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Atomic arrangements and their symmetries govern the physical properties of materials, including nanosheets that are low-dimensional nanomaterials. Although they have the same composition, symmetric changes associated with atomic displacements sometimes induce unexpected physical properties. Herein, we report that symmetric breakage induces a semimetallic state in chemically exfoliated ruthenate nanosheets. The atomic arrangements and symmetries are determined by a pair distribution function (PDF); subsequently, the physical properties are discussed using ab initio calculations and resistivity measurements. Ruthenate nanosheets can adopt an electronic structure similar to that of graphene owing to symmetric breakage. We experimentally confirmed the polymorphism in ruthenate nanosheets that highlights the importance of symmetric analysis, even in low-dimensional materials.

Organic–inorganic hybrid halide perovskites (ABX3, where A = CH3NH3+ (methylammonium ion, MA); B = Pb2+; and X = Br–, I–, or Cl–) have excellent optoelectronic properties and are highly efficient photovoltaic materials, but their chemical instability impedes their development for use in next-generation solar cells, wherein they serve as the light-harvesting material. Here, we propose a mechanism of photoluminescence red-shift, a performance-loss phenomenon known as light-induced halide segregation, in mixed-halide perovskites upon illumination using in situ single-particle spectroscopy and synchrotron-based X-ray techniques. Our experimental analyses suggest a defect-assisted photoinduced transition from ordinary nonpolar phases to polar phases at the local scale within seconds is coupled with organic cation reorientation, which in turn narrows the bandgap; first-principles calculations quantitatively supported this result. Our findings provide deeper insights into the nature of local polar domains in hybrid perovskite materials and help improve device stability and efficiency.

Sodium niobate (NaNbO3) attracts attention for its great potential in a variety of applications, for instance, due to its unique optical properties. Still, optimization of its synthetic procedures is hard due to the lack of understanding of the formation mechanism under hydrothermal conditions. Through in situ X-ray diffraction, hydrothermal synthesis of NaNbO3 was observed in real time, enabling the investigation of the reaction kinetics and mechanisms with respect to temperature and NaOH concentration and the resulting effect on the product crystallite size and structure. Several intermediate phases were observed, and the relationship between them, depending on temperature, time, and NaOH concentration, was established. The reaction mechanism involved a gradual change of the local structure of the solid Nb2O5 precursor upon suspending it in NaOH solutions. Heating gave a full transformation of the precursor to HNa7Nb6O19·15H2O, which destabilized before new polyoxoniobates appeared, whose structure depended on the NaOH concentration. Following these polyoxoniobates, Na2Nb2O6·H2O formed, which dehydrated at temperatures ≥285 °C, before converting to the final phase, NaNbO3. The total reaction rate increased with decreasing NaOH concentration and increasing temperature. Two distinctly different growth regimes for NaNbO3 were observed, depending on the observed phase evolution, for temperatures below and above ≈285 °C. Below this temperature, the growth of NaNbO3 was independent of the reaction temperature and the NaOH concentration, while for temperatures ≥285 °C, the temperature-dependent crystallite size showed the characteristics of a typical dissolution–precipitation mechanism.

To obtain an ideal electrocatalysts for hydrogen fuel cells, we investigated group 4 and 5 oxide-based compounds because of their high degree of freedom. First-principles calculations revealed that oxide surfaces such as those of titanium oxide could break down the universal scaling to achieve the ideal state of the oxygen reduction reaction. We experimentally clarified that the active sites were oxygen vacancies for tantalum and zirconium oxides, in addition to doped foreign elements and crystalline structures for titanium oxide. We successfully demonstrated that precious metal-free and carbon-free oxide-based cathodes have high quality active sites and superior durability in 0.1 M sulfuric acid at 80°C. Our strategy was developed as follows: (1) Active sites are created on the oxide surface by modifying the crystalline structure and electronic states and (2) electrons participating in the oxygen reduction reaction are supplied by nanosized oxide particles and oxide films through the tunneling effect of electrons.

Controlling the shape and size of nanostructured materials has been a topic of interest in the field of material science for decades. In this work, the ferroelectric material Srx Ba1-x Nb2 O6 (x=0.32-0.82, SBN) was prepared by hydrothermal synthesis, and the morphology is controllably changed from cube-shaped to hollow-ended structures based on a fundamental understanding of the precursor chemistry. Synchrotron X-ray total scattering and PDF analysis was used to reveal the structure of the Nb-acid precursor, showing Lindqvist-like motifs. The changing growth mechanism, from layer-by-layer growth forming cubes to hopper-growth giving hollow-ended structures, is attributed to differences in supersaturation. Transmission electron microscopy revealed an inhomogeneous composition along the length of the hollow-ended particles, which is explained by preferential formation of the high entropy composition, SBN33, at the initial stages of particle nucleation and growth.

Hard carbon possesses the ability to store Li, Na, and K ions between stacked sp2 carbon layers and voids (micropores). We have explored hard carbon as a candidate for negative electrode materials ...

Zeolites are microporous aluminosilicate materials that have been used as industrial catalysts and adsorbents. The mechanism of formation of crystalline structures during the synthesis and the poss...

Magneli-phase Ti4O7, known for its high electrical conductivity and corrosion resistance, is typically prepared by hydrogen reduction at high temperatures (∼1000 °C), leading to large particles. Na...

Development of microporous materials, like zeolites and metal-organic frameworks (MOFs), with unique and better properties, is crucially important, while yet challenging, for many energy applications. Herein, we report on a new family of microporous hybrids having well-defined permanent porosity, which is formed by pillaring a layered silicate with packed coordination polymers. This inorganic-organic hybrid material, having well-defined/two-faced micropores surrounded by the polymers and silicate walls, exhibits superior adsorption toward methanol due to co-operative interactions compared with conventional microporous materials. The material could be used as an adsorbent to selectively and effectively recover methanol from a methanol/water vapour mixture.

To investigate local electron transfer in metal-organic frameworks (MOFs), we synthesized a new MOF structure composed of zinc cations and 1,4-naphthalenedicarboxylate (14ndc) linker anions. The cr...

In contrast to usual iron oxides, molecularly small iron oxides synthesized and stabilized on a porous silica scaffold exhibited an unprecedentedly high photocatalytic performance unrealized by previous photocatalysts like TiO2., Although iron oxides have been extensively studied as photocatalysts because of their abundance and environmental compatibility, their performance is notoriously low due to factors such as low photoinduced charge-separation efficiency. Iron oxides, thus, must be modified with expensive and/or toxic materials to attain higher performances, which devalues their appeal as sustainable materials. Here, we design an iron oxide exhibiting an unprecedentedly high photocatalytic performance unrealized by previous photocatalysts such as TiO2 for reactions including the selective oxidation of cyclohexane to industrial nylon precursors. The iron oxide photocatalyst consists of ferric dimers, otherwise extremely unstable, formed via etching of Fe and O sites from ferric oxide nanoparticles immobilized within porous silica. We demonstrate a remarkably high photoinduced charge-separation efficiency (long lifetime of active species) of the ferric dimers due to their electronic structure and the potential of this supported photocatalyst for many more reactions.

Sodium niobate (NaNbO3) attracts attention for its great potential in a variety of applications, for instance, due to its unique optical properties. Still, optimization of its synthetic procedures is hard due to the lack of understanding of the formation mechanism under hydrothermal conditions. Through in situ X-ray diffraction, hydrothermal synthesis of NaNbO3 was observed in real time, enabling the investigation of the reaction kinetics and mechanisms with respect to temperature and NaOH concentration and the resulting effect on the product crystallite size and structure. Several intermediate phases were observed, and the relationship between them, depending on temperature, time, and NaOH concentration, was established. The reaction mechanism involved a gradual change of the local structure of the solid Nb2O5 precursor upon suspending it in NaOH solutions. Heating gave a full transformation of the precursor to HNa7Nb6O19·15H2O, which destabilized before new polyoxoniobates appeared, whose structure depended on the NaOH concentration. Following these polyoxoniobates, Na2Nb2O6·H2O formed, which dehydrated at temperatures ≥285 °C, before converting to the final phase, NaNbO3. The total reaction rate increased with decreasing NaOH concentration and increasing temperature. Two distinctly different growth regimes for NaNbO3 were observed, depending on the observed phase evolution, for temperatures below and above ≈285 °C. Below this temperature, the growth of NaNbO3 was independent of the reaction temperature and the NaOH concentration, while for temperatures ≥285 °C, the temperature-dependent crystallite size showed the characteristics of a typical dissolution–precipitation mechanism., To understand the pathway from T-Nb2O5 to hydrothermally produced NaNbO3, the reaction was studied in situ with powder X-ray diffraction, small-angle scattering, and total scattering with pair-distribution function analysis. The full reaction scheme and kinetics were revealed, showing two different temperature-dependent growth mechanisms.

A new apparatus for total scattering measurements has been developed with a variable camera length using a 16-inch two-dimensional flat-panel detector to observe structural changes in amorphous and disordered crystalline materials substantially in real time on beamlines BL08W and BL04B2 at SPring-8. This paper presents the successful time-resolved pair distribution function analysis at SPring-8, and a newly developed program for data conversion from two-dimensional images into one-dimensional total scattering patterns., A dedicated apparatus has been developed for studying structural changes in amorphous and disordered crystalline materials substantially in real time. The apparatus, which can be set up on beamlines BL04B2 and BL08W at SPring-8, mainly consists of a large two-dimensional flat-panel detector and high-energy X-rays, enabling total scattering measurements to be carried out for time-resolved pair distribution function (PDF) analysis in the temperature range from room temperature to 873 K at pressures of up to 20 bar. For successful time-resolved analysis, a newly developed program was used that can monitor and process two-dimensional image data simultaneously with the data collection. The use of time-resolved hardware and software is of great importance for obtaining a detailed understanding of the structural changes in disordered materials, as exemplified by the results of commissioned measurements carried out on both beamlines. Benchmark results obtained using amorphous silica and demonstration results for the observation of sulfide glass crystallization upon annealing are introduced.

International audience; In order to develop stable non-platinum cathodes based on group 4 and 5 metal oxides, we investigated factors affecting the use of Nb2O5-doped TiO2 for the oxygen reduction reaction (ORR). Multi-walled carbon nanotubes (MWCNTs) were used as support to maintain sufficient electrical conductivity. Nb2O5-doped TiO2/MWCNTs prepared by hydrolysis was heat-treated at the desired temperature for a certain time under argon containing 4% hydrogen to investigate the relationship between ORR activity and physicochemical properties such as crystalline structure and electronic state. We confirmed that the density of the low-valence state of titanium ions, Ti3+, affected ORR activity. In addition, crystalline distortion of Nb2O5-doped anatase might be essential in order to show ORR activity.

Two-dimensional (2D) materials are widely investigated as electronic or catalytic materials as well as being conventionally used as adsorbents for accommodating guest molecules in the interlayer spaces. 2D coordination polymers have flexible structures, which are transformed even by a weak external stimulus such as a humidity change. Here we report a structural analysis and proton conductivity measurements of a 2D cyano-bridged coordination polymer of the Mn[Ni(CN)4] system upon dehydration and rehydration. The structure of the sample at high humidity was determined by single-crystal diffraction, while the structure at low humidity was solved by Rietveld analysis of synchrotron powder diffraction data. At high humidity, the material contains coordinated and non-coordinated water molecules as [Mn(H2O)2Ni(CN)4]·3H2O. These water molecules were further analyzed by TG-DTA and classified into three types: (i) two coordinated molecules, (ii) two weakly adsorbed non-coordinated molecules and (iii) a strongly adsorbed non-coordinated molecule. These water molecules play a key role in crystal structure transformation upon dehydration/hydration, where the two-dimensional coordination network is retained but the curvature changes by tilting of MnO6 octahedra owing to the change in hydrogen bonds between the water molecules. Because the water molecules form hydrogen bonding networks, proton conductivity was expected. Thus, we investigated the proton conductivity using the single-crystal AC impedance method and found that the crystals were insulating. This in turn suggests that the water molecules in the interlayer spaces do not dissociate into protons mostly, and the spaces are non-ionic.

Aqueous chemical solution deposition is a promising route for ferroelectric K0.5Na0.5NbO3 (KNN) thin films, requiring a stable precursor solution with complexed Nb5+. Here, we report on the local structure of Nb-complexes forming during synthesis of KNN using Nb5+ complexed with either oxalic or malic acid. In situ total X-ray scattering during the decomposition, pyrolysis and crystallization of KNN precursor powders using the two routes revealed information of the changes in the atomic bond distances during the thermal processing, and a reaction scheme was presented. The structures of the Nb-complexes were proposed based on cluster modelling. In situ X-ray diffraction demonstrated the crystallization of KNN thin films from the precursor solutions, revealing how the complexing agents affect the formation of crystalline KNN films. The structure of the Nb-complexes was found to influence the kinetics of the combustion of the organic part of the deposited films, which further determined the crystallization temperature.

Boron-based two-dimensional materials are of interest for use in electronic devices and catalytic applications, for which it is important that they are chemically stable. Here, we explore the chemical stability of hydrogen boride nanosheets in water. Experiments reveal that mixing hydrogen boride and water produces negligible amounts of hydrogen, suggesting that hydrolysis does not occur and that hydrogen boride is stable in water, which is in contrast to most boron hydride materials. First-principles calculations reveal that the sheets interact weakly with water even in the presence of defects and that negatively charged boron prevents the onset of hydrolysis. We conclude that the charge state of boron and the covalent boron-boron bond network are responsible for the chemical and structural stability. On the other hand, we found that proton exchange with hydrogen boride nanosheets does occur in water, indicating that they become acidic in the presence of water. Nanoscale boron-based materials are promising for electronic devices, and it is important to understand their chemical stability. Here, hydrogen boride nanosheets are stable against hydrolysis in water, which ab initio calculations attribute to the charge state of boron and the boron-boron bond network.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an average yield of 42.3% at room temperature. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair dist...

Titanium oxides crystals are widely used in a variety of fields, but little has been reported on the functionalities of noncrystalline intermediates formed in their structural transformation. We measured the oxygen reduction reaction activity of titanium oxide nanoparticles heat-treated for a different time and found that the activity abruptly increased at a certain time of the treatment. We analyzed their structures by using X-ray pair distribution functions with the help of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy and ascertained that the abrupt increase in the activity corresponded to a structural transformation from a reduced lepidocrocite-type layered titanate to a disordered structure consisting of domains of brookite-like TiO6 octahedral linkages. The further treatment transformed these brookite-like domains into another phase having more edge-sharing sites like the TiO-type cubic structure. This finding would position noncrystalline, disordered structure as a possible origin of the catalytic activity, though nanocrystalline rutile particles might be also considered as the origin.

We report a methodology for creating protonated layered titanate–rutile heterojunctions on the outer particle surface of protonated layered titanate by treating layered potassium titanate (K0.8Ti1.73Li0.27O4) with dilute HCl and then drying it at room temperature under reduced pressure. After Pt co-catalyst loading, this protonated layered titanate/rutile composite with heterojunctions showed higher photocatalytic H2 evolution activity from water under simulated solar light compared to that of Pt-loaded P25, the standard photocatalyst for this reaction. The high photocatalytic activity was ascribable to enhanced photocatalytic activity of the protonated layered titanate based on an efficient charge separation at the protonated layered titanate–rutile heterojunction in addition to the sensitization effects of rutile, which absorbs light with longer wavelengths compared to those of protonated layered titanate.

Amorphous solid dispersions (ASDs) play a key role in the pharmaceutical industry through the use of high-energy amorphous state to improve solubility of pharmaceutical agents. Understanding the physical stability of pharmaceutical glasses is of great importance for their successful development. We focused on the anti-HIV agent, ritonavir (RTV), and investigated the influence of annealing at temperatures below the glass transition temperature (sub-Tg) on physical stability, and found that the sub-Tg annealing effectively stabilized RTV glasses. Through the atomic structure analyses using X-ray pair distribution functions and infrared spectroscopy, we ascertained that this fascinating effect of the sub-Tg annealing originated from strengthened hydrogen bonding between molecules and probably from a better local packing associated with the stronger hydrogen bonds. The sub-Tg annealing is effective as a physical stabilization strategy for some pharmaceutical molecules, which have relatively large energy barri...

Magnéli-phase Ti

Bixbyite α-Mn2O3 is an inexpensive Earth-abundant mineral that can be used to drive both oxygen evolution (OER) and oxygen reduction reactions (ORR) in alkaline conditions. It possesses a subtle orthorhombic → cubic phase change near room temperature that suppresses Jahn–Teller distortions and presents a unique opportunity to study how atomic structure affects the electronic structure and catalytic activity at a temperature range that is easily accessible in OER/ORR experiments. Previously, we observed that heat-treated α-Mn2O3 had a better performance as a bifunctional catalyst in the oxygen evolution (OER) and oxygen reduction reactions (ORR) (Dalton Trans. 2016, 45, 18,494–18,501). We hypothesized that heat-treatment pinned the material into a more electrochemically active cubic phase. In this manuscript, we use high-resolution X-ray diffraction to collect the temperature-dependent structures of α-Mn2O3, and then input them into ab initio calculations. The electronic structure calculations indicate that the orthorhombic → cubic phase transition causes the Mn 3d and O 2p bands to overlap and mix covalently, transforming α-Mn2O3 from a semiconductor to a semimetal. This subtle change in structure also modifies Mn-O-Mn bond distances, which may improve the activity of the material in oxygen electrochemistry. OER and ORR experiments were performed using the same electrode at various temperatures. They show a jump in the exchange current density near the phase change temperature, demonstrating the higher activity of the cubic phase., GRAPHICAL ABSTRACT

The discovery of novel lightweight materials with metallic properties is important for future smart applications, and two-dimensional materials with metallic conductivity are quite rare in this regard. Herein, we report an electrically conductive two-dimensional hydrogen boride material (borophane) that was synthesized in powder form by an ion-exchange reaction. The produced freestanding borophane was amorphous by X-ray diffractometry and found to consist of curved layers of elongated hexagonal networks of boron and hydrogen atoms that bridge pairs of boron atoms with H/B ratio of 1.0. This hexagonal borophane exhibits metallic conduction with a conductivity of 0.13 S cm−1 at around room temperature, and a unique metal-to-insulator transition at around 30 °C.

Hybrid organic–inorganic metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of bulk metal halide perovskites has been widely studied, the properties of perovskite nanocrystals are less well-understood because synthesizing them is still very challenging, in part because of stability. Here we demonstrate a simple and versatile method to grow monodisperse CH3NH3PbBrxIx-3 perovskite nanocrystals inside mesoporous silica templates. The size of the nanocrystal is governed by the pore size of the templates (3.3, 3.7, 4.2, 6.2, and 7.1 nm). In-depth structural analysis shows that the nanocrystals maintain the perovskite crystal structure, but it is slightly distorted. Quantum confinement was observed by tuning the size of the particles via the template. This approach provides an additional route to tune the optical bandgap of the nanocrystal. The level of quantum confinement was modeled taking into account the dimensions of t...

The synthesis of a novel family of cyano-bridged trimetallic coordination polymers (CPs) with various compositions and shapes has been reported by changing the compositional ratios of Fe, Co, and Ni species in the reaction system. In order to efficiently control the nucleation rate and the crystal growth, trisodium citrate dihydrate plays an important role as a chelating agent. After the obtained cyano-bridged trimetallic CPs undergo thermal treatment in air at three different temperatures (250, 350, and 450 °C), nanoporous spinel metal oxides are successfully obtained. Interestingly, the obtained nanoporous metal oxides are composed of small crstalline grains, and the grains are oriented in the same direction, realizing pseudo-single crystals with nanopores. The resultant nanoporous spinel oxides feature interesting magnetic properties. Cyano-bridged multimetallic CPs with various sizes and shapes can provide a pathway toward functional nanoporous metal oxides that are not attainable from simple cyano-bridged CPs containing single metal ions.

Platinum nanoparticles with continuously tunable mesoporous structures were prepared by a simple, one-step polymeric approach. By virtue of their large pore size, these structures have a high surface area that is accessible to reagents. In the synthetic method, variation of the solvent composition plays an essential role in the systematic control of pore size and particle shape. The mesoporous Pt catalyst exhibited superior electrocatalytic activity for the methanol oxidation reaction compared to commercially available Pt catalysts. This polymeric-micelle approach provides an additional design concept for the creation of next generation of metallic catalysts.

Deposition of Ni-based cyanide bridged coordination polymer (NiCNNi) flakes onto the surfaces of graphene oxide (GO) sheets, which allows precise control of the resulting lamellar nanoarchitecture by in situ crystallization, is reported. GO sheets are utilized as nucleation sites that promote the optimized crystal growth of NiCNNi flakes. The NiCNNi-coated GO sheets then self-assemble and are stabilized as ordered lamellar nanomaterials. Regulated thermal treatment under nitrogen results in a Ni3 C-GO composite with a similar morphology to the starting material, and the Ni3 C-GO composite exhibits outstanding electrocatalytic activity and excellent durability for the oxygen reduction reaction.

Mesoporous Au films consisting of a network of interconnected Au ligaments around ultra-large pores were found to exhibit a promising electrocatalytic activity towards sluggish reactions. Mesoporous Au films with pore sizes up to 25 nm were successfully fabricated using a polymeric micelle approach. A superior catalytic activity of the mesoporous Au films towards methanol oxidation was confirmed, which was thoroughly analyzed and compared with that of other Au materials. An intrinsic investigation on the high catalytic activity revealed that the superior performance of the as-prepared mesoporous Au film was related to its unique atomic structures around the mesopores with well-crystallized facets and several step/kink sites on the Au surfaces. These findings showcase a strategic and feasible design for preparing highly active Au-based catalysts that could be used as promising candidates in electrocatalytic applications.

A novel strategy for large-scale synthesis of shape- and size-controlled mesoporous Pt nanospheres (MPNs) through a slow reduction reaction in the presence of surfactant is reported here for the first time. The slow reduction reaction exclusively results in well-defined mesoporous architectures distinctly different from the dendritic constructions reported previously. More importantly, abundant catalytically active sites are created on the highly accessible mesoporous surfaces by the selective adsorption of bromide ions. The MPNs prepared by using the new synthetic route not only show superior electrochemical performance toward methanol oxidation reaction and oxygen reduction reaction, but also exhibit extremely high structural thermostability, which makes them promising catalysts for industrial applications.

A mesostructured tin phosphate (SnPi) material has been prepared in the presence of an amphiphilic block copolymer (F127), tin chloride (SnCl4), and phosphoric acid (H3PO4) in an ethanol–water mixed solvent medium. The mesoporous SnPi material, with a large pore diameter (7.4 nm), nanocrystalline walls, a high surface area (310 m2 g−1), and a unique flake-like particle shape, is successfully synthesized by a two-step heat treatment of the parent mesostructured SnPi under flowing N2 gas followed by flowing air. Under moderate conditions (293 K and 60% relative humidity), our mesoporous SnPi shows 6.5 times more proton (H+) conductivity compared to its non-porous/bulk analogue (SnPi-B), due to its higher surface area and unique nanocrystalline porous structure enriched with free O–H groups. The preliminary electrochemical properties of our crystalline mesoporous SnPi as an anode for lithium-ion batteries (LIBs) have been studied as well, which exhibits good reversible specific capacity with good cycling stability and excellent capacity retention of 92%.

An oriented and controlled crystal growth of cyano-bridged coordination polymers is realized by a controlling agent (e.g., trisodium citrate dihydrate (TSCD)) as a reaction precursor. In the presence of TSCD, the reaction is slow as the complex appears to be more stable, leading to a preferentially oriented crystal growth. For instance, after mixing manganese acetate with TSCD, the formed Mn–citrate complex tends to release few Mn2+ ions steadily and slowly, which then react with the ligands at the initial stage of the reaction. Subsequently, the generated nuclei further grow from the interaction between the released Mn2+ and [Mn(CN)6]3−, [Co(CN)6]3−, or [Ru(CN)6]4− anions to form several types of cyano-bridged coordination polymers (abbreviated as MnCNMn, MnCNCo, or MnCNRu, respectively). After thermal treatment in air, the as-prepared coordination polymers can be decomposed into their corresponding nanoporous Mn-based oxides. Surprisingly, the electrochemical analysis reveals that the Mn–Ru oxide prepared from MnCNRu is a promising catalyst for the production of H2O2 by selectively catalyzing the oxygen reduction reaction (ORR) through an exact 2-electron pathway. Compared to previously reported materials, our electrocatalyst demonstrates an outstanding activity, a strict selectivity, and a long-term stability for the production of H2O2. The present catalyst design sheds new light on the production of H2O2 by a safe and sustainable way.

Synthesizing manganese oxide materials with exact control of the nanoparticle shape and phase is difficult, making it challenging to understand the influence of the surface structure on electrocatalysis. Here we describe an inexpensive, low-temperature method to synthesize single-crystal orthorhombic phase α-Mn2O3 prisms bound by the {100} facets. The synthesis is the first method to use the cation bridging effect to assist in the creation of α-Mn2O3 prisms. According to structural analysis using X-ray diffraction, X-ray pair-distribution function (PDF) measurements and high resolution transmission electron microscopy, the material is composed exclusively of α-Mn2O3 prisms, and no additional amorphous or nanocrystalline phases are present. Heating the prisms transformed the material to a more symmetrical, cubic phase α-Mn2O3 that exhibited strong bifunctional electrocatalytic activity for the oxygen evolution (OER) and oxygen reduction (ORR) reactions. We compared the oxygen electrode activities (OEA) and found that the α-Mn2O3 prisms performed 79% better than commercially-produced α-Mn2O3 powders, indicating that these α-Mn2O3 prisms perform well as inexpensive, earth-abundant materials for reversible electrodes.

The understanding of lithium–oxygen coordination systems is important for making better lithium conductors as well as active materials for lithium ion batteries. Here, we report a systematic investigation on coordination environments in lithium coordination polymers (LCPs) through the syntheses and analyses of six new crystals composed of lithium ions and anthraquinone (aq) derivative anions, where the negative charges are distributed in π-conjugation systems. Their structures were determined by single-crystal X-ray diffraction to be (1) [Li2(23dcaq)(H2O)] in space group P21/c, (2) [Li(23dcaqH)] in P21/c, (3) [Li2(15dhaq)(H2O)2] in P21/c, (4) [Li2(14dhaq)(H2O)2] in Pnma, (5) [Li(14dhaqH)(H2O)] in P212121 and (6) [Li(14hnaq)(H2O)] in P212121 (23dcaq2− = 2,3-dicarboxy-aq, 14dhaq2− = 1,4-dihydroxy-aq, 15dhaq2− = 1,5-dihydroxy-aq and 14hnaq− = 1-hydroxy-4-nitro-aq). Through the comprehensive structure analysis of these materials as well as other LCPs, we found that when considering the longest C–O bond in the π-conjugation system of an anionic organic molecule and its coordination to a Li ion, there is a weak inverse relationship between the C–O and Li–O bond lengths. In addition, despite exhibiting optical band edges below 2 eV and 1D π-stacking connectivity, conductivity measurements on single crystals of 1–6 confirmed that they are all electronic insulators. We rationalize this finding on the basis of π-orbital delocalization, which is more restricted in the aq-based LCPs compared to known semiconducting hybrid materials.

Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction. The synthetic trends were investigated using high-throughput synthesis under systematic variation of concentration and reagent stoichiometry: for complexes containing Co, Ni or Cu crystallisation was improved by low ligand : metal ratios, while the effect of concentration depended on the metal used. The compounds crystallise as discrete clusters, apart from two, which contain long Cu–O bonds which may allow the two compounds to be considered one-dimensional coordination polymers. One of these compounds shows a distance between aryl rings of less than 3.26 A, which is shorter than that in graphite, suggesting applications as an organic–inorganic semiconductor. The compound was found to be insulating by single-crystal and powder AC-impedance measurements, and this result is discussed with reference to the electronic structure calculated using density-functional theory.

Hitherto, many reports on composite materials for electrochemical applications are based on one-dimensional carbon nanotubes or two-dimensional graphene materials. However, these composite materials usually suffer from a stacking problem during electrochemical cycling. A smart nanoarchitectural design is needed for composite materials in order to overcome this problem. Recent research on electrochemical energy storage (EES) applications has focused on the development of three-dimensional (3-D) core–shell structures. The basis for high performance electrochemical energy storage is to control the efficient intercalation of ions in such a 3-D structure. Here, we demonstrate controlled synergy between the physicochemical properties of nanoporous carbon and conducting polyaniline polymer (carbon–PANI), which leads to some new interesting electrochemical properties. The time-dependent controlled optimization of the core–shell nanocomposites consisting of nanoporous carbon with a thin layer of PANI nanorod arrays gives useful control over supercapacitor performance. Furthermore, these carbon–PANI nanocomposites can electrochemically access ions with remarkable efficiency to achieve a capacitance value in the range of 300–1100 F g−1. When assembled in a two electrode cell configuration, the symmetric supercapacitor (SSC) based on carbon–PANI//carbon–PANI shows the highest specific energy of 21 W h kg−1 and the highest specific power of 12 kW kg−1. More interestingly, the SSC shows capacitance retention of 86% after 20 000 cycles, which is highly superior compared to previous research reports.