Hidetsugu Shiozawa

Rechargeable batteries predominantly rely on cation intercalation or metal conversion reactions, which often suffer from structural degradation, limited reversibility, and safety concerns. We report a symmetric halide-ion battery based on a bipolar redox metal-organic framework (MOF), in which energy storage is governed by reversible intraframework halogenation rather than metal--halide conversion chemistry. The bipolar redox chemistry of the μ ₃ -oxo-bridged trinuclear copper centres in the MOF enables reversible halogenation and dehalogenation, allowing identical electrodes consisting of MOF microcrystals embedded within binder-free carbon nanotube (CNT) films to function as either cathode or anode depending on the halide species involved. Operando Raman spectroelectrochemistry reveals the underlying redox mechanism, while density-functional theory (DFT) suggests a thermodynamic preference for bromination over chlorination, rationalising the framework's dual functionality. In a symmetric configuration using a mixture of chloride- and bromide-based neat ionic liquids, the cell reaches a specific capacity of 68.7 mAh g ^-1 and an energy density of 35.4 Wh kg ^-1 under extended charging conditions. The cell operates for more than 200 charge--discharge cycles under repeated short-charge cycling. This non-flammable, moisture-resistant system composed entirely of earth-abundant elements highlights the potential of redox-active MOFs for alternative battery chemistries.

This study presents the synthesis, structural characterization and magnetic properties of a one-dimensional coordination polymer composed of copper(II) chloride and 1H-1,2,4-triazole. Crystals of the coordination polymer were synthesized in hydrochloric acid at room temperature. Single crystal X-ray diffraction reveals an array of copper atoms bridged by two chloride ions and a triazole ligand. Magnetization data on a single crystal show no hysteresis but deviate from the curves derived from the Ising Hamiltonian at low temperature, indicating the presence of antisymmetric exchange. This study highlights the importance of synthesizing large crystals of coordination polymers to facilitate detailed investigations into their magnetic properties.

Contemporary thermoelectric devices are typically made from inorganic chalogenides, which are expensive, inflexible, toxic, brittle, and difficult to recycle. These limitations have hindered their widespread application as energy scavengers in heat engines. By contrast, organic semiconductor polymers such as poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are inexpensive, nontoxic, flexible, easy to process, and sustainable. However, their thermopower is around three orders of magnitude lower than that of the inorganic tellurides. Here, we report a facile fabrication framework based on producing metal/polymer superlattice structures. These form extended 2‐dimensional delocalized systems that exhibit enhanced thermoelectric performance. Within this framework, we report a power factor of 2800 µW m ⁻¹ K ⁻² , two orders of magnitude greater than that of pristine PEDOT:PSS and only around 1.5 times lower than that of the telluride materials. This represents a significant improvement. We also report that using Fe and Cr in the superlattice results in changing the semiconductor doping type from P‐type to N‐type. Structural, spectroscopic, and electrical analysis reveal modifications to the band structure resulting from these doping changes. These observations were corroborated using density functional modeling. The results also show the metal layers introduce solid–solid dedoping effects to the PEDOT:PSS via a carrier transfer mechanism, resulting in significantly improved thermoelectric performance.

A dimer of pentacyanopropenide encapsulated in a single crystal of melamine exhibits strong fluorescence emission in the visible range.

Utilizing biowaste to generate precious carbon-based electrodes offers a sustainable and cost-effective approach to advanced energy storage technologies while addressing environmental and waste management issues. In contrast to dry pyrolysis, ionic liquid-assisted hydrothermal carbonization of biomass to produce functional carbon materials has garnered significant attention due to the catalytic carbonization effects and simultaneous tuning of carbon chemistry by the inorganic salt. Herein, we report the carbonization of spruce cone biowaste in the presence of an ionic liquid i.e., 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl₄]). The obtained nanospheres of hydrochar were further heat-treated and modified with ceria (CeO₂) (denoted as Ce-IHSC-x). Experimental results showed the post-heat treatment increased the degree of graphenization and specific surface area (SSA) of hydrochar, while ceria nanoparticles along with contributing to redox active sites, help to preserve the mesoporosity in hydrochar materials. Simultaneously, [Bmim]⁺ and [FeCl₄]⁻ ions from ionic liquids induced Fe and N-species in the hydrochar matrix during the carbonization process, further enhancing the functionality of hydrochar. The Ce-IHSC-x materials exhibited a synergistic combination of high SSA, a well-tuned meso- and microporous structure, and a nitrogen-doped conductive interface. This unique architecture enabled efficient multi-dimensional ion and electron transport during charge–discharge processes. As a result, the optimized Ce-IHSC-x electrode demonstrated a high specific capacitance of 992.7 F g⁻¹ at 0.5 A g⁻¹ and 752.7 F g⁻¹ at 9 A g⁻¹, outperforming many biomass-derived carbon materials. In addition, Ce-IHSC-x adhered good tolerance to long-term cycling with 98.8% and 95.2% retention of coulombic efficiency and specific capacitance after 7000 GCD cycles. This work further highlights the versatility of this carbonization approach combined with redox-active modification, showcasing its effectiveness in enhancing the electrochemical performance of biomass-derived supercapacitor electrodes.

The global renewable energy industry awaits new battery technologies that power the future. Here we conceptualize and fabricate a halogen-ion battery that is charged up via halogenation of a water-stable metal-organic framework (MOF) made of trinuclear copper and triazole. A battery cell uses a pure imidazolium ionic liquid electrolyte, and binder-free carbon nanotube electrodes, one of which accommodates microcrystals of the MOF. It offers redox potentials greater than 0.6 V, energy densities and specific capacitances as high as 7 Wh/kg and 10 mAh/g, respectively, with an excellent cyclic stability over 100 cycles, that are sufficient for practical applications. Spectroelectrochemistry reveals the redox states responsible for the energy storage. This rechargeable battery is non-flammable and moisture resistant, as well as all elements used are abundant, hence it is a promising alternative to some of the existing batteries.

Aggregation-induced optical properties of molecules are at the forefront of materials sciences. Here, tetracyanoethylene (TCNE) is reacted and encapsulated in melamine. Crystallization in aqueous tetrahydrofuran solutions of melamine and TCNE at different concentrations yields colorful crystals with fluorescence emission at multiple wavelengths. Combined infrared spectroscopy and mass spectrometry reveal that the crystals are melamine doped with a trace amount of 1,1,2,3,3,-pentacyanopropenide. The fluorescence excitation-emission spectral mapping elucidates concentration dependences of the fluorescence emission in both precursor solutions and crystals. Based on density functional theory calculations the multi-wavelength emissions can be attributed to aggregates of the pentacyanopropenide. Highly stable doped melamines have the potential as multifunctional optical materials in optielectronics.

The present work reports the synthesis, structure, and magnetic properties of a one-dimensional coordination polymer made of copper(II) chloride and 1,2,4- triazole. The coordination polymer is synthesized in hydrochloric acid at room temperature. The structure determination by single crystal X-ray diffraction reveals an array of copper atoms bridged via two chlorine and a triazole. Magnetisation data show no hysteresis at temperatures down to 2 K, but suggest antisymmetric exchange and antiferromagnetic coupling between the neighbouring spins of Cu(II) ions. This work gives impetus for the synthesis of large crystals of coordination polymers based on which magnetic properties can be studied in depth.