B18-Core EXAFS
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Diamond Proposal Number(s):
[26801]
Open Access
Abstract: Foaming during vitrification of radioactive waste in Joule-Heated Ceramic Melters (JHCM) is exacerbated by trapping of evolving gases, such as CO2, NOx and O2, beneath a viscous reaction layer. Foaming restricts heat transfer during melting. Sucrose is employed as the baseline additive at the Hanford site in Washington State, USA to reduce foaming. Alternative carbon-based reductant additives were explored in simulated, inactive Hanford high-iron HLW-NG-Fe2 feeds, for both their effect on foaming and to give insight to the behaviour of multivalent species in glass melts under different redox conditions. Graphite, coke (93% C), formic acid and HEDTA additives were compared with sucrose, and a feed with no additive. Graphite and coke additions proved most effective in reducing the maximum foam volume by 51 ± 3% and 54 ± 2%, respectively, compared with 24 ± 5% for sucrose. Lower foaming could result in more efficient vitrification in JHCMs. Reductants also affected redox ratios in the multivalent species present in the feed. The order of reduction, Mn3+/Mn2+ > Cr6+/Cr3+ > Ce3+/Ce4+ > Fe3+/Fe2+ was as predicted on the basis of their redox potentials. There is less reduction overall, particularly in the Fe3+ → Fe2+, than predicted by the calculations, attributed to the oxygenated atmosphere of the experiments.
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May 2023
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I10-Beamline for Advanced Dichroism
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Zihan
Li
,
Shanshan
Liu
,
Jiabao
Sun
,
Jiayi
Zhu
,
Yanhui
Chen
,
Yunkun
Yang
,
Linfeng
Ai
,
Enze
Zhang
,
Ce
Huang
,
Pengliang
Leng
,
Minhao
Zhao
,
Xiaoyi
Xie
,
Yuda
Zhang
,
Nesta Benno
Joseph
,
Rajdeep
Banerjee
,
Awadhesh
Narayan
,
Jin
Zou
,
Wenqing
Liu
,
Xiaodong
Xu
,
Faxian
Xiu
Diamond Proposal Number(s):
[22532]
Abstract: Two-dimensional (2D) magnets offer valuable electrical and mechanical properties, and could be used to create 2D nanoelectromechanical systems. However, the low Curie temperature of most 2D magnets limits practical applications. Here we report van der Waals ferromagnetic low-pass filters based on wafer-scale iron germanium telluride (Fe5+xGeTe2) thin films grown by molecular-beam epitaxy. We show that the Curie temperature of the Fe5+xGeTe2 system can be continuously modulated from 260 to 380 K via in situ iron doping. Few-layer Fe5+xGeTe2 is used to fabricate planar spiral inductors, with the 2D magnetic core providing inductance enhancement of 74% at room temperature compared with an inductor without the core. Low-pass Butterworth filters are then created from inductance–capacitance circuits built with these inductors. The filters offer a broad dynamic range of around 40 dB, and the –3 dB cut-off frequency can be tuned from 18 to 30 Hz by using different inductors in the inductance–capacitance circuit.
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Mar 2023
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[21872, 27487]
Open Access
Abstract: The topological surface states (TSSs) in topological insulators (TIs) offer exciting prospects for dissipationless spin transport. Common spin-based devices, such as spin valves, rely on trilayer structures in which a non-magnetic (NM) layer is sandwiched between two ferromagnetic (FM) layers. The major disadvantage of using high-quality single-crystalline TI films in this context is that a single pair of spin-momentum locked channels spans across the entire film, meaning that only a very small spin current can be pumped from one FM to the other, along the side walls of the film. On the other hand, using nanocrystalline TI films, in which the grains are large enough to avoid hybridization of the TSSs, will effectively increase the number of spin channels available for spin pumping. Here, we used an element-selective, x-ray based ferromagnetic resonance technique to demonstrate spin pumping from a FM layer at resonance through the TI layer and into the FM spin sink.
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Mar 2023
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Jack E. N.
Swallow
,
Elizabeth S.
Jones
,
Ashley R.
Head
,
Joshua S.
Gibson
,
Roey
Ben David
,
Michael W.
Fraser
,
Matthijs A.
Van Spronsen
,
Shaojun
Xu
,
Georg
Held
,
Baran
Eren
,
Robert S
Weatherup
Diamond Proposal Number(s):
[25834]
Open Access
Abstract: The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.
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Mar 2023
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Runjia
Lin
,
Liqun
Kang
,
Karolina
Lisowska
,
Weiying
He
,
Siyu
Zhao
,
Shusaku
Hayama
,
Dan
Brett
,
Graham
Hutchings
,
Furio
Corà
,
Ivan
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[29254, 29207]
Open Access
Abstract: Electrocatalytic oxygen reduction reaction (ORR) has been intensively studied for efficient and environmentally benign energy conversion processes. However, insufficient understanding of ORR 2e--pathway mechanism at the atomic level inhibits rational design of electrocatalysts with both high activity and selectivity, causing concerns including catalyst degradation due to Fenton reaction or poor efficiency of H2O2 electrosynthesis. Herein we show that the generally accepted ORR electrocatalyst design based on a Sabatier volcano plot argument optimises activity but is unable to account for the 2e--pathway selectivity; an extended “dynamic active site saturation” model that examines in addition the hydrogenation kinetics linked to the OOH* adsorption energy enables us to resolve the activity-selectivity compromise. Through electrochemical and operando spectroscopic studies on the ORR process governed by a series of Co-N x /carbon nanotube hybrids, a construction-driven approach that aims to create the maximum number of 2e- ORR sites by directing the secondary ORR electron transfer step towards the 2e- intermediate is proven to be attainable by manipulating O2 hydrogenation kinetics. Control experiments reveal the O2 hydrogenation chemistry is related to a catalyst reconstruction with lower symmetry around the Co active centre induced by the application of a cathodic potential. The optimised catalyst exhibits a ~100% H2O2 selectivity and an outstanding activity with an ORR potential of 0.82 V versus the reversible hydrogen electrode to reach the ring current density of 1 mA cm-2 by using rotating ring-disk electrode measurement, which is the best-performing 2e- ORR electrocatalyst reported to date, and approaches the thermodynamic limit.
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Mar 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[25120]
Open Access
Abstract: The development of multielectron redox-active cathode materials is a top priority for achieving high energy density with long cycle life in the next-generation secondary battery applications. Triggering anion redox activity is regarded as a promising strategy to enhance the energy density of polyanionic cathodes for Li/Na-ion batteries. Herein, K2Fe(C2O4)2 is shown to be a promising new cathode material that combines metal redox activity with oxalate anion (C2O42–) redox. This compound reveals specific discharge capacities of 116 and 60 mAh g–1 for sodium-ion batterie (NIB) and lithium-ion batterie (LIB) cathode applications, respectively, at a rate of 10 mA g–1, with excellent cycling stability. The experimental results are complemented by density functional theory (DFT) calculations of the average atomic charges.
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Mar 2023
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I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
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A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
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Mar 2023
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B18-Core EXAFS
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Panpan
Zhang
,
Mingchao
Wang
,
Yannan
Liu
,
Yubin
Fu
,
Mingming
Gao
,
Gang
Wang
,
Faxing
Wang
,
Zhiyong
Wang
,
Guangbo
Chen
,
Sheng
Yang
,
Youwen
Liu
,
Renhao
Dong
,
Minghao
Yu
,
Xing
Lu
,
Xinliang
Feng
Abstract: Although two-dimensional conjugated metal–organic frameworks (2D c-MOFs) provide an ideal platform for precise tailoring of capacitive electrode materials, high-capacitance 2D c-MOFs for non-aqueous supercapacitors remain to be further explored. Herein, we report a novel phthalocyanine-based nickel-bis(dithiolene) (NiS4)-linked 2D c-MOF (denoted as Ni2[CuPcS8]) with outstanding pseudocapacitive properties in 1 M TEABF4/acetonitrile. Each NiS4 linkage is disclosed to reversibly accommodate two electrons, conferring the Ni2[CuPcS8] electrode a two-step Faradic reaction with a record-high specific capacitance among the reported 2D c-MOFs in non-aqueous electrolytes (312 F g–1) and remarkable cycling stability (93.5% after 10,000 cycles). Multiple analyses unveil that the unique electron-storage capability of Ni2[CuPcS8] originates from its localized lowest unoccupied molecular orbital (LUMO) over the nickel-bis(dithiolene) linkage, which allows the efficient delocalization of the injected electrons throughout the conjugated linkage units without inducing apparent bonding stress. The Ni2[CuPcS8] anode is used to demonstrate an asymmetric supercapacitor device that delivers a high operating voltage of 2.3 V, a maximum energy density of 57.4 Wh kg–1, and ultralong stability over 5000 cycles.
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Mar 2023
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B07-B-Versatile Soft X-ray beamline: High Throughput
E02-JEM ARM 300CF
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Longxiang
Liu
,
Liqun
Kang
,
Arunabhiram
Chutia
,
Jianrui
Feng
,
Martyna
Michalska
,
Pilar
Ferrer
,
David
Grinter
,
Georg
Held
,
Yeshu
Tan
,
Fangjia
Zhao
,
Fei
Guo
,
David
Hopkinson
,
Christopher
Allen
,
Yanbei
Hou
,
Junwen
Gu
,
Ioannis
Papakonstantinou
,
Paul
Shearing
,
Dan
Brett
,
Ivan P.
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[29340, 32501, 30614, 29809, 32058]
Open Access
Abstract: The electrochemical synthesis of hydrogen peroxide (H2O2) via a two-electron (2e-) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. However, the development of efficient electrocatalysts is still facing lots of challenges like insufficient understanding of active sites. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst (PCC) for H2O2 electrochemical production. The optimized PCC900 exhibits unprecedented activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H2O2 selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2e- ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis.
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Mar 2023
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B18-Core EXAFS
|
Jonathan
Ruiz Esquius
,
David J.
Morgan
,
Gerardo
Algara Siller
,
Diego
Gianolio
,
Matteo
Aramini
,
Leopold
Lahn
,
Olga
Kasian
,
Simon A.
Kondrat
,
Robert
Schlögl
,
Graham J.
Hutchings
,
Rosa
Arrigo
,
Simon J.
Freakley
Diamond Proposal Number(s):
[15151]
Open Access
Abstract: The oxygen evolution reaction (OER) is crucial to future energy systems based on water electrolysis. Iridium oxides are promising catalysts due to their resistance to corrosion under acidic and oxidizing conditions. Highly active iridium (oxy)hydroxides prepared using alkali metal bases transform into low activity rutile IrO2 at elevated temperatures (>350 °C) during catalyst/electrode preparation. Depending on the residual amount of alkali metals, we now show that this transformation can result in either rutile IrO2 or nano-crystalline Li-intercalated IrOx. While the transition to rutile results in poor activity, the Li-intercalated IrOx has comparative activity and improved stability when compared to the highly active amorphous material despite being treated at 500 °C. This highly active nanocrystalline form of lithium iridate could be more resistant to industrial procedures to produce PEM membranes and provide a route to stabilize the high populations of redox active sites of amorphous iridium (oxy)hydroxides.
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Mar 2023
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