B18-Core EXAFS
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Diamond Proposal Number(s):
[14239]
Abstract: Increased demand for lithium products for use in lithium-ion batteries has led to a search for new lithium resources in recent years to meet projected future consumption. One potential lithium resource is low lithium bearing brines that are discharged from hydraulically fractured oil and gas wells as flowback and produced water (FPW). In this way, hydraulic fracturing presents an opportunity to turn what is normally considered wastewater into a lithium resource. In this research, two manganese-based lithium-selective adsorbents were prepared using a co-precipitation method and were employed for lithium recovery from FPW. At optimized conditions, lithium uptake reached 18 mg g−1, with a > 80% lithium recovery within 30 minutes. The recovered lithium was isolated and concentrated to 15 mM in an acidic final product. The degree of sorbent loss during acid desorption of lithium was significantly higher for sorbents used in the FPW as compared to recovery from a synthetic lithium-bearing brine (4.5% versus 0.8%). Thus, we propose that organic molecules present in the FPW reduce manganese in the sorbent structure during lithium sorption, leading to increased sorbent loss through reductive dissolution. Systematic characterization including wet chemical manganese valence measurements, along with EXAFS, XPS, and TEM-EELS show that exposure to FPW causes tetravalent manganese in the bulk sorbent structure to be reduced during lithium sorption, and subsequently dissolves during acid desorption. Partial removal of these organic molecules by nanofiltration leads to decreased sorbent dissolution in acid. In this way, we show that dissolved organic molecules represent a critical control on the reductive dissolution of manganese-based lithium ion exchange sorbents. This research provides some promising results on the use of manganese-based lithium sorbents in FPW.
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Jun 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[14239]
Abstract: Platinum functions exceptionally well as a nanoparticulate catalyst in many important fields, such as in the removal of atmospheric pollutants, but it is scarce, expensive and not always sufficiently durable. Here, we report a perovskite system in which 0.5 wt% Pt is integrated into the support and its subsequent conversion through exsolution to achieve a resilient catalyst. Owing to the instability of most Pt oxides at high temperatures, a thermally stable platinum oxide precursor, barium platinate, was used to preserve the platinum as an oxide during the solid-state synthesis in an approach akin to the Trojan horse legend. By tailoring the procedure, it is possible to produce a uniform equilibrated structure with active emergent Pt nanoparticles strongly embedded in the perovskite surface that display better CO oxidation activity and stability than those of conventionally prepared Pt catalysts. This catalyst was further evaluated for a variety of reactions under realistic test environments—CO and NO oxidation, diesel oxidation catalysis and ammonia slip reactions were investigated.
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May 2021
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B18-Core EXAFS
I09-Surface and Interface Structural Analysis
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Robert A.
House
,
Urmimala
Maitra
,
Liyu
Jin
,
Juan G.
Lozano
,
James W.
Somerville
,
Nicholas H.
Rees
,
Andrew J.
Naylor
,
Laurent C.
Duda
,
Felix
Massel
,
Alan V.
Chadwick
,
Silvia
Ramos
,
David M.
Pickup
,
Daniel E.
Mcnally
,
Xingye
Lu
,
Thorsten
Schmitt
,
Matthew R.
Roberts
,
Peter G.
Bruce
Diamond Proposal Number(s):
[14239, 20870]
Open Access
Abstract: It is possible to increase the charge capacity of transition metal oxide cathodes in alkali-ion batteries by invoking redox reactions on the oxygen. However, oxygen loss often occurs. To explore what affects oxygen loss in oxygen redox materials, we have compared two analogous Na-ion cathodes, P2-Na0.67Mg0.28Mn0.72O2 and P2-Na0.78Li0.25Mn0.75O2. On charging to 4.5 V, >0.4 e- are removed from the oxide ions of these materials, but neither compound exhibits oxygen loss. Li is retained in P2-Na0.78Li0.25Mn0.75O2 but displaced from the transition metal to the alkali metal layers, showing that vacancies in the transition metal layers, which also occur in other oxygen redox compounds that exhibit oxygen loss such as Li[Li0.2Ni0.2Mn0.6]O2, is not a trigger for oxygen loss. On charging at 5 V, P2-Na0.78Li0.25Mn0.75O2 exhibits oxygen loss whereas P2-Na0.67Mg0.28Mn0.72O2 does not. Under these conditions both Na+ and Li+ are removed from P2-Na0.78Li0.25Mn0.75O2 resulting in underbonded oxygen (fewer than 3 cations coordinating oxygen) and surface localised O loss. In contrast, for P2-Na0.67Mg0.28Mn0.72O2, oxygen remains coordinated by at least 2 Mn4+ and 1 Mg2+ ions, stabilising the oxygen and avoiding oxygen loss.
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Apr 2019
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B18-Core EXAFS
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Urmimala
Maitra
,
Robert A.
House
,
James W.
Somerville
,
Nuria
Tapia-Ruiz
,
Juan G.
Lozano
,
Niccolo
Guerrini
,
Rong
Hao
,
Kun
Luo
,
Liyu
Jin
,
Miguel A.
Pérez-Osorio
,
Felix
Massel
,
David M.
Pickup
,
Silvia
Ramos
,
Xingye
Lu
,
Daniel E.
Mcnally
,
Alan V.
Chadwick
,
Feliciano
Giustino
,
Thorsten
Schmitt
,
Laurent C.
Duda
,
Matthew R.
Roberts
,
Peter G.
Bruce
Diamond Proposal Number(s):
[12559]
Abstract: The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds to have promise as a new class of high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion charge compensated by the transition-metal ions. The additional capacity is provided through charge compensation by oxygen-redox chemistry and some oxygen loss. It has been reported previously that O-redox occurs in O-2p orbitals that interact with alkali-ions in the transition-metal and alkali-ion layers (i.e. O-redox occurs in compounds containing Li+ - O2p - Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits excess capacity; here we show this is also due to O-redox, despite Mg2+ residing in the transition-metal (TM) layers rather than alkali-metal ions, demonstrating that excess alkali-metal ions are not required to activate O-redox. We also show that unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose O. Extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen promoting oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2 stabilising oxygen.
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Jan 2018
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B18-Core EXAFS
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Diamond Proposal Number(s):
[12777]
Abstract: Ca2Mn3O8 exhibits a complex layered structure comprised of Mn3O84− layers separated by Ca2+ ions. In contrast with the more traditional triangular delafossite layered materials the Mn3O84− layers additionally exhibit an ordered vacancy, which forms a ‘bow-tie’ like arrangement of the Mn4+ ions. We report a comprehensive study of the magnetic properties of a series of Ca2Mn3O8 materials with different morphologies. EXAFS and XANES analysis confirm no differences in either manganese environment or oxidation state between materials. Apparent differences in magnetic order from SQUID magnetometry can be rationalised by uncompensated surface spins arising as a result of changes to the surface to volume ratio between morphologies. Furthermore, these data suggest these materials are potentially frustrated in nature, due to the triangular connectivity of Mn4+ spins, with a simple ‘spin-up/spin-down’ (↑↓) antiferromagnetic model unable to explain the data collected.
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Sep 2017
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B18-Core EXAFS
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Andre
Duvel
,
Paul
Heitjans
,
Pavel
Fedorov
,
Gudrun
Scholz
,
Giannantonio
Cibin
,
Alan V.
Chadwick
,
David M.
Pickup
,
Silvia
Ramos
,
Lewis W.l.
Sayle
,
Emma K
Sayle
,
Thi X. T.
Sayle
,
Dean C.
Sayle
Diamond Proposal Number(s):
[8912]
Abstract: Ionic conductivity is ubiquitous to many industrially important applications such as fuel cells, batteries, sensors and catalysis. Tunable conductivity in these systems is therefore key to their commercial viability. Here, we show that geometric frustration can be exploited as a vehicle for conductivity tuning. In particular, we imposed geometric frustration upon a prototypical system, CaF2, by ball milling it with BaF2, to create nanostructured Ba1-xCaxF2 solid solutions and increased its ionic conductivity by over 5 orders of magnitude. By mirroring each experiment with MD simulation, including ‘simulating synthesis’, we reveal that geometric frustration confers, on a system at ambient temperature, structural and dynamical attributes that are typically associated with heating a material above its superionic transition temperature. These include: structural disorder, excess volume, pseudo vacancy arrays and collective transport mechanisms; we show that the excess volume correlates with ionic conductivity for the Ba1-xCaxF2 system. We also present evidence that geometric frustration-induced conductivity is a general phenomenon, which may help explain the high ionic conductivity in doped fluorite-structured oxides such as ceria and zirconia, with application for solid oxide fuel cells. A review on geometric frustration [Nature 2015, 512, 303] remarks that ‘classical crystallography is inadequate to describe systems with correlated disorder, but that geometric frustration has clear crystallographic signatures’. Here, we identify two possible crystallographic signatures: excess volume and correlated ‘snake-like’ ionic transport; the latter infers correlated disorder. In particular, as one ion in the chain moves, all the other (correlated) ions in the chain move simultaneously. Critically, our simulations reveal snake-like chains, over 40 Å in length, which indicates long-range correlation in our disordered systems. Similarly, collective transport in glassy materials is well documented [for example, J. Chem. Phys. 2013, 138, 12A538]. Possible crystallographic nomenclatures, to be used to describe long-range order in disordered systems, may include, for example, the shape, length, branching of the ‘snake’ arrays. Such characterizations may ultimately provide insight and differences between long-range order in disordered, amorphous or liquid states, and processes such as ionic conductivity, melting and crystallization.
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Mar 2017
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B18-Core EXAFS
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Kun
Luo
,
Matthew R.
Roberts
,
Niccoló
Guerrini
,
Nuria
Tapia-Ruiz
,
Rong
Hao
,
Felix
Massel
,
David M.
Pickup
,
Silvia
Ramos
,
Yi-Sheng
Liu
,
Jinghua
Guo
,
Alan V.
Chadwick
,
Laurent C.
Duda
,
Peter
Bruce
Diamond Proposal Number(s):
[14239]
Open Access
Abstract: Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g., Mn3+/4+ in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O-2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V versus Li+/Li. The capacity at 4.5 V is dominated by oxidation of the O-2(-) anions accounting for similar to 0.43 e(-)/formula unit, with an additional 0.06 e(-)/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V is mainly O loss, similar to 0.08 e(-)/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn4+/Li+). The results have been obtained by combining operando electrochemical mass spec on 180 labeled Li[Li0.2Ni0.2Mn0.6]O-2 with XANES, soft X-ray spectroscopy, resonant inelastic X-ray spectroscopy, and Raman spectroscopy. Finally the general features of O redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal oxygen interaction on anion redox in lithium rich cathode materials.
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Sep 2016
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B18-Core EXAFS
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Diamond Proposal Number(s):
[8169]
Abstract: Polycrystalline Y2CoGe4O12 has been prepared by standard ceramic methods. The crystal structure (space group P4/nbm; a=9.8465(2), c=4.92986(9) Å) consists of metal-rich layers separated from each other by Ge4O12 groups comprised of four corner-sharing GeO4 tetrahedra. Two cation sites lie within the layers; an eight-coordinate site occupied by yttrium and a six-coordinate site occupied by a 1:1 disordered distribution of yttrium and cobalt. Neutron diffraction revealed two-fold disorder on the oxide sublattice; this has been elucidated using Co K-edge EXAFS spectroscopy. The availability of two sites allows each oxide ion to accommodate the coordination preferences of its single Co/Y neighbour; the GeO4 tetrahedra distort to absorb any consequent strain. The octahedron of anions around each Co2+ cation shows a pseudo-tetragonal distortion with a strain (Co–O)eq–(Co–O)ax/(Co–O)eq=−0.173. This results in an unusually large effective magnetic moment of 6.05 µB per Co2+ cation.
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Aug 2015
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B18-Core EXAFS
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Diamond Proposal Number(s):
[8912]
Open Access
Abstract: Nanocrystalline samples of Ba1-xCaxF2 prepared by high-energy milling show an unusually high F- ion conductivity, which exhibit a maximum in the magnitude and a minimum in the activation energy at x = 0.5. Here, we report an X-ray absorption spectroscopy (XAS) at the Ca and Sr K edges and the Ba L3 edge and a molecular dynamics (MD) simulation study of the pure and mixed fluorides. The XAS measurements on the pure binary fluorides, CaF2, SrF2 and BaF2 show that high-energy ball-milling produces very little amorphous material, in contrast to the results for ball milled oxides. XAS measurements of Ba1-xCaxF2 reveal that for 0 < x <1 there is considerable disorder in the local environments of the cations which is highest for x = 0.5. Hence the maximum in the conductivity corresponds to the composition with the maximum level of local disorder. The MD calculations also show a highly disordered structure consistent with the XAS results and similarly showing maximum disorder at x = 0.5.
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Apr 2015
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B18-Core EXAFS
I19-Small Molecule Single Crystal Diffraction
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Jack
Blandy
,
Artem M.
Abakumov
,
Kirsten
Christensen
,
Joke
Hadermann
,
Paul
Adamson
,
Simon
Cassidy
,
Silvia
Ramos
,
David
Free
,
Harry
Cohen
,
Daniel
Woodruff
,
Amber
Thompson
,
Simon J
Clarke
Open Access
Abstract: Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2 Cu 1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides.
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Apr 2015
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