I20-Scanning-X-ray spectroscopy (XAS/XES)
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Maryia
Zinouyeva
,
Martina
Fracchia
,
Giulia
Maranini
,
Davide
Impelluso
,
Nicholas B.
Brookes
,
Lorenzo
Grilli
,
Kurt
Kummer
,
Francesco
Rosa
,
Matteo
Aramini
,
Giacomo
Ghiringhelli
,
Paolo
Ghigna
,
Marco
Moretti Sala
,
Mauro
Coduri
Open Access
Abstract: We employ several X-ray based techniques, including X-ray diffraction, X-ray absorption spectroscopy and resonant inelastic X-ray scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn–Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of various chemical species in shaping the physical properties of high-entropy oxides.
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Nov 2025
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[34632, 31578]
Open Access
Abstract: Biomass conversion involves transforming sustainable feedstocks into valuable intermediates for the chemical industry. A key biomass-derived platform molecule, 5-hydroxymethylfurfural (HMF), can be converted into various intermediates, including 2,5-diformylfuran (DFF), which has several industrial applications due to its versatile chemical reactivity. Herein, Cu loaded MOF-808, with three different Cu loadings, were synthesised and tested as catalysts for the liquid phase selective oxidation of HMF to DFF with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) were performed to assess the speciation of Cu, with the development of a structure model of MOF-808(Cu3). The structural analysis reveals that single square planar Cu(II) sites are located near the Zr6 cluster and are bonded by coordinating to oxygen atoms of capping MeOH and H2O ligands. Amongst the synthesised catalysts, MOF-808(Cu3) exhibited the highest catalytic activity after 12 h, achieving a high HMF conversion (95.5 ± 2.7%) and DFF yield (78.9 ± 1.3%) at 30 °C. The nature of the catalytic reaction is heterogeneous as the yield of DFF decreases after the removal of the solid catalyst. The demonstration of catalytic activity with high selectivity under near ambient conditions advances the application of porous metal–organic framework-based catalysts for selective liquid phase oxidations.
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Oct 2025
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[33415, 34976]
Open Access
Abstract: Electro-oxidation is one of the most promising and eco-friendly technologies for water decontamination. However, its industrial application is still limited by the high cost, poor faradaic efficiency, low durability, and potential toxicity of common high-power oxidation anodes. These challenges have been addressed by developing a novel composite comprising a mixed metal oxide (NiMnO3) and reduced graphene oxide (rGO). The NiMnO3–rGO anode allowed the fast and complete removal of phenol. Among different highly porous substrates, graphite felt (GF) led to the highest energy efficiency, since the GF/NiMnO3–rGO anode yielded 100% phenol removal within only 30 min at a current density as low as 10 mA cm−2, which was accompanied by 85% COD removal at 120 min. This anode demonstrated excellent stability, maintaining 100% phenol removal efficiency across five consecutive cycles while also showing low energy consumption (60–65 Wh (kg COD)−1). Operando X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) analysis provided mechanistic insights. It is demonstrated that rGO shifts the ˙OH production pathway towards the lattice oxygen mechanism (LOM), in contrast to the adsorbate evolution mechanism (AEM) observed for NiMnO3 alone. This mechanistic shift supports the enhanced stability and sustained electrocatalytic activity, contributing to the high performance of the GF/NiMnO3–rGO composite anode in the context of a more sustainable technology for treating organic contaminants.
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Oct 2025
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[39034]
Open Access
Abstract: Composite co-ionic ceramic electrolytes that combine proton and oxide ion conductors hold potential for co-electrolysis of CO2 and H2O for syngas production due to flexible control of the transport numbers of the two charge carriers. Contrary to purely oxide ion co-electrolysis, co-ionic co-electrolysis embodies the supply of CO2 and H2O separately to the negative and positive electrodes, respectively. This study focuses on the development of a chemically stable co-ionic composite electrolyte of an acceptor-doped Ba(Zr,Ce)O3 proton conducting perovskite phase and an acceptor-doped (Ce,Zr)O2 oxide ion conducting fluorite phase, annealed at temperatures between 800 and 1600 °C. Comprehensive evaluations of the composites' microstructure, hydration, and conductivity were performed, revealing that annealing temperature and cation selection significantly impact the properties and performance of co-ionic electrolytes. Higher annealing temperatures drive cation redistribution, with the perovskite phase becoming zirconium-rich at its B-site and depleted in acceptor dopants, resulting in diminished hydration and protonic conductivity. Herein, we show that composites pairing cerium-rich fluorite phases (e.g., Ce0.8Gd0.2O1.9, CGO20, or Ce0.8Y0.2O1.9, CYO20) display markedly improved performance. The BaCe0.8Y0.2O2.9 (BCY20)–CYO20 system (1[thin space (1/6-em)]:[thin space (1/6-em)]1 weight ratio) achieved the highest conductivity (σ = 0.01 Scm−1 at 650 °C in wet Ar), establishing itself as a promising candidate for co-ionic electrolyte applications in solid oxide electrochemical cells.
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Sep 2025
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[33172, 14239]
Open Access
Abstract: Recent reviews have highlighted borate polyanion systems as promising high-voltage cathode candidates for rechargeable Mg-ion batteries (RMBs) [Coordination Chemistry Reviews, 427, 213551 (2021)]. However, evaluating the electrochemical performance of cathodes for Mg-ion batteries is challenging, with many reports relying on an observed electrochemical capacity rather than demonstrating Mg-ion (de)intercalation. To address these two points, we study three classes of borate polyanions: orthoborates M3(BO3)2, ludwigites M3BO5, and pyroborates M2B2O5 and use a suite of experimental techniques to investigate de-magnesiation on charging vs Li metal with a Li electrolyte. We select five representative materials Mg2Mn(BO3)2, Mg2Ni(BO3)2, Mg2FeBO5, MgFeB2O5 and MgFe0.5Mn0.5B2O5. Whilst promising first charge capacities up to 200 mAh g−1 are observed for ball-milled cathodes cycled at 55°C in a Li containing electrolyte, extensive post-cycling analysis using ex-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Synchrotron Powder X-ray Diffraction (SXRD), combined with operando X-ray Absorption Spectroscopy (XAS) and operando Online Electrochemical Mass Spectrometry (OEMS), show that the capacities obtained are not associated with Mg2+ mobility in the cathodes, de-magnesiation or transition-metal redox. The observed capacity originates from a process enhanced by ball-milling, which is common to all borate polyanions investigated in this work. This process is in part attributed to the irreversible reaction of an amorphous surface layer on the polycrystalline particle, rich in carbonate and glassy borate phases. Here we present the first systematic study of the viability of transition-metal borate polyanions as intercalation cathode materials for RMBs and conclude that, despite the promising electrochemistry, these materials do not de-magnesiate under our tested conditions.
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Sep 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[29996]
Open Access
Abstract: The Li–N–H system spans a rich network of reactive phases that encompass Li3N – Li4NH – Li2NH – LiNH2 – LiH, interconnected through a number of solid solutions and mediated via NH3, H2, and/or N2 exchange. Realizing the full potential of these Li–N–H systems in ammonia catalysis and hydrogen storage applications has been hindered by the inability to ‘nano-design’ them beyond conventional bulk synthesis. Here, we present a novel solvothermal route for the synthesis and nanostructurisation of Li–N–H and Li–Na–N–H materials, providing a solution-phase route to these air-sensitive and reactive materials. The method enables enhanced morphological and dimensional control compared to solid-state routes, yielding nanostructures such as wires, rods, and particles with characteristic sizes from 300 to 900 nm. We systematically explore the structural and microstructural evolution of these phases, and demonstrate the influence of mineralisers on the sample morphology. We report evidence of enhanced nitrogen activation, air-stability and ammonia synthesis activity for these samples, balanced against their propensity for carbon contamination. This work opens the possibility of a significantly expanded synthesis approaches to Li–N–H materials, and M-N-H materials more broadly.
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Sep 2025
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[34797]
Open Access
Abstract: MOF@COF composites have emerged as a promising class of engineered materials with unique functionalities, combining the high porosity and tunability of metal-organic frameworks (MOFs) with the chemical and mechanical stability of covalent-organic frameworks (COFs). While their advantageous properties are well-recognized, their structural intricacies and the nature of the interfacial interactions remain insufficiently explored. In this study, a Fe-MOF@COF composite is presented, exhibiting dual functionalities for the efficient removal of organic pollutants from water. The enhanced performance is attributed to the unique properties of the MOF-COF interface, where synergistic interactions between the two porous materials play a critical role. Advanced synchrotron techniques were employed to probe interfacial interactions at the atomic and molecular levels. These findings underscore the potential of Fe-MOF@COF composite as a highly effective material for water remediation, providing deeper insights into their structural behavior and interfacial properties.
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Aug 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Diamond Proposal Number(s):
[34894, 32322]
Open Access
Abstract: This study focusses on the surface and bulk properties of Ti–O thin film photoanodes for water splitting to generate green hydrogen. Here, TiOx thin films were deposited by reactive RF magnetron sputtering of Ti in an Ar + O2 atmosphere. The oxygen flow rate ηO2, was varied to grow a sequence of TiO, Ti2O3 and TiO2 layers, as determined by X-ray diffraction. The spectral dependence of the optical absorption coefficient reveals a significant colour evolution, which is due to the interference of light, as well as black appearance, resulting from strong absorption within the visible range. Electrical resistivity from impedance spectroscopy increased from 5.2 × 10−2 for black TiO (ηO2 = 5%) to 9 × 104 ohm cm for transparent anatase TiO2 (ηO2 = 30%). X-ray photoelectron spectra were collected at different photon energies, 200 and 1200 eV above the O 1s and Ti 2p core levels, probing the surface and subsurface states, respectively. The depth distribution of the OH–Ti3+ defects indicated their increased surface/subsurface concentration at higher ηO2. X-ray absorption spectroscopy (XAS) showed that the crystal field splitting increased from 1.7–2.1 eV to 2.2–2.3 eV as the amount of Ti3+ states decreased from 20% to 10%. Surface photovoltage (SPV) and the photoelectrochemical performance were correlated. The anatase/rutile mixture or pure anatase TiO2 photoanodes with the highest SPV values of about 270 mV demonstrated the best combination of high negative flat band potential (−650 mV), photocurrent density (350 μA cm−2 at 0 V vs. Ag/AgCl) and a reasonable shape factor (0.75). These findings highlight the critical role of surface-sensitive characterization in optimizing TiOx photoanodes for efficient solar-driven hydrogen development.
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Aug 2025
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I22-Small angle scattering & Diffraction
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Open Access
Abstract: Carbon materials are essential for emerging energy applications and there is a pressing need to be able to produce carbons with controlled properties from sustainable precursors. Iron-catalysed graphitization of biomass is an attractive approach, where simple iron salts are used to convert organic matter to graphitic carbons at relatively low temperature. The choice of iron salt can have a significant impact on the chemical and structural properties of carbons derived from biomass. In this paper, we report a detailed mechanistic investigation of iron catalysed graphitization of cellulose by Fe(NO3)3 and FeCl3. In situ small and wide angle X-ray scattering and electron microscopy show that the evolution of catalyst particles from the two salts follows very different pathways. Remarkably, graphitization by FeCl3 is an order of magnitude faster than by Fe(NO3)3.
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Jul 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[36397]
Abstract: Li-rich cathodes with an O2-type layer stacking offer high gravimetric capacities and fast charge–discharge rates, and are structurally more stable with respect to transition metal migration than O3-type Li-rich cathodes. However, the nature and reversibility of their charge–discharge processes remain poorly understood, in part because these materials can only be obtained through soft chemistry routes. This work provides a new structural model for a recently-reported O2-type cathode with nominal composition Li1.1Al0.04Mn0.65Ni0.21O2 and excellent structural and potential stability. Our new model hints at the impact of short-range cation ordering and phase separation on the electrochemical performance. Neutron and X-ray diffraction indicate that the as-synthesized compound comprises two crystallographically distinct phases—a Li2MnO3 component and a Li-poor (Li0.78Al0.02Mn0.67Ni0.31O2) component—most likely stacked epitaxially along the c-axis. 7Li, 17O and 27Al solid-state NMR measurements further reveal a tendency towards honeycomb ordering on the transition metal sublattice—long-range ordering in Li2MnO3 and partial, short-range ordering in Li0.78Al0.02Mn0.67Ni0.31O2—and highlight the presence of dilithium environments within the transition metal layer in Li2MnO3, with important consequences on structural stability during electrochemical cycling.
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May 2025
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