B18-Core EXAFS
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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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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Xiang
Ding
,
Charles C.
Tam
,
Xuelei
Sui
,
Yan
Zhao
,
Minghui
Xu
,
Jaewon
Choi
,
Huaqian
Leng
,
Ji
Zhang
,
Mei
Wu
,
Haiyan
Xiao
,
Xiaotao
Zu
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Xiaoqiang
Wu
,
Qingyuan
Wang
,
Peng
Gao
,
Sean
Li
,
Bing
Huang
,
Ke-Jin
Zhou
,
Liang
Qiao
Diamond Proposal Number(s):
[30296]
Abstract: The newly discovered nickelate superconductors so far only exist in epitaxial thin films synthesized by a topotactic reaction with metal hydrides1. This method changes the nickelates from the perovskite to an infinite-layer structure by deintercalation of apical oxygens1,2,3. Such a chemical reaction may introduce hydrogen (H), influencing the physical properties of the end materials4,5,6,7,8,9. Unfortunately, H is insensitive to most characterization techniques and is difficult to detect because of its light weight. Here, in optimally Sr doped Nd0.8Sr0.2NiO2H epitaxial films, secondary-ion mass spectroscopy shows abundant H existing in the form of Nd0.8Sr0.2NiO2Hx (x ≅ 0.2–0.5). Zero resistivity is found within a very narrow H-doping window of 0.22 ≤ x ≤ 0.28, showing unequivocally the critical role of H in superconductivity. Resonant inelastic X-ray scattering demonstrates the existence of itinerant interstitial s (IIS) orbitals originating from apical oxygen deintercalation. Density functional theory calculations show that electronegative H– occupies the apical oxygen sites annihilating IIS orbitals, reducing the IIS–Ni 3d orbital hybridization. This leads the electronic structure of H-doped Nd0.8Sr0.2NiO2Hx to be more two-dimensional-like, which might be relevant for the observed superconductivity. We highlight that H is an important ingredient for superconductivity in epitaxial infinite-layer nickelates.
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Mar 2023
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B18-Core EXAFS
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Abstract: During my PhD research activity, I was involved in the development of smart materials with self-healing functionalities, the possibility to repair the "tissue" that constitutes the electrode, and the electrode/electrolyte interface is the first step towards improve batteries reliability. Concerning the anodic compartment, the active materials subjected to research were black phosphorus-based nanocomposite with carbon and advanced high entropy oxides with rock-salt structure. Subsequently, innovative functional cathode materials were developed for application in lithium-ion batteries that exhibits excellent cycling stability in a wide voltage range and high specific capacities. During the last year I focused on improving lithium metal battery technology, by realizing an enhanced polymer gel electrolyte by means of a Janus separator that showed excellent electrochemical performance, reduced capacity loss and the ability to intercept dendrite growth. A further improvement were Cu-based 3D current collectors as advanced anodes. They showed good capacity, life cycle of more than 300 hours and enhanced safety due to the greater surface area as well as the decrease in local current densities.
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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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Diamond Proposal Number(s):
[22687]
Abstract: Designing CO2 methanation catalysts that meet industrial requirements is still challenging. We report Ni-Fe hydrotalcite-derived catalysts with a wide range of Ni and Mg loadings showing that an optimised composition with Ni0.4 gives a very high CO2 conversion rate of 0.37 mmol/gcat/s at 300°C. This catalyst is studied by in-situ APXPS and NEXAFS spectroscopies and compared with the other synthesised samples to obtain new mechanistic insights on methanation catalysts active for low-temperature (300°C) methanation, which is an industrial requirement. Under methanation conditions, in-situ investigations revealed the presence of metallic Ni sites and low nuclearity Ni-Fe species at
(Ni loading) = 21.2 mol%. These sites are oxidised on the low Ni-loaded catalyst (
= 9.2 mol%). The best CO2 conversion rate and CH4 selectivity are shown at intermediate
(21.2 mol%), in the presence of Mg. These superior performances are related to the high metallic surface area, dispersion, and optimal density of basic sites. The
(turnover frequency of CO2 conversion) increases exponentially with the fractional density of basic to metallic sites (
) from 1.1 s-1 (
= 29.2 mol%) to 9.1 s-1 (
= 7.6 mol%). It follows the opposite trend of the CO2 conversion rate. In-situ DRIFTS data under methanation conditions evidence that the
at high
is related to the presence of a formate route which is not predominant at low
(high
). A synergistic interplay of basic and metallic sites is present. This contribution provides a rationale for designing industrially competitive CO2 methanation catalysts with high catalytic activity while maintaining low Ni loading.
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Mar 2023
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I20-EDE-Energy Dispersive EXAFS (EDE)
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Diamond Proposal Number(s):
[29667]
Abstract: Single-atoms on carbon-nitrogen supports are considered catalysts for a multitude of reactions. However, doubts remain whether really these species or subnanometer clusters formed under reaction conditions are the active species. In this work, we investigate the dynamics of palladium single-atoms on graphitic carbon nitride during ethylene hydrogenation and H2-D2 exchange. By employing aberration-corrected scanning transmission electron microscopy, x-ray photoelectron spectroscopy and x-ray absorption spectroscopy, we will show that palladium, originally present as single-atoms, agglomerates to clusters at 100 °C in a gas atmosphere that contains both ethylene and hydrogen. This agglomeration goes in hand with the emergence of catalytic activity in both ethylene hydrogenation and H2-D2 exchange, suggesting that clusters, rather than single-atoms, are the active species. The results presented herein highlight the potential of analytics over the course of reaction to identify the active species and provide new insights into the influence of gas atmosphere on metal speciation.
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Mar 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Abstract: Spinel oxides are well-known functional materials but rarely show superconductivity. Recently, emergent superconductivity was discovered in
MgTi
2
O
4
, which is attributed to the increase of electron doping and the suppression of orbital order. Here, we utilized Ti
L
-edge resonant inelastic x-ray scattering to study the orbital excitations in superconducting (SC) and insulating
MgTi
2
O
4
films. We find that the spectral weight of orbital excitations is enhanced and the energy of
t
2
g
intraband excitation is softened in the SC film compared to the insulating one, suggesting higher electron doping and a suppressed orbital order gap in the SC sample. These observations were further supported by our multiplet calculations using the minimal two-site model. Our results provide spectroscopic evidence for the competition between orbital order and superconductivity in
MgTi
2
O
4
and shed light on searching for novel superconductors in spinel oxides.
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Mar 2023
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15475, 15215, 12700]
Open Access
Abstract: The agricultural soils of West Limerick, Ireland, contain very localised, extremely high natural Se concentrations that reach levels that are very toxic to grazing livestock. The Carboniferous shales that formed in anoxic deep-water marine environments are the source of the selenium, which, along with the other redox-sensitive elements of molybdenum, uranium, arsenic and vanadium, were mobilised and reprecipitated in post-glacial anoxic marshes. The result has been a history of selenosis and molybdenosis in livestock in this important dairy province. Soils collected at 10–20 cm from five different agricultural sites were analysed, and all yielded concentrations greatly in excess of the safe Se limits of 3–10 mg kg−1; the highest value recorded was 1265.8 mg kg−1 Se. The highest recorded value for Mo in these soils was 1627.5 mg kg−1, and for U, 658.8 mg kg−1. There was a positive correlation between Se, Mo U and organic matter in the soils. Analysis of non-accumulator pasture grasses (Lolium perenne (perennial ryegrass), Festuca arundinacea (tall fescue), Dactylis glomerata (cocksfoot) and Phleum pretense (timothy grass)) revealed the shoot/leaf to contain up to 78.05 mg kg−1 Se while Trifolium repens (white clover) leaves contained 296.15 mg kg−1 Se. An in situ growing experiment using the Se accumulator species Brassica oleracea revealed 971.2 mg kg−1 Se in the leaves of premier kale, which also contained 1000.4 mg kg−1 Mo. Translocation factors (TFs) were generally higher for Mo than Se across all plant species. Combined X-ray absorption near edge spectroscopy (XANES) with micro-X-ray fluorescence (μ-XRF) showed the Se was present in the soil predominantly as the reduced immobile phase, elemental Se (Se0), but also as bioavailable organoselenium species, mainly selenomethionine (SeMet). SeMet was also the main species identified within both the Se non-accumulator and Se accumulator plants. The Se soil–plant system in West Limerick is dominated by SeMet, and uptake into the cattle pasture results in selenosis in the grazing dairy herds. The hyperaccumulating Brassica oleracea species could be used to extract both the Se and Mo to reduce the toxicity of the blighted fields.
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Mar 2023
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15947]
Open Access
Abstract: The alteration of olivine-rich rocks to serpentine minerals, (hydr)oxides, and aqueous hydrogen through serpentinization is long thought to have influenced the distribution of habitable environments on early Mars and the evolution of the early Martian hydrosphere and atmosphere. Nevertheless, the planetary importance of Martian serpentinization has remained a matter of debate. To constrain the process and products of Martian serpentinization, we studied serpentinized iron-rich olivines from the 1.1-billion-year Duluth Complex. These data indicate that serpentinized iron-rich olivine would have been accompanied by a fivefold increase in hydrogen production relative to serpentinized terrestrial mantle peridotites. In contrast to previous expectations, this style of serpentinization yields hisingerite as the dominant iron serpentine mineral at comparatively low temperature and pH, consistent with meteorite mineralogy and in situ rover data. The widespread occurrence of oxidized iron-bearing phyllosilicates in highly magnetized regions of the Martian crust supports the hypothesis that serpentinization was more pervasive on early Mars than currently estimated.
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Feb 2023
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I06-Nanoscience
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Diamond Proposal Number(s):
[14135]
Abstract: The size of the orbital moment in
Fe
3
O
4
has been the subject of a long-standing and contentious debate. In this paper, we make use of ferromagnetic resonance (FMR) spectroscopy and x-ray magnetic circular dichroism (XMCD) to provide complementary determinations of the size of the orbital moment in “bulklike” epitaxial
Fe
3
O
4
films grown on yttria-stabilized zirconia (111) substrates. Annealing the 100 nm as-grown films to
1100
∘
C
in a reducing atmosphere improves the stoichiometry and microstructure of the films, allowing for bulklike properties to be recovered as evidenced by x-ray diffraction and vibrating sample magnetometry. In addition, in-plane angular FMR spectra exhibit a crossover from a fourfold symmetry to the expected sixfold symmetry of the (111) surface, together with an anomalous peak in the FMR linewidth at
∼
10
GHz; this is indicative of low Gilbert damping in combination with two-magnon scattering. For the bulklike annealed sample, a spectroscopic splitting factor
g
≈
2.18
is obtained using both FMR and XMCD techniques, providing evidence for the presence of a finite orbital moment in
Fe
3
O
4
.
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Feb 2023
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
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Huihuang
Fang
,
Simson
Wu
,
Tugce
Ayvali
,
Jianwei
Zheng
,
Joshua
Fellowes
,
Ping-Luen
Ho
,
Kwan Chee
Leung
,
Alexander
Large
,
Georg
Held
,
Ryuichi
Kato
,
Kazu
Suenaga
,
Yves Ira A.
Reyes
,
Ho Viet
Thang
,
Hsin-Yi Tiffany
Chen
,
Shik Chi Edman
Tsang
Open Access
Abstract: Ammonia is regarded as an energy vector for hydrogen storage, transport and utilization, which links to usage of renewable energies. However, efficient catalysts for ammonia decomposition and their underlying mechanism yet remain obscure. Here we report that atomically-dispersed Ru atoms on MgO support on its polar (111) facets {denoted as MgO(111)} show the highest rate of ammonia decomposition, as far as we are aware, than all catalysts reported in literature due to the strong metal-support interaction and efficient surface coupling reaction. We have carefully investigated the loading effect of Ru from atomic form to cluster/nanoparticle on MgO(111). Progressive increase of surface Ru concentration, correlated with increase in specific activity per metal site, clearly indicates synergistic metal sites in close proximity, akin to those bimetallic N2 complexes in solution are required for the stepwise dehydrogenation of ammonia to N2/H2, as also supported by DFT modelling. Whereas, beyond surface doping, the specific activity drops substantially upon the formation of Ru cluster/nanoparticle, which challenges the classical view of allegorically higher activity of coordinated Ru atoms in cluster form (B5 sites) than isolated sites.
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Feb 2023
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