B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Diamond Proposal Number(s):
[37075]
Open Access
Abstract: Synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been used to investigate a novel Sn:SiO2 composite thin layer grown by organometallic chemical vapor deposition technique (CVD) on a single crystalline silicon wafer with additional treatment by argon ions. According to a previously reported thermodynamic anomaly, an efficient exchange of oxygen between the silicon and tin dioxide surfaces occurs during the growth of the metal oxide thin layer. The present study focuses on the visualization of the atomic and electronic structure of tin nanostructures localized in silica matrix. It is found that no significant chemical alterations are observed during argon ions treatment of the initial composite layer. The removal of atmospheric residues, which partially passivated defects in the highly defective SnO2-x top layer, did not significantly change the initial NEXAFS Sn M4,5 edge spectrum. Based on these results, we found that the main state in which tin nanoparticles localized in the amorphous silica matrix is the metallic state. In addition based on the NEXAFS Si L2,3-edge studies, we found that silica is most associated with the stoichiometric structure of thermally deposited SiO2 layer with the presence of silicon suboxides. These results provide insights into the atomic and electronic structure of Sn:SiO2 composites and contribute to the possible implementation of such materials in various application concepts related to thermal energy storage and novel photonic devices.
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Jun 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Abstract: This article presents the synthesis and evaluation of a novel double perovskite Dy2NiRu0.5Ir0.5O6, as a promising catalyst precursor for the oxygen evolution reaction (OER) in acidic electrolyte. In this perovskite, which was synthesised by a simple sol-gel process, there are two different B sites, one with Ni2+ atoms, and the other in which half of the Ir4+ atoms are replaced by Ru4+.
Electrochemical measurements revealed and exceptional OER activity, with an Ir-normalised mass activity 5–7 times higher than the state-of-the-art IrO2 benchmarks. The catalyst also exhibited remarkable stability, maintaining a stable performance for at least 36,000 OER cycles. Structural and compositional analyses during cycling revealed a transformation of the pristine double perovskite structure into a 3D-hollow Ir0.9Ru0.1Ox framework. The reconstruction, which is driven by the dissolution of Dy3+, Ni2+ and part of Ru4+, results in a highly active and durable electrocatalyst. The enhanced OER performance is attributed to the composition and increased surface area of the reconstructed Ir0.9Ru0.1Ox hollow structure.
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May 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
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Diamond Proposal Number(s):
[32514]
Open Access
Abstract: Fe/N/C based catalysts are the best positioned ones to replace the state-of-the-art Pt-based catalysts for the oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cells (PEMFCs). Here, a Fe/N/C catalyst characterized by a high N/C ratio, has been synthesized from the pyrolysis of a N-rich imine-based polymer. In acidic electrolyte (0.1 M HClO4). The catalyst demonstrates notable ORR activity with Eonset and E1/2 values of 1.09 and 0.77 V vs. RHE, respectively. Furthermore, the catalyst’s performance has been assessed in a single cell PEMFC setup. The optimization of the membrane electrode assembly (MEA) with the Fe/N/C catalyst entails examining various ionomer to catalyst ratios (I/C) as well as two coating methods: spray coating and drop casting. The optimized MEA achieved a cell performance of 725 mA cm-2 at 0.3 V and a power density close to 220 mW cm-2. In order to understand the factors influencing PEMFC polarisation curves, electrochemical impedance spectroscopy (EIS) was performed under potentiostatic conditions. The effect of operational parameters, such as ionomer to catalyst ratios (I/C) and the use of either O2 or air at the anode feed, has been investigated. EIS spectra allow the calculation of the distribution of relaxation times (DRT), providing insights into the rate and resistance of the ORR process occurring at the MEA. Notably, the cathode with an I/C=2, prepared by drop casting, exhibited superior performance attributed to reduced ORR resistances. The current density and power density reached with the 25 cm2 MEA are comparable to those obtained with the 5 cm2 MEA using O2 as cathode reactant.
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Apr 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Abstract: The work presented in this thesis is focused on the application of an innovative spectroscopic technique, operando Near Edge X-ray Fine Structure (NEXAFS), to investigate the surface reactivity of Solid Oxide Fuel Cells (SOFCs) electrodes and electrolytes. As this technique requires the use of synchrotron radiation, all the measurements reported in this thesis have been performed by using reaction cells available at the beamlines APE-HE (Elettra Synchrotron Facility, Italy) and BO7-B (Diamond Light Source, UK). In detail, this work was focused on studying the surface interaction with H2 of A-site doped SrTiO3 and BaZr0.6Ce0.2Y0.2O3-, this latter being a proton conductor for intermediate temperature fuel cells. In this regard, operando NEXAFS can give fundamental information on the oxidation state of Ti and Ce in these compounds, therefore helping to correlate their working performance with their chemical structure and reactivity. In this thesis, operando NEXAFS was coupled with other characterization techniques such as XPS, XRD, SEM and DFT simulations to gain a complete overview of the chemical and morphological features of the samples.
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Apr 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I09-Surface and Interface Structural Analysis
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Nickil
Shah
,
Galo J.
Paez Fajardo
,
Hrishit
Banerjee
,
Gaurav C.
Pandey
,
Ashok S.
Menon
,
Muhammad
Ans
,
Veronika
Majherova
,
Gerard
Bree
,
Satish
Bolloju
,
David .
Grinter
,
Pilar
Ferrer
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Melanie
Loveridge
,
Andrew J.
Morris
,
Clare P.
Grey
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[30201, 33459]
Open Access
Abstract: In Ni-rich layered oxide cathodes, cycling above the oxygen-loss threshold voltage (∼4.3 V vs Li+/Li) promotes structural transformations at the cathode surface. These transformations can result in various thermodynamically favorable rocksalt-like (RSL) structures (NiO, NiOx, and/or LiyNizO) that have different Li+ transport properties. Elucidating the precise phase type in the RSL can help determine design strategies to improve Li+ kinetics and identify design rules to suppress capacity fade in Ni-rich cathodes. This study utilizes surface-sensitive X-ray absorption spectroscopy in combination with first-principles simulations and distinguishes the layered oxide spectroscopic features from those of surface-reduced layers of pure NiO and LixNi1–xO. The transport of lithium ions through this oxygen-loss-induced surface-reconstructed layer is studied with operando X-ray diffraction in a pouch cell as a function of cycling aging and constant voltage protocols.
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Feb 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
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Abstract: The energy density of layered oxides of Li-ion batteries can be enhanced by inducing oxygen redox through replacing transition metal (TM) ions with Li ions in the TM layer. Undesirably, the cathodes always suffer from unfavorable structural degradation, which is closely associated with irreversible TM migration and slab gliding, resulting in continuous capacity and voltage decay. Herein, attention is paid to the Li ions in the TM layer (LiTM) and find their extra effects beyond inducing oxygen redox, which has been rarely mentioned. With the aid of 7Li solid-state NMR and density functional theory (DFT) calculations, the controllable migration of LiTM is verified. The mystery is uncovered that the preferential migration of LiTM plays an imperative role in preventing the structural transformation by postponing the slab gliding of the layered structure. Integrated with the inhibited TM migration, the structural robustness and reversibility of Li2RuO3 can be drastically improved after Zr-substitution, providing a solid foundation for achieving ultra-stable electrochemical performance even after thousands of cycles (2500 cycles). The discovery highlights the significance of LiTM with respect to the structural robustness and provides a potential route toward high-energy-density Li-ion batteries.
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Jan 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Namrata
Ramesh
,
Hrishit
Banerjee
,
Jack E. N.
Swallow
,
Erik
Bjorklund
,
Ava
Dean
,
Prvanin
Didwal
,
Michael
Fraser
,
Conor M. E.
Phelan
,
Lijin
An
,
Jasper
Singh
,
Jarrod
Lewis
,
Weixin
Song
,
Robert A.
House
,
Andrew J.
Morris
,
Robert S.
Weatherup
,
Rebecca J.
Nicholls
Diamond Proposal Number(s):
[33283]
Open Access
Abstract: Core loss spectroscopies can provide powerful element-specific insight into the redox processes occurring in Li-ion battery cathodes, but this requires an accurate interpretation of the spectral features. Here, we systematically interpret oxygen K-edge core loss spectra of layered lithium transition-metal (TM) oxides (LiMO2, where M = Co, Ni, Mn) from first principles using density-functional theory (DFT). Spectra are simulated using three exchange–correlation functionals, comprising the generalized gradient approximation (GGA) functional PBE, the DFT–PBE + Hubbard U method, and the meta-GGA functional rSCAN. In general, rSCAN provides a better match to experimentally observed excitation energies of spectral features compared to both PBE and PBE + U, especially at energies close to the main edge. Projected density of states of core-hole calculations show that the O orbitals are better described by rSCAN. Hybridization, structural distortions, chemical composition, and magnetism significantly influence the spectra. The O K-edge spectrum of LiNiO2 obtained using rSCAN shows a closer match to the experimental X-ray absorption spectroscopy (XAS) when derived from a simulation cell which includes a Jahn–Teller distortion, showing that the DFT-calculated pre-edge feature contains information about not only chemical species but also geometric distortion. Core loss spectra derived from DFT can also differentiate between materials with the same structure and magnetic configuration but comprising different TMs; these differences are comparable to those observed in experimental XAS from the same materials. This foundational work helps establish the extent to which DFT can be used to bridge the interpretation gap between experimental spectroscopic signatures and ab initio methods describing complex battery materials, such as lithium nickel manganese cobalt oxides.
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Nov 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I10-Beamline for Advanced Dichroism - scattering
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Lijin
An
,
Ruomu
Zhang
,
Prvanin N.
Didwal
,
Michael W.
Fraser
,
Leanne A. H.
Jones
,
Conor M. E.
Phelan
,
Namrata
Ramesh
,
Grant
Harris
,
Robert S.
Weatherup
,
Jack E. N.
Swallow
,
Peixi
Cong
,
Andrey
Poletayev
,
Erik
Bjorklund
,
Christophe J.
Sahle
,
Pilar
Ferrer
,
David C.
Grinter
,
Peter
Bencok
,
Shusaku
Hayama
,
Saiful
Islam
,
Robert
House
,
Peter D.
Nellist
,
Robert J.
Green
,
Rebecca J.
Nicholls
Diamond Proposal Number(s):
[33283, 33062, 32010]
Open Access
Abstract: Ni-rich layered oxide cathodes can deliver higher energy density batteries, but uncertainties remain over their charge compensation mechanisms and the degradation processes that limit cycle life. Trapped molecular O2 has been identified within LiNiO2 at high states of charge, as seen for Li-rich cathodes where excess capacity is associated with reversible O-redox. Here we show that bulk redox in LiNiO2 occurs by Ni-O rehybridization, lowering the electron density on O sites, but importantly without the involvement of molecular O2. Instead, trapped O2 is related to degradation at surfaces in contact with the electrolyte, and is accompanied by Ni reduction. O2 is removed on discharge, but excess Ni2+ persists forming a reduced surface layer, associated with impeded Li transport. This implicates the instability of delithiated LiNiO2 in contact with the electrolyte in surface degradation through O2 formation and Ni reduction, highlighting the importance of surface stabilisation strategies in suppressing LNO degradation.
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Sep 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I10-Beamline for Advanced Dichroism - scattering
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Diamond Proposal Number(s):
[33639, 34919, 36558]
Open Access
Abstract: Spinel ferrites exhibit significant promise in photocatalysis and other applications due to their compositional diversity and favourable electronic structure, magnetism, and partially tuneable cation distribution. However, their complex properties, for example, the different behaviour of bulk and nanostructured materials, are not well understood. Here, we combine advanced computational and experimental methods with reactivity measurements to explore the inversion degrees, electronic structures, and photocatalytic activities of MFe2O4 spinels (M = Co, Cu, Zn). X-ray diffraction and anomalous X-ray scattering measurements determined bulk inversion degrees of 0.81, 0.91, and 0.26 for CoFe2O4, CuFe2O4, and ZnFe2O4, respectively. Photocatalytic tests showed that only ZnFe2O4 is active in the oxygen evolution reaction (OER), which correlates with its favourable band alignment, as determined through electronic structure simulations. Surface-sensitive X-ray Absorption Spectroscopy (XAS) measurements provided insights into the cation distributions at the surfaces, showing significant deviations from bulk properties, particularly in ZnFe2O4 in which 52% of the near-surface tetrahedral sites are occupied by Fe cations, compared to 26% in the bulk. DFT simulations of ZnFe2O4 illustrated how the surface terminations can alter the thermodynamic preference for cation distribution in comparison with the bulk. Our findings illustrate the complex interplay between surface and bulk properties in spinel ferrites.
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Sep 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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F.
Bassato
,
S.
Mauri
,
L.
Braglia
,
A. Yu.
Petrov
,
E.
Dobovičnik
,
F.
Tavani
,
A.
Tofoni
,
P.
Ferrer
,
D.
Grinter
,
G.
Held
,
P.
D'Angelo
,
P.
Torelli
Diamond Proposal Number(s):
[33111]
Abstract: A-site doped SrTiO3 is considered as a promising substitute for traditional anodic metals in solid oxide fuel cells (SOFCs). In this study, we present the reactivity of La0.2Sr0.25Ca0.45TiO3 (LCSTO), La0.2Sr0.7TiO3 (LSTO), and SrTiO3 (STO) toward H2 by operando ambient pressure NEXAFS spectroscopy and theoretical spectra simulation with FDMNES code. The samples were synthesized by MBE (molecular beam epitaxy), hydrothermal, and modified-Pechini routes. We found that the reducibility of the samples depends not only on their stoichiometry but also on the morphology, which is determined by the synthetic method. The results of these experiments give insight into the reducibility of Ti4+ in perovskites as well as the opportunity to further optimize the synthesis of these materials to obtain the best performance for SOFC applications.
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Aug 2024
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