Double-Layered Perovskite Oxyfluoride Cathodes with High Capacity Involving O-O Bond Formation for Fluoride-Ion Batteries.

Developing electrochemical high-energy storage systems is of crucial importance toward a green and sustainable energy supply. A promising candidate is fluoride-ion batteries (FIBs), which can deliver a much higher volumetric energy density than lithium-ion batteries. However, typical metal fluoride cathodes with conversion-type reactions cause a low-rate capability. Recently, layered perovskite oxides and oxyfluorides, such as LaSrMnO4 and Sr3Fe2O5F2, have been reported to exhibit relatively high rate performance and cycle stability compared to typical metal fluoride cathodes with conversion-type reactions, but their discharge capacities (∼118 mA h/g) are lower than those of typical cathodes used in lithium-ion batteries. Here, we show that double-layered perovskite oxyfluoride La1.2Sr1.8Mn2O7-δF2 exhibits (de) intercalation of two fluoride ions to rock-salt slabs and further (de) intercalation of excess fluoride ions to the perovskite layer, leading to a reversible capacity of 200 mA h/g. The additional fluoride-ion intercalation leads to the formation of O-O bond in the structure for charge compensation (i.e., anion redox). These results highlight the layered perovskite oxyfluorides as a new class of active materials for the construction of high-performance FIBs.

Angle-resolved X-ray emission spectroscopy facility realized by an innovative spectrometer rotation mechanism at SPring-8 BL07LSU.

The X-ray emission spectrometer at SPring-8 BL07LSU has recently been upgraded with advanced modifications that enable the rotation of the spectrometer with respect to the scattering angle. This major upgrade allows the scattering angle to be flexibly changed within the range of 45-135°, which considerably simplifies the measurement of angle-resolved X-ray emission spectroscopy. To accomplish the rotation system, a sophisticated sample chamber and a highly precise spectrometer rotation mechanism have been developed. The sample chamber has a specially designed combination of three rotary stages that can smoothly move the connection flange along the wide scattering angle without breaking the vacuum. In addition, the spectrometer is rotated by sliding on a flat metal surface, ensuring exceptionally high accuracy in rotation and eliminating the need for any further adjustments during rotation. A control system that integrates the sample chamber and rotation mechanism to automate the measurement of angle-resolved X-ray emission spectroscopy has also been developed. This automation substantially streamlines the process of measuring angle-resolved spectra, making it far easier than ever before. Furthermore, the upgraded X-ray emission spectrometer can now also be utilized in diffraction experiments, providing even greater versatility to our research capabilities.

The role of carboxylate ligand orbitals in the breathing dynamics of a metal-organic framework by resonant X-ray emission spectroscopy.

Metal-organic frameworks (MOFs) exhibit structural flexibility induced by temperature and guest adsorption, as demonstrated in the structural breathing transition in certain MOFs between narrow-pore and large-pore phases. Soft modes were suggested to entropically drive such pore breathing through enhanced vibrational dynamics at high temperatures. In this work, oxygen K-edge resonant X-ray emission spectroscopy of the MIL-53(Al) MOF was performed to selectively probe the electronic perturbation accompanying pore breathing dynamics at the ligand carboxylate site for metal-ligand interaction. It was observed that the temperature-induced vibrational dynamics involves switching occupancy between antisymmetric and symmetric configurations of the carboxylate oxygen lone pair orbitals, through which electron density around carboxylate oxygen sites is redistributed and metal-ligand interactions are tuned. In turn, water adsorption involves an additional perturbation of π orbitals not observed in the structural change solely induced by temperature.

Soft X-ray ptychography system using a Wolter mirror for achromatic illumination optics.

A soft X-ray ptychography system using a Wolter mirror for the illumination optics has been developed. By taking advantage of the achromaticity of the optics, the system is capable of seamlessly imaging at half-period resolution of 50 nm with a broad photon-energy range from 250 eV to 2 keV while maintaining the focal position. Imaging a mammalian cell at various wavelengths was demonstrated, and high-resolution visualization of organelle was achieved. Stereo imaging was also performed with a long working distance of 20 mm. In combination with in-situ/operando and tomographic measurements, this system will be a powerful tool for observing biological and material targets with complex features.

Interpretation of the X-Ray Emission Spectra of Liquid Water through Temperature and Isotope Dependence.

The interpretation of x-ray emission spectroscopy (XES) spectra in terms of their sensitivity to the hydrogen bonding and the consequent microheterogeneity in liquid water has been debated over a decade. To shed a light on this problem, we report the theoretical reproduction of the debated 1b_{1} peaks observed in the XES spectra of liquid water using semiclassical Kramers-Heisenberg formula. The essence of the temperature and isotope dependence of the 1b_{1} double peaks is explained by molecular dynamics simulations including full vibrational (O─H stretching, bending, and) modes, rotational combined with the density functional theory and core-hole induced dynamics. Some inconsistencies exist with the experimental XES profile, which illustrates the need to employ a more precise theoretical calculations for both geometry sampling and electronic structure using a more sophisticated procedure.

Critical In-Plane Density of Polyelectrolyte Brush for the Ordered Hydrogen-Bonded Structure of Incorporated Water.

A polymer electrolyte brush is a reasonable platform to confine water molecules within a nanoscopic area to study their role in the function of interacting media because of their adjustable nanospace and charge by changing the in-plane density and side chains of the brush. Here, we demonstrate how the in-plane spacing of cationic polymer brush chains, poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMTAC), affects the hydrogen bond configuration of incorporated water using soft X-ray emission spectroscopy. At the critical in-plane density σ = 0.30 chains/nm2 of PMTAC, tetrahedrally coordinated water molecules started to melt into distorted or broken hydrogen-bonded configurations. Considering the charge on the quaternary ammonium cations, the electric field required to form a tetrahedrally coordinated hydrogen-bonded configuration was estimated as ∼500 kV cm-1 and is effective up to ∼1 nm from the surface of the polymer chain. These findings are useful for designing specific interface properties and the resultant surface function of polyelectrolyte-based materials.

Hydration Mechanism in Blood-Compatible Polymers Undergoing Phase Separation.

Interactions involving intermediate water are crucial for the design of novel blood-compatible materials. Herein, we use a combination of atomic force microscopy, quartz crystal microbalance measurements, and soft X-ray emission spectroscopy to investigate the local hydrogen-bonded configuration of water on blood-compatible poly(2-methoxyethyl acrylate) and non-blood-compatible poly(n-butyl acrylate) grafted on a gold substrate. We find that the initially incorporated water induces polymer-dependent phase separation, facilitating further water uptake. For the blood-compatible polymer, tetrahedrally coordinated water coexists with water adsorbed on C═O groups in low-density regions of the grafted polymer surface, providing a scaffold for the formation of intermediate water. The amount of intermediate water is determined by the type of functional groups, local polymer configuration, and polymer morphology. Thus, blood compatibility is governed by the complex water/polymer interactions.

Operando resonant soft X-ray emission spectroscopy of the LiMn2O4 cathode using an aqueous electrolyte solution.

The Mn 3d electronic-structure change of the LiMn2O4 cathode during Li-ion extraction/insertion in an aqueous electrolyte solution was studied by operando resonant soft X-ray emission spectroscopy (RXES). The Mn L3 RXES spectra for the charged state revealed the Mn4+ state with strong charge-transfer from the O 2p to Mn 3d orbitals dominates, while for the open-circuit-voltage and discharged states it is ascribed to the mixture of sites with Mn3+ and Mn4+ states. The degree of charge transfer is significantly different between the Mn3+ and Mn4+ states, indicating that the redox reaction takes place on the strongly-hybridized Mn 3d-O 2p orbital rather than the localized Mn 3d orbital.

Soft X-ray emission spectroscopy for the electronic state of water molecules influenced by plasma-treated multi-walled carbon nanotubes.

In this study, soft X-ray emission spectroscopy of an aqueous colloidal dispersion of multi-walled carbon nanotubes modified via the plasma process in an aqueous solution was performed for investigating the electronic state of water molecules on the colloidal particles. In the aqueous dispersion, reconstruction of the hydrogen-bonded network was implied by the O 1s spectral changes in the 1b1' and 1b1'' peaks. Furthermore, the O 1s spectral intensity around the 3a1 state was enhanced to an unusually broad energy range in comparison with previous studies. This unusual spectral change might be attributed to the hybridization of the electronic states of oxygen-containing functional groups on the surface of the plasma-modified multi-walled carbon nanotubes and that of the surrounding water molecules. Our observation indicates not only reconstruction of the hydrogen-bonded network in the aqueous dispersion but also a significant interaction of the electronic states between the water molecules and the plasma-modified multi-walled carbon nanotubes.

Improved developmental potential of mouse vitrified-warmed oocytes achieved by culturing in recovery medium with glutathione ethyl ester (GSH-OEt).

PURPOSE: The aim of the present study was to investigate the effect of glutathione ethyl ester (GSH-OEt) in the recovery medium on the developmental competence of mouse vitrified-warmed MII oocytes. METHODS: Vitrified-warmed oocytes were incubated for 1 h in recovery medium in the presence or absence of 0.5 mM GSH-OEt. The authors examined the effects of GSH-OEt, first on the levels of glutathione (GSH) and reactive oxygen species (ROS) in vitrified-warmed oocytes, and second, on in vitro blastocyst development, division speed to blastocysts, and total cell numbers of blastocysts from vitrified-warmed oocytes fertilized by Intracytoplasmic sperm injection (ICSI). RESULTS: Adding GSH-OEt to the recovery medium significantly (p < 0.05) increased GSH content and decreased ROS levels in vitrified-warmed oocytes. The blastocyst rate did not differ significantly between the two groups, but the speed of development to blastocysts in the GSH-OEt (+) group was significantly more rapid. In addition, the total blastocyst cell number was significantly higher in the GSH-OEt (+) group than in the GSH-OEt (-) group (92.8 ± 5.1 vs. 71.4 ± 3.5, p < 0.01). CONCLUSION: Adding GSH-OEt to the recovery medium of vitrified-warmed mouse oocytes enhances the development potential of oocytes and improves the quality of blastocysts.

Anisotropic X-Ray Scattering of Transiently Oriented Water.

We study the structural dynamics of liquid water by time-resolved anisotropic x-ray scattering under the optical Kerr effect condition. In this way, we can separate the anisotropic scattering decay of 160 fs from the delayed temperature increase of ∼0.1 K occurring at 1 ps and quantify transient changes in the O-O pair distribution function. Polarizable molecular dynamics simulations reproduce well the experiment, indicating transient alignment of molecules along the electric field, which shortens the nearest-neighbor distances. In addition, analysis of the simulated water local structure provides evidence that two hypothesized fluctuating water configurations exhibit different polarizability.

Time-lapse monitoring of mouse embryos produced by injecting sonicated, frozen-thawed sperm heads with high or low chromosomal integrity.

PURPOSE: To investigate the first-division kinetics and in vitro development of embryos produced by injecting sonicated sperm heads with high or low chromosomal integrity into oocytes. METHODS: Mouse spermatozoa were frozen after separating the sperm heads from the tails by sonication in an EGTA solution (EGTA group) or M2 medium (M2 group). The chromosomal integrity of sonicated mouse spermatozoa was analyzed by injecting the sperm heads into fresh mouse oocytes. The developmental potential of spermatozoa was examined by injecting the sperm heads into vitrified-warming mouse oocytes. We used a time-lapse monitoring system to compare the first-division kinetics. RESULTS: Chromosomal integrity was preserved significantly more frequently in the EGTA group (90.6%) than in the M2 group (32.7%). Blastocysts developed significantly more often in the EGTA group (80.8%) than in the M2 group (39.6%). In the M2 group, with frequent chromosome aberrations, the time between the sperm injection and first cleavage was delayed (18.4 hours), compared to the EGTA group (16.5 hours). All results of the EGTA group were similar to that of fresh epididymal spermatozoa. CONCLUSION: The EGTA solution for sonication maintained the integrity of sperm chromosomes. Our results revealed a relationship between sperm chromosome integrity and first-division kinetics.

Selection of high-quality and viable blastocysts based on timing of morula compaction and blastocyst formation.

PURPOSE: The time-lapse system is a device that allows continuous monitoring without removing embryos from the incubator. Using a time-lapse system, we retrospectively investigated cleavage speed time points as potential indicators for selecting high-quality viable blastocysts. METHODS: This study included 963 zygotes of two pronuclei retrieved from 196 patients between January 2015 and December 2016. All embryos in culture were monitored by time-lapse after intracytoplasmic sperm injection. Of 492 blastocysts developed in vitro, 128 vitrified-warmed single blastocyst transfers were classified into pregnancy and non-pregnancy groups, and the parameters were compared. RESULTS: In the pregnancy group, timing of both morula compaction and regular blastocyst formation was significantly faster than in the non-pregnancy group. Furthermore, the optimal cutoff values for compacted morula (94.9 hours) and regular blastocyst (113.9 hours) were determined using the receiver operator characteristic curve analysis. Embryos that formed compacted morulae within 94.9 hours and developed into regular blastocysts within 113.9 hours were associated with a significantly higher pregnancy rate than those that did not (44.4% vs 16.0%). CONCLUSION: The timing of morula compaction and regular blastocyst formation is important as an indicator of high-quality blastocysts to increase odds for pregnancy after embryo transfer.

Ion Selectivity of Water Molecules in Subnanoporous Liquid-Crystalline Water-Treatment Membranes: A Structural Study of Hydrogen Bonding.

We demonstrate hydrogen-bonded structures of water in self-organized subnanoporous water treatment membranes obtained using synchrotron-based high-resolution soft X-ray emission spectroscopy. The ion selectivity of these water treatment membranes is usually understood by the size compatibility of nanochannels in the membrane with the Stokes radius of hydrated ions, or by electrostatic interaction between charges inside the nanochannels and such ions. However, based on a comparison between the hydrogen-bonded structures of water molecules in the nanochannels of the water treatment membrane and those surrounding the ions, we propose a definite contribution of structural consistency among the associated hydrogen-bonded water molecules to the ion selectivity. Our observation delivers a novel concept to the design of water treatment membranes where water molecules in the nanochannel can be regarded as a part of the material that controls the ion selectivity.

Operando soft X-ray emission spectroscopy of the Fe2O3 anode to observe the conversion reaction.

Drastic electronic-structure changes in an Fe2O3 thin film anode for a Li-ion battery during discharge (lithiation) and charge (delithiation) processes were observed using operando Fe 2p soft X-ray emission spectroscopy (XES). The conversion reaction forming metallic iron due to the lithiation reaction was confirmed by operando XES in combination with the analysis using full-multiplet calculation. The valence of Fe at the open-circuit voltage (OCV) before the second cycle was not Fe3+, but Fe2+ with a weak p-d hybridization, suggesting a considerable irreversibility upon the first discharge-charge cycle and a weakened Fe-O bond after the first cycle. Moreover, we revealed that the Fe 3d electronic-structure change during the second cycle was to some extent reversible as Fe2+ (2.7 V vs. Li/Li+: open circuit voltage) → Fe0 (0.1 V vs. Li/Li+: discharged) → Fe(2+δ)+ (3.0 V vs. Li/Li+: charged). This operando Fe 2p XES in combination with the full-multiplet calculation provides detailed information for redox chemistry during a discharge-charge operation that cannot be obtained by other methods such as crystal-structure and morphology analyses. XES is thus very powerful for investigating the origin and limitation of the lithiation function of anodes involving conversion reactions.

Mn 2p resonant X-ray emission clarifies the redox reaction and charge-transfer effects in LiMn2O4.

High-energy-resolution soft X-ray emission spectroscopy (XES) was applied to understand the changes in the electronic structure of LiMn2O4 upon Li-ion extraction/insertion. Mn 2p-3d-2p resonant XES spectra were analyzed by configuration-interaction full-multiplet (CIFM) calculations, which reproduced both dd and charge-transfer (CT) excitations. From the resonant XES spectra it is found that Mn3+ and Mn4+ coexist in the initial state, while this changes into Mn4+ in the charged-state. For the discharged-state, the Mn3+ component appears again although the dd excitations are slightly modified from those for the initial state. Furthermore, negative CT energy is expected for the Mn4+ configuration, which suggests very strong hybridization between the Mn 3d and O 2p orbitals. The large difference in the CT effect between the Mn4+ and Mn3+ states should give mechanical stress to the Mn-O bond during charge-discharge cycling, leading to capacity fading.

Measurements of ultrafast dissociation in resonant inelastic x-ray scattering of water.

There has been a discussion on the interpretation of the resonant inelastic x-ray scattering (RIXS) spectra of liquid water in terms of either different structural environments or that core hole dynamics can generate well-resolved dissociative spectral components. We have used RIXS with high resolution in the OH stretch vibration energy part, at extremely high overtones going toward the continuum of full OH bond breakage, to identify the amount of dissociative contributions in the valence band RIXS spectra at different excitation energies. We observe that at low excitation energies, corresponding to population of states with strongly antibonding character, the valence band RIXS spectra have a large contribution from a well-resolved dissociative feature. Instead, at higher excitations, this spectral component diminishes and becomes a weak structure on the high-energy side of one of the spectral peaks related to the 1b1 state from tetrahedral configurations. This result brings both interpretations to be essential for the understanding of RIXS spectra of liquid water.

Probing the Valence Electronic Structure of Low-Spin Ferrous and Ferric Complexes Using 2p3d Resonant Inelastic X-ray Scattering (RIXS).

Understanding the detailed electronic structure of transition metal ions is essential in numerous areas of inorganic chemistry. In particular, the ability to map out the many particle d-d spectrum of a transition metal catalyst is key to understanding and predicting reactivity. However, from a practical perspective, there are often experimental limitations on the ability to determine the energetic ordering, and multiplicity of all the excited states. These limitations derive in part from parity and spin-selection rules, as well as from the limited energy range of many standard laboratory instruments. Herein, we demonstrate the ability of 2p3d resonant inelastic X-ray scattering (RIXS) to obtain detailed insights into the many particle spectrum of simple inorganic molecular iron complexes. The present study focuses on low-spin ferrous and ferric iron complexes, including [FeIII/II(tacn)2]3+/2+ and [FeIII/II(CN)6]3-/4-. This series thus allows us to assess the contribution of d-count and ligand donor type, by comparing the purely σ-donating tacn ligand to the π-accepting cyanide. In order to highlight the conceptual difference between RIXS and traditional optical spectroscopy, we compare first RIXS results with UV-vis and magnetic circular dichroism spectroscopy. We then highlight the ability of 2p3d RIXS to (1) separate d-d transitions from charge transfer transitions and (2) to determine the many particle d-d spectrum over a much wider energy range than is possible by optical spectroscopy. Our experimental results are correlated with semiempirical multiplet simulations and ab initio complete active space self-consistent field calculations in order to obtain detailed assignments of the excited states. These results show that Δ S = 1, and possibly Δ S = 2, transitions may be observed in 2p3d RIXS spectra. Hence, this methodology has great promise for future applications in all areas of transition metal inorganic chemistry.

Electronic Spectra of Iron-Sulfur Complexes Measured by 2p3d RIXS Spectroscopy.

Iron sulfur (FeS) proteins perform a wide range of biological functions including electron transfer and catalysis. Understanding the complex reactivity of these systems requires a detailed understanding of their electronic properties, which are encoded in the low-energy d-d excited states. Here we demonstrate that iron L-edge 2p3d resonant inelastic X-ray scattering (RIXS) can measure d-d excitation spectra in a series of monomeric, dimeric, and tetrameric FeS model complexes. RIXS provides advantages over traditional optical spectroscopies, because it is capable of measuring low-energy electronic excitations (0-10 000 cm-1) and spin-flip transitions. RIXS reveals the dense manifold of d-d excited states in dimeric [2Fe-2S] and tetrameric [MFe3S4]2+ (M = V or Mo) complexes resulting from covalency and exchange coupling. These results support recent ab initio theoretical predictions that FeS clusters possess a much greater number of low-lying excited states than predicted by model Hamiltonians.

X-ray and Electron Spectroscopy of Water.

Here we present an overview of recent developments of X-ray and electron spectroscopy to probe water at different temperatures. Photon-induced ionization followed by detection of electrons from either the O 1s level or the valence band is the basis of photoelectron spectroscopy. Excitation between the O 1s and the unoccupied states or occupied states is utilized in X-ray absorption and X-ray emission spectroscopies. These techniques probe the electronic structure of the liquid phase and show sensitivity to the local hydrogen-bonding structure. Both experimental aspects related to the measurements and theoretical simulations to assist in the interpretation are discussed in detail. Different model systems are presented such as the different bulk phases of ice and various adsorbed monolayer structures on metal surfaces.