X-ray Absorption Near-edge Spectroscopy Research Articles

Regulating Intermediate Adsorption and Promoting Charge Transfer of CoCr-LDHs by Ce Doping for Enhancing Electrooxidation of 5-Hydroxymethylfurfural.

Electrochemical oxidation of 5-hydroxymethylfurfural (HMFOR) to generate high-value chemicals under mild conditions acts as an energy-saving and sustainable strategy. However, it is still challenging to develop electrocatalysts with high efficiency and good durability. Here, nickel foam (NF) supported CoCrCe(7.5%)-LDH (layered double hydroxides) by doping Ce into CoCr-LDH show high 5-hydroxymethylfurfural (HMF)conversion (99%), 2,5-furandicarboxylic acid (FDCA) yield (99%), and Faraday efficiency (100%) at 1.4 VRHE. The CoCrCe(7.5%)-LDH also exhibits remarkable stability with 97% conversion of HMF after 10 cycles. The X-ray absorption near-edge spectroscopy (XANES) and theoretical calculation show that Ce doping into CoCr-LDH is beneficial to the formation of high-valance Co and significantly facilitates the electron transfer, regulates the adsorption behavior of intermediates, reduces the Gibbs free energy barrier and accelerates the reaction rate. This work promotes the use of rare earth elements as electrocatalysts to promote the oxidation of HMF.

Zero-Valent Copper Catalysis Enables Regio- and Stereoselective Difunctionalization of Alkynes.

The development of a metallic copper-based catalyst system remains a significant challenge. Herein, we report the synthesis of highly stable, active, and reusable Cu0 catalyst for the carboboration of alkynes using carbon electrophiles and bis(pinacolato)diboron (B2pin2) as chemical feedstocks to afford di- and trisubstituted vinylboronate esters in a regio- and stereoselective manner with appreciable turnover number (TON) of up to 2535 under mild reaction conditions. This three-component coupling reaction works well with a variety of substituted electrophiles and alkynes with broad functional group tolerance. In addition, a wide range of terminal and challenging internal alkynes were efficiently converted into hydroborated products in up to >99% yield with excellent regioselectivity in the absence of carbon electrophiles. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) analysis confirm that the oxidation state of the copper in the catalyst is zero. The broad range of organic transformations, effectiveness, and recyclability of this Cu0 catalyst are the major achievements that provide an environmentally friendly route for the efficient production of tri- and tetrasubstituted olefins, key intermediates in organic synthesis. The gram-scale reaction and synthetic transformations further highlights the usefulness of these methods.

Zero‐Valent Copper Catalysis Enables Regio‐ and Stereoselective Difunctionalization of Alkynes

The development of a metallic copper‐based catalyst system remains a significant challenge. Herein, we report the synthesis of highly stable, active, and reusable Cu0 catalyst for the carboboration of alkynes using carbon electrophiles and bis(pinacolato)diboron (B2pin2) as chemical feedstocks to afford di‐ and trisubstituted vinylboronate esters in a regio‐ and stereoselective manner with appreciable turnover number (TON) of up to 2535 under mild reaction conditions. This three‐component coupling reaction works well with a variety of substituted electrophiles and alkynes with broad functional group tolerance. In addition, a wide range of terminal and challenging internal alkynes were efficiently converted into hydroborated products in up to >99% yield with excellent regioselectivity in the absence of carbon electrophiles. X‐ray photoelectron spectroscopy and X‐ray absorption near‐edge spectroscopy (XANES) analysis confirm that the oxidation state of the copper in the catalyst is zero. The broad range of organic transformations, effectiveness, and recyclability of this Cu0 catalyst are the major achievements that provide an environmentally friendly route for the efficient production of tri‐ and tetrasubstituted olefins, key intermediates in organic synthesis. The gram‐scale reaction and synthetic transformations further highlights the usefulness of these methods.

Impact of Manganese Carbonate Precipitation on Uranium(VI) Fate in Conditions Relevant to Carbonate-Buffered Aquifers.

Widespread geogenic uranium (U) contamination of Indian groundwaters is of serious concern; yet little is known of the dominant forms and release mechanisms of U in these aquifers. Interestingly, manganese (Mn)-rich aquifers, highly buffered by dissolved inorganic carbon (DIC) and saturated with rhodochrosite [MnCO3(s)], have shown low U (<WHO limit of 30 μg L-1) concentrations. Given the limited understanding of U and MnCO3(s) interaction, this study investigates the impact of rhodochrosite precipitation on U(VI) fate in simple solutions supersaturated with respect to MnCO3(s) (Saturation Index ∼ 2.7) under conditions relevant to carbonate-buffered mixed oxic aquifers. Year-long batch experiments were performed over variable initial U concentrations (0-500 μM). While uranium uptake was ∼50% within 30 days, the uptake was near-complete after 1 year for all conditions. No known U-bearing solid phases were detected, except for the highest initial U concentrations (500 μM), consistent with solution saturation states. Characterization of solids collected after 30 days and 1 year with X-ray diffraction, electron-based imaging, X-ray absorption near-edge, X-ray photoelectron, and Raman spectroscopies confirmed rhodochrosite as the only major precipitated phase, with slightly altered crystal structure from uranyl incorporation. While these incorporations seemed to initially (30 days) reduce the crystallinity of rhodochrosite, all U-incorporated rhodochrosite turned crystalline in the long term (1 year). Also, the incorporated U did not undergo a redox change. Instead, the U(VI) coordination environment changed as U(VI) uptake increased. Reactive modeling of Mn and DIC data exhibited a decrease in the surface area normalized rate constants of MnCO3(s) precipitation from 5.9 to 3.3 × 10-8 mol m-2 h-1 with an increase in initial U(VI) from 0 to 500 μM. The notable incorporation of U(VI) by MnCO3(s) in just 30 days, a phenomenon that is rapid on a geological time scale, has implications on U(VI) fate in high carbonated oxic-anoxic aquifers with high Mn concentrations.

Use of In Situ X-ray Absorption to Probe Reactivity: A Catalysis Golden Rule.

The decomposition of ozone on supported manganese oxide catalysts, studied here, exemplifies reactions involving electron transfer. In situ extended X-ray absorption fine-structure spectra (Mn K-edge) on in situ treated samples show that the supported phase in MnOx/SiO2 resembles Mn3O4 while that in MnOx/Al2O3 samples resembles MnO2. In situ Raman spectroscopy shows the involvement of a common peroxide surface species. Kinetic data indicate a nonuniform surface and a rate-determining step (rds) involving electron transfer from the peroxide intermediate. The activation energy for all the catalysts is the same, indicating that the pre-exponential factor controls the rate. This can be associated with the electronic partition function (unoccupied density of states (DOS)), and X-ray absorption near-edge spectroscopy duly shows that the areas of the pre-edge peaks due to 1s to 3d transitions track the reactivity trends. The relation to the unoccupied DOS is analogous to Fermi's Golden Rule for electronic transitions, and we denote the finding here, applicable to reactions involving electron transfer, as a Catalysis Golden Rule.

Post-Synthetic Modification of a MOF via Continuous Flow Methods for Gold E-Waste Recycling.

This work represents a pioneering effort in utilizing continuous flow methods for the post-synthetic modification of a nanoporous metal-organic framework (Fe-BTC or MIL-100(Fe)) with short-chain redox-active oligomers (poly-p-phenylenediamine, PpPDA). The Fe-BTC/PpPDA composite has been previously demonstrated to rapidly and selectively extract gold from complex liquids. Thus, in the present study, Fe-BTC/PpPDA was synthesized on a 250 g scale and tested in eight industrially relevant solutions used for leaching metals from electronic waste. These leachates (e. g., cyanide, thiourea, and aqua regia) exhibited varying effectiveness, pH, and gold speciation, which led to significant differences in the composite's performance during gold extraction. Notably, Fe-BTC/PpPDA performed best in leaching solutions containing [AuCl4]- species. Subsequently, Fe-BTC/PpPDA was structured into spherical beads using a novel microdroplet technique in continuous flow. These structured adsorbents were then placed in a column and assessed for gold recovery from real e-waste solutions containing [AuCl4]- species. The composite reached a capacity of ~600 mg of gold per gram before breakthrough and a capacity of ~900 mg of gold per gram at a gold recovery rate of ~60 %. The selectivity of the composite was calculated to be 972, 262, and 193 for Au/Ni, Au/Co, and Au/Fe, respectively. Also, in situ X-ray absorption near edge spectroscopy (XANES) was employed to monitor the gold oxidation state, providing the first evidence of gold reduction occurring on a timescale relevant to flow-through experiments. It was confirmed that the redox-active oligomers facilitate the reduction of Au3+ to metallic Au during extraction, enhancing the composite's capacity and selectivity. Additionally, Fe-BTC/PpPDA outperformed several commercial resins commonly used in gold recovery. Considering the scalability of the composite and its outstanding performance in realistic solutions, this work suggests a promising future for MOF/polymer composites in selective metal recovery from waste streams. Furthermore, the continuous flow methods used for post-synthetic modification of the MOF may pave the way for more scalable production in the future.

New Insights into the Crystal Structure of Fe0.5TiOPO4 Anode Material for Lithium-Ion Batteries Using Non-Ambient X-Ray Diffraction Measurements

The search for alternative electrode materials for lithium and sodium ion batteries is an expanding field with a continuous effort of research. Among the various materials, polyanionic phosphate compounds M0.5TiOPO4 (M= Fe, Ni, Co, Cu) have been investigated as anode materials for Lithium-ion batteries due to their several advantages.Our research group has been investigating the crystal and electronic structure changes of Fe0.5TiOPO4/C material that occur during the insertion/extraction of lithium ions. Hence, Operando X-ray diffraction (XRD) measurements on Fe0.5TiOPO4/C composite were conducted. The experiments were performed using special electrochemical coin cells with glass windows, which enabled us to conduct operando XRD measurements on the battery cell during operation. The coin cells were prepared in a glovebox under an Argon atmosphere. In-situ Iron-57 Mössbauer and in-situ X-ray Absorption Near Edge Spectroscopy (XANES) were also performed to reveal the electrochemical mechanisms of this material.After analyzing all the results at high and low voltage cut-offs, we found that Fe0.5TiOPO4/C electrode materials maintain their structure crystallinity after cycling between [3.0-1.3V], showing the formation of a new phase at the end of the first discharge. At highly lithiated states, [3.0-0.02V] voltage range, a reduction–decomposition reaction highlights the Li-insertion/extraction behaviors, and low phase crystallinity is observed during cycling.Furthermore, the Iron-57 Mössbauer analysis on the pristine material Fe0.5TiOPO4/C revealed the presence of two distinct Iron environments, which contradicts the previously reported structural observations. To gain more insights into the crystal structure of the pristine material, we conducted XRD measurements between 13 and 300 K conditions. From Rietveld refinements, we determined the newly found crystal structure of Fe0.5TiOPO4/C, which shows that the Fe2+ cations can be in two triangular-based antiprism crystallographic sites. This finding is further supported by DFT calculations, which demonstrate the possibility of the co-existence of several host sites for Fe2+.

Laboratory-Scale X-Ray Absorption Spectroscopy for in Situ Analysis of Li+-Insertion Mechanisms in Vanadium Ferrites

Vanadium–iron oxides (VFe2Ox) exhibit promising Li+-storage properties when expressed in high-surface-area, disordered/defective forms such aerogels.1 We have also shown that the specific capacity for VFe2Ox can be further increased by compositional substitution with minority amounts of electro-inactive cations such as Al3+ and Zr4+.2 To deconvolve the relative contributions of V- and Fe-based redox and the effects of metal substitution, we turn to X-ray absorption spectroscopy (XAS) as performed with a bench-scale instrument. X-ray absorption near-edge spectroscopy (XANES) provides vital element-specific information on electronic properties and metal oxidation state, while extended absorption fine-structure spectroscopy (EXAFS) produces information on local bonding/coordination, even for amorphous/disordered materials. Using pouch cells designed specifically for the bench-scale spectrometer, we collect in situ spectra on VFe2Ox electrodes as they undergo electrochemical cycling between 2.0 and 3.8 V vs Li/Li+ in conventional nonaqueous electrolyte. We show that the first stages of Li+-insertion are accompanied by Fe3+/2+ redox, with V5+/4+ redox becoming active only at lower cell voltages (<2.5 V). Parallel DFT calculations on a representative spinel-type VFe2Ox structure confirms that V incorporates at tetrahedral sites. The combination of Fe/V tetrahedral occupation and vacancy-induced disorder also lowers the overall energy to open an electronic energy gap that establishes the Fe3+/2+-to-V5+/4+ redox sequence during lithiation, in confirmation of experimental XAS findings. The role of additional metal substitution is also assessed by parallel XAS measurements and DFT computation. 1. C. N. Chervin, J. S. Ko, B. W. Miller, L. Dudek, A. N. Mansour, M. D. Donakowski, T. Brintlinger, P. Gogotsi, S. Chattopadhyay, T. Shibata, J. F. Parker, B. P. Hahn, D. R. Rolison, and J. W. Long, J. Mater. Chem. A 3, 12059 (2015). 2. C. N. Chervin, R.H. DeBlock, J. F. Parker, B. M. Hudak, N. L. Skeele, J. S. Ko, D. R. Rolison, and J. W. Long, RSC Adv. 11, 14495 (2021).

Isovalent Co-Substitution of Iron and Titanium into Single-Crystal NMC622

Recently, all-dry (i.e., solvent-free) synthesis methods for Ni-rich nickel-manganese-cobalt (NMC) cathode active materials, Li(Ni a Mn b Co1-a-b )O2 (NMC, a ≥ 0.5), have enabled the use of metal oxide feedstocks to be used as precursors.1 Such all-dry methods provide new opportunities for compositional modification in NMCs. In the search for more sustainable, high-performance Ni-rich alternatives to NMC, Fe and Ti have been identified as attractive substitutes for Co and Mn, respectively.2–4 Herein, using all-dry synthesis methods, both individual and isovalent co-substitution of Fe and Ti into single-crystal (SC) NMC622, according to Li(Ni0.6Mn0.2-y Co0.2-x Fe x Ti y )O2 (0 ≤ x, y ≤ 0.2), were conducted.In these studies, it was found that Fe-substitution resulted in increased inter-site mixing, resulting in increased polarization and reduced capacity retention. However, Ti-substitution resulted in an increase in Ni3+ content, leading to improved capacity retention. These effects were found to be independent of each other, so that Ti additions could effectively offset some of the negative aspects of Fe-substitution. Such studies could point the way to enabling increased Fe-content in NMC. Additionally, layered Mn-free Li(Ni0.6Ti0.2Co0.2)O2 (NTC622) was produced as an endmember of this series with low levels of cation mixing. This is the first time to our knowledge that a fully ordered NTC622 composition has been reported. As a consequence of its ordered structure, the NTC622 made here was found to have far superior electrochemical performance in comparison to previous attempts reported in the literature.5,6 These results demonstrate the viability of Ti-rich cathode material compositions, such as NTC622, presenting an avenue for cathode materials synthesized by all-dry methods.7In this presentation the effects of Ti and Fe individual and co-substitution in single-crystal Li(Ni0.6Mn0.2-y Co0.2-x Fe x Ti y )O2 (0 ≤ x, y ≤ 0.2) made by all-dry methods will be discussed, including structural changes, changes in oxidation states as measured by X-ray absorption near-edge spectroscopy (XANES), and electrochemical performance; with special emphasis on the end-member composition of NTC622.References(1) Zheng, L.; Bennett, J. C.; Obrovac, M. N. All-Dry Synthesis of Single Crystal NMC Cathode Materials for Li-Ion Batteries. J Electrochem Soc 2020, 167 (13), 130536. https://doi.org/10.1149/1945-7111/abbcb1.(2) Lu, M.; Han, E.; Zhu, L.; Chen, S.; Zhang, G. The Effects of Ti4+-Fe3+ Co-Doping on Li[Ni1/3Co1/3Mn1/3]O2. Solid State Ion 2016, 298, 9–14. https://doi.org/10.1016/j.ssi.2016.10.014.(3) Mi, C.; Han, E.; Sun, L.; Zhu, L. Effect of Ti4+ Doping on LiNi0.35Co0.27Mn0.35Fe0.03O2. Solid State Ion 2019, 340. https://doi.org/10.1016/j.ssi.2019.05.011.(4) Meng, Y. S.; Wu, Y. W.; Hwang, B. J.; Li, Y.; Ceder, G. Combining Ab Initio Computation with Experiments for Designing New Electrode Materials for Advanced Lithium Batteries: LiNi1/3Fe1/6Co1/6Mn1/3O2. J Electrochem Soc 2004, 151 (8), A1134. https://doi.org/10.1149/1.1765032.(5) Baster, D.; Paziak, P.; Ziąbka, M.; Wazny, G.; Molenda, J. LiNi0.6Co0.4-ZTizO2 - New Cathode Materials for Li-Ion Batteries. Solid State Ion 2018, 320, 118–125. https://doi.org/10.1016/j.ssi.2018.03.002.(6) Fujimoto, K.; Ikezawa, K.; Ito, S. Charge-Discharge Properties of a Layered-Type Li(Ni,Co,Ti)O2 Powder Library. Sci Technol Adv Mater 2011, 12 (5). https://doi.org/10.1088/1468-6996/12/5/054203.(7) Tahmasebi, M. H.; Obrovac, M. N. Quantitative Measurement of Compositional Inhomogeneity in NMC Cathodes by X-Ray Diffraction. J Electrochem Soc 2023, 170 (8), 080519. https://doi.org/10.1149/1945-7111/acefff. Figure 1

Three-Dimensional Visualization of Inhomogeneous Reaction within Individual Active Material Particles in Composite Solid-State Battery Electrodes Using Nano CT-XANES

Introduction Solid-state batteries (SSBs) are next-generation batteries that are expected to exhibit higher energy density, power density, and safety than current lithium-ion batteries. In composite SSB electrodes, randomly distributed particles of active material (AM) and solid electrolyte (SE), and voids form three-dimensionally complicated ion/electron conduction paths and AM/SE interfaces. Such complex mass transport paths and limited AM/SE interfaces can locally impede the ion/electron supply to AM particles particularly under the rapid (dis)charging, potentially leading to a three-dimensional (3D) inhomogeneous reaction within each AM particle, as well as between particles. The occurrence of such inhomogeneous reaction can severely deteriorate the capacity, power output, and cycle life of SSBs. Therefore, it is essential to understand the mechanism of the occurrence of the inhomogeneous reaction and to design electrodes that enable uniform reaction progression. The most effective approach for this is the direct observation of the 3D inhomogeneous reaction within individual AM particles in actual composite SSB electrodes. However, most of existing methods enables only one- or two-dimensional observation of the inhomogeneous reaction1, 2, offering limited insight into the 3D reaction inhomogeneity in AM particles in SSB electrodes. With this background, in this work, we developed a 3D visualization technique of inhomogeneous reaction within individual AM particles in a composite SSB electrode using X-ray nano computed tomography technique combined with X-ray absorption near-edge structure spectroscopy (nano CT-XANES). Using this technique, we three-dimensionally observed the inhomogeneous reaction in each of thousands of AM particles in composite SSB electrodes. Furthermore, based on the obtained information, we discussed the optimal AM particle parameters (e.g., size, shape, particle distribution) that can alleviate the inhomogeneous reaction within and between AM particles, thereby maximizing electrode performance. Experimental The composite cathodes to be observed were prepared by mixing LiNi1/3Mn1/3Co1/3O2 (NMC) primary particle powders and Li2.2C0.8B0.2O3 (LCBO) solid electrolyte powders in a 1:1 weight ratio. The model SSBs were fabricated with the composite cathode (~50 μm thickness), LCBO solid electrolyte, poly (ethylene oxide) (PEO)-based polymer electrolyte, and Li metal anode. The model SSBs were charged to 100 mAh/g at 0.1~0.2 C, and the inhomogeneous reactions within AM particles in the composite cathodes after charging were visualized using nano CT-XANES. In the nano CT-XANES measurements, CT measurements were conducted near the Ni K-edge (8345.9-8352.4 eV) by incrementing the X-ray energy in 0.2 eV steps, with the entire set of measurements requiring approximately 25 minutes. The state-of-charge (SOC) of NMC (x in Li x Ni1/3Mn1/3Co1/3O2) in each voxel in the 3D CT images was evaluated based on the peak top energy shift of the Ni K-edge XANES spectrum in the respective voxels. Results and discussion Figures 1(a) and (b) show 3D SOC maps of the composite cathode after charging to 100 mAh/g at 0.2 C viewed from two different angles, and the corresponding charging curve, respectively. The observation area was approximately 34 × 47 μm in the in-plane direction of the electrode and approximately 34 μm thick with the voxel size of approximately 0.3 μm. The red/blue colored regions represent the charged (x = 0.45)/uncharged (x = 1.0) AM particles, respectively, while the transparent regions correspond to the SE or voids. As shown in this figure, the SOC of individual AM particles after charging varied significantly among the particles. While some particles, such as particle A, were charged to a Li content corresponding to the charging capacity of the entire electrode of 100 mAh/g (x = 0.64), there were also insufficiently charged particles (particle B) and excessively charged ones (particle C) relative to the average capacity of the entire electrode. These results indicates that the charge reactions proceeded inhomogeneously between AM particles. Furthermore, as shown in the 3D SOC maps of representative AM particles in Fig. 1(c), the reaction proceeded inhomogeneously within a particle. While the reaction progressed relatively uniformly within particles 1 and 2, the reaction proceeded quite inhomogeneously within particles 3 and 4. As described above, the charging state and its intra-particle inhomogeneity varied significantly among AM particles. To identify the characteristics of AM particles that determine the charging state and its inhomogeneity in each particle, in the presentation, we will statistically investigate the correlation between reaction states of each particle and morphological characteristics such as size and shape, for thousands of AM particles in the observation area.

(Invited) Development of a 5D Analytical Tool for Probing Electrochemical Reactions in Composite Solid-State Battery Electrodes: Toward Designing Better Electrodes

The emergence of solid lithium superionic conductors exhibiting conductivity surpassing that of liquid electrolytes has positioned solid-state batteries (SSBs) as one of the most promising and realistic next-generation energy storage devices. SSBs are expected to demonstrate superior safety, as well as higher capacity and power density compared to conventional lithium-ion batteries. In practice, however, SSBs often fail to achieve the high performance expected from the superior properties of their individual constituent materials. This is partly because the performance of SSBs is not solely dependent on the constituent materials but also heavily influenced by the design of each battery component. For example, for the electrode of SSBs, composite electrodes consisting of active materials and solid electrolytes (and conductive additives, if necessary) are often employed. Within these composite electrodes, particles of active materials and solid electrolytes, along with voids, are randomly interspersed, forming a complex microstructure. This intricate microstructure creates highly tortuous electron and ion conduction pathways and complex heterogeneous material interfaces within the electrode. Consequently, particularly under high current charging/discharging, local stagnation of ion/electron transport within the electrode can arise, leading to spatially inhomogeneous electrochemical reactions throughout the entire electrode or within individual active material particles. Such inhomogeneous electrochemical reactions hinder the materials from fully exhibiting their inherent performance, potentially leading to severe degradation of battery capacity, power output, as well as the impairment of cycle life due to localized overcharging/overdischarging. To suppress the occurrence of such inhomogeneous reactions and maximize battery performance and lifespan, it is necessary to directly observe the electrochemical reaction within composite electrodes during (dis)charging and establish appropriate design guidelines based on these observations. However, conventional characterization techniques have been unable to directly observe the time-varying electrochemical reactions that take place three-dimensionally and inhomogeneously within electrodes at both the particle scale (~few micron) and electrode scale (~hundreds of microns) during (dis)charging. Therefore, previous studies have been limited to obtaining averaged information on the overall electrochemical reactions within electrodes using conventional electrochemical measurements, estimating the electrochemical reactions in electrodes through numerical simulations, or conducting lower-dimensional (1D or 2D) observations of the 3D electrochemical reaction using X-ray or electron probe imaging techniques. Against this background, we have developed operando 3D imaging techniques for probing electrochemical reactions in SSB electrodes based on computed tomography combined with X-ray absorption near-edge structure spectroscopy (CT-XANES)1–4. These techniques can track the spatiotemporal evolution of the electrochemical reaction within composite electrodes during (dis)charge cycles, thereby allowing for the analysis of electrochemical reactions in five dimensions (5D), encompassing 3D spatial coordinates, time, and chemical state information. As shown in Fig. 1a1, our technique based on micro CT-XANES enables the operando 3D imaging of the evolution of the electrochemical reactions at the electrode scale with a spatial resolution of a few micrometers and a temporal resolution of approximately 30 minutes. This allows for the evaluation of the state of charge (SOC) distribution at any arbitrary cross-section in the thickness and in-plane directions within the same bulk region in electrodes at any given time. Consequently, it enables the quantitative analysis of when, where, how, and why low SOC regions appear within the electrode1,2,4, and allows for uncovering the correlation between local capacity degradation during cycling and electrode microstructures or the reaction history in previous (dis)charge cycles3. Furthermore, our advanced technique based on nano CT-XANES enables the operando, 3D, and simultaneous observation of the intra- and inter-particle reaction distributions among thousands of active material particles within SSB electrodes with a spatial resolution of sub-micrometers and a temporal resolution of approximately 30 minutes, as illustrated in Fig. 1b. The obtained information allows for the quantitative and statistical analysis of the correlations between the reaction characteristics of each active particle and its morphological features, facilitating the data-driven determination of optimal active material particle parameters, such as particle size, shape, arrangement, and size distribution. In the presentation, we will demonstrate how our 5D electrochemical reaction analysis techniques can provide useful insights for battery research. References Y. Kimura et al., J. Phys. Chem. Lett., 11, 3629–3636 (2020).Y. Kimura et al., ACS Appl. Energy Mater., 3, 7782–7793 (2020).Y. Kimura et al., Small Methods, 7, 2300310 (2023).S. Huang et al., J. Phys. Chem. C (2024) https://doi.org/10.1021/acs.jpcc.4c00318. Acknowledgements This work was supported by JST PRESTO Grant Number JPMJPR23J3, JST Mirai Program Grant Number JPMJMI21G3, and JST GteX Grant Number JPMJGX23S2, Japan. Figure 1

Operando XANES Reveals the Chemical State of Iron-Oxide Monolayers During Low-Temperature CO Oxidation.

We have used grazing incidence X-ray absorption near edge spectroscopy (XANES) to investigate the behavior of monolayer FeO films on Pt(111) under near ambient pressure CO oxidation conditions with a total gas pressure of 1 bar. Spectra indicate reversible changes during oxidation and reduction by O and CO at 150 °C, attributed to a transformation between FeO bilayer and FeO trilayer phases. The trilayer phase is also reduced upon heating in CO+O , consistent with a Mars-van-Krevelen type mechanism for CO oxidation. At higher temperatures, the monolayer film dewets the surface, resulting in a loss of the observed reducibility. A similar iron oxide film prepared on Au(111) shows little sign of reduction or oxidation under the same conditions. The results highlight the unique properties of monolayer FeO and the importance of the Pt support in this reaction. The study furthermore demonstrates the power of grazing-incidence XAFS for in situ studies of these model catalysts under realistic conditions.

Sulfur-species in Zinc-specific Condylar Zones of a Rat Temporomandibular Joint.

In this study, we performed synchrotron-based micro-X-ray fluorescence (μ-XRF) imaging of elements Zn and S, and X-ray absorption near edge spectroscopy (XANES) coupled with μ-XRF for identification of Zn and S species in the condylar zones of a rat temporomandibular joint (TMJ). Histologic localization of Zn and hypoxia-inducible factor-1α (HIF-1α) were mapped using an optical microscope. These data were visually correlated with μ-XRF and XANES data to provide insights into plausible biological S-species in Z-enriched condylar zones of a rat TMJ. Furthermore, μ-XRF coupled with micro-X-ray diffraction (μ-XRD) was used to underline Z-incorporated biological apatite in the subchondral bone and bone of the rat TMJ. Results illustrated the potential dependence between biometal Zn and nonmetal S and their collective governance of cell and tissue functions in a zone-specific manner. Elemental Zn with organic and inorganic S-species at the cartilage-bone interface and transformation of plausible Zn-enriched mineralization kinetics of biological apatite from subchondral bone to condylar bone were ascertained using μ-XRF-XANES and μ-XRD. The coupled μ-XRF-XANES complementing with μ-XRD and immunohistology provided an informative view of S and Zn and their association with zone-specific biological pathways in situ. Understanding the spatial distributions of the main S-species with redox-inert Zn in regions of cartilage, bone, and the interface is essential for further unlocking questions surrounding formation and resorption-related biomineralization pathways as related to osteoarthritis or genetically inherited diseases. Using these complementary techniques with microspectroscopic spatial information provided insights into the associations between biometal Zn and nonmetal S and a window into detecting the plausible early-stage diagnostic biomarkers for humans with TMJ osteoarthritis.

Molecular mechanisms of iron nanominerals formation in fungal extracellular polymeric substances (EPS) layers during fungus-mineral interactions

Extracellular polymeric substances (EPS), which envelop on fungal hyphae surface, interact strongly with minerals and play a crucial role in the formation of nanoscale minerals during biomineralization in nature environments. However, it remains poorly understood about the molecular mechanisms of nanominerals (i.e., iron nanominerals) formation in fungal EPS halos during fungus-mineral interactions. This process is vital because fungi typically grow attached to various mineral surfaces in nature. According to the changes of thickness of the fungal cell and EPS layers during the Trichoderma guizhouense NJAU 4742 and hematite cultivation experiments, we found that fungal biomineralization could trigger the formation of EPS layers. Fe-dominated nanominerals, aromatic C (283-286.1 eV), alkyl C (287.6-288.3 eV), and carboxylic C (288.4-289.1 eV) were the dominant chemical groups on the EPS layers, as determined by nanoscale secondary ion mass spectrometry (NanoSIMS), high-resolution transmission electron microscope (HRTEM), and carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Further, evidence from Fe K-edge X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) spectra indicated that oxygen vacancy (OV) was formed on the Fe-dominated nanomineral surface during fungus-mineral interactions, which played an important role in catalyzing H2O2 decomposition and HO∗ production. Taken together, the intrinsic peroxidase-like activity by reactive oxygen species (ROS) could modulate the Fe-dominated nanominerals formation in EPS layers to newly form a physical barrier between the cell and the external environments around hyphae, providing novel insights into the effects of ROS-mediated fungal-mineral interactions on fungal nutrient recycling, attenuation of contaminants, and biological control in nature environments.

Unveiling the Redox Noninnocence of Metallocorroles: Exploring K-Edge X-ray Absorption Near-Edge Spectroscopy with a Multiconfigurational Wave Function Approach.

X-ray absorption near-edge spectroscopy (XANES) is an advanced technique for probing the local electronic structure of catalysts, effectively identifying the noninnocent nature of ligands in transition-metal complexes. Metallocorroles with noninnocent corrole rings exhibit unusual electronic structures that challenge traditional density functional theory (DFT) methods, necessitating more rigorous approaches to describe electron correlation accurately. We explored K-edge XANES spectra of Fe, Mn, and Co metallocorroles using TDDFT and wave function-based methods. This is the first investigation employing multireference methods, specifically RASSCF, RASPT2, and MC-PDFT, to analyze the redox noninnocent nature of metallocorroles reflected in their XANES spectra. We quantified the noninnocent character of the corrole and the oxidation states of the metals, capturing more than singly excited excitations responsible for the pre-edge peak. Our findings demonstrate the importance of these advanced computational techniques for accurately predicting XANES spectra, providing a reliable understanding of the electronic properties of such complexes. This study offers a new strategy for investigating ligand redox noninnocence via integrated experimental and computational XANES.

Redox Dynamic Interactions of Arsenic(III) with Green Rust Sulfate in the Presence of Citrate.

Arsenic is a global pollutant. Recent studies found that Fe(II) can oxidize As(III), but the extent of oxidation with mixed-valent iron minerals and the mechanisms involved are unknown. In this study, we investigated whether As(III) can be oxidized under reducing conditions using green rust sulfate (GR-SO4), an Fe mineral containing both Fe(II) and Fe(III). Batch sorption experiments showed that GR-SO4 (1 g L-1) effectively sorbs environmentally relevant concentrations of As(III) (50-500 μg L-1) under anoxic, neutral pH conditions with and without citrate (50 μM). X-ray absorption near-edge structure spectroscopy analysis at the As K-edge demonstrated that approximately 76% of As(III) was oxidized to As(V) by GR-SO4. Complete oxidation of As(III) was observed in the presence of citrate. As(III) oxidation can be linked to the phase transformation of GR-SO4 to goethite, resulting in new reactive Fe(III) species that plausibly drive oxidation. Citrate enhanced this process by stabilizing Fe on the mixed GR-SO4/goethite surface, preventing its reduction back to Fe(II) and facilitating further As(III) oxidation without significant Fe loss to the solution. This study highlights the cryptic As(III) oxidation that occurs under reducing conditions, providing new insights into the cycling of arsenic in mixed phases of iron-rich, anoxic environments.

Chromium Immobilization as Cr-Spinel by Regulation of Fe(II) and Fe(III) Concentrations

The complex environmental conditions at Cr-contaminated sites, characterized by uneven ion distribution, oxidants competition, and limited solid-phase mobility, lead to inadequate mixing of Fe-based reducing agents with Cr, posing significant challenges to the effectiveness of Cr remediation through Cr-spinel precipitation. This study investigates the distinct roles of Fe(II), Fe(III), and Cr(III) in Cr-spinel crystallization under ambient temperature and pressure. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray absorption near-edge structure spectroscopy, and Mössbauer spectroscopy were employed to elucidate the phase composition, microstructure, and ion coordination within the precipitates. Our findings indicate that Fe(II) acts as a catalyst in the formation of the spinel phase, occupying octahedral sites within the spinel structure. Under the catalytic influence of Fe(II), Fe(III) transitions into the spinel phase, occupying both the tetrahedral and the remaining octahedral sites. Meanwhile, Cr(III), due to its high octahedral site preference energy, preferentially occupies the octahedral sites. When Fe(II) or Fe(III) is present but does not meet the ideal stoichiometric ratio, a deficiency in Fe(II) leads to low yield and poor crystallinity of Cr-spinel, whereas a deficiency in Fe(III) can completely inhibit its formation. Conversely, when either Fe(II) or Fe(III) is in excess, the formation of Cr-spinel remains feasible. Furthermore, metastable Cr phases can be transformed into stable Cr-spinel by adjusting the Fe(II)/Fe(III)/Cr(III) ratio. These results highlight the broad range of conditions under which Cr-spinel mineralization can occur in environmental settings, enhancing our understanding of the mechanisms driving Cr-spinel formation in Cr-contaminated sites treated with Fe-based reducing agents. This research provides critical insights for optimizing Cr remediation strategies.

Role of Structural and Compositional Changes of Cu2O Nanocubes in Nitrate Electroreduction to Ammonia.

Nitrate electroreduction reaction (NO3RR) to ammonia (NH3) still faces fundamental and technological challenges. While Cu-based catalysts have been widely explored, their activity and stability relationship are still not fully understood. Here, we systematically monitored the dynamic alterations in the chemical and morphological characteristics of Cu2O nanocubes (NCs) during NO3RR in an alkaline electrolyte. In 1 h of electrolysis from -0.10 to -0.60 V vs RHE, the electrocatalyst achieved the maximum NH3 faradaic efficiency (FE) and yield rate at -0.3 V (94% and 149 μmol h-1 cm-2, respectively). Similar efficiency could be found at a lower overpotential (-0.20 V vs RHE) in long-term electrolysis. At -0.20 V vs RHE, the catalyst FE increased from 73% in the first 2 h to ∼90% in 10 h of electrolysis. Electron microscopy revealed the loss of the cubic shape with the formation of sintered domains. In situ Raman, X-ray diffraction (XRD), and in situ Cu K-edge X-ray absorption near-edge spectroscopy (XANES) indicated the reduction of Cu2O to oxide-derived Cu0 (OD-Cu). Nevertheless, a remaining Cu2O phase was noticed after 1 h of electrolysis at -0.3 V vs RHE. This observation indicates that the activity and selectivity of the initially well-defined Cu2O NCs are not solely dependent on the initial structure. Instead, it underscores the emergence of an OD-Cu-rich surface, evolving from near-surface to underlying layers over time and playing a crucial role in the reaction pathways. By employing online differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIR), we experimentally probed the presence of key intermediates (NO and NH2OH) and byproducts of NO3RR (N2 and N2H x ) for NH3 formation. These results show a complex relationship between activity and stability of the nanostructured Cu2O oxide catalyst for NO3RR.

Strong Magnetic Exchange Interactions and Delocalized Mn-O States Enable High-Voltage Capacity in the Na-Ion Cathode P2-Na0.67[Mg0.28Mn0.72]O2.

The increased capacity offered by oxygen-redox active cathode materials for rechargeable lithium- and sodium-ion batteries (LIBs and NIBs, respectively) offers a pathway to the next generation of high-gravimetric-capacity cathodes for use in devices, transportation and on the grid. Many of these materials, however, are plagued with voltage fade, voltage hysteresis and O2 loss, the origins of which can be traced back to changes in their electronic and chemical structures on cycling. Developing a detailed understanding of these changes is critical to mitigating these cathodes' poor performance. In this work, we present an analysis of the redox mechanism of P2-Na0.67[Mg0.28Mn0.72]O2, a layered NIB cathode whose high capacity has previously been attributed to trapped O2 molecules. We examine a variety of charge compensation scenarios, calculate their corresponding densities of states and spectroscopic properties, and systematically compare the results to experimental data: 25Mg and 17O nuclear magnetic resonance (NMR) spectroscopy, operando X-band and ex situ high-frequency electron paramagnetic resonance (EPR), ex situ magnetometry, and O and Mn K-edge X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Spectroscopy (XANES). Via a process of elimination, we suggest that the mechanism for O redox in this material is dominated by a process that involves the formation of strongly antiferromagnetic, delocalized Mn-O states which form after Mg2+ migration at high voltages. Our results primarily rely on noninvasive techniques that are vital to understanding the electronic structure of metastable cycled cathode samples.

Iron distribution and speciation in a 3D-printed hybrid food using synchrotron X-ray fluorescence and X-ray absorption spectroscopies

The bioavailability of iron from a food depends on its concentration and chemical form but also on dietary factors and nutrient interactions, which are affected by storage conditions and time. Here we investigated the time-course profile of iron in a hybrid 3D-printed food composed of alternating layers of liver and lentils after 0, 5, 7, 14 and 21 days of storage at 4 °C under oxygen or nitrogen packaging. Synchrotron X-ray fluorescence highlighted major variations in iron distribution in both the animal and plant parts of the food as a function of storage conditions. FeP and FeS positive spatial correlations pointed to iron-associated compounds. X-ray absorption near-edge structure spectroscopy showed spectral signatures specific to the animal and plant mixtures, and then highlighted interactions between animal and plant parts during food storage, with a change in iron forms in the plant part.