X-ray Pair Distribution Function Research Articles

In situ imaging of amorphous intermediates during brucite carbonation in supercritical CO2.

Progress in understanding crystallization pathways depends on the ability to unravel relationships between intermediates and final crystalline products at the nanoscale, which is a particular challenge at elevated pressure and temperature. Here we exploit a high-pressure atomic force microscope to directly visualize brucite carbonation in water-bearing supercritical carbon dioxide (scCO2) at 90 bar and 50 °C. On introduction of water-saturated scCO2, in situ visualization revealed initial dissolution followed by nanoparticle nucleation consistent with amorphous magnesium carbonate (AMC) on the surface. This is followed by growth of nesquehonite (MgCO3·3H2O) crystallites. In situ imaging provided direct evidence that the AMC intermediate acts as a seed for crystallization of nesquehonite. In situ infrared and thermogravimetric-mass spectrometry indicate that the stoichiometry of AMC is MgCO3·xH2O (x = 0.5-1.0), while its structure is indicated to be hydromagnesite-like according to density functional theory and X-ray pair distribution function analysis. Our findings thus provide insight for understanding the stability, lifetime and role of amorphous intermediates in natural and synthetic systems.

Subtle Local Structural Details Influence Ion Transport in Glassy Li+ Thiophosphate Solid Electrolytes.

Many of the promising, high-performing solid electrolytes for lithium-ion batteries are amorphous or contain an amorphous component, particularly in the Li thiophosphate Li2S-P2S5 (LPS) compositional series. An explicit study of the local structure in four samples of ostensibly identically prepared 70Li2S-30P2S5 glass reveals substantial variation in the ratio between the two main local structural units in this system: PS43- tetrahedra and P2S74- corner-sharing tetrahedral pairs. Local structural and compositional probes including Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray pair distribution function analysis are employed here to arrive at a consistent description of the relative amounts of isolated tetrahedral units, which vary by 13% across the samples measured. This local structure variation translates to differences in the activation energies measured by electrochemical impedance spectroscopy in these samples, such that the higher concentration of isolated tetrahedra corresponds to a lower activation energy. The measured temperature-dependent ionic conductivity data are compared to conductivity results across the literature reported on the same compositions, highlighting the variation in the measured activation energy for nominally identical samples. These findings have implications for the critical need to play close attention to the local structure in solid electrolytes, particularly in systems that are glasses or glass ceramics, or those that comprise any amorphous contribution.

Exploring the Role of Cluster Formation in UiO Family Hf Metal-Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis.

The structures of Zr and Hf metal-organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.

Deep insights into the local structure of amorphous Ta2O5 thin films by x-ray pair distribution function analysis

Amorphous films of tantalum oxide (Ta2O5) are widely applied to build highly reflective mirrors used in interferometric gravitational wave detectors, such as the Laser Interferometer Gravitational Wave Observatory (LIGO). Despite a large number of studies, the structural properties of amorphous Ta2O5 at the local scale still deserve several further investigations. Such information is essential to any attempt to understand the properties of this important material and no property modelling efforts can be expected to yield reliable information until the local structure in the amorphous phase is better understood. In this paper we report the results obtained by analysing the synchrotron X-ray pair distribution functions of pure and Ti-doped amorphous Ta2O5 film, deposited by ion beam sputtering, as prepared and after a thermal treatment. As a result, it is found that 1) the arrangement of Ta atoms in amorphous Ta2O5 strongly resembles that characterizing the high-pressure Z-Ta2O5 polymorph, whereas the topological properties of O atoms resembles that observed in delta-Ta2O5; 2) structural correlations in amorphous Ta2O5 start to vanish above ~ 5 Angstrom and are completely suppressed for r > 10 Angstrom on account of disorder; 3) Ti substitution retains the short-range topological ordering characterizing the as prepared Ta2O5 amorphous film even after thermal treatment; conversely, pure Ta2O5 films undergoes a significant rearrangement of the local structure after thermal treatment.

Total x-ray scattering setup for crystalline particles at SPring-8 BL15XU NIMS beamline.

We report a total x-ray scattering (TXS) system for structural analysis of crystalline particle materials at the BL15XU NIMS beamline of SPring-8 in Japan. To achieve a high angular resolution over a high Q region up to 25 Å-1, the TXS system was capable of measuring to 120° at an x-ray energy of 29.02keV with five CdTe pin detectors. The sample alignment and measuring system were controlled by LabView software. The x-ray pair distribution function (PDF) results for Ni bulk powder and Pt and AgRh nanoparticles were successfully simulated by the PDFgui program. In addition, Rietveld refinement results were also obtained from x-ray diffraction patterns, reflecting long-range order in the Pt nanoparticles. We expect that this TXS system may be useful for understanding structural information of crystalline nanoparticles, including amorphous features at their surface region.

Time-dependent phase quantification and local structure analysis of hydroxide-activated slag via X-ray total scattering and molecular modeling

Here, an approach to quantify the amorphous-to-disordered/crystalline transformation occurring in NaOH-activated ground granulated blast-furnace slag (GGBS) is outlined that combines atomistic modeling with in situ pair distribution function (PDF) analysis. Firstly, by using force-field molecular dynamics (MD) simulations, a detailed structural representation is generated for the amorphous GGBS that is in agreement with experimental X-ray scattering data. Use of this structural representation along with literature-derived structures for the reaction products allows for real space X-ray PDF refinement of the alkaline activation of GGBS, resulting in the quantification of all phases and the degree of reaction (DOR) as a function of reaction time. All phases and the DOR are seen to approximately follow a logarithmic-type time-dependent behavior up to 5 months, while at the early age (up to 11 h), the DOR is accurately captured by a modified pseudo-single step first-order reaction model. Lastly, the evolution of DOR is found to agree with several other complementary in situ data containing quantitative reaction information, including isothermal conduction calorimetry, Fourier transform infrared spectroscopy, and quasi-elastic neutron scattering.

Reversible Dual Anionic-Redox Reaction in Layered Chalcogenide Cathode Materials

Utilizing the reversible sulfur redox reaction in layered chalcogenides opens new approaches for the development of new battery cathode materials with higher capacities for sodium-ion batteries. However, only limited number of studies on the nature of anionic redox chemistry in layered chalcogenides has been reported in the literature. We have designed and synthesized a series of layered chalcogenide cathode materials NaCrS1-xSex and investigated their sodium storage performances. Among them, NaCrSeS exhibits a unique charge/discharge feature with a quite small polarization of 0.15 V and more than 90% high coulombic efficiency. At the same time, a very high charge capacities of 115.5mAh g-1 (0.80 Na+/CrSSe) is achieved at a charging rate as high as 27.8 C. The charge compensation mechanisms and structural evolution of these cathode materials have been investigated using synchrotron based multi-model characterization techniques such as ex situ x-ray absorption spectroscopy, x-ray diffraction and x-ray pair distribution function analysis combined with DFT calculation. The results show that the charge compensation in NaCrSSe cathode is mainly through the dual anionic-redox reaction with the reversible formation of (S)n– and (Se)n– as well as (S/Se)2 m– species during the Na intercalation/deintercalation processes. These results will provide valuable information for developing new anion redox based cathode materials with high-capacity and fast kinetics. Acknowledgment: The work at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704. This research used resources at beamlines 7-BM (QAS) and 28-ID-2 (XPD) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

Atomic and microstructural origins of stored energy release in neutron-irradiated silicon carbide

Here, we employ a combination of advanced synchrotron-based scattering characterization techniques to understand and unravel the atomic origins of the colossal stored energy release in neutron-irradiated silicon carbide. The quantification of the neutron irradiation-induced defects and their impact on the structure-property relationship are important for the design and safe operation of advanced fission and fusion reactors. Our experimental results show that the atomic structure in the as-irradiated samples is significantly perturbed due to a large fraction of vacancy- and interstitial-type defects that lead to complex microstructures and additional components in the x-ray diffraction and pair distribution function (PDF) results. We directly correlate the stored energy release to the recovery of the sublattices with PDF analysis, highlighting that the carbon interstitial- and vacancy-type defects contribute to stored energy more than those of silicon. We find these results to be striking and believe our discoveries to be timely and noteworthy given the technological importance of silicon carbide to the nuclear fission and fusion communities.

Emphanisis in Cubic (SnSe)0.5(AgSbSe2)0.5: Dynamical Off-Centering of Anion Leads to Low Thermal Conductivity and High Thermoelectric Performance.

The structural transformation generally occurs from lower symmetric to higher symmetric structure on heating. However, the formation of locally broken asymmetric phases upon warming has been evidenced in PbQ (Q = S, Se, Te), a rare phenomenon called emphanisis, which has significant effect on their thermal transport and thermoelectric properties. (SnSe)0.5(AgSbSe2)0.5 crystallizes in rock-salt cubic average structure, with the three cations occupying the same Wycoff site (4a) and Se in the anion position (Wycoff site, 4b). Using synchrotron X-ray pair distribution function (X-PDF) analysis, herein, we show the gradual deviation of the local structure of (SnSe)0.5(AgSbSe2)0.5 from the overall cubic rock-salt structure with warming, resembling emphanisis. The local structural analysis indicates that Se atoms remain in off-centered position by a magnitude of ∼0.25 Å at 300 K along the [111] direction and the magnitude of this distortion is found to increase with temperature resulting in three short and three long M-Se bonds (M = Sn/Ag/Sb) within the average rock-salt lattice. This hinders phonon propagation and lowers the lattice thermal conductivity (κlat) to 0.49-0.39 W/(m·K) in the 295-725 K range. Analysis of phonons based on density functional theory (DFT) reveals significant soft modes with high anharmonicity which involve localized Ag and Se vibrations primarily. Emphanisis induced low κlat and favorable electronic structure with multiple valence band extrema within close energy concurrently give rise to a promising thermoelectric figure of merit (zT) of 1.05 at 706 K in p-type carrier optimized Ge doped new rock-salt phase of (SnSe)0.5(AgSbSe2)0.5.

Real-Time Observation of "Soft" Magic-Size Clusters during Hydrolysis of the Model Metallodrug Bismuth Disalicylate.

Colloidal bismuth therapeutics have been used for hundreds of years, yet remain mysterious. Here we report an X-ray pair distribution function (PDF) study of the solvolysis of bismuth disalicylate, a model for the metallodrug bismuth subsalicylate (Pepto-Bismol). This reveals catalysis by traces of water, followed by multistep cluster growth. The ratio of the two major species, {Bi9O7} and {Bi38O44}, depends on exposure to air, time, and the solvent. The solution-phase cluster structures are of significantly higher symmetry in comparison to solid-state analogues, with reduced off-center Bi3+ displacements. This explains why such "magic-size" clusters can be both stable enough to crystallize and sufficiently labile for further growth.

Origin and Absence of Giant Negative Thermal Expansion in Reduced and Oxidized Ca2RuO4

Negative thermal expansion (NTE) is an intriguing physical phenomenon. Layered Ca2RuO4 exhibits giant NTE over a wide temperature range from 200 to 400 K, which makes it attractive for fundamental research and industrial applications. However, a clear physical understanding is lacking for the appearance of NTE over such a wide temperature range and the oxygen-content-dependent switch from NTE to positive thermal expansion (PTE). Herein, we present insights into the average crystal structure, local structure, and electronic and orbital states of Ca2RuO4. Surprisingly, a previously overlooked monoclinic distortion is identified by electron diffraction and synchrotron X-ray diffraction (SXRD). X-ray absorption fine structure (XAFS) and synchrotron X-ray pair distribution function (PDF) analyses show large local distortions in monoclinic Ca2RuO4. Moreover, local stress on Ru cations is confirmed by the existence of over-bonding states, which relaxes along with NTE. Theoretical calculations indicate that dxy orbital ordering and disordering in the monoclinic structure are the origins of NTE. Moreover, interstitial oxygen plays a critical role in stabilizing elongated RuO6 and locally breaks the dxy orbital ordering, facilitating the occurrence of PTE. This work elucidates the electronic and orbital states in NTE materials with defective lattices and provides a different route to designing unconventional NTE materials.

Local ferroelectric polarization switching driven by nanoscale distortions in thermoelectric {text {Sn}}_{0.7}{text {Ge}}_{0.3}{text {Te}}

A remarkable decrease in the lattice thermal conductivity and enhancement of thermoelectric figure of merit were recently observed in rock-salt cubic SnTe, when doped with germanium (Ge). Primarily, based on theoretical analysis, the decrease in lattice thermal conductivity was attributed to local ferroelectric fluctuations induced softening of the optical phonons which may strongly scatter the heat carrying acoustic phonons. Although the previous structural analysis indicated that the local ferroelectric transition temperature would be near room temperature in {text {Sn}}_{0.7}{text {Ge}}_{0.3}{text {Te}}, a direct evidence of local ferroelectricity remained elusive. Here we report a direct evidence of local nanoscale ferroelectric domains and their switching in {text {Sn}}_{0.7}{text {Ge}}_{0.3}{text {Te}} using piezoeresponse force microscopy(PFM) and switching spectroscopy over a range of temperatures near the room temperature. From temperature dependent (250–300 K) synchrotron X-ray pair distribution function (PDF) analysis, we show the presence of local off-centering distortion of Ge along the rhombohedral direction in global cubic {text {Sn}}_{0.7}{text {Ge}}_{0.3}{text {Te}}. The length scale of the {text {Ge}}^{2+} off-centering is 0.25–0.10 Å near the room temperatures (250–300 K). This local emphatic behaviour of cation is the cause for the observed local ferroelectric instability, thereby low lattice thermal conductivity in {text {Sn}}_{0.7}{text {Ge}}_{0.3}{text {Te}}.

A high-throughput method for combinatorial screening of metal nanoparticles using X-ray pair distribution function analysis

A high-throughput method for combinatorial screening of metal nanoparticles using X-ray pair distribution function analysis

Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis

Abstract The structure of opal-A was not fully understood due to its poorly crystalline nature. To better understand its structural characteristics, we have analyzed opal-AN (amorphous-network) and opal-AG (amorphous-gel) using synchrotron X-ray diffraction (XRD), pair-distribution function (PDF) analysis, and transmission electron microscopy (TEM). Opal-AN mainly exists as an aggregation of different sizes of nanospheres (<5 nm) generating banded features, whereas opal-AG displays close-packed silica nanospheres with a diameter of ~400 nm. TEM energy-dispersive X-ray spectroscopy (EDS) indicates that Na, Al, K, and Ca are present as trace elements in opal-AN and opal-AG. XRD patterns of both samples show one prominent peak at ~4.0 Å, together with broad peaks at ~2.0, ~1.45, and ~1.2 Å. Previous studies only identified the ~4.0 Å diffraction peak for the definition of opal-A. Hence, opal-A needs to be redefined by taking into account the newly observed three broad peaks. PDF patterns of opal-AN and opal-AG reveal short-range atomic pairs (<15 Å) with almost identical profiles. Both phases exhibit Si-O correlation at 1.61 Å and O-O correlation at 2.64 Å in their [SiO4] tetrahedra. The currently accepted opal structure is disordered intergrowths of cristobalite- and tridymite-like domains consisting of six-membered rings of [SiO4] tetrahedra. Our PDF analyses have identified additional, coesite-like nanodomains comprising four-membered [SiO4] rings. Moreover, we have identified eight-membered rings that can be generated by twinning and stacking faults from six-membered rings. The coesite nanodomains in opal-A may be a precursor for coesite micro-crystals formed by the impact of supersonic micro-projectiles at low pressures. More broadly, our study has also demonstrated that the combined approach of synchrotron XRD/PDF with TEM is a powerful approach to determine the structures of poorly crystallized minerals.

Mechanistic Insights into Nanoparticle Formation from Bimetallic Metal–Organic Frameworks

Understanding and controlling nanomaterial structure, chemistry, and defects represents a synthetic and characterization challenge. Metal-organic frameworks (MOFs) have recently been explored as unconventional precursors from which to prepare nanomaterials. Here we use in situ X-ray pair distribution function analysis to probe the mechanism through which MOFs transform into nanomaterials during pyrolysis. By comparing a series of bimetallic MOFs with trimeric node different compositions (Fe3, Fe2Co, and Fe2Ni) linked by carboxylate ligands in a PCN-250 lattice, we demonstrate that the resulting nanoparticle structure, chemistry, and defect concentration depend on the node chemistry of the original MOF. These results suggest that the preorganized structure and chemistry of the MOF offer new potential control over the nanomaterial synthesis under mild reaction conditions. In the case of Fe2Ni-PCN-250, selective extraction of one Ni ion from each node without collapsing the framework (i.e., node-ligand connectivity) leaves a metal-deficient MOF state that may provide a new route to post-synthetically tune the chemistry the MOF and subsequent nanomaterials.

Cluster mediated conversion of amorphous Al(OH)3 to γ-AlOOH

We report a synthetic pathway by which amorphous Al(OH)3 is converted to γ-AlOOH through hydrothermal reaction in the presence of water at temperature T ​= ​473 ​K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH)3 possesses a locally γ-Al(OH)3-like structure, while nanocrystalline γ-AlOOH precipitates within 1 ​h of continuous hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20 ​min of hydrothermal treatment, and ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to γ-AlOOH with 10 ​min of exposure, indicating a coexistence region of γ-Al(OH)3-like and γ-AlOOH-like amorphous species. Powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in distinct, power law-defined stages with initial γ-AlOOH nucleation occurring within the first 20 ​min, followed by a ~ 1 ​h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.

Local Structures of Soft Carbon and Electrochemical Performance of Potassium-Ion Batteries.

Due to climate variation and global warming, utilization of renewable energy becomes increasingly imperative. Rechargeable potassium-ion batteries (PIBs) have lately attracted much attention due to their earth-abundance and cost-effectiveness. Because soft carbon materials are cheap, abundant, and safe, extensive feasible research studies have indicated that they could become promising anode materials for PIBs. In spite of gaining achievements, fundamental questions regarding effects of the basic structure unit inside soft carbon on potassium storage potential have not been sufficiently addressed yet. Here, a series of soft carbon pyrolyzed from 900 to 2900 °C were systematically and quantitatively characterized by combining Raman spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray pair distribution function analysis, and advanced evaluation of wide-angle X-ray scattering data. All these characterizations reveal structural details of soft carbon with increasing pyrolysis temperature. Our results show that the potassium storage behavior, especially the potential plateau is closely correlated to non-uniformity in interlayer distance and defect concentration in soft carbon, which is further confirmed by reverse Monte Carlo (RMC) modeling and density functional theory calculation. On the basis of these results, optimizing strategies are discussed to design an advanced soft carbon anode. This work provides significant insights into the structure engineering of soft carbon for high-performance rechargeable PIBs.

Structural and Electrochemical Investigation of High Energy Spinel LiMn1.5Ni0.5O4 Produced at Low Temperature

Spinel LiMn1.5Ni0.5O4 (LMNO) materials, without the environmentally toxic Co, are one of the most promising potential cathode materials for lithium ion batteries operated at high voltages. According to the distribution of Mn and Ni within the cubic crystal structure, spinel LMNO can be categorized into either ordered or disordered. Normally, disordered LMNO materials are produced at temperatures which are higher than the theoretical oxygen release temperature of spinel LMNO (715 ℃)[1, 2]. This leads to some Mn4+ atoms being reduced to Mn3+ to maintain the electroneutrality of spinel LMNO. The existence of Mn3+ causes Jahn-Teller distortion and affects the structural stability of spinel LMNO. In order to reduce the amount of Mn3+, high temperature produced LMNO materials are post-annealed at lower temperature, i.e. 700 ℃, to introduce O into spinel LMNO again[3]. Both the high calcination temperatures and the long annealing times increase the preparation cost of the spinel LMNO. In other words, low-temperature calcination without post-annealing would be a preferred way to produce spinel LMNO at lower cost. However, LMNO materials calcinated at 700 ℃ in air show ordered distribution of Mn and Ni, which is supposed to be the reason for poor cycling and rate performance[4, 5]. This indicates changing the ordered distribution of Mn and Ni in 700 ℃ produced LMNO may improve the electrochemical performance.In the present work, different co-precipitation processes are attempted to change the distribution of the Mn and Ni precursors used in the LMNO synthesis. Three different spinel LMNO materials, named as N-, CS- and SW-LMNO, are produced by three hydroxide precursors with stoichiometric Li2CO3 at 700 ℃ without post-annealing. Scanning electron microscope (SEM) images, shown in Figure 1(a) – (c), demonstrate different morphologies of N-, CS- and SW-LMNO. This indicates that different precipitation approaches result in different particle sizes and shapes of spinel LMNO. However, the use of different precipitation processes has little effect on the bulk crystal structure of spinel LMNO, reflected by similar X-ray diffraction (XRD) patterns in Figure 1(d). As shown in Figure 1(e), SW-LMNO shows high initial discharge capacity (140 mAhꞏg-1) at room temperature which is the highest amongst all reported LMNO[6]. SW-LMNO also shows good cycling performance in the first 100 cycles at 1 C (1 C = 150 mAꞏg-1), which are not only better than those of other low-temperature produced spinel LMNO but also comparable with those of most reported high-temperature produced spinel LMNO[7]. This means, this work provides a new strategy to produce high-energy spinel LMNO by controlling the microstructure but save energy consumption. Moreover, transmission electron microscope (TEM), X-ray pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) are performed to explain the reason for improvement of SW-LMNO in comparison with N- and CS-LMNO.Reference[1] A. Manthiram et al. A perspective on the high-voltage LiMn1.5Ni0.5O4 spinel cathode for lithium-ion batteries. Energy & Environmental Science[J]. 2014, 7 (4): 1339-1350[2] M. Kunduraci et al. Effect of oxygen non-stoichiometry and temperature on cation ordering in LiMn2-xNixO4 (0.50≥ x≥ 0.36) spinels. Journal of Power Sources[J]. 2007, 165 (1): 359-367[3] D. W. Shin et al. Role of cation ordering and surface segregation in high-voltage spinel LiMn1.5Ni0.5-xMxO4 (M= Cr, Fe, and Ga) cathodes for lithium-ion batteries. Chemistry of Materials[J]. 2012, 24 (19): 3720-3731[4] Z. Moorhead-Rosenberg et al. Electronic and electrochemical properties of Li1-xMn1.5Ni0.5O4 spinel cathodes as a function of lithium content and cation ordering. Chemistry of Materials[J]. 2015, 27 (20): 6934-6945[5] B. Aktekin et al. Cation ordering and oxygen release in LiNi0. 5-xMn1.5+xO4-y (LNMO): In situ neutron diffraction and performance in Li ion full cells. ACS Applied Energy Materials[J]. 2019, 2 (5): 3323-3335[6] O. Tiurin et al. Atomic layer deposition (ALD) of lithium fluoride (LiF) protective film on Li-ion battery LiMn1.5Ni0.5O4 cathode powder material. [J]. 2020, 448: 227373[7] G. Liang et al. Developing high-voltage spinel LiNi0.5Mn1.5O4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects. Journal of Materials Chemistry A[J]. 2020, 8, 15373-15398 Figure 1

Resolving Single-layer Nanosheets as Short-lived Intermediates in the Solution Synthesis of FeS

Short-lived reaction intermediates play a critical role in mediating material synthesis. Such short-lived species often elude characterization because of the mismatch between the time scale of measurements capable of describing them and their lifetimes. Thus, we have limited ability to probe, understand, and control the mechanism for material synthesis. Here we demonstrate a new approach to in situ X-ray pair distribution function (PDF) measurements of dynamic nanomaterials structure that yields an unprecedented combination of reaction time resolution and sensitivity. Reaction time is resolved spatially as a function of position along a flow path. By applying this approach to the well-studied aqueous reaction leading to FeS, mackinawite, we identify a novel metastable intermediate, FeSlayer, that forms in the first second of the reaction and which can be described as individual FeS nanosheets. Recognizing these nanosheets as synthons in the reaction opens up the possibility to deliberately redirect this assembly of the nanosheet toward different phases, including novel heterostructures.

Observation of a potential-dependent switch of water-oxidation mechanism on Co-oxide-based catalysts

Summary O–O bond formation is a key elementary step of the water-oxidation reaction. However, it is still unclear how the mechanism of O–O coupling depends on the applied electrode potential. Herein, using water-in-salt electrolytes, we systematically altered the water activity, which enabled us to probe the O–O bond-forming mechanism on heterogeneous Co-based catalysts as a function of applied potential. We discovered that the water-oxidation mechanism is sensitive to the applied potential: At relatively low driving force, the reaction proceeds through an intramolecular oxygen coupling mechanism, whereas the water nucleophilic attack mechanism prevails at high driving force. The observed mechanistic switch has major implications for the understanding and control of the water-oxidation reaction on heterogeneous catalysts.