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Vasculature-on-a-chip is a microfluidic cell culture device used for modeling vascular functions by culturing endothelial cells. Porous membranes are widely used to create cell culture environments. However, in situ real-time measurements of cellular metabolites in microchannels are challenging. In this study, a novel microfluidic device with a porous membrane electrode was developed for the in situ monitoring of nitric oxide (NO) released by endothelial cells in real time. In this system, a porous Au membrane electrode was placed directly beneath the cells for in situ and real-time measurements of NO, a biomarker of endothelial cells. First, the device was electrochemically characterized to construct a calibration plot for NO. Next, NO released by human umbilical vein endothelial cells under l-arginine stimulation was successfully quantified. Furthermore, the changes in NO release with culture time (in days) using the same sample were successfully recorded by exploiting minimally invasive measurements. This is the first report on the combination of a microfluidic device and porous membrane electrode for the electrochemical analysis of endothelial cells. This device will contribute to the development of organ-on-a-chip technology for real-time in situ cell analyses.

We report the synthesis, characterization, and electronic properties of the quinoid-based three-dimensional metal-organic framework [Fe 2 (dhbq) 3 ]. The MOF was synthesized without using cations as a template, unlike other reported X 2 dhbq 3 -based coordination polymers, and the crystal structure was determined by using single-crystal X-ray diffraction. The crystal structure was entirely different from the other reported [Fe 2 (X 2 dhbq 3 )] 2- ; three independent 3D polymers were interpenetrated to give the overall structure. The absence of cations led to a microporous structure, investigated by N 2 adsorption isotherms. Temperature dependence of electrical conductivity data revealed that it exhibited a relatively high electrical conductivity of 1.2 × 10 -2 S cm -1 ( E a = 212 meV) due to extended d-π conjugation in a three-dimensional network. Thermoelectromotive force measurement revealed that it is an n-type semiconductor with electrons as the majority of charge carriers. Structural characterization and spectroscopic analyses, including SXRD, Mössbauer, UV-vis-NIR, IR, and XANES measurements, evidenced the occurrence of no mixed valency based on the metal and the ligand. [Fe 2 (dhbq) 3 ] upon incorporating as a cathode material for lithium-ion batteries engendered an initial discharge capacity of 322 mAh/g.

Magnesium rechargeable batteries (MRBs) promise to be the next post lithium-ion batteries that can help meet the increasing demand for high-energy, cost-effective, high-safety energy storage devices. Early prototype MRBs that use molybdenum-sulfide cathodes have low terminal voltages, requiring the development of oxide-based cathodes capable of overcoming the sulfide's low Mg 2+ conductivity. Here, we fabricate an ultraporous (>500 m 2 g -1 ) and ultrasmall (<2.5 nm) cubic spinel MgMn 2 O 4 (MMO) by a freeze-dry assisted room-temperature alcohol reduction process. While the as-fabricated MMO exhibits a discharge capacity of 160 mAh g -1 , the removal of its surface hydroxy groups by heat-treatment activates it without structural change, improving its discharge capacity to 270 mAh g -1 ─the theoretical capacity at room temperature. These results are made possible by the ultraporous, ultrasmall particles that stabilize the metastable cubic spinel phase, promoting both the Mg 2+ insertion/deintercalation in the MMO and the reversible transformation between the cubic spinel and cubic rock-salt phases.

Endothelial cells have been widely used for vascular biology studies; recent progress in tissue engineering have offered three-dimensional (3D) culture systems for vascular endothelial cells which can be considered as physiologically relevant models. To facilitate the studies, we developed an electrochemical device to detect nitric oxide (NO), a key molecule in the vasculature, for the evaluation of 3D cultured endothelial cells. Using an NO-sensitive catalyst composed of Fe-N co-doped reduced graphene oxide, the real-time monitoring of NO release from the endothelial cell spheroids was demonstrated., (© 2022. The Author(s), under exclusive licence to The Japan Society for Analytical Chemistry.)

Increasing mass loadings of battery electrodes critically enhances the energy density of an overall battery by eliminating much of the inactive components, while compacting the battery size and lowering the costs of the ingredients. A hard carbon microlattice, digitally designed and fabricated by stereolithography 3D-printing and pyrolysis, offers enormous potential for high-mass-loading electrodes. In this work, sodium-ion batteries using hard carbon microlattices produced by an inexpensive 3D printer are demonstrated. Controlled periodic carbon microlattices are created with enhanced ion transport through microchannels. Carbon microlattices with a beam width of 32.8 µm reach a record-high areal capacity of 21.3 mAh cm -2 at a loading of 98 mg cm -2 without degrading performance, which is much higher than the conventional monolithic electrodes (≈5.2 mAh cm -2 at 92 mg cm -2 ). Furthermore, binder-free, pure-carbon elements of microlattices enable the tracking of structural changes in hard carbon that support the hypothesized intercalation of ions at plateau regions by temporal ex situ X-ray diffraction measurements. These results will advance the development of high-performance and low-cost anodes for sodium-ion batteries as well as help with understanding the mechanisms of ion intercalations in hard carbon, expanding the utilities of 3D-printed carbon architectures in both applications and fundamental studies., (© 2022 Wiley-VCH GmbH.)

The electrochemical CO 2 reduction reaction (CO 2 RR) activity of Ni 2 MnIn and Ni 2 MnSn Heusler alloys was investigated. Although pure In, Sn and Ni 2 MnIn generated formate as the major product, Ni 2 MnSn generated H 2 as the major product. The CO 2 RR selectivity could be controlled by selecting the constituent elements of the intermetallic catalysts.

While organic batteries have attracted great attention due to their high theoretical capacities, high-voltage organic active materials (> 4 V vs Li/Li + ) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium-ion battery cathode material in both dimethyl sulfoxide and γ-butyrolactone (GBL) electrolytes. DFT calculations demonstrate that CA dilitium salt (CA-Li 2 ) has two enolate groups that undergo redox reactions above 4.0 V and a material-level theoretical energy density of 1949 Wh kg -1 for storing four lithium ions in GBL-exceeding the value of both conventional inorganic and known organic cathode materials. Cyclic-voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. Battery-performance tests of CA as lithium-ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g -1 with no capacity loss after five cycles. With the higher discharge voltages compared to the known, state-of-the-art organic small molecules, CA promises to be a prime cathode-material candidate for future high-energy-density lithium-ion organic batteries., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Inexpensive, high-performing, and environmentally friendly energy storage devices are required for smart grids that efficiently utilize renewable energy. Energy storage devices consisting of organic active materials are promising because organic materials, especially quinones, are ubiquitous and usually do not require harsh conditions for synthesis, releasing less CO 2 during mass production. Although fundamental research-scale aqueous quinone-based organic supercapacitors have shown excellent energy storage performance, no practical research has been conducted. In this study, we aimed to develop a practical-scale aqueous-quinone-based organic supercapacitor. By connecting 12 cells of size 10 cm × 10 cm × 0.5 cm each in series, we fabricated a high-voltage (> 6 V) aqueous organic supercapacitor that can charge a smartphone at a 1 C rate. This is the first step in commercializing aqueous organic supercapacitors that could solve environmental problems, such as high CO 2 emissions, air pollution by toxic metals, and limited electricity generation by renewable resources., (© 2022. The Author(s).)

Electrochemical CO 2 reduction (CO 2 RR) is a key technology to convert greenhouse gas CO 2 to value-added products, such as CO and formic acid (HCOOH). In the present study, two-dimensional Cu- and Al-based layered double hydroxides (Cu-Al/LDHs) were applied as CO 2 RR catalysts. The catalysts were synthesized using a simple co-precipitation method employing sodium carbonate solutions with different pH and synthesis temperatures. The elemental ratio of Cu and Al, and sheet size were controlled. The most active Cu-Al/LDH showed a faradaic efficiency for CO generation of 42 % and one for formate generation of 22 % at the current density of 50 mA using a gas diffusion electrode system under galvanostatic conditions. Our result indicates that the sheet size of the LDH sheet is a critical parameter for determining CO 2 RR activity., (© 2021 Wiley-VCH GmbH.)

3D printing technologies have been adapted to enable the fabrication of lithium-ion batteries (LIBs), allowing flexible designs such as micro-scale 3D shapes. Here, we demonstrate 3D-printable gel electrolytes, printed at room temperature. The electrolyte gel solidified by UV irradiation maintains its structural integrity and high lithium-ion conductivity, enabling fully 3D-printed quasi-solid-state LIBs.

To enhance the oxygen evolution reaction mass activity of cobalt-manganese layered oxide (CMO), we develop a one-pot synthetic process to anchor CMO onto graphene sheets (CMO/G). Its mass activity is 66-fold higher than that of physically mixed bare CMO with graphene and even better than those of previously reported graphene-supported first-row transition metal oxide-based electrocatalysts. The remarkable mass activity is attributed to the excellent intrinsic activity of CMO, small and well-dispersed CMO nanosheets on graphene sheets and hydrophilized graphene due to the synthetic process. Furthermore, CMO/G exhibits excellent stability.

Redox-active metal-organic frameworks (MOFs) have great potential for use as cathode materials in lithium-ion batteries (LIBs) with large capacities because the organic ligands can undergo multiple-electron redox processes. However, most MOFs are electrical insulators, limiting their application as electrode materials. Here, we report an electron-conductive MOF with a 2,5-dihydroxy-1,4-benzoquinone (dhbq) ligand, Fe(dhbq). This compound had an electrical conductivity of 5 × 10 -6 S cm -1 at room temperature due to d-π interactions between the Fe ion and the ligand and the permanent microporosity. Fe(dhbq) had an initial discharge capacity of 264 mA h g -1 , corresponding to the two-electron redox process of dhbq.

The electroreduction of carbon dioxide is considered a key reaction for the valorization of CO 2 emitted in industrial processes or even present in the environment. Cobalt-nitrogen co-doped carbon materials featuring atomically dispersed Co-N sites have been shown to display superior activities and selectivities for the reduction of carbon dioxide to CO, which, in combination with H 2 (i.e., as syngas), is regarded as an added-value CO 2 -reduction product. Such catalysts can be synthesized using heat treatment steps that imply the carbonization of Co-N-containing precursors, but the detailed effects of the synthesis conditions and corresponding materials' composition on their catalytic activities have not been rigorously studied. To this end, in the present work, we synthesized cobalt-nitrogen co-doped carbon materials with different heat treatment temperatures and studied the relation among their surface- and Co-speciation and their CO 2 -to-CO electroreduction activity. Our results reveal that atomically dispersed cobalt-nitrogen sites are responsible for CO generation while suggesting that this CO-selectivity improves when these atomic Co-N centers are hosted in the carbon layers that cover the Co nanoparticles featured in the catalysts synthesized at higher heat treatment temperatures.

Hard carbon (HC) is the most promising candidate for sodium-ion battery anode materials. Several material properties such as intensity ratio of the Raman spectrum, lateral size of HC crystallite (L a ), and interlayer distance (d 002 ) have been discussed as factors affecting anode performance. However, these factors do not reflect the bulk property of the Na + intercalation reaction directly, since Raman analysis has high surface sensitivity and L a and d 002 provide only one-dimensional crystalline information. Herein, it was proposed that the crystallite interlayer area (A i ) defined using L a , d 002 , and stacking height (L c ) governs Na + intercalation behavior of various HCs. It was revealed that various wood-derived HCs exhibited the similar total capacity of approximately 250 mAh g -1 , whereas the Na + intercalation capacity (C i ) was proportional to A i with the correlation coefficient of R 2 =0.94. The evaluation factor of A i was also adaptable to previous reports and strongly correlated with their C i , indicating that A i is more widely adaptable than the conventional evaluation methods., (© 2020 Wiley-VCH GmbH.)

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the most critical reactions that limit the efficiency of fuel cells, water electrolyzers, and metal-air batteries. Therefore, a need exists to develop cost-effective and highly active alternative electrocatalysts for ORR and OER. This study investigates the influence of metal coordination fashion on electrocatalytic ORR and OER activities among three types of Co-Mn bimetallic oxides (CMOs): tunnel-type (CMO&#95;T), layer-type (CMO&#95;L), and spinel-type (CMO&#95;S) structures. An electrochemical evaluation for CMOs verifies that CMO&#95;L has the highest ORR and OER specific activities, which is relatively better than the previously reported bifunctional metal oxides. Additionally, atomic configuration analysis for the oxides suggests that the excellent ORR and OER activities of CMO&#95;L result from the difference in Co and Mn coordination states. This paper not only presents an excellent electrocatalyst for alkaline fuel cells and water electrolyzers but also provides an important guideline for the design of oxygen electrocatalysts., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Multielectron reaction electrode materials using partial oxygen redox can be potentially used as cathodes in lithium-ion batteries, as they offer numerous advantages, including high reversible capacity and energy density and low cost. Here, a reversible three-electron reaction is demonstrated utilizing topotactic phase transition between antifluorite and rocksalt in a cation-disordered antifluorite-type cubic Li 6 CoO 4 cathode. This cubic phase is synthesized by a simple mechanochemical treatment of conventionally prepared tetragonal Li 6 CoO 4 . It displays a reversible capacity of 487 mAh g -1 , a high value because of a reversible three-electron reaction using Co 2+ /Co 3+ , Co 3+ /Co 4+ , and O 2- /O 2 2- redox, occurring without O 2 gas evolution. The mechanochemical treatment is assumed to reduce its lattice distortion by cation-disordering and facilitate a reversible topotactic phase transition between antifluorite and rocksalt structures via a dynamic cation pushing mechanism.

Molybdenum disulfide (MoS2), an attractive material for energy conversion devices, is known to exhibit varying properties depending on the number of layers and the phase structure. In this study, we developed a supercritical hydrothermal process that allows the controllable synthesis of MoS2 nanosheets with various structural and morphological characteristics. Detailed characterization of the synthesized materials confirmed that the number of layers in the MoS2 nanosheets could be controlled by varying the organic reducing agent under supercritical hydrothermal conditions. In addition, the MoS2 phase could be controlled kinetically by varying the reaction time with ascorbic acid as the reducing agent. Because water and elemental sulfur were respectively used as the solvent and sulfur source and as the reaction time was minimal, the developed hydrothermal process represents a facile processing method for different types of MoS2 nanosheets.

In recent years, organic electrode materials have been strongly considered for use in sustainable batteries. However, most organic electrode materials have low electrical conductivity and require a lot of conductive additives, which decrease the effective capacity based on the entire electrode weight/volume. In this study, we propose a novel electrical conductivity-relay system that imparts electrical conductivity to organic small molecular electrodes without any conductive additive throughout the charge/discharge cycles. It consists of the combination of the charge-transfer phenomenon in a pristine state and the formation of organic radical salts in redox states. Herein, we demonstrate this electrical conductivity-relay system using a simply mixed molecular crystal couple of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) as a cathode without any conductive additive and aqueous sodium bromide as an electrolyte. During charge/discharge, the electrical conductivity of the cathode is supported by charge-transfer at the TTF/TCNQ interface and (TTF)Br n (0.7 ≤ n ≤ 0.8) and NaTCNQ radical salts, and the cathode exhibits a specific capacity of 112 mAh g -1 and a retention rate of 80.7% at the 30th cycle. Furthermore, the molecular crystal couple electrode of TTF and TCNQ shows better charge/discharge performance than the pure charge-transfer complex electrode, indicating that this system expands candidates for organic electrode materials to various pairs and mixing ratios of small molecules that do not form charge-transfer complexes.

Magnesium metal complex oxides are potential electrode materials for magnesium ion batteries with high specific capacities. However, the strong electrostatic interaction between Mg 2+ and the host lattice due to its divalency induces slow intercalation kinetics of Mg ions within the crystal lattices. Thus, nanocrystalline particles with shortened Mg ion diffusion distance enable the insertion/extraction of Mg ions and improve the specific capacities of the batteries. Herein, we report the facile rapid production of crystalline MgCo 2 O 4 and Mg 2/3 Ni 4/3 O 2 nanocrystals by rapid supercritical fluid processing. The phase transition from spinel to rocksalt during the Mg 2+ ion intercalation has been confirmed by high-resolution transmission electron microscopy. The nanosheets of Mg 2/3 Ni 4/3 O 2 rocksalt nanocrystals were controllably synthesized for the first time, which are active materials for magnesium-ion batteries., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Reducing the particle size of cathode materials is effective to improve the rate capability of Mg-ion batteries. In this study, ultrasmall cubic Mg-Mn spinel oxide nanoparticles approximately 5 nm in size were successfully synthesized via an alcohol reduction process within 30 min at room temperature. Though the particles aggregated to form large secondary particles, the aggregation could be suppressed by covering the particles with graphene. The composite exhibited a specific capacity of 230 mA h g -1 , and could be cycled more than 100 times without any large capacity loss even at a moderate current density with the Mg(ClO 4 ) 2 /CH 3 CN electrolyte., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

This study presents a simple one-pot synthesis method to achieve few-layered and defective Mo(S,Se) 2 and (Mo,W)S 2 by using supercritical water with organic reducing agents from simple and less-toxic precursors. This synthesis process is expected to be suitable for preparing other various kinds of TMD solid solutions., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Structural defects, including point defects, dislocation and planar defects, significantly affect the physical and chemical properties of low-dimensional materials, such as layered compounds. In particular, inversion domain boundary is an intrinsic defect surrounded by a 60° grain boundary, which significantly influences electronic transport properties. We study atomic structures of the inversion domain grain boundaries (IDBs) in layered transition metal dichalcogenides (MoSe 2 and MoS 2 ) obtained by an exfoliation method, based on the aberration-corrected scanning transmission electron microscopy observation and density functional theory (DFT) calculation. The atomic-scale observation shows that the grain boundaries consist of two different types of 4-fold ring point shared and 8-fold ring edge shared chains. The results of DFT calculations indicate that the inversion domain grain boundary behaves as a metallic one-dimensional chain embedded in the semiconducting MoSe 2 matrix with the occurrence of a new state within the band gap., Competing Interests: There is no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Thin film of amorphous tungsten-doped cobalt oxide (W:CoO) was successfully grown on a conducting electrode via an electrochemical oxidation process employing a [Co(WS 4 ) 2 ] 2- deposition bath. The W:CoO catalyst displays an attractive performance for the oxygen evolution reaction in an alkaline solution. In an NaOH solution of pH 13, W:CoO operates with a moderate onset overpotential of 230 mV and requires 320 mV overpotential to generate a catalytic current density of 10 mA cm -2 . A low Tafel slope of 45 mV decade -1 was determined, indicating a rapid O 2 -evolving kinetics. The as-prepared W:CoO belongs to the best cobalt oxide-based catalysts ever reported for the oxygen evolution (OER) reaction., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO) 6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm 2 . Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.

Top-down graphene production via exfoliation from graphite produces a mass of graphene with structural variation in terms of the number of layers, sheet size, edge type, and defect density. All of these characteristics affect its electronic structure. To develop useful applications of graphene, structural separation of graphene is necessary. In this study, we investigate the adsorption behavior of different types of graphene fragments using a multicolumn gel chromatography system with a view to developing an efficient method for separating high-quality graphene. The graphene was dispersed in an aqueous sodium dodecyl sulfate (SDS) surfactant solution and flown through allyl-dextran-based gel columns connected in series. In the chromatographic operation, we observed that the small-sized or oxidized graphene fragments tended to bind to the gel and the relatively large-sized graphene with a low oxygen content eluted from the gel column. In this system, the adsorbed SDS molecules on the graphitic surface prevented graphitic materials from binding to the gel and the oxygen functional groups on the graphene oxide or at the abundant edge of small-sized graphene hindered SDS adsorption. We hypothesize that the reduced SDS adsorption density results in the preferential adsorption of small-sized or oxidized graphene fragments on the gel. This type of chromatographic separation is a cost-effective and scalable method for sorting nanomaterials. The structural separation of graphene based on the adsorption priority found in this study will improve the quality of graphene nanosheets on an industrial scale.

The ultrathin two-dimensional nanosheets of layered transition-metal dichalcogenides (TMDs) have attracted great interest as an important class of materials for fundamental research and technological applications. Solution-phase processes are highly desirable to produce a large amount of TMD nanosheets for applications in energy conversion and energy storage such as catalysis, electronics, rechargeable batteries, and capacitors. Here, we report a rapid exfoliation by supercritical fluid processing for the production of MoS 2 and MoSe 2 nanosheets. Atomic-resolution high-angle annular dark-field imaging reveals high-quality exfoliated MoS 2 and MoSe 2 nanosheets with hexagonal structures, which retain their 2H stacking sequence. The obtained nanosheets were tested for their electrochemical performance in a hybrid Mg-Li-ion battery as a proof of functionality. The MoS 2 and MoSe 2 nanosheets exhibited the specific capacities of 81 and 55 mA h g -1 , respectively, at a current rate of 20 mA g -1 ., Competing Interests: The authors declare no competing financial interest.

Exploring novel electrode materials is critical for the development of a next-generation rechargeable magnesium battery with high volumetric capacity. Here, we showed that a distinct amorphous molybdenum sulfide, being a coordination polymer of disulfide-bridged (Mo3S11) clusters, has great potential as a rechargeable magnesium battery cathode. This material provided good reversible capacity, attributed to its unique structure with high flexibility and capability of deformation upon Mg insertion. Free-terminal disulfide moiety may act as the active site for reversible insertion and extraction of magnesium.

Molybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete [Mo3S13](2-) building blocks. Of the three terminal disulfide (S2(2-)) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum.

Structural studies of high voltage cathode materials are necessary to understand their chemistry to improve the electrochemical performance for applications in lithium ion batteries. LiNiPO4 nanorods and nanoplates are synthesized via a one pot synthesis using supercritical fluid process at 450 °C for 10 min. The X-ray diffraction (XRD) analysis confirmed that LiNiPO4 phase is well crystallized, phase purity supported by energy dispersive spectroscopy (EDS) and elemental mapping by scanning electron transmission electron microscopy (STEM). For the first time, we have carried out direct visualization of atom-by-atom structural observation of LiNiPO4 nanomaterials using high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) analysis. The Rietveld refinement analysis was performed to find out the percentage of antisite defects presents in LiNiPO4 nanoplates and about 11% of antisite defects were found. Here, we provide the direct evidence for the presence of Ni atoms in Li sites and Li in Ni sites as an antisite defects are provided for understanding of electrochemical behavior of high voltage Li ion battery cathode materials.

The development of high energy-density lithium-ion secondary batteries as storage batteries in vehicles is attracting increasing attention. In this study, high-voltage bipolar stacked batteries with a quasi-solid-state electrolyte containing a Li-Glyme complex were prepared, and the performance of the device was evaluated. Via the successful production of double-layered and triple-layered high-voltage devices, it was confirmed that these stacked batteries operated properly without any internal short-circuits of a single cell within the package: Their plateau potentials (6.7 and 10.0 V, respectively) were two and three times that (3.4 V) of the single-layered device, respectively. Further, the double-layered device showed a capacity retention of 99% on the 200th cycle at 0.5 C, which is an indication of good cycling properties. These results suggest that bipolar stacked batteries with a quasi-solid-state electrolyte containing a Li-Glyme complex could readily produce a high voltage of 10 V.

Atomic-resolution imaging of the crystal defects of cathode materials is crucial to understand their formation and the correlation between the structure, electrical properties, and electrode performance in rechargeable batteries. The polytype, a stable form of varied crystal structure with uniform chemical composition, holds promise to engineer electronic band structure in nanoscale homojunctions.1-3 Analyzing the exact sites of atoms and the chemistry of the boundary in polytypes would advance our understanding of their formation and properties. Herein, the polytype and stacking faults in the lithium cobalt silicates are observed directly by aberration-corrected scanning transmission electron microscopy. The atomic-scale imaging allows clarification that the polytype is formed by stacking of two different close-packed crystal planes in three-dimensional space. The formation of the polytype was induced by Li-Co cation exchange, the transformation of one phase to the other, and their stacking. This finding provides insight into intrinsic structural defects in an important Li2 CoSiO4 Li-ion battery cathode., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Designing a lithium ion battery (LIB) with a three-dimensional device structure is crucial for increasing the practical energy storage density by avoiding unnecessary supporting parts of the cell modules. Here, we describe the superior secondary battery performance of the bulk all-solid-state LIB cell and a multilayered stacked bipolar cell with doubled cell potential of 6.5 V, for the first time. The bipolar-type solid LIB cell runs its charge/discharge cycle over 200 times in a range of 0.1-1.0 C with negligible capacity decrease despite their doubled output cell potentials. This extremely high performance of the bipolar cell is a result of the superior battery performance of the single cell; the bulk all-solid-state cell has a charge/discharge cycle capability of over 1500 although metallic lithium and LiFePO₄ are employed as anodes and cathodes, respectively. The use of a quasi-solid electrolyte consisting of ionic liquid and Al₂O₃ nanoparticles is considered to be responsible for the high ionic conductivity and electrochemical stability at the interface between the electrodes and the electrolyte. This paper presents the effective applications of SiO₂, Al₂O₃, and CeO₂ nanoparticles and various Li(+) conducting ionic liquids for the quasi-solid electrolytes and reports the best ever known cycle performances. Moreover, the results of this study show that the bipolar stacked three-dimensional device structure would be a smart choice for future LIBs with higher cell energy density and output potential. In addition, our report presents the advantages of adopting a three-dimensional cell design based on the solid-state electrolytes, which is of particular interest in energy-device engineering for mobile applications.

Lithium-ion batteries offer promising opportunities for novel energy storage systems and future application in hybrid electric vehicles or electric vehicles. Cathode materials with high energy density are required for practical application. Herein, high-voltage LiCoPO4 cathode materials with different shapes and well-developed facets such as nanorods and nanoplates with exposed {010} facets have been synthesized by a one-pot supercritical fluid (SCF) processing. The effect of different amines and their roles on the morphology-control has been investigated in detail. It was found that amine having long alkyl chain such as hexamethylenediamine played important roles to manipulate the shape of the nanocrystals by selective adsorption on the specific {010} facets. More importantly, the nanorods and nanoplates showed better electrochemical performance than that of nanoparticles which was attributed to their unique crystallographic orientation with short Li ion diffusion path. The present study emphasizes the importance of crystallographic orientation in improving the electrochemical performance of the high voltage LiCoPO4 cathode materials for Li-ion batteries.

Safe and inexpensive energy storage devices with long cycle lifetimes and high power and energy densities are mandatory for the development of electrical power grids that connect with renewable energy sources. In this study, we demonstrated metal-free aqueous redox capacitors using couples comprising low-molecular-weight organic compounds. In addition to the electric double layer formation, proton insertion/extraction reactions between a couple consisting of inexpensive quinones/hydroquinones contributed to the energy storage. This energy storage mechanism, in which protons are shuttled back and forth between two electrodes upon charge and discharge, can be regarded as a proton rocking-chair system. The fabricated capacitor showed a large capacity (>20 Wh/kg), even in the applied potential range between 0-1 V, and high power capability (>5 A/g). The support of the organic compounds in nanoporous carbon facilitated the efficient use of the organic compounds with a lifetime of thousands of cycles.

Ternary metal Prussian blue analogue nanoparticles were applied as cathode materials for Li-ion batteries. Heterometal substitution suppressed phase separation induced by over-lithiation, leading to both a long cycle life and a high rate capability.

LiCoPO4 cathode materials have been synthesized by a sol-gel route. X-ray diffraction analysis confirmed that LiCoPO4 was well-crystallized in an orthorhombic structure in the Pmna space group. From the high-resolution transmission electron microscopy (HR-TEM) image, the lattice fringes of {001} and {100} are well-resolved. The HR-TEM image and selected area electron diffraction pattern reveal the highly crystalline nature of LiCoPO4 having an ordered olivine structure. The atom-by-atom structure of LiCoPO4 olivine has been observed, for the first time, using high-angle annular dark-field (HAADF) and annual bright-field scanning transmission electron microscopy. We observed the bright contrast in Li columns in the HAADF images and strong contrast in the ABF images, directly indicating the antisite exchange defects in which Co atoms partly occupy the Li sites. The LiCoPO4 cathode materials delivered an initial discharge capacity of 117 mAh/g at a C/10 rate with moderate cyclic performance. The discharge profile of LiCoPO4 shows a plateau at 4.75 V, revealing its importance as a potentially high-voltage cathode. The direct visualization of atom-by-atom structure in this work represents important information for the understanding of the structure of the active cathode materials for Li-ion batteries.

We developed a one-step method for production of anisotropically etched graphene using supercritical fluid (SCF). Anisotropic etching of a graphite substrate and dispersed graphite powder with Ag nanoparticles was conducted in supercritical water (SCW). Because of the exfoliation effect of SCF, graphene was isolated from the graphite simultaneously with the anisotropic etching. High-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy revealed the production of multilayer graphene exfoliated from the anisotropically etched graphite surface.

We develop a simple approach to fabricate graphene-loaded TiO(2) thin films on glass substrates by the spin-coating technique. Our graphene-loaded TiO(2) films were highly conductive and transparent and showed enhanced photocatalytic activities. More significantly, graphene/TiO(2) films displayed superhydrophilicity within a short time even under a white fluorescent light bulb, as compared to a pure TiO(2) film. The enhanced photocatalytic activity of graphene/TiO(2) films is attributed to its efficient charge separation, owing to electrons injection from the conduction band of TiO(2) to graphene. The electroconductivity of the graphene-loaded TiO(2) thin film also contributes to the self-cleaning function by its antifouling effect against particulate contaminants. The present study reveals the ability of graphene as a low cost cocatalyst instead of expensive noble metals (Pt, Pd), and further shows its capability for the application of self-cleaning coatings with transparency. The promising characteristics of (inexpensive, transparent, conductive, superhydrophilic, and highly photocatalytically active) graphene-loaded TiO(2) films may have the potential use in various indoor applications.

Investigations of the electronic structure of graphene nanosheets synthesized by the reduction of oxidized graphene nanosheets were carried out using ultra-soft X-ray emission spectroscopy (USXES). Oxidized graphene nanosheets were produced from carbon nanofiber starting material using a modified Hummers method. X-ray diffraction, and scanning and transmission electron microscopy investigations were used in addition to USXES to study the electronic structure evolution from carbon nanofibers to graphene nanosheets. The effect of the degree of corrugation of the graphene nanosheets on the fine structure of the CK(alpha)-emission bands was revealed by USXES. It was found that corrugation of the graphene nanosheets is caused by overlapping of the pi-orbitals and formation of mixed (sigma + pi)-states.

Novel ultrathin Li(2)MnSiO(4) nanosheets have been prepared in a rapid one pot supercritical fluid synthesis method. Nanosheets structured cathode material exhibits a discharge capacity of ~340 mAh/g at 45 ± 5 °C. This result shows two lithium extraction/insertion performances with good cycle ability without any structural instability up to 20 cycles. The two-dimensional nanosheets structure enables us to overcome structural instability problem in the lithium metal silicate based cathode materials and allows successful insertion/extraction of two complete lithium ions., (© 2012 American Chemical Society)

Monodispersed Li(2)MnSiO(4) nanoparticles are synthesized via a supercritical solvothermal method at 300 °C for 5 min reaction time. The as-synthesized nanoparticles are free from impurities and have 15-20 nm diameter. After coating with conductive polymer, a discharge capacity of 313 mA h g(-1) is obtained for the first time because of nearly 2Li(+) reaction., (This journal is © The Royal Society of Chemistry 2012)

Utilization of metal-free low-cost high-capacity organic cathodes for lithium batteries has been a long-standing goal, but critical cyclability problems owing to dissolution of active materials into the electrolyte have been an inevitable obstacle. For practical utilisation of numerous cathode-active compounds proposed over the past decades, a novel battery construction strategy is required. We have designed a solid state cell that accommodates organic cathodic reactions in solid phase. The cell was successful at achieving high capacity exceeding 200 mAh/g with excellent cycleability. Further investigations confirmed that our strategy is effective for numerous other redox-active organic compounds. This implies hundreds of compounds dismissed before due to low cycleability would worth a re-visit under solid state design.

In this study, we achieve the direct conversion of metallic Cu-In films to compound semiconductor CuInSe(2) films, at quite low temperature around 300 °C using less hazardous metalorganic selenium source in supercritical fluid (SCF). We investigated the effects of temperature and fluid (ethanol) density, and found that supercritical ethanol plays a crucial role in this low-temperature selenization reaction. Such SCF-assisted direct conversion reactions can facilitate large-scale, low-temperature, and rapid synthesis of CuInSe(2) films, which can potentially lead to the low-cost production of solar cells.

We report a rapid one-pot supercritical fluid approach to prepare the desired size and morphology controlled LiMPO(4) nanocrystals, using oleylamine as both capping and reducing agent.

Although artificial capsule structures have been thoroughly investigated, functionality at the surfaces of their interiors has been surprisingly overlooked. In order to exploit this aspect of capsular structure, we here report the breakthrough fabrication of metallic (platinum) microcapsules with sufficient accessibility and electroactivity at both interior and exterior surfaces (open-mouthed platinum microcapsules), and also we demonstrate improvements in electrochemical and catalytic functions to emphasize the practical importance of our concept. The open-mouthed platinum microcapsules were prepared by template synthesis using polystyrene spheres, where surface-fused crystalline nanoparticles formed a capsule shell. Subsequent removal of the polystyrene spheres induced formation of mouth-like openings. The open-mouthed platinum microcapsules exhibit a substantial increase of their electrode capability for methanol oxidation and catalytic activities for carbon monoxide (CO) oxidation. Notably, activity loss during CO oxidation due to undesirable particle agglomeration can be drastically suppressed using the open-mouthed microcapsules.

Graphene has attracted a great deal of attention in recent years due to its unusual electronic, mechanical, and thermal properties. Exploiting graphene properties in a variety of applications requires a chemical approach for the large-scale production of high-quality, processable graphene sheets (GS), which has remained an unanswered challenge. Herein, we report a rapid one-pot supercritical fluid (SCF) exfoliation process for the production of high-quality, large-scale, and processable graphene for technological applications. Direct high-yield conversion of graphite crystals to GS is possible under SCF conditions because of the high diffusivity and solvating power of SCFs, such as ethanol, N-methyl-pyrrolidone (NMP), and DMF. For the first time, we report a one-pot direct conversion of graphite crystals to a high yield of graphene sheets in which about 90-95% of the exfoliated sheets are < 8 layers with approximately 6-10% monolayers and the remaining 5-10% are > or = 10 layers.