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Abstract: Hard carbons are the leading candidate anode materials for sodium-ion batteries. However, the sodium-insertion mechanisms remain under debate. Here, employing a novel analysis of operando and ex situ pair distribution function (PDF) analysis of total scattering data, supplemented by information on the local electronic structure provided by operando 23Na solid-state NMR, we identify the local atomic environments of sodium stored within hard carbon and provide a revised mechanism for sodium storage. The local structure of carbons is well-described by bilayers of curved graphene fragments, with fragment size increasing, and curvature decreasing with increasing pyrolysis temperature. A correlation is observed between the higher-voltage (slope) capacity and the defect concentration inferred from the size and curvature of the fragments. Meanwhile, a larger lower-voltage (plateau) capacity is observed in samples modeled by larger fragment sizes. Operando PDF data on two commercially relevant hard carbons reveal changes at higher-voltages consistent with sodium ions stored close to defective areas of the carbon, with electrons localized in the antibonding π*-orbitals of the carbon. Metallic sodium clusters approximately 13–15 Å in diameter are formed in both carbons at lower voltages, implying that, for these carbons, the lower-voltage capacity is determined by the number of regions suitable for sodium cluster formation, rather than by having microstructures that allow larger clusters to form. Our results reveal that local atomic structure has a definitive role in determining storage capacity, and therefore the effect of synthetic conditions on both the local atomic structure and the microstructure should be considered when engineering hard carbons.

Open Access

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Abstract: Binary metal oxides have received sustained interest as anode materials due to their desirable capacities, exceeding theoretical values particularly in the first discharge. Although they have received increasing attention in recent years, topical debates persist regarding not only their lithiation mechanisms but also the origin of additional capacity. Aiming to resolve these disagreements, we perform a systematic study of a series of iron and manganese oxides to investigate their phase behavior during first discharge. Using a combination of in operando pair distribution function measurements and our recently developed Metropolis non-negative matrix factorization approach to address the analytical challenges concerning materials’ nanoscopic nature and phase heterogeneity, here we report unexpected observation of non-equilibrium FeOx solid-solution phases and pulverization of MnO. These processes are correlated with the extra capacities observed at different depths of discharge, pointing to a metal-dependent nature of this additional capacity and demonstrating the advantage of our approach with promising prospects for diverse applications.

Open Access

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Abstract: A series of modified solid polymethylaluminoxane (sMAO) catalyst supports have been developed for slurry phase ethylene polymerisation, using aryl di-ol modifier groups. Characterisation using ICP-MS analysis, X-ray total scattering, SEM–EDX, diffuse FT-IR and solid state NMR spectroscopy shows that the organic linker groups are uniformly distributed in a proposed organic framework stucture we call a “sMAOF”. When used as a support for rac-ethylene{bis(1-indenyl)} zirconium dichloride, (EBI)ZrCl2, these linker modified sMAOF materials provide a 40% enhancement in polymerisation activity with respect to unmodified sMAO: activities of 163 × 103 and 116 × 103 kgPE molZr−1 h−1 at 80 °C for (EBI)ZrCl2 supported on sMAOF(1,4-HO(C6F4)OH) and sMAO, respectively. The observed activity increase is correlated with the higher BET surface area and increased porosity in the linker modified sMAOF activating support.

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Abstract: Extended X-ray absorption fine structure (EXAFS) and X-ray Pair Distribution Function (XPDF) analysis are versatile complementary techniques that provide information about local structure and bonding in crystalline and non-crystalline materials. Both techniques provide information about the coordination number of neighbouring atoms, bond distances and the degree of static/thermal disorder. EXAFS is a well-established element-specific method that provides short-range order information around the X-ray absorber of interest. XPDF is not element-specific, but provides short-range order information similar to EXAFS, alongside long- range structure. Calcium methoxide (Ca(OCH3)2) is one of the prominent heterogeneous catalysts that are being used in the formation of sustainable biolubricants and biodiesel from natural/synthetic oils via transesterification. Other compounds that have been considered as viable catalysts include calcium oxide (CaO) and calcium hydroxide (Ca(OH)2). Unlike these two bases, which have been comprehensively characterised using EXAFS, the short-range crystalline structure of Ca(OCH3)2 is yet to be fully determined. Not much is known about its structure beyond the indication that it has the same hexagonal space group (P-3m1) as Ca(OH)2. This was determined over 40 years ago, using powder X-ray diffraction and mid infrared spectroscopy, and has not been investigated since. Hence, we present a comparative study on the local structure of CaO, Ca(OH)2 and Ca(OCH3)2 using EXAFS and XPDF analysis. Our results demonstrate how a new/refined model crystal Ca(OCH3)2 structure was obtained using XPDF data, crystal symmetry and unit cell dimensions. This model was subsequently used in EXAFS simulations to determine atom coordination numbers, bond distances and static disorder in Ca(OCH3)2. To the best of our knowledge, this is the first time EXAFS and XPDF data has been presented on a calcium alkoxide. The structural information obtained from this study could benefit development of more sophisticated alkoxide-based heterogenous catalysts. This multi-technique ex situ analysis of the three basic calcium catalysts could also inform operando studies of alkaline-earth metal catalysis with these techniques.

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Abstract: The formation of different nickel, cobalt and copper layered hydroxide phases by a variety of solution and solid-state synthesis methods have been investigated. Initially, the preparative conditions were varied to generate single-phase products from metal(II) nitrate hexahydrate that were characterised by powder X-ray diffraction, vibrational spectroscopy and thermogravimetric analysis. As well as the β-M(OH)2 and α-M(OH)2 phases (where M = Ni, Co) two different hydroxynitrate phases with the generic formula M(OH)2-x(NO3)x materials were isolated with x = 0.67 and 1.0 (where M = Ni, Co). The reduction of symmetry of the nitrate anion from D3h to C2v can allow the alpha-phase to be distinguished from the two layered hydroxynitrate phases in both infrared and Raman spectroscopy. The symmetric N-O stretch enables the two hydroxynitrate phases to be distinguished through the sharp absorptions at ca. 1000 cm-1 (x = 0.67) and ca. 1050 cm-1 (x = 1.0). The TGA data of the pure phases showed key differences between the layered hydroxides, with anhydrous phases having singular weight losses over short temperature ranges while hydrated phases have multiple losses over larger ranges. Short-range characterisation techniques were used to characterise the poorly crystalline alpha-phases of nickel and cobalt together with beta-phase copper hydroxide, and the results compared with the three copper hydroxide minerals malachite, azurite and georgeite. Two synthetic forms of georgeite were also analysed, prepared by supercritical antisolvent precipitation with carbon dioxide and sodium carbonate precipitation. The alpha-phases and georgeite were both shown through infrared spectroscopic analysis to have uncoordinated nitrate and carbonate with D3h symmetry incorporated into the structures. Synchrotron X-ray pair distribution function analysis showed only short-range order (<15 Å) in the alpha-phases with only intralayer atom pair distances present. Shorter atom pair distances were observed for georgeite phases (<5 Å), but were matched to intralayer bond distances expected of alpha-phase type layered hydroxides of 2.0 Å and 3.0 Å. This redefines georgeite as an alpha-phase hydroxide for the first time contrary to the literature definition of a hydroxysalt phase. The disordering of beta-phase nickel hydroxide through the formation of stacking faults and interstratification was investigated by varying temperature and time using nickel(II) nitrate. Stacking faulted materials were formed at low temperature and identified by broadening of the 00l reflections while interstratified materials were identified through the splitting of the 001 into two lines. In contrast to interstratified materials presented in previous studies as alpha-phase and beta-phase layering, this work has shown through vibrational spectroscopy that layered hydroxysalts can also undertake the interstratification process. Standard mixtures of hydroxynitrate and beta-phase were prepared to investigate if the intensity of particular vibrational bands could be correlated with the proportion of the particular phases in mixtures. The intensity of the infrared bands at 990 cm-1 and the Raman bands at 1315 cm-1 were shown to correlate with content, theoretically providing a method to determine mixture compositions.