Synchrotron X-ray Spectroscopy Research Articles

A survey study on arsenic speciation in coal fly ash and insights into the role of coal combustion conditions

Coal fly ashes (CFAs) are the low-density byproducts of the coal combustion process. Improper or uncontrolled CFA disposal poses significant environmental and health concerns due to the potential leaching of toxic heavy metals such as arsenic (As). Previous studies have investigated the content and speciation of As in different CFA samples, yet systematic information on As speciation in CFA with representative coal source and combustion conditions is still missing. Based on a recent survey study on the typical coal sources and combustion conditions across the U.S., this study selected 19 representative CFA samples to systematically investigate As speciation and potential correlations with these parameters. The composition, morphology, mineralogy, and As speciation of these CFA samples were characterized by complementary analytical, microscopic, and spectroscopic techniques. Synchrotron X-ray spectroscopy and microscopy analyses revealed the dominant As oxidation state to be As(V) and with strong associations to Ca, with the exception of 3 samples that had 19–51% As(III), likely due to the use of selective catalytic reduction (SCR) process. Principal component analysis was conducted to identify potential correlations of As concentration and oxidation state with parameters such as major element content, loss on ignition (LOI), average particle size, coal source, and combustion condition. Al2O3 and FeO content were found to capture a majority of the variability. Results from this study provide fundamental basis for understanding the correlations between coal source, combustion conditions, CFA characteristics, and As speciation, and providing insights for downstream beneficial utilization or disposal management.

Short communication: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions for luminescence dating

Abstract. During ionizing irradiation, potassium (K)-rich feldspar grains emit infrared (IR) light, which is used for infrared radiofluorescence (IR-RF) dating. The late-saturating IR-RF emission centred at ∼880 nm represents a promising tool to date Quaternary sediments. In the present work, we report the presence of individual grains in the K-feldspar density fraction displaying an aberrant IR-RF signal shape, whose combined intensity contaminates the sum signal of an aliquot composed of dozens of grains. Our experiments were carried out at the National Synchrotron Light Source (NSLS-II) at the submicron-resolution X-ray spectroscopy (SRX) beamline. We analysed coarse (>90 µm) K-feldspar-bearing grains of five samples of different ages and origin in order to characterize the composition of grains yielding the desired or contaminated IR-RF emission. Using micro-X-ray fluorescence (μ-XRF), we successfully acquired element distribution maps of up to 15 elements (<1 µm resolution) of sections of full grains previously used for IR-RF dating. In keeping with current theories of IR-RF signal production, we observed a trend between the relative proportions of Pb and Fe and the shape of the IR-RF signal, namely that most grains with the desired IR-RF signal shape had high Pb and low Fe contents. Interestingly, these grains were also defined by high Ba and low Ca contents. Our study also represents a proof of concept for mapping the oxidation states of Fe using micro-X-ray absorption near-edge structure spectroscopy (μ-XANES) on individual grains. The high spatial resolution enabled by synchrotron X-ray spectroscopy makes it a powerful tool for future experiments to elucidate long-standing issues concerning the nature and type of defect(s) associated with the main dosimetric trap in feldspar.

Electronic structure and composition of tin oxide thin epitaxial and magnetron layers according to synchrotron XANES studies

The materials of the tin-oxygen system and thin-film structures based on them are modern and actual for the creation of a wide range of electronic devices, for example, resistive gas sensors of high sensitivity and short response time with low energy consumption and high manufacturability. An important direction in the study of such materials and structures is the control of properties with variations in technological formation regimes. Information on the composition, local atomic and electronic structure of thin layers of the tin-oxygen system with varying approaches to their production is in demand. The work is devoted to the study of the electronic structure of thin layers of tin oxides obtained by modern methods of molecular beam epitaxy and magnetron sputtering. A study of the local partial density of electronic states in the conduction band by X-ray absorption near edge structure spectroscopy of tin and oxygen has been carried out. The data were obtained using high-intensity synchrotron radiation, which allows varying the monochromatized radiation quantum energy without loss in intensity, that is necessary to obtain high-resolution X-ray spectral data. It is shown that the composition, local atomic surrounding, electronic spectrum and their features depend on the technology of formation and storage conditions of the studied structures. Synchrotron X-ray spectroscopy data show the presence of intermediate oxides of the tin-oxygen system in the studied materials after prolonged storage in laboratory conditions. The data obtained indicate the possibility of controlled variation in the composition, local atomic surrounding and electronic spectrum of thin-film structures of tin oxides of small thickness. The results of the work can be used in the formation and subsequent modification of thin and ultrathin layers of tin oxides by magnetron sputtering and molecular beam epitaxy, as well as in their further application as active layers of microelectronics devices

Efficient chemical and microbial removal of iron and manganese in a rapid sand filter and impact of regular backwash

Aeration followed by rapid sand filtration is a common method in drinking water treatment to remove iron (Fe) and manganese (Mn) from anoxic groundwater. To ensure the successful removal of Fe and Mn within a single filter, several factors such as raw water characteristics, backwash procedures and chemical and microbial interactions with the filter medium need to be considered. Here, we assess the characteristics of a single medium rapid sand filter with highly efficient removal of Fe and Mn. Using synchrotron X-ray spectroscopy, we show that formation of ferrihydrite-type Fe oxides in the top of the filter (0–50 cm) accounts for >95 % of the removal of dissolved Fe2+ in the filter. Birnessite-type Mn- oxides, which are thought to be biogenic, form over a wider depth interval (0–110 cm). Results of 16S rRNA gene amplicon sequencing indicate a corresponding distinct vertical stratification of the microbial community, with potential iron-oxidizing Gallionella, Leptothrix and Sideroxydans dominating in the upper part of the filter, and nitrifiers being more prevalent deeper in the filter. Besides Fe and Mn-oxide, Fe-flocs and bacteriological hollow sheets form in the upper part of the filter. Both the Fe-flocs, hollow Fe-sheets and part of the Fe and Mn coatings are removed through backwashing, thereby reducing the pressure difference measured over the filter medium linked to clogging of pores (from 14 kPa to 1.5 kPa) and ensuring continued water flow. Backwashing removes part of the Gallionella, but this does not negatively impact the filter performance. Strikingly, SEM imaging with EDS mapping revealed alternating layers of Fe and Mn-oxides on the coated grains throughout the filter. This indicates slow mixing of the filter medium between the upper 30 cm and the rest of the filter during backwashing. Slow mixing likely contributes to continued success of the filter by ensuring homogeneous filter bed growth, while still allowing for stratification of the microbial community.

Exploring Cr and molten salt interfacial interactions for molten salt applications.

Molten salts play an important role in various energy-related applications such as high-temperature heat transfer fluids and reaction media. However, the extreme molten salt environment causes the degradation of materials, raising safety and sustainability challenges. A fundamental understanding of material-molten salt interfacial evolution is needed. This work studies the transformation of metallic Cr in molten 50/50 mol% KCl-MgCl2via multi-modal in situ synchrotron X-ray nano-tomography, diffraction and spectroscopy combined with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Notably, in addition to the dissolution of Cr in the molten salt to form porous structures, a δ-A15 Cr phase was found to gradually form as a result of the metal-salt interaction. This phase change of Cr is associated with a change in the coordination environment of Cr at the interface. DFT and AIMD simulations provide a basis for understanding the enhanced stability of δ-A15 Cr vs. bcc Cr, by revealing their competitive phase thermodynamics at elevated temperatures and probing the interfacial behavior of the molten salt at relevant facets. This study provides critical insights into the morphological and chemical evolution of metal-molten salt interfaces. The combination of multimodal synchrotron analysis and atomic simulation also offers an opportunity to explore a broader range of systems critical to energy applications.

Praziquantel Fifty Years on: A Comprehensive Overview of Its Solid State.

This review discusses the entire progress made on the anthelmintic drug praziquantel, focusing on the solid state and, therefore, on anhydrous crystalline polymorphs, amorphous forms, and multicomponent systems (i.e., hydrates, solvates, and cocrystals). Despite having been extensively studied over the last 50 years, new polymorphs and the greater part of their cocrystals have only been identified in the past decade. Progress in crystal engineering science (e.g., the use of mechanochemistry as a solid form screening tool and more strategic structure-based methods), along with the development of analytical techniques, including Synchrotron X-ray analyses, spectroscopy, and microscopy, have furthered the identification of unknown crystal structures of the drug. Also, computational modeling has significantly contributed to the prediction and design of new cocrystals by considering structural conformations and interactions energy. Whilst the insights on praziquantel polymorphs discussed in the present review will give a significant contribution to controlling their formation during manufacturing and drug formulation, the detailed multicomponent forms will help in designing and implementing future praziquantel-based functional materials. The latter will hopefully overcome praziquantel's numerous drawbacks and exploit its potential in the field of neglected tropical diseases.

Temperature Dependent EXAFS to Address Functional Mechanisms in Battery Materials

Increasing the contribution of renewable energy sources is necessary to meet the fast increase of global energy needs and match the CO2 reduction targets. In order to address these challenges, intensive research efforts are ongoing both in energy harvesting and storage technologies such as solar panels, fuel cells, supercapacitors and batteries. The latter are required to match the energy demand and supply; in fact, batteries are by far the most ubiquitous energy storage technology currently employed.Synchrotron x-ray spectroscopies have played a key role in the continuous development and breakthroughs in battery science, thanks to their capability to provide accurate information on electronic structure of the redox active element, local structure, and morphological information. In particular, X-ray absorption spectroscopy (XAS) is more and more employed for addressing battery materials [1]. Generally, XAS studies on battery materials are performed at a single temperature as a function of charge, to access information on the electrochemical behavior and charge transfer mechanism during the intercalation or deintercalation process. However, the fact that the charging/discharging process is expected to have direct influence on the bond length characteristics, strength and disorder, it is important to perform temperature dependence measurements to find a realistic correlation between the local structure and the battery characteristics. Indeed, temperature-dependent studies quantitatively allow to discriminate in between static and dynamic disorder, and to have direct access to the local force constant between the atom pairs. Here the interest of performing temperature dependent extended X-ray absorption fine structure (EXAFS) studies is highlighted by exploiting several examples. In Li and Mn-rich NMC cathodes temperature-dependent EXAFS investigation revealed the evolution of the lattice rigidity which directly affects the reversible anionic redox contribution [2-3]. Similar studies on Ti based MXene-type [4], NaxCoO2 [5], and V2O5 [6] electrode materials underline the importance of the local atomic correlations as limiting factor in the ion diffusion in battery materials.

Unraveling Effects of Current Density and Silicon on Silicon-Graphite Composite Anodes By in-Situ Synchrotron X-Ray Diffraction

The development of lithium-ion batteries (LIBs) with high capacity and rate capabilities is imperative to meet energy demands for both transport and grid storage in the future. Due to its relative abundance and excellent cycling stability, state of the art LIBs contains graphite as the main anode component. However, graphite suffers from a low theoretical specific capacity of 372 mAhg-1 [ 1 ]. Alternatively, silicon (Si) has emerged as a promising energy-dense anode material with a theoretical specific capacity 10 times higher than graphite, but their widespread application is impeded by low electrical conductivity and extremely poor cycling stability due to large volume variations when alloying with lithium during electrochemical cycling [ 2 ]. Interestingly, silicon-graphite (SiG) composites have been pinpointed as promising options for producing improved anodes, which aims to combine graphite’s high electronic conductivity and structural stability with silicon’s high specific capacity. As expected, increasing the silicon content of SiG anodes reduces the cycling stability [3]. Optimization of SiG with respect to silicon content and utilization of silicon is not straightforward, and a comprehensive analysis on the effect of variations of silicon content and current density on SiG andoes is key. To investigate these interactions, in-situ synchrotron X-ray diffraction (XRD) analysis of composite anodes with varying silicon content at increasing c-rates was performed.In situ experiments were performed at BM01 of the European Synchrotron Radiation Facility (ESRF). An in-situ electrochemical cell consisting of two current collectors, in which the lower current collector is made of brass and the upper current collector is made of stainless steel, was utilized [ 4 ]. A half-cell was then assembled between the two current collectors in a coin cell configuration using lithium metal as the counter electrode and a glass fiber separator. 1M LIFSI in 1:1 vol EC: DMC was used as the liquid electrolyte. The current collectors each have a thin single crystal sapphire window that is mostly transparent to X-ray but have distinct signals that can be masked out in post-processing. To avoid diffraction signal from the underlying copper current collector of the electrode, the composite anode consists of electrodes cast on copper foil as well as a free-standing section. The assembled cell was galvanostatically cycled between 1 V and 50 mV while XRD data was acquired. In this study 4 different electrodes containing 0, 20 %wt., 30 %wt. and 70 %wt. of Si in the active material of the electrode were cycled at C/5, C/2, 1C and 2C rates.Analysis of the XRD results showed that tracking of the evolution of graphite main reflections during electrochemical cycling while completely avoiding the copper signal has been achieved. The degree of graphite lithiation was tracked by following the distinct 002, 100 and 110 peaks of graphite where phase transitions to LiC12 and LiC6 can be identified. Consistent with the results of other studies, graphite has been found to be both lithiated and delithiated at lower potentials than silicon [ 3 ]. Increasing silicon content was found to decrease the degree of graphite lithiation as silicon will be preferentially lithiated. Increasing the current density was found to reduce the overall degree of lithiation of graphite as the specific capacity decreases and the material is not sufficiently lithiated to undergo the expected phase transitions. This study has therefore unraveled the effect of silicon content and current density on composite anode behavior which could allow for the design of better next-generation composite anodes. Tarascon, J.-M. & Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 414, 359–367 (2001). Ashuri, M., He, Q. & Shaw, L. L. Silicon as a potential anode material for Li-ion batteries: where size, geometry and structure matter. Nanoscale 8, 74–103 (2015). Moyassari, E. et al. The Role of Silicon in Silicon-Graphite Composite Electrodes Regarding Specific Capacity, Cycle Stability, and Expansion. J. Electrochem. Soc. 169, 010504 (2022). Drozhzhin, O. A. et al. An electrochemical cell with sapphire windows for operando synchrotron X-ray powder diffraction and spectroscopy studies of high-power and high-voltage electrodes for metal-ion batteries. J. Synchrotron Radiat. 25, 468–472 (2018). Figure 1

Uncovering atomic-scale polymer-to-ceramic transformations in SiC polymer derived ceramics from polycarbosilanes

Polycarbosilanes (PCS) are organosilicon polymers that can be converted into silicon carbide (SiC) ceramics upon pyrolysis. The phase compositions and microstructure of the final ceramic are notably impacted by the interplay of both polymer morphology and chemical functionality. Such characteristics hold tremendous potential for developing polymer derived ceramics (PDCs) with optimized properties if the complexities inherent to such materials are better understood at the atomic-scale. This study investigates the structural changes associated with the polymer-to-ceramic conversion in SiC systems derived from the pyrolysis of commercial PCS: SMP-10, SMP-877 and SMP-730, across a temperature range of 250–1600 °C. Using a combination of synchrotron X-ray spectroscopy and scattering methods, we reveal heterogeneous structures with varied compositions, influenced by both pyrolysis conditions and initial PCS functionalities. This study offers a promising approach for understanding the devitrification and compositional heterogeneity (C vs. SiC phases) in polymer-to-ceramic conversion.

Mapping biochemical and nutritional changes in durum wheat due to spoilage during storage

Synchrotron X-ray imaging and spectroscopy techniques were used for studying changes during post-harvest storage of food grains. Three varieties (AAC Spitfire, CDC Defy, and AAC Stronghold) of the Canada Western Amber Durum (CWAD) wheat class were stored for five weeks at 17 % moisture content (wb). Control (dry) and stored moistened seeds were analyzed for biochemical and nutritional changes using synchrotron bulk X-ray fluorescence spectroscopy (SR-XRF), X-ray fluorescence imaging (SR-XFI), and mid-infrared (mid-IR) spectroscopy at the Canadian Light Source (CLS), Saskatoon, SK. All varieties of durum wheat were spoiled at the end of five week, and AAC Spitfire and CDC Defy varieties were most affected in nutritional composition and their distribution than AAC Stronghold. Variable response to changes in biochemical and nutrition were found in all three spoiled varieties of the same durum wheat class.

Design Principles for Transition Metal Nitride Stability and Ammonia Generation in Acid

Transition metal nitrides have shown great promise for reducing or eliminating the use of expensive precious-metal-based catalysts (e.g., Pt) in proton exchange membrane fuel cells and electrolyzers, but the use of these nitrides in such technologies is severely hindered by their dissolution at acidic pHs [1-2]. More importantly, the decomposition of transition metal nitrides in acid generates ammonia from the protonation of lattice nitrogen, giving rise to many false positives in previous reports of nitride catalysts for electrochemical nitrogen reduction to ammonia. For example, while nitrides such as VN [3], NbN [4], and Mo2N [5] have been computationally predicted to catalyze the reduction of nitrogen to ammonia, the experimentally observed ammonia has been attributed to the decomposition of nitrides in acid [6-8]. To tackle this challenge, motivated by our previous work [9-12] on the design principles of transition-metal-oxide-based catalysts, we established the stability descriptors of transition metal nitrides in acid. Such stability descriptors not only offer a fundamental understanding of nitride dissolution but also provide new guiding principles to optimize the intrinsic stability of nitrides for diverse acidic applications.In this work [13], combining ab initio calculations with synchrotron X-ray spectroscopies, we identified electronic-structure-based design principles governing the extent and kinetics of nitride dissolution and ammonia production in acid. We found that lowering the nitrogen 2p band center of transition metal nitrides with respect to the Fermi level leads to weakened metal-nitrogen bonds, increased labile metallic character, and a reduced barrier for the protonation of lattice nitrogen to produce ammonia, correlating with faster dissolution kinetics of nitrides in acid. Moreover, increasing the solubility of dissolved metal ions in acid was found to be critical in preventing surface oxide passivation to ensure the complete conversion from transition metal nitrides to ammonia. Based on these observations, a new mechanistic picture was formulated, where the initial protonation step of lattice nitrogen is critical to trigger nitride dissolution, and this proposed reaction scheme was supported by the pH-dependent dissolution kinetics of nitrides in acid.These design principles and mechanistic insights for producing ammonia and dissolving metal cations from the decomposition of nitrides in acid are essential for a variety of clean energy applications. For instance, such design principles can be leveraged to boost the stability of nitride catalysts for proton-exchange membrane fuel cells and electrochemical ammonia synthesis, where the dissolution of nitrides in acid has hindered their functions. Moreover, these descriptors for nitride dissolution and ammonia formation in acid provide emerging opportunities for designing novel nitride chemistries for distributed, on-demand ammonia generation. As nitrides represent an exciting, yet markedly unexplored chemical space, this work provides a blueprint to design multinary nitrides in such a vast materials space for various acidic applications, including electrocatalysis and beyond.

Single-atom cobalt-incorporating carbon nitride for photocatalytic solar hydrogen conversion: An X-ray spectromicroscopy study

The use of carbon nitride-based materials and light to drive catalytic water splitting has enormous potential for the production of hydrogen. Revealing the processes of molecular conjugation, nucleation, and crystallization in crystalline carbon nitride is expected to enhance the photocatalytic activity through the creation of isotype heterojunctions and active sites. In this work, the addition of cobalt salts in ionothermal synthesis was found to promote the phase transition of heptazine-based crystalline carbon nitride (CCN) to triazine-based poly (triazine imide) (PTI), resulting in the formation of a single-atom cobalt-doped coordinated isotype CCN/PTI heterojunction. The new hybrid orbital modulates the atomic/electronic structure and the band gap of the CCN/PTI heterojunction, and synergistically increases the absorption of visible light, accelerating the separation and transfer of photoexcited electrons and holes. Synchrotron-based X-ray spectroscopy and microscopy are used to identify the origin of the improved performance of the single-atom cobalt-doped CCN/PTI heterojunction in the photocatalytic hydrogen evolution reaction. This work demonstrates that synchrotron X-ray spectroscopy is a promising tool for designing materials aimed at enhancing photocatalytic activity in solar energy conversion applications.

Atomic Nickel on Graphitic Carbon Nitride as a Visible Light-Driven Hydrogen Production Photocatalyst Studied by X-ray Spectromicroscopy

The photocatalytic production of solar hydrogen through water splitting by graphitic carbon nitride (g-C3N4) has gained substantial interest due to its advantageous characteristics, such as eco-friendliness, wealth on the earth, favorable bandgap, and easy preparation. Nevertheless, the performance for photocatalytic overall water splitting has been significantly restricted owing to the rapid recombination of charge carriers and slow catalytic kinetics. This investigation demonstrates the utilization of a single-atom Ni-terminating agent to coordinate with the heptazine moieties of g-C3N4, resulting in the formation of a new electronic orbital. g-C3N4 with single-atom Ni-termination can achieve highly efficient photocatalytic overall water splitting into H2 and H2O2 upon visible light irradiation, without requiring the use of any additional cocatalysts. The underlying cause of the enhanced photocatalytic performance of single-atom Ni-incorporated g-C3N4 in hydrogen evolution reaction is identified using synchrotron X-ray spectroscopy and microscopy. The X-ray spectro-microscopic results discover that the new hybrid orbital that is critical for optimizing photocatalysis is associated with carbon defects. The atomic and electronic structures and the band gap of g-C3N4 are adjusted by the new hybrid orbital. Moreover, it synergistically enhances visible light absorption, thereby promoting the separation and transfer of photogenerated charge carriers. The single-atom Ni and the adjacent C atom are recognized as the active sites for water oxidation and reduction, respectively, supporting the efficient photocatalytic splitting of water via a two-electron transfer pathway. This study demonstrated a promising material design for promoting photocatalytic activity in solar energy conversion applications.

Kinetics and evolution of solid-state metal dealloying in thin films with multimodal analysis

Thin-film solid-state metal dealloying (thin-film SSMD) is an emerging technique that uses self-organization to design nanostructured thin films. The resulting 3D bicontinuous nanostructures are promising for a wide range of applications, such as catalysis and energy storage. In this work, we prepared thin films by SSMD using Ti-Cu as the parent alloy and Mg as the solvent. Using a multimodal approach, we combined synchrotron X-ray spectroscopy, diffraction, and high-resolution electron-based spectroscopy and imaging to study their morphological, structural, and chemical evolution. The processing-structure relationship was analyzed as a function of parent alloy composition and dealloying temperature and time. Morphological transitions from globular, to lamellar, to bicontinuous structures, in conjunction with a ligament size evolution, were identified as functions of the parent alloy composition. The dealloying rate increased with increasing concentration of interdiffusing elements (dissolving component) in the parent alloy. The parting limit, a dealloying compositional threshold, was systematically analyzed and determined to be 30%–40%. The order of crystalline phase formation is CuMg2, Cu2Mg, and Ti; the Ti phase first shows self-reorganization during dealloying, separate from the crystallization process. The coarsening in thin-film SSMD was identified and not entirely self-similar; in addition to the increase of ligament size over time, the formation of larger globular ligaments were also observed. This work furthers our fundamental understanding of thin-film SSMD and nanostructured thin-film design, where the thermodynamic and kinetic effects differ from the bulk counterparts. The fact that dealloying and diffusion outpaces the crystallization and new phase formation also offers opportunities to utilize thin-film SSMD in certain alloy systems in which deleterious intermetallic phases need to be suppressed, that may not be possible in the bulk geometry.

Redox Evolution of Li-Rich Layered Cathode Materials

Li-rich layered oxides utilizing reversible oxygen redox are promising cathodes for high-energy-density lithium-ion batteries. However, they exhibit different electrochemical profiles before and after oxygen redox activation. Therefore, advanced characterization techniques have been developed to explore the fundamental understanding underlying their unusual phenomenon, such as the redox evolution of these materials. In this review, we present the general redox evolution of Li-rich layered cathodes upon activation of reversible oxygen redox. Various synchrotron X-ray spectroscopy methods which can identify charge compensation by cations and anions are summarized. The case-by-case redox evolution processes of Li-rich 3d/4d/5d transition metal O3 type layered cathodes are discussed. We highlight that not only the type of transition metals but also the composition of transition metals strongly affects redox behavior. We propose further studies on the fundamental understanding of cationic and anionic redox mixing and the effect of transition metals on redox behavior to excite the full energy potential of Li-rich layered cathodes.

Improved multiferroic in EuTiO3 films by interphase strain engineering

Interphase strain engineering provides a unique methodology to significantly modify the lattice structure across a single film, enabling the emergence and manipulation of novel functionalities that are inaccessible in the context of traditional strain engineering methods. In this work, by using the interphase strain, we achieve a ferromagnetic state with enhanced Curie temperature and a room-temperature polar state in EuO secondary phase-tunned EuTiO3 thin films. A combination of atomic-scale electron microscopy and synchrotron X-ray spectroscopy unravels the underlying mechanisms of the ferroelectric and ferromagnetic properties enhancement. Wherein, the EuO secondary phase is found to be able to dramatically distort the TiO6 octahedra, which favors the non-centrosymmetric polar state, weakens antiferromagnetic Eu-Ti-Eu interactions, and enhances ferromagnetic Eu-O-Eu interactions. Our work demonstrates the feasibility and effectiveness of interphase strain engineering in simultaneously promoting ferroelectric and ferromagnetic performance, which would provide new thinking on the property regulation of numerous strongly correlated functional materials.

Two-color synchrotron X-ray spectroscopy based on transverse resonance island buckets

We report on a novel multi-color method of X-ray spectroscopy at a Synchrotron radiation source that uses two simultaneously filled electron orbits in an electron storage ring to generate multiple soft or tender X-ray beams of different wavelength. To establish the second orbit, we use nonlinear beam dynamics in the so called TRIBs—transverse resonance island buckets—mode of the BESSY II storage ring, where a second electron orbit winds around the regular one leading to transversely separated source points. X-ray beams of multiple colors are generated by imaging the individual source points via different pathways through a monochromator. The particular colors can be varied by changing the traversal electron beam positions through storage-ring parameters and/or via the monochromator dispersion. As a proof of principle, X-ray absorption spectroscopy is performed on thin Fe films in transmission as well as a scanning transmission measurement on a Fe3GeTe2 sample of inhomogeneous thickness normalizing resonant signals with the pre-edge intensity. Using the extraordinary pointing fidelity of successive X-ray macro-pulses arriving at MHz repetition rates, a detection of tiny contrasts in diluted systems, contrast enhancement in X-ray microscopy as well as fast dynamics studies come into reach.

Metal Complex/ZnS-Modified Ni Foam as Magnetically Stirrable Photocatalysts: Roles of Redox Mediators and Carrier Dynamics Monitored by Operando Synchrotron X-ray Spectroscopy.

Magnetically stirrable photocatalysts binding the ZnS-decorated Ni foam with the metal complex cocatalyst as a redox mediator and light-absorbing composition were investigated. Loading metal complex can improve light absorption, surface hydrophilicity, interfacial charge migration, and H2 production activity. The variation of the metal valences of the composite photocatalysts in an operando environment (with sacrificial agent solution) with and without light irradiation was investigated by X-ray absorption near-edge structure (XANES) spectra and Fourier-transformed extended X-ray absorption fine structure (EXAFS) spectra to monitor the charge carrier dynamics of photocatalysis and explain how the macrocyclic Cu complex (CuC) acted as a redox mediator better than the Ni complex. The smaller valence difference of copper valence in ZS/CuC for dark and light states revealed that the Cu complex facilitates a reversible electron transfer between the ZnS photocatalyst and H+. Loading the Cu complex can improve the separation of photogenerated carriers by the redox couple of complexes, leading to a significantly improved photocatalytic H2 production activity of 8150 μmol h-1 g-1. The reactants can flow through these magnetically stirrable Ni foam-based photocatalysts by magnetic-field-driven stirring, which improves the contact between photocatalysts and the sacrificial agents. The operando synchrotron provides new insights for understanding the roles of redox mediators.

(Invited) Probing the Atomic and Electronic Structure of Working Energy Materials with x-Ray Spectroscopy

Improving energy conversion/generation/storage efficiency of energy materials has always been a great challenge. Monitoring the atomic/electronic structures close to interface in many important energy materials, such as nanostructured catalysts, artificially photosynthesizing materials, smart materials, and energy storage devices, is of great importance. Designing such a material with improved performance without understanding its atomic/electronic structures, and their changes under operating conditions, is difficult. Understanding and controlling the interfacial electronic structures of energy materials require in-situ characterizations, of which synchrotron x-ray spectroscopy is the one with many unique features. The last decade has witnessed a golden age of in situ synchrotron x-ray spectroscopy for energy materials. X-ray absorption spectroscopy can be used to determine unoccupied electronic structures while X-ray emission spectroscopy can be utilized to examine occupied electronic structure. The additional use of resonant inelastic X-ray scattering further reveals inter-band d-d excitation or intra-band charge transfer excitation that can reflect the fundamental chemical and physical properties. An emerging technique, scanning transmission x-ray microscopy is a spectro-microscopic approach, providing regional x-ray absorption spectroscopy, is also gearing up for energy science. This presentation will report recent studies and perspectives of the application of in situ/operando synchrotron x-ray spectroscopy to energy materials. Tamkang University (TKU) end-stations constructed at the Taiwan Photon Source (TPS) 45A & 27A beamlines for the x-ray spectroscopic investigation of energy materials will also be introduced.

Dimensionality effect of conductive carbon fillers in LiNi1/3Mn1/3Co1/3O2 cathode

Developing advanced electrode architectures through modifying active materials, conductive fillers, binders, and electrolytes as well as processing methods has drawn significant research interest. Due to the insufficient electrical conductivity of many active materials, adding conductive carbon fillers to composite electrodes provides the necessary electrical conductivity. The dimensionality effect among different conductive fillers has a significant impact on electrochemistry, which can be associated with morphological and chemical heterogeneities of electrodes. Here, synchrotron X-ray mosaic nanotomography and X-ray spectroscopy nanoimaging provided direct three-dimensional (3D) visualization and quantification capabilities to investigate the dimensionality effects of Super P (SP) and single-walled carbon nanotube (SWCNT) fillers on the capacity retention of LiNi1/3Mn1/3Co1/3O2 (NMC111). The results indicate that NMC/SWCNT electrodes, with a wrapping effect from the SWCNTs, exhibited more homogeneous particle size distributions, morphological changes, and chemical states than NMC/SP electrodes, without the wrapping effect. This work developed a framework of 3D quantification methods to study the capacity fading behavior associated with morphological and chemical heterogeneities and paved the way toward designing electrodes for high rate energy storage applications.