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Abstract: Current industrial production of ammonia from the Haber-Bosch process and its transport concomitantly produces a large quantity of CO2. Herein, we successfully synthesize inorganic-structure-based catalysts with [Fe-S2-Mo] motifs with a connecting structure similar to that of FeMoco (a cofactor of nitrogenase) by placing iron atoms on a single molecular layer of MoS2 at various loadings. This type of new catalytic material functionally mimics the nitrogenase to convert N2 to ammonia and hydrogen in water without adding any sacrificial agent under visible-light illumination. Using the elevated temperature boosts the ammonia yield and the energy efficiency by one order of magnitude. The solar-to-NH3 energy-conversion efficiency can be up to 0.24% at 270°C, which is the highest efficiency among all reported photocatalytic systems. This method of ammonia production and the photocatalytic materials may open up an exciting possibility for the decentralization of ammonia production for fertilizer provision to local farmlands using solar illumination.

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Abstract: Antiferroelectric perovskites form an important family of functional electric materials, which have high potential in energy storage and conversion applications. However, a full understanding of their crystal structural formation is still lacking. PbZrO 3 -based materials can serve as a model system for investigation, not only because PbZrO 3 was the first discovered antiferroelectric, but also because it undergoes a typical phase transition sequence from a high-temperature paraelectric to the low-temperature antiferroelectric phase, passing through a possible intermediate phase that is poorly understood. Here we employ a combination of optical and scattering experiments and theoretical calculations to reveal the nature of the intermediate state. Evidence is found that this peculiar state consists of multiple short-range and long-range structural components, and their competition is crucial in stabilizing the antiferroelectric phase. External stimuli such as temperature change or chemical substitution can easily alter each component's energy landscape and thereby change the materials' electrical properties. These findings provide insights into understanding antiferroelectric-ferroelectric competition and can be useful in designing alternative antiferroelectric materials.

Open Access

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Abstract: Tantalum‐doped lithium lanthanum zirconate garnet (Li7‐xLa3Zr2‐xTaxO12, LLZTO) has received interest as a solid electrolyte for solid‐state lithium batteries due to its good electrochemical properties and ionic conductivity. However, the source of discrepancies for reported values of ionic conductivity in nominally or nearly equivalent compositions of LLZTO is not completely clear. Herein, synthesis‐related factors that may contribute to the differences in performance of garnet electrolytes are systematically characterized. The conductivity of samples with composition Li6.4La3Zr1.4Ta0.6O12 prepared by various methods including solid‐state reaction, combustion, and molten salt synthesis are compared. Varying levels of elemental inhomogeneity, comprising a variation in Ta and Zr‐content on the level of individual LLZTO particles, are identified. The elemental inhomogeneity is found to be largely preserved even after high temperature sintering and correlated with reduced ionic conductivity. We show that the various synthesis and processing‐related variables in each of the preparation methods play a role in these compositional variations, and that even LLZTO synthesized via conventional, high‐temperature solid‐state reaction can exhibit substantial variability in local composition. However, by improving reagent mixing and employing LLZTO powder with low agglomeration and small particle size distribution, the compositional uniformity, and hence ionic conductivity, of sintered garnet electrolytes can be improved.

Open Access

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Abstract: Binary metal oxides are attractive anode materials for lithium-ion batteries. Despite sustained effort into nanomaterials synthesis and understanding the initial discharge mechanism, the fundamental chemistry underpinning the charge and subsequent cycles—thus the reversible capacity—remains poorly understood. Here, we use in operando X-ray pair distribution function analysis combining with our recently developed analytical approach employing Metropolis Monte Carlo simulations and non-negative matrix factorisation to study the charge reaction thermodynamics of a series of Fe- and Mn-oxides. As opposed to the commonly believed conversion chemistry forming rocksalt FeO and MnO, we reveal the two oxide series topotactically transform into non-native body-centred cubic FeO and zincblende MnO via displacement-like reactions whose kinetics are governed by the mobility differences between displaced species. These renewed mechanistic insights suggest avenues for the future design of metal oxide materials as well as new material synthesis routes using electrochemically-assisted methods.

Open Access

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Abstract: Biogenic and synthetic hydroxyapatites are confounding materials whose properties remain uncertain, even after years of study. Pair distribution function (PDF) analysis was applied to hydroxyapatites in the 1970’s and 1980’s, but this area of research has not taken full advantage of the relatively recent advances in synchrotron facilities. Here, synchrotron X-ray PDF analysis is compared to techniques commonly used to characterise hydroxyapatite (such as wide angle X-ray scattering, Fourier-transform infrared spectroscopy and thermogravimetric analysis) for a range of biogenic and synthetic hydroxyapatites with a wide range of carbonate substitution. Contributions to the pair distribution function from collagen, carbonate and finite crystallite size were examined through principal component analysis and comparison of PDFs. Noticeable contributions from collagen were observed in biogenic PDFs when compared to synthetic PDFs (namely r < 15 Å), consistent with simulated PDFs of collagen structures. Additionally, changes in local structure were observed for PDFs of synthetic hydroxyapatites with differing carbonate content, notably in features near 4 Å, 8 Å and 19 Å. Regression models were generated to predict carbonate substitution from peak position within the PDFs.