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Abstract: The formation of stacking faults and phase interstratification disorder in layered nickel(II) hydroxides during the chemical precipitation synthesis of materials using nickel(II) nitrate and potassium hydroxide solutions has been investigated in the temperature range of 5 °C to 95 °C and time intervals from 1 hour to 1 week. Stacking faulted materials were identified by broadening of the 00l reflections, while interstratified materials were identified through the splitting of the 001 into two lines. In contrast to the disorder concepts presented in previous studies of these materials, this work has shown through vibrational spectroscopy that both the alpha-phase and beta-phase hydroxides are present in materials described with stacking fault disorder, while layered hydroxysalts were additionally present in the materials considered to be interstratified. Standard mixtures of Ni3(OH)4(NO3)2 and β-Ni(OH)2 were prepared to investigate if the intensity of particular vibrational bands could be correlated with the proportion of the particular phases in mixtures. The intensities of the C2v nitrate infrared and Raman bands at 990 cm−1 and 1315 cm−1 were shown to correlate with the amount of layered hydroxynitrate incorporated in the phase, theoretically providing a method to determine the components in mixed compositions. Since disorder and phase impurities in layered nickel hydroxide materials affect both their electroactive stability and performance as cathode materials, this work has important implications in several research fields.

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Abstract: Chalcopyrite, CuFeS2 is considered one of the promising n-type thermoelectric materials with high natural abundance as a mineral. In this work, partial substitution of germanium in materials CuFe1−xGexS2, (0.0 ≤ x ≤ 0.10), leads to an almost six-fold enhancement of thermoelectric properties. X-Ray photoelectron spectroscopy (XPS) reveals that germanium is present in two oxidation states: Ge2+ and Ge4+. The stereochemically-active 4s2 lone-pair of electrons associated with Ge2+ induces a local structural distortion. Pair-distribution function (PDF) analysis reveal that Ge2+ ions are displaced from the centre of the GeS4 tetrahedron towards a triangular face, leading to pseudo-trigonal pyramidal coordination. This distortion is accompanied by lattice softening and an increase of the strain-fluctuation scattering parameter (ΓS), leading to a decrease in thermal conductivity. Phonon calculations demonstrate that germanium substitution leads to the appearance of resonant phonon modes. These modes lie close in energy to the acoustic and low-energy optical modes of the host matrix, with which they can interact, providing an additional mechanism for reducing the thermal conductivity. The weak chemical bonding of germanium with sulphur also leads to localized electronic states near the Fermi level which results in a high density-of-states effective mass, enabling a relatively high Seebeck coefficient to be maintained, despite the reduced electrical resistivity. This combination produces an almost three-fold improvement in the power factor, which when coupled with the substantial reduction in thermal conductivity, leads to a maximum figure-of-merit, zT ∼ 0.4 at 723 K for CuFe0.94Ge0.06S2.

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Abstract: Sn-Beta has emerged as a state-of-the-art catalyst for a range of sustainable chemical transformations. Conventionally prepared by bottom-up hydrothermal synthesis methods, recent research has demonstrated the efficiency of several top-down methods of preparation. One attractive top-down approach is Solid-State Incorporation, where a dealuminated Beta zeolite is physically mixed with a solid Sn precursor, in particular Sn (II) acetate, prior to heat treatment at 550 °C. This procedure is fast and benign, and metal incorporation requires no solvents and hence produces no aqueous Sn-containing waste streams. Although the performances of these catalysts have been well explored in recent years, the mechanism of heteroatom incorporation remains unknown, and hence, opportunities to improve the synthetic procedure via a molecular approach remain. Herein, we utilise a range of in situ spectroscopic techniques, alongside kinetic and computational methods, to elucidate the mechanisms that occur during preparation of the catalyst, and then improve the efficacy of the synthetic protocol. Specifically, we find that successful incorporation of Sn into the lattice occurs in several distinct steps, including i) preliminary coordination of the metal ion to the vacant lattice sites of the zeolite during physical grinding; ii) partial incorporation of the metal ion into the zeolite framework upon selective decomposition of the acetate ligands, which occurs upon heating the physical mixture in an inert gas flow from room temperature to 550 °C; and iii) full isomorphous substitution of Sn into the lattice alongside its simultaneous oxidation to Lewis acidic Sn(IV), when the physically mixed material is exposed to air during a short (<1 h) isotherm period. Long isotherm steps are shown to be unnecessary, and fully oxidised Sn(IV) precursors are shown to be unsuitable for successful incorporation into the lattice. We also find that the formation of extra-framework Sn oxides is primarily dependent on the quantity of Sn present in the initial physical mixture. Based on these findings, we demonstrate a faster synthetic protocol for the preparation of Sn-Beta materials via Solid-State Incorporation, and benchmark their performance of the catalyst for the Meerwein-Ponndorf-Verley transfer hydrogenation reaction and for the isomerisation of glucose to fructose.

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Abstract: Disordered rock salt (DRS) cathodes have attracted considerable attention because of their high first charge capacities and relatively low cost. Here we investigate operando the structure and charge evolution of the Li1.1Mn0.7Ti0.2O2 Li-excess rock salt cathode with a first charge capacity of 270 mA h g−1. We associate a certain extent of the capacity fade in DRS to the in situ formation of locally ordered layered nanodomains during the electrochemical cycling of the long-range cation disordered rock salt. We quantify the short-range ordering of cations during cycling and evaluate its effect on the lithium-ion diffusion and charge compensation using operando studies based on X-ray total scattering and advanced spectroscopic methods at the Mn K-edge, namely high energy resolution fluorescence detected XANES and emission spectroscopies including main and valence-to-core transitions.

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Abstract: Emerging technologies in solar energy will be critical in enabling worldwide society in overcoming the present energy challenges and reaching carbon net zero. Inefficient and unstable charge transport materials limit current emerging energy conversion and storage technologies. Low-dimensional coordination polymers represent an alternative, unprecedented class of charge transport materials, comprised of molecular building blocks. Here, we provide a comprehensive study of mixed-valence coordination polymers from an analysis of the charge transport mechanism to their implementation as hole conducting layers. CuII dithiocarbamate complexes afford morphology control of 1D polymer chains linked by (CuI2X2) copper halide rhombi. Concerted theoretical and experimental efforts identified the charge transport mechanism at the transition to band-like transport with an modeled effective hole mass of 6 me. The iodide-bridged coordination polymer showed an excellent conductivity of 1 mS cm-1 and a hole mobility of 5.8 10-4 cm2(Vs)-1 at room temperature. Nanosecond selective hole injection into coordination polymer thin films was captured by nanosecond photoluminescenceof halide perovskite films. The coordination polymers constitute a sustainable, tunable alternative to the current standard of heavily doped organic hole conductors.