the concentration profiles show striking reactive phenomena at the interface with a variety of micrometer-sized secondary phases: In particular, X-ray absorption spectra reveal at least three different chemical states for manganese (from +3 to +6). Also in LSM/SDC, a couple previously reported as chemically stable, we found the formation of small islets of SmMnO3 after the migration of manganese to the SDC side; these may constitute the nuclei for the subsequent formation of an interfacial resistive layer after more prolonged operation. The ability of manganese to adopt several oxidation states and crystal chemical environments is indicated as a possible cause for these behaviors.

Scheelite-type materials such as LaNbO4 are increasingly attracting attention as a possible alternative to the most common fluorite and perovskite structure as ion conductors. However, they are much less used and investigated. The introduction of tungsten in lanthanum orthoniobate leads to conduction properties that are compatible with oxygen ion conductivity. In this paper, we studied the effect of the introduction of tungsten in the LaNbO4 structure. High resolution X-ray diffraction showed that in LaNb1-xWxO4+x/2 with x = 0.16 the monoclinic distortion is largely suppressed and the tetragonal phase is predominant at room temperature. By XANES/EXAFS we proved that tungsten is in its 6+ valence state and no W5+ was detected. With X-ray microspectroscopy, we studied in detail with a submicrometre-probe the interdiffusion and degradation processes taking place between the material and LSM, a common electrode material, during their long-term contact at high temperatures.

Ca:LaNbO4 (LNC) constitutes the last real breakthrough in high-temperature proton conductors, with better chemical and mechanical stability with respect to cerate and zirconate perovskites. However, the low amount of bivalent dopant that can be hosted in the LaNbO4 matrix poses a limit to the proton concentration in the electrolyte. Using synchrotron X-ray microspectroscopy, we investigated the compatibility of annealed LNC/LSM electrolyte/cathode bilayers for proton-conducting SOFCs. The element maps are complemented by microEXAFS and microXANES, giving information on the fate of different cations after diffusion. The X-ray microspectroscopy approach described here is applied for the first time to the study of materials for energy, and it is proposed as a useful structural tool, complementary to electrochemical characterization, for the investigation of the compatibility between materials for SOFCs. We demonstrate that an impressive calcium drift towards the LSM cathode takes place: the dopant is depleted throughout a region of LNC several micrometers wide, causing a decrease of charge carriers in the electrolyte and eventually impairing its conductivity. This poses a significant challenge for evaluating electrolyte/electrode couples in proton-conducting SOFCs based on LNC.

Diimidazolium-based organic salts, bearing peptides or amino acids as anions have been synthesised and tested for their gelling ability in biocompatible solvents. These low molecular weight salts were successfully used as gelators in phosphate buffered saline (PBS) solution and ionic liquids. Then, the properties of the obtained soft materials were analysed in terms of melting temperature and gel strength as accounted for by rheological investigations. The gel-phase formation was studied by using UV/Vis and resonance light scattering measurements, whereas the morphology of the soft materials was analysed by using polarised optical microscopy and scanning electron microscopy. To get information about the organisation of the gelator in the gelatinous matrix, X-ray diffraction measurements were performed both on the neat gelators and their gels. The results collected show that the properties of the gel phases, like the thermal stability, the self-repairing ability, the resistance to flow as well as the morphology, are dependent on the nature of the anion. Furthermore, bioassays revealed that the obtained diimidazolium organic salts possessed antimicrobial activity, against gram-negative and gram-positive tester strains. In particular and noteworthy, the diimidazolium organic salts exert a bactericidal capability, which was retained even if they are included in the gel phase. Thus, a novel kind of bioactive soft material was obtained that could be fruitfully employed as a non-covalent coating exerting antibacterial capability.

An Au/CeO2 model catalyst was prepared by deposition–precipitation, with the aim of obtaining a sample suitable for a detailed X-ray absorption fine structure (XAFS) analysis of the gold–ceria interface structure. The results demonstrate the existence of a large interface between the gold particle and the support oxide, characterized by well-defined Au–O and Au–Ce interactions extending up to ∼6.4 A. The complex interface structure is retained after CO treatment up to 250 °C and subsequent reoxidation at 400 °C. The analysis of the XANES spectra, and the Au–O distance of 2.21 A, longer than Au–O bond lengths previously reported for Au/ceria catalysts, suggest a low oxidation state for the gold atoms placed at the interface between Au and ceria.

In this study, we investigate the effect of decorating the grain boundaries of nanocrystalline undoped ceria on the electrical transport properties. For the decoration, different acceptors (Yb, Y, Bi) were chosen. On decoration, the conduction switches from electronic to ionic. Upon sintering the grains are characterized by a core-shell configuration, in which the core remains undoped while the shell is heavily doped as a consequence of the diffusion of the acceptors toward the grain interior. The shell dominates the overall transport properties of the nanocrystalline ceria and is found to be in the mesoscopic regime.