B18-Core EXAFS
|
Mohamed M. M.
Kashbor
,
Dedi
Sutarma
,
James
Railton
,
Naoko
Sano
,
Peter J.
Cumpson
,
Diego
Gianolio
,
Giannantonio
Cibin
,
Luke
Forster
,
Carmine
D’agostino
,
Xi
Liu
,
Liwei
Chen
,
Volkan
Degirmenci
,
Marco
Conte
Diamond Proposal Number(s):
[24728]
Open Access
Abstract: In this study, we use zeolite Y as a support for the synthesis of Sn and Ga doped zeolites aimed at the isomerization of glucose to fructose. Though these materials are inactive in water, they are active in methanol and we could ascertain a reaction pathway involving a hydride shift for the interconversion of glucose to fructose and mannose, and a Brønsted acid pathway with the formation of a methyl fructoside intermediate and its hydrolysis to fructose if water was added afterwards. By using characterizations comprising: chemisorption, XPS, XRD, HAADF-STEM and EXAFS; it was possible to demonstrate that a straightforward impregnation protocol for the preparation of our catalysts, led to Sn/Y mainly consisting of small SnO2 clusters on the external surface of the zeolite, whereas Ga/Y consisting of highly dispersed Ga species mostly inside the zeolite pores; and a catalytic activity that appears to be dominated by Brønsted acid sites.
|
May 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[14239]
Open Access
Abstract: Sodium layered oxides showing oxygen redox activity are promising positive electrodes for sodium‑ion batteries (SIBs). However, structural degradation typically results in limited reversibility of the oxygen redox activity. Herein, the effect of Zn‑doping on the electrochemical properties of P3-type sodium manganese oxide, synthesised under air and oxygen is investigated for the first time. Air‑Na 0.67 Mn 0.9 Zn 0.1 O 2 and Oxy‑Na 0.67 Mn 0.9 Zn 0.1 O 2 exhibit stable cycling performance between 1.8 and 3.8 V, each maintaining 96% of their initial capacity after 30 cycles, where Mn 3+ /Mn 4+ redox dominates. Increasing the voltage range to 1.8‑4.3 V activates oxygen redox. For the material synthesised under air, oxygen redox activity is based on Zn, with limited reversibility. The additional transition metal vacancies in the material synthesised under oxygen result in enhanced oxygen redox reversibility with small voltage hysteresis. These results may assist the development of high‑capacity and structurally stable oxygen redox‑based materials for SIBs.
|
Apr 2022
|
|
B18-Core EXAFS
|
Manjil
Das
,
Sayantika
Bhowal
,
Jhuma
Sannigrahi
,
Abhisek
Bandyopadhyay
,
Anupam
Banerjee
,
Giannantonio
Cibin
,
Dmitry
Khalyavin
,
Niladri
Banerjee
,
Devashibhai
Adroja
,
Indra
Dasgupta
,
Subham
Majumdar
Diamond Proposal Number(s):
[17752]
Abstract: We address the concomitant metal-insulator transition (MIT) and antiferromagnetic ordering in the novel pyrochlore iridate
Eu
2
Ir
2
O
7
by combining x-ray absorption spectroscopy, x-ray and neutron diffractions, and density functional theory (DFT)-based calculations. The temperature dependent powder x-ray diffraction clearly rules out any change in the lattice symmetry below the MIT, nevertheless a clear anomaly in the Ir-O-Ir bond angle and Ir-O bond length is evident at the onset of MIT. From the x-ray absorption near edge structure (XANES) spectroscopic study of Ir-
L
3
and
L
2
edges, the effective spin-orbit coupling is found to be intermediate, at least quite far from the strong atomic spin-orbit coupling limit. Powder neutron diffraction measurement is in line with an all-in-all-out magnetic structure of the Ir-tetrahedra in this compound, which is quite common among rare-earth pyrochlore iridates. The sharp change in the Ir-O-Ir bond angle around the MIT possibly arises from the exchange striction mechanism, which favors an enhanced electron correlation via weakening of Ir-Ir orbital overlap and an insulating phase below
T
M
I
. The theoretical calculations indicate an insulating state for shorter bond angle validating the experimental observation. Our DFT calculations show a possibility of intriguing topological phase below a critical value of the Ir-O distance, which is shorter than the experimentally observed bond length. Therefore, a topological state may be realized in bulk
Eu
2
Ir
2
O
7
sample if the Ir-O bond length can be reduced by the application of sufficient external pressure.
|
Apr 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[22410]
Abstract: Metal–organic frameworks (MOFs) can serve as precursors for new nanomaterials via thermal decomposition. Such MOF-derived nanomaterials (MDNs) are often comprised of metal and/or metal oxide particles embedded on porous carbon. The morphology of MDNs is similar to that of the precursor MOF, and improved stability and catalytic properties have been demonstrated. However, the pathway from MOF to MDN is only well understood for a few systems, and in situ studies are needed to elucidate the full phase behaviour and time/temperature dependency. In this work, we follow the MOF-to-MDN transformation in situ by using three complementary techniques: X-ray absorption spectroscopy (XAS), powder X-ray diffraction (PXRD), and X-ray total scattering/pair distribution function (TS/PDF) analysis. The thermal decomposition of HKUST-1, i.e. the archetypical MOF Cu3(btc = 1,3,5-benzenetricarboxylate)2, is followed from room temperature to 500 °C by applying different heating ramps. Real space correlations are followed by PDF and extended X-ray absorption fine structure (EXAFS) analysis, and quantitative phase fractions are obtained by refinement of PXRD and PDF data, and by linear combination analysis (LCA) of X-ray absorption near edge Structure (XANES) data. We find that HKUST-1 decomposes at 300–325 °C into copper(I) oxide and metallic copper. Above 350–470 °C, metal particles remain as the only copper species. There is an overall good agreement between all three techniques with respect to the phase evolution, and the study paves the road towards rational synthesis of a Cu2O/Cu/carbon material with the desired metal/metal oxide composition. More importantly, our investigations serve as a benchmark study demonstrating that this methodology is generally applicable for studying the thermal decomposition of MOFs.
|
Apr 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[21906]
Abstract: Thermoelectrics are well recognized materials for energy harvesting and many solid-state cooling devices are already present on the market. SnSe is an inexpensive binary system made by earth-abundant elements that holds the record-high performance among the semiconductor materials although the origin of its ultralow thermal conductivity is still not understood. Both X-ray and neutron diffraction experiments identified in SnSe at high temperature a transition from the α-phase (Pnma) to the β-phase (Cmcm). In this contribution using for the first time in-situ temperature-dependent X-ray Absorption Fine structure spectroscopy (T-XAFS) at Sn and Se K-edge, we showed the occurrence in the XAS data of two isosbestic points, which support the coexistence of two phases in a wide temperature range. Moreover, in the SnSe matrix Sn-O bonds are continuously formed and SnO2, SeO2 and SnSe2 nanophases are emerging at high temperature. The experiment points out how these local nanophases are formed above 600 K. These emerging nano-phases affect the mean free path of phonons reducing the lattice thermal conductivity and, together with the crystal structural phase transition, may account for the low thermal conductivity measured in SnSe single crystals.
|
Mar 2022
|
|
B18-Core EXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
|
Runjia
Lin
,
Liqun
Kang
,
Tianqi
Zhao
,
Jianrui
Feng
,
Veronica
Celorrio
,
Guohui
Zhang
,
Giannantonio
Cibin
,
Anthony
Kucernak
,
Dan
Brett
,
Furio
Cora
,
Ivan P.
Parkin
,
Guanjie
He
Diamond Proposal Number(s):
[25410, 29207]
Open Access
Abstract: Electrocatalytic organic compound oxidation reactions (OCORs) have been intensively studied for energy and environmentally benign applications. However, relatively little effort has been devoted to developing a fundamental understanding of OCOR, including the detailed competition with side reactions and activity limitations, thus inhibiting the rational design of high-performance electrocatalysts. Herein, by taking NiWO4-catalysed urea oxidation reaction (UOR) in aqueous media as an example, the competition between the OCOR and the oxygen evolution reaction (OER) within a wide potential range is examined. It is shown that the root of the competition can be ascribed to insufficient surface concentration of dynamic Ni3+, an active site shared by both UOR and OER. Similar phenomenon are observed in other OCOR electrocatalysts and systems. To address the issue, a “controllable reconstruction of pseudo-crystalline bimetal oxides” design strategy is proposed to maximise the dynamic Ni3+ population and manipulate the competition between UOR and OER. The optimised electrocatalyst delivers best-in-class performance and a ~10-fold increase in current density at 1.6 V versus the reversible hydrogen electrode for alkaline urea electrolysis compared to that of the pristine materials.
|
Mar 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[28383]
Open Access
Abstract: Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.
|
Jan 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[20060]
Abstract: Various electrode materials are considered for sodium-ion batteries (SIBs) and one important prerequisite for developments of SIBs is a detailed understanding about charge storage mechanisms. Herein, we present a rigorous study about Na storage properties of ultra-small Fe3S4 nanoparticles, synthesized applying a solvothermal route, which exhibit a very good electrochemical performance as anode material for SIBs. A closer look into electrochemical reaction pathways on the nanoscale, utilizing synchrotron-based X-ray diffraction and X-ray absorption techniques, reveals a complicated conversion mechanism. Initially, separation of Fe3S4 into nanocrystalline intermediates occurs accompanied by reduction of Fe3+ to Fe2+ cations. Discharge to 0.1 V leads to formation of strongly disordered Fe0 finely dispersed in a nanosized Na2S matrix. The resulting volume expansion leads to a worse long-term stability in the voltage range 3.0–0.1 V. Adjusting the lower cut-off potential to 0.5 V, crystallization of Na2S is prevented and a completely amorphous intermediate stage is formed. Thus, the smaller voltage window is favorable for long-term stability, yielding highly reversible capacity retention, e.g., 486 mAh g−1 after 300 cycles applying 0.5 A g−1 and superior coulombic efficiencies >99.9%. During charge to 3.0 V, Fe3S4 with smaller domains are reversibly generated in the 1st cycle, but further cycling results in loss of structural long-range order, whereas the local environment resembles that of Fe3S4 in subsequent charged states. Electrokinetic analyses reveal high capacitive contributions to the charge storage, indicating shortened diffusion lengths and thus, redox reactions occur predominantly at surfaces of nanosized conversion products.
|
Jan 2022
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[21847]
Open Access
Abstract: Here we report the synthesis via ceramic methods of the high-performance Mn-rich Na2.4Al0.4Mn2.6O7 oxygen-redox cathode material for Na-ion batteries which we use as a testbed material to study the effects of Al substitution and subsequent Na excess in the high-capacity, anionic redox-based cathode material Na2Mn3O7. The material shows a stable electrochemical performance, with a specific capacity of 200 mAh g-1 in the 1.5 - 4.7 voltage window at C/20 and capacity retention of 90 % after 40 cycles. Using a combination of electrochemical and structural analysis together with hybrid density functional theory calculations we explain the behaviour of this material with changes in Mn/anionic redox reactions and associated O2 release reactions occurring in the material during electrochemical cycling (Na insertion/extraction) and compare these findings to Na2Mn3O7. We expect that these results will advance understanding of the effect of dopants in Mn-rich cathode materials with oxygen redox activity to pave their way towards real applications in high-performing sodium-ion battery applications.
|
Dec 2021
|
|
B18-Core EXAFS
|
Diamond Proposal Number(s):
[14239]
Abstract: Bulk isocubanite (CuFe2S3) was synthesized via a multistep high-temperature synthesis and was investigated as an anode material for sodium-ion batteries. CuFe2S3 exhibits an excellent electrochemical performance with a capacity retention of 422 mA h g–1 for more than 1000 cycles at a current rate of 0.5 A g–1 (0.85 C). The complex reaction mechanism of the first cycle was investigated via PXRD and X-ray absorption spectroscopy. At the early stages of Na uptake, CuFe2S3 is converted to form crystalline CuFeS2 and nanocrystalline NaFe1.5S2 simultaneously. By increasing the Na content, Cu+ is reduced to nanocrystalline Cu, followed by the reduction of Fe2+ to amorphous Fe0 while reflections of nanocrystalline Na2S appear. During charging up to −5 Na/f.u., the intermediate NaFe1.5S2 appears again, which transforms in the last step of charging to a new unknown phase. This unknown phase together with NaFe1.5S2 plays a key role in the mechanism for the following cycles, evidenced by the PXRD investigation of the second cycle. Even after 400 cycles, the occurrence of nanocrystalline phases made it possible to gain insights into the alteration of the mechanism, which shows that CuxS phases play an important role in the region of constant specific capacity.
|
Nov 2021
|
|
