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      Hidden diversity of vacancy networks in Prussian blue analogues


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          Prussian blue analogues (PBAs) are a diverse family of microporous inorganic solids, famous for their gas storage, 1 metal-ion immobilization, 2 proton conduction, 3 and stimuli-dependent magnetic, 4, 5 electronic, 6 and optical 7 properties. The family includes the double-metal cyanide (DMC) catalysts 8, 9 and the hexacyanoferrate/hexacyanomanganate (HCF/HCM) battery materials. 10, 11 Central to the various physical properties of PBAs is the ability to transport mass reversibly, a process enabled by structural vacancies. Normally presumed random, 12, 13 vacancy arrangements are crucial because they control micropore network characteristics, and hence diffusivity and adsorption profiles. 14, 15 The long-standing obstacle to characterising PBA vacancy networks is the inaccessibility of single crystals. 16 Here we report the growth of single crystals of a range of PBAs. By measuring and interpreting their X-ray diffuse scattering patterns, we identify a striking diversity of non-random vacancy arrangements that is hidden from conventional crystallographic analysis of powders. Moreover, we rationalise this unexpected phase complexity in terms of a simple microscopic model based on local rules of electroneutrality and centrosymmetry. The hidden phase boundaries that emerge demarcate vacancy-network polymorphs with profoundly different micropore characteristics. Our results establish a foundation for correlated defect engineering in PBAs as a means of controlling storage capacity, anisotropy, and transport efficiency.

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          Algorithms and tools for high-throughput geometry-based analysis of crystalline porous materials

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            Is Open Access

            Defect-Engineered Metal–Organic Frameworks

            Defect engineering in metal–organic frameworks (MOFs) is an exciting concept for tailoring material properties, which opens up novel opportunities not only in sorption and catalysis, but also in controlling more challenging physical characteristics such as band gap as well as magnetic and electrical/conductive properties. It is challenging to structurally characterize the inherent or intentionally created defects of various types, and there have so far been few efforts to comprehensively discuss these issues. Based on selected reports spanning the last decades, this Review closes that gap by providing both a concise overview of defects in MOFs, or more broadly coordination network compounds (CNCs), including their classification and characterization, together with the (potential) applications of defective CNCs/MOFs. Moreover, we will highlight important aspects of “defect-engineering” concepts applied for CNCs, also in comparison with relevant solid materials such as zeolites or COFs. Finally, we discuss the future potential of defect-engineered CNCs.
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              Copper hexacyanoferrate battery electrodes with long cycle life and high power.

              Short-term transients, including those related to wind and solar sources, present challenges to the electrical grid. Stationary energy storage systems that can operate for many cycles, at high power, with high round-trip energy efficiency, and at low cost are required. Existing energy storage technologies cannot satisfy these requirements. Here we show that crystalline nanoparticles of copper hexacyanoferrate, which has an ultra-low strain open framework structure, can be operated as a battery electrode in inexpensive aqueous electrolytes. After 40,000 deep discharge cycles at a 17 C rate, 83% of the original capacity of copper hexacyanoferrate is retained. Even at a very high cycling rate of 83 C, two thirds of its maximum discharge capacity is observed. At modest current densities, round-trip energy efficiencies of 99% can be achieved. The low-cost, scalable, room-temperature co-precipitation synthesis and excellent electrode performance of copper hexacyanoferrate make it attractive for large-scale energy storage systems.

                Author and article information

                24 December 2019
                12 February 2020
                February 2020
                12 August 2020
                : 578
                : 7794
                : 256-260
                [1 ]Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, U.K.
                [2 ]Laboratory for Multifunctional Ferroic Materials, Department of Materials, ETH Zürich, Zürich, Switzerland
                [3 ]Centre for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium
                [4 ]Department of Chemistry, Uppsala University, Uppsala, Sweden
                [5 ]Departamento de Polímeros, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
                [6 ]Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, U.K.
                [7 ]Swiss-Norwegian Beam Lines at the European Synchrotron Radiation Facility, Grenoble, France
                [8 ]European Synchrotron Radiation Facility, Grenoble Cedex, France
                [9 ]Department of Chemistry, University of Zürich, Zürich, Switzerland
                [10 ]Department of Chemistry and Biochemistry, University of Berne, Bern, Switzerland
                Author notes
                [* ] Correspondence and requests for materials should be addressed to A.L.G. andrew.goodwin@ 123456chem.ox.ac.uk .

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