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Electrochemistry and X-ray absorption spectroscopy (XAS) of MnO2/reduced graphene oxide (RGO) were made to evaluate capacitive performance and electronic structure as a supercapacitor. MnO2 was deposited on the surface of RGO by a spontaneous redox reaction. At low current density (1 A g−1), the specific capacitance of MnO2/RGO (MRGO) greatly increased with increasing growth time from 281 to 462 F g−1. Electrochemical results show that the specific capacitance of RGO and MRGO arises from the combined contributions of electrochemical double-layer capacitance (EDLC) and pseudo-capacitance. To gain insights into the charge storage mechanism of RGO and MRGO, it was characterized using ex-situ soft XAS techniques at Mn L-edge and C, O K-edges in the charging/discharging process. The ex-situ soft XAS results provide evidence that the contribution of RGO to specific capacitance involves an oxygen-functionality-related contribution of pseudocapacitance and EDLC. In addition, the specific capacitance of MRGO reveals pseudocapacitive contributions from the redox processes that involve the Mn(III)/Mn(IV) redox reaction in MnO2. This work utilizes electrochemical and ex-situ XAS techniques to elucidate charge storage mechanism for supercapacitor applications.

Summary Noble metals are considered a key branch of electrocatalysts. Unfortunately, their contributions to anodic reactions still face a big challenge. Here, guided by density functional theory, significant breakthroughs have been achieved by constructing a unique spontaneously oxidized interface in noble metal sub-nanocluster (SNC) catalysts depending on strong surface affinity. The spontaneous oxide interfaces with the amorphous covering on the rhodium (Rh) SNCs (diameter

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2 gRu-1 s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

The new TPS 44A beamline at the Taiwan Photon Source is presented. The beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans and on-the-fly scans for XAFS spectroscopy experiments, including XANES and EXAFS spectral measurements., The new TPS 44A beamline at the Taiwan Photon Source, located at the National Synchrotron Radiation Research Center, is presented. This beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans (s-scans) and on-the-fly scans (q-scans) for X-ray absorption fine-structure (XAFS) spectroscopy experiments, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectral measurements. Ti and Te K-edge XAFS spectra were used to demonstrate the capability of collecting spectra at the limits of the working energy range. The Ni and Cu K-edge XAFS spectra for a Cu-doped Pt/Ni nanocomposite were acquired to test the performance of the newly commissioned beamline. Pt L 3- and Ru K-edge quick-scanning XAFS (QXAFS) spectra for standard Pt and Ru foils, respectively, revealed the stability of the q-scan technique. The results also demonstrated the beamline’s ability to collect XAFS spectra on a sub-second timescale. Furthermore, a Zn(s)|Zn2+ (aq)|Cu(s) system was tested to indicate that the states of the Zn electrode could be observed in real time for charging and discharging conditions using an in situ/operando setup combined with QXAFS measurements.

Single-atom nickel catalysts hold great promise for photocatalytic water splitting due to their plentiful active sites and cost-effectiveness. Herein, we adopt a reactive-group guided strategy to prepare atomically dispersed nickel catalysts on red phosphorus. The hydrothermal treatment of red phosphorus leads to the formation of P-H and P-OH groups, which behave as the reactive functionalities to generate the dual structure of single-atom P-Ni and P-O-Ni catalytic sites. The produced single-atom sites provide two different functions: P-Ni for water reduction and P-O-Ni for water oxidation. Benefitting from this specific Janus structure, Ni-red phosphorus shows an elevated hydrogen evolution rate compared to Ni nanoparticle-modified red phosphorus under visible-light irradiation. The hydrogen evolution rate was additionally enhanced with increased reaction temperature, reaching 91.51 μmol h

We demonstrate that the single-site catalyst Pt1/CeO2 greatly enhances the selectivity of cyclization and aromatization in the n-hexane reforming reaction. Specifically, the selectivity of single-site Pt1/CeO2 toward both cyclization and aromatization is above 86% at 350 °C. The turnover frequency of Pt1/CeO2 is 58.8 h-1 at 400 °C, which is close to that of Pt cluster/CeO2 (61.4 h-1) and much higher than that of Pt nanoparticle/CeO2 with Pt sizes of 2.5 and 7 nm. On the basis of the catalytic results for methylcyclopentane reforming, the dehydrocyclization and further aromatization of n-hexane are attributed to the prominent adsorption of ring intermediate products on the single-site Pt1/CeO2 catalysts. On the other side, with the multiple Pt adjacent active sites, the cluster and nanoparticle Pt/CeO2 samples favor the C-C bond cracking reaction. Ultimately, this in-depth study unravels the principles of hydrocarbon activation with different Pt sizes and represents a key step toward the rational design of new heterogeneous catalysts.

While the effects of environmental factors (e.g., coexisting organic macromolecules and solar irradiation) on the phase transformation and oxidative dissolution of chemically exfoliated molybdenum nanosheets (ceMoS

This study develops and successfully demonstrates visualization methods for the characterization of europium (Eu)-doped BaAl

Hydrogen is regarded as an attractive alternative energy carrier due to its high gravimetric energy density and only water production upon combustion. However, due to its low volumetric energy density, there are still some challenges in practical hydrogen storage and transportation. In the past decade, using chemical bonds of liquid organic molecules as hydrogen carriers to generate hydrogen in situ provided a feasible method to potentially solve this problem. Research efforts on liquid organic hydrogen carriers (LOHCs) seek practical carrier systems and advanced catalytic materials that have the potential to reduce costs, increase reaction rate, and provide a more efficient catalytic hydrogen generation/storage process. In this work, we used methanol as a hydrogen carrier to release hydrogen in situ with the single-site Pt1/CeO2 catalyst. Moreover, in this reaction, compared with traditional nanoparticle catalysts, the single site catalyst displays excellent hydrogen generation efficiency, 40 times higher than 2.5 nm Pt/CeO2 sample, and 800 times higher compared to 7.0 nm Pt/CeO2 sample. This in-depth study highlights the benefits of single-site catalysts and paves the way for further rational design of highly efficient catalysts for sustainable energy storage applications.

Amines, especially primary amines, are value-added fine chemicals widely used in modern industries. Here, a PtCo/CeO2 catalyst is designed for the hydrogen-borrowing amination of alcohols, especially the conversion of cyclopentanol to cyclopentanylamine. CoOx decoration over Pt/CeO2 is able to enhance both selectivity to primary amine and catalytic activity. These CoOx species play two roles in alcohol amination, enhancing alcohol dehydrogenation and inhibiting overhydrogenation of a Schiff base intermediate (cyclopentyl cyclopentylidene amine). Comprehensive characterization demonstrates that promotional effects of the CoOx additive have two causes: (1) CoOx species provide an additional Pt-CoO interface for the rate-determining dehydrogenation step; (2) CoOx species block low-coordinated Pt sites for H2 activation in the overhydrogenation of the Schiff base intermediate, thus suppressing the formation of undesirable secondary amines. This work provides an in-depth understanding of the role of the CoOx additive in PtCo/CeO2 and new insights into the design of Pt-based catalysts for primary amine production via hydrogen-borrowing amination.

The ruthenium-nickel bimetallic nanoparticles supported on carbon black (Ru-Ni/C) with various Ru and Ni loadings, while keeping a constant Ru/Ni atomic ratio (51/49), were synthesized at ambient temperature by liquid reduction with hydrazine hydrate as reducing agent and galvanic replacement reaction approaches. Different Ru-Ni interfaces (Ru-Ni-NiO with 1.250 wt% or 0.630 wt% Ru, and RuO2-NiO with 0.160 wt% Ru) were formed after being annealed in N2 at 380 °C for 3 h. Several techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and synchrotron radiation X-ray absorption spectroscopy (XAS) and in-situ XAS (in hydrogen) have been employed for structural characterization. It was found that most Ru atoms and a small amount of Ni atoms at the Ru-Ni-NiO interface were reduced, leading to the occurrence of hydrogen spillover and hence synergy effect of Ru, Ni and NiO active sites. However, such a synergy was not observed at the RuO2-NiO interface. The catalytic properties of the Ru-Ni/C nanocatalysts in the hydrogenation of benzene reaction were significantly improved due to the presence of particular Ru-Ni-NiO interface.

Herein, we present a scalable approach for the synthesis of a hydrogen-bonded organic–inorganic framework via coordination-driven supramolecular chemistry, for efficient remediation of trace heavy metal ions from water. In particular, using copper as our model ion of interest and inspired by nature’s use of histidine residues within the active sites of various copper binding proteins, we design a framework featuring pendant imidazole rings and copper-chelating salicylaldoxime, known as zinc imidazole salicylaldoxime supramolecule. This material is water-stable and exhibits unprecedented adsorption kinetics, up to 50 times faster than state-of-the-art materials for selective copper ion capture from water. Furthermore, selective copper removal is achieved using this material in a pH range that was proven ineffective with previously reported metal–organic frameworks. Molecular dynamics simulations show that this supramolecule can reversibly breathe water through lattice expansion and contraction, and that water is initially transported into the lattice through hopping between hydrogen-bond sites., Heavy metals and metalloids pose major threats to health and environmental ecosystems, thus systems for low-cost remediation are needed. Here the authors report the scalable design of a hydrogen-bonded organic–inorganic framework for selective removal of trace heavy metal ions from water.

A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu3+ (SSO:xEu3+, x = 1.0, 2.0 and 5.0%), were synthesized by a sol–gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic α'-SSO and monoclinic β-SSO phases of the SSO:xEu3+ phosphors. When SSO:xEu3+ phosphors are excited under ultraviolet (UV) light (λ = 250 nm, ~ 4.96 eV), they emit yellow (~ 590 nm), orange (~ 613 nm) and red (~ 652 and 703 nm) PL bands. These PL emissions typically correspond to 4f–4f electronic transitions that involve the multiple excited 5D0 → 7FJ levels (J = 1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu3+ phosphors is strongly related to the local electronic/atomic structures of the Eu3+–O2− associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and Kα X-ray emission spectroscopy. In the synthesis of SSO:xEu3+ phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the Eu 5d and/or O 2p–Eu 4f/5d states (mostly the O 2p–Eu 5d states) to the 5D0 levels, facilitating the recombination of electrons that have transitioned from the 5D0 level to the 7FJ level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO:xEu3+ phosphors. This PL-related behavior indicates that SSO:xEu3+ phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.

Electrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. Here, we report an efficient catalyst (Ag-D) with suitable defect concentration operando formed during ECR within several minutes. Utilizing the powerful fast operando X-ray absorption spectroscopy, the evolving electronic and crystal structures are unraveled under ECR condition. The catalyst exhibits a ~100% faradaic efficiency and negligible performance degradation over a 120-hour test at a moderate overpotential of 0.7 V in an H-cell reactor and a current density of ~180 mA cm−2 at −1.0 V vs. reversible hydrogen electrode in a flow-cell reactor. Density functional theory calculations indicate that the adsorption of intermediate COOH could be enhanced and the free energy of the reaction pathways could be optimized by an appropriate defect concentration, rationalizing the experimental observation., Efficient electrocatalysts are crucial to the electrochemical carbon dioxide reduction. Here, the authors use the fast operando technique to explore a silver-based catalyst with improved catalytic performance benefiting from the suitable defect structures.

A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu3+ (SSO:xEu3+, x = 1.0, 2.0 and 5.0%), were synthesized by a sol–gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic α'-SSO and monoclinic β-SSO phases of the SSO:xEu3+ phosphors. When SSO:xEu3+ phosphors are excited under ultraviolet (UV) light (λ = 250 nm, ~ 4.96 eV), they emit yellow (~ 590 nm), orange (~ 613 nm) and red (~ 652 and 703 nm) PL bands. These PL emissions typically correspond to 4f–4f electronic transitions that involve the multiple excited 5D0 → 7FJ levels (J = 1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu3+ phosphors is strongly related to the local electronic/atomic structures of the Eu3+–O2− associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and Kα X-ray emission spectroscopy. In the synthesis of SSO:xEu3+ phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the Eu 5d and/or O 2p–Eu 4f/5d states (mostly the O 2p–Eu 5d states) to the 5D0 levels, facilitating the recombination of electrons that have transitioned from the 5D0 level to the 7FJ level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO:xEu3+ phosphors. This PL-related behavior indicates that SSO:xEu3+ phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.

A novel redox-active quinone-based organic building block 1,4-dicyano-2,3,5,6-tetrahydroxybenzene (LH4) has been synthesized and used as a bridging ligand to form a new 1D copper-benzoquinoid coordination polymer [CuL(DMF)2]n. The compound is able to deliver an initial capacity as high as 268 mA h g−1 at 30 mA g−1 (∼C/2.5) when used as the cathode in Li batteries. Ex situ XPS and FT-IR reveal the involvement of both Cu and organic moieties in the multi-electron redox reaction. Cu K-edge XANES and EXAFS measurements confirm the change in the oxidation state and coordination environment of Cu during the discharge–charge process. In situ generated metallic nanoparticles have been observed by TEM. The obtained mechanistic understanding of the metal–organic electrode materials for Li-based batteries may pave the way for the design of next-generation energy-storage systems.

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source. Then, bridged periodic mesoporous organosilica (BBM-PMO) spherical nanoparticles were synthesized by co-condensation using cetyltrimethylammonium bromide (CTAB) as structure directing agent. The optical properties showed that BBM qualifies as an “aggregation induced emission enhanced” (AIEE) molecule, exhibiting characteristics of excited-state intramolecular proton transfer (ESIPT), such as a large Stokes shift and dual fluorescence emission. For the BBM-PMO materials, the silica skeleton provides a rigid environment that limits molecular rotation, resulting in improved fluorescence emission. In particular, the BBM-PMOs exhibited dual emission of the enol and keto forms, achieving a ratiometric response to Cu2+ with high sensitivity and selectivity in a broad pH range. Additionally, the limit of detection was as low as 7.15 × 10−9 M in aqueous solution. The X-ray absorption near-edge spectroscopy (XANES) showed the coordination structure through the interaction between copper ions and N atoms of benzimidazole in the BBM-PMO coordinated to Cu2+. These results demonstrate that BBM-PMO hybrid materials have potential applications in the fields of bio-imaging and environmental monitoring.

SBA-15-supported Pd catalysts were prepared by impregnation, thermal pretreatment, and H2 reduction. The pretreatment conditions have an important influence on the resulting size (from 1.3 to 10.3 nm) of the Pd particles; the catalyst prepared under vacuum conditions possessed the smallest particles (size 1.3 nm). X-ray absorption spectra were used to analyze the transformation of the Pd precursor in each step of the preparation. These catalysts were applied to the oxidation of benzyl alcohol by molecular oxygen; the catalyst with the smallest Pd particles exhibited the highest turnover frequency (9684 h−1). The catalyst was reusable three times without loss of activity (with conversion >96%). X-ray absorption spectra were recorded ex situ to monitor the oxidation and the coordination structure of Pd at varied temperatures of reaction; when the reaction temperature was above 100 °C, the Pd species were in the metallic state. This result indicates that metallic Pd might be the active phase in the oxidation of benzyl alcohol by molecular oxygen.

A simple and scalable wet chemical method was adopted to synthesize a series of single-phase nanosized SnSe at room temperature with the solution controlled at various pH values. The lattice constants, chemical compositions, carrier concentration, bond length of bonded atoms, reaction yield, and antisite defects of resulting materials exhibit significant dependence on the pH values of the aqueous solution in the synthesis. Detailed studies on the formation mechanism of SnSe indicate that our approach involves the reaction between elemental Sn and Se, instead of the competitive precipitating reaction between Sn2+ and Se2−. The energetic elemental Se might be provided by polyselenide ions Sex2−. The reaction yield increases after treating SnSe with hydrochloric acid. According to both elemental analyses using electron probe microanalyzer and studies of extended x-ray absorption fine structure spectra, the Se vacancy is generated and is accompanied by formation of antisite defects by treating SnSe with hydrochloric acid.

Metal oxide-containing SBA-15-supported gold catalysts were prepared by depositing gold on the SBA-15 pre-loaded CeO 2 , TiO 2 or ZrO 2 and applied to the base-free aerobic homocoupling of phenylboronic acid in water. The results of catalytic tests showed that the small-sized metallic gold nanoparticles (size 1.3–2.3 nm) deposited on the metal oxides were all active for the reaction and possessed much greater activity than cationic gold species. The conversions and the product selectivities for the catalysts are high (>72% and >94% respectively) and the catalysts were reusable under mild conditions. X-ray absorption investigation indicated that the gold nanoparticles in the catalysts retained a metallic nature under reaction conditions. Furthermore, results indicated that the nucleophilic tetravalent boron was formed in neutral reaction conditions and that both oxygen and water were involved in the reaction. Based on these experiments, a reaction mechanism was proposed for the base-free aerobic homocoupling reaction by the metal oxide-containing SBA-15-supported gold catalysts.

International audience; Understanding the mechanisms of catalytic and reactions calls for in situ/operando spectroscopic characterization. Here we report the developments of in situ reaction cells at the Advanced Light Source for soft X-ray spectroscopic studies of nanoparticle catalysts during the catalytic reactions. The operation of these various cells and their capabilities are illustrated with examples from the studies of Co-based nanocatalysts.

We report x-ray absorption near edge structure (XANES) on bulk samples of Ca1−xGdxMnO3+δ with x = 0, 0.02, and 0.05. The transport properties measurements indicate that both resistivity and the absolute value of thermopower decrease with increasing x. Meanwhile, the temperature dependence of resistivity changes from non-metallic CaMnO3−δ to metallic for samples of x = 0.02 and 0.05. XANES spectra at the O K-edge, Mn L2,3-edge, and Ca L2,3-edge indicate that Mn 3d–O 2p hybridization increases considerably, and unoccupied (3d–4s) states of Ca decrease with increasing substitution content. The increases of Mn 3d–O 2p hybridization might be responsible for the decrease of the resistivity and the absolute value of thermopower upon partial Gd substitution for Ca.

The structural properties of (Bi0.5Na0.5)Ti1-xZrxO3 (where 0 ≤ x ≤ 0.7) have been investigated using powder diffraction and X-ray absorption spectroscopy. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Doping small amounts of Zr into the B site of (Bi0.5Na0.5)TiO3 initially stabilizes the rhombohedral phase before the orthorhombic Pnma phase begins to form at x = 0.5. Analysis of the Ti K-edge and Zr L3-edge XANES spectra show that the crystallographic phase change has very little effect on the local structure of Ti(4+)/Zr(4+) cations, suggesting that there is little change in the cation off-center displacement within the BO6 octahedra with each successive phase change.

Correction for ‘Morphology-maintaining synthesis of NbN and its catalytic performance in epoxidation’ by Tianhao Zhao et al., Catal. Sci. Technol., 2019, DOI: 10.1039/c9cy00890j.

We perform a combined experimental-theoretical study of the Fe-oxychalcogenides (FeO$\emph{Ch}$) series La$_{2}$O$_{2}$Fe$_{2}$O\emph{M}$_{2}$ (\emph{M}=S, Se), which is the latest among the Fe-based materials with the potential \ to show unconventional high-T$_{c}$ superconductivity (HTSC). A combination of incoherent Hubbard features in X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectra, as well as resitivity data, reveal that the parent FeO$\emph{Ch}$ are correlation-driven insulators. To uncover microscopics underlying these findings, we perform local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that unravel a Mott-Kondo insulating state. Based upon good agreement between theory and a range of data, we propose that FeO$\emph{Ch}$ may constitute a new, ideal testing ground to explore HTSC arising from a strange metal proximate to a novel selective-Mott quantum criticality.

The activity of electrocatalysts strongly depends on the number of active sites, which can be increased by downsizing electrocatalysts. Single-atom catalysts have attracted special attention due to atomic-scale active sites. However, it is a huge challenge to obtain atomic-scale CoOx catalysts. The Co-based metal-organic frameworks (MOFs) own atomically dispersed Co ions, which motivates to design a possible pathway to partially on-site transform these Co ions to active atomic-scale CoOx species, while reserving the highly porous features of MOFs. In this work, for the first time, the targeted on-site formation of atomic-scale CoOx species is realized in ZIF-67 by O-2 plasma. The abundant pores in ZIF-67 provide channels for O-2 plasma to activate the Co ions in MOFs to on-site produce atomic-scale CoOx species, which act as the active sites to catalyze the oxygen evolution reaction with an even better activity than RuO2.

A novel electrochemical setup has been developed for soft X-ray absorption studies of the electronic structure of electrode materials during electrochemical cycling. In this communication we illustrate the operation of the cell with a study of the corrosion behavior of copper in aqueous NaHCO3 solution via the electrochemically induced changes of its electronic structure. This development opens the way for in situ investigations of electrochemical processes, photovoltaics, batteries, fuel cells, water splitting, corrosion, electrodeposition, and a variety of important biological processes. Keywords: Soft X-ray absorption spectroscopy, In situ, Cyclic voltammetry, Corrosion, Copper

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

The electronic structure change during the reversible Li-ion storage reaction in a bimetallic MnFe-Prussian blue analogue (Li${}_{x}$K${}_{0.14}$Mn${}_{1.43}$[Fe(CN)${}_{6}$] $\ifmmode\cdot\else\textperiodcentered\fi{}$ 6H${}_{2}$O) was investigated by soft x-ray absorption spectroscopy. The Mn ${L}_{2,3}$-edge spectra revealed the unchanged Mn${}^{2+}$ high-spin state regardless of Li-ion concentration ($x$). On the other hand, the Fe ${L}_{2,3}$-edge spectra clearly revealed a reversible redox behavior as ${\mathrm{Fe}}^{3+}\ensuremath{\leftrightarrow}{\mathrm{Fe}}^{2+}$ states with Li-ion insertion/extraction. Experimental findings suggested strong metal-to-ligand charge transfer in conjunction with the ligand-to-metal one. The resulting charge delocalization between the Fe and CN is considered to contribute to the high reversibility of the Li-ion storage process.

X-ray absorption spectroscopy (XAS) Fe K-edge spectra of the FeSex (x=1–0.8) single crystals cleaved in situ under vacuum reveal characteristic Fe 4sp states and a lattice distortion. The Se K-edge spectra point to a strong Fe 3d-Se 4p hybridization giving rise to itinerant charge carriers. A formal charge of ~1.8+ for Fe and ~2.2− for Se was evaluated from these spectra in the FeSex (x=0.88). The charge balance between Fe and Se is assigned to itinerant electrons located in the Fe-Se hybridization bond. As x decreases the 4p hole count increases and a crystal structure distortion is observed that in turn causes the Fe separation in the ab-plane change from 4p orbital to varying (modulating) coordination. Powder X-ray diffraction (XRD) measurements also show a slight increase in lattice parameters as x decreases (increasing Se deficiency).

Soft X-ray absorption and emission spectroscopy was used to determine the electronic density of states of oxygen vacated PrFeAsO. The measured oxygen and iron spectra are in good agreement with mean field theory and local density approximations. Iron-arsenic hybridized spectral features reveal that Fe-As bonding is involved in the process of electron addition near the Fermi-level. X-ray emission and absorption spectra shows an increase in the Fe density of states at the Fermi-level as the doping decreases. This doping dependent electronic behavior indicates the possibility of a magnetic instability in the undoped compound.

Electrochromic switching devices have elicited considerable attention because these thin films are among the most promising materials for energy-saving applications. The vanadium oxide system is simple and inexpensive because only a single-layer film of this material is sufficient for coloration. Vanadium dioxide thin films are fabricated by electrochemical deposition and cyclic voltammetry. Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate. Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined. In the present study, in situ X-ray absorption spectroscopy (XAS) is employed to determine the electronic and atomic structures of V2O5 thin films during electrochemical growth and then electrochromic coloration. In situ XAS results demonstrate the growth mechanism of the electrodeposited V2O5 thin film and suggest that its electrochromic performance strongly depends on the local atomic structure. This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.