The strong correlations between thermal conductivities and electronic spin states in the crystals of Fe(III) spin crossover complexes.

Solids that change their thermal conductivity during a phase transition can be useful in the development of a thermal switch to allow control of heat flow and reduce energy consumption. Although a crystal of a spin crossover (SCO) complex is a representative solid with spin states correlated with heat transporting lattice vibrations, the heat transporting property of a crystal of the SCO complex during a spin state transition has not yet been reported. In this work, we report that the temperature dependence of the thermal conductivity of mononuclear Fe(III) SCO complexes is greatly affected by spin state transitions. It was found that the thermal conductivity was minimized at temperatures near the beginning edge of the spin state transitions, and the product of the velocity and the mean free path of phonons also reached a minimum close to the temperature at which the spin state transition progressed by 50%. These findings suggest that the spin state transitions accompanying the coordination bond length elongation and lowering of the vibration energy are allowed at a temperature where the mean-free path of phonons is minimized to the extent of intermolecular distances. These findings also indicate that SCO complexes reported in the literature are promising candidates for heat transportation switch materials.

Mesoporous Carbon Fibers with Tunable Mesoporosity for Electrode Materials in Energy Devices.

To improve the properties of mesoporous carbon (MC), used as a catalyst support within electrodes, MC fibers (MCFs) were successfully synthesized by combining organic-organic self-assembly and electrospinning deposition and optimizing heat treatment conditions. The pore structure was controlled by varying the experimental conditions. Among MCFs, MCF-A, which was made in the most acidic condition, resulted in the largest pore diameter (4-5 nm), and the porous structure and carbonization degree were further optimized by adjusting heat treatment conditions. Then, since the fiber structure is expected to have an advantage when MCFs are applied to devices, MCF-A layers were prepared by spray printing. For the resistance to compression, MCF-A layers showed higher resistance (5.5% change in thickness) than the bulk MC layer (12.8% change in thickness). The through-plane resistance was lower when the fiber structure remained more within the thin layer, for example, +8 mΩ for 450 rpm milled MCF-A and +12 mΩ for 800 rpm milled MCF-A against the gas diffusion layer (GDL) 25BC carbon paper without a carbon layer coating. The additional advantages of MCF-A compared with bulk MC demonstrate that MCF-A has the potential to be used as a catalyst support within electrodes in energy devices.

Development of Porous Pt Electrocatalysts for Oxygen Reduction and Evolution Reactions.

Porous Pt electrocatalysts have been developed as an example of carbon-free porous metal catalysts in anticipation of polymer electrolyte membrane (PEM) fuel cells and PEM water electrolyzers through the assembly of the metal precursor and surfactant. In this study, porous Pt was structurally evaluated and found to have a porous structure composed of connected Pt particles. The resulting specific electrochemical surface area (ECSA) of porous Pt was 12.4 m2 g-1, which was higher than that of commercially available Pt black. Accordingly, porous Pt showed higher oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity than Pt black. When the activity was compared to that of a common carbon-supported electrocatalyst, Pt/ketjen black (KB), porous Pt showed a comparable ORR current density (2.5 mA cm-2 at 0.9 V for Pt/KB and 2.1 mA cm-2 at 0.9 V for porous Pt), and OER current density (6.8 mA cm-2 at 1.8 V for Pt/KB and 7.0 mA cm-1 at 1.8 V), even though the ECSA of porous Pt was only one-sixth that of Pt/KB. Moreover, it exhibited a higher durability against 1.8 V. In addition, when catalyst layers were spray-printed on the Nafion® membrane, porous Pt displayed more uniform layers in comparison to Pt black, showing an advantage in its usage as a thin layer.

Gram-scale synthesis of alkoxide-derived nitrogen-doped carbon foam as a support for Fe-N-C electrocatalysts.

Non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR) are set to reduce the cost of polymer electrolyte membrane fuel cells (PEFCs) by replacing platinum at the cathode. We previously developed unique nitrogen-doped carbon foams by template-free pyrolysis of alkoxide powders synthesized using a high temperature and high pressure solvothermal reaction. These were shown to be effective ORR electrocatalysts in alkaline media. Here, we present a new optimised synthesis protocol which is carried out at ambient temperature and pressure, enabling us to safely increase the batch size to 2 g, increase the yield by 60%, increase the specific surface area to 1866 m2 g-1, and control the nitrogen content (between 1.0 and 5.2 at%). These optimized nitrogen-doped carbon foams are then utilized as effective supports for Fe-N-C catalysts for the ORR in acid media, whilst multiphysics modelling is used to gain insight into the electrochemical performance. This work highlights the importance of the properties of the carbon support in the design of Pt-free electrocatalysts.

Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application.

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4(-), and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.

Immobilization of an Enzyme Into Nano-Space of Nanostructured Carbon and Evaluation as Electrochemical Sensors.

The aims of this study are immobilization of formaldehyde dehydrogenase (FDH) into nano-space of nanostructured carbon and evaluation as a possible sensor detecting low concentration formaldehyde. In order to understand the effect of carbon pore size on activity and stability of FDH, mesoporous carbon (MC), originally made in our lab, and commercially available ketjen black (KB) were used in this study. Enzyme activity and electrochemical sensing ability of FDH encapsulated into such two carbon materials were compared. Our original MC resulted in favourable in some evaluated conditions but not in other conditions. MC adsorbed FDH less than KB, but enzyme activity was higher on MC per FDH. Stability against methanol increased on MC, but stability against water was rather lower on MC. Electrochemical sensing ability toward formaldehyde resulted in much better on KB, which was able to detect the sub-ppb level of formaldehyde. Consequently, such dependence is resulted by available nano-space of carbon, and so tuning the pore size of carbon is an important factor in order to develop enzyme based electrochemical sensors with high sensitivity and stability.

Electrochemical enzymatic biosensor with long-term stability using hybrid mesoporous membrane.

An acetylcholinesterase-immobilized sensor unit was successfully prepared by encapsulating the enzyme within hybrid mesoporous silica membranes (F127-MST). Through a novel combination with tetracyanoquinodimethane, both acetylcholine and organophosphorus pesticides were successfully detected with high sensitivity. Furthermore, we manufactured the working prototype of an enzyme sensor with this sensor unit for detecting dichlorvos, aldicarb and parathion. At present, the detection limit in this working prototype either equaled or surpassed that of others. Also, we have the advantage of increased stability of the enzyme against the outer environment by encapsulation of the enzymes into a silica nanospace. Consequently, acetylcholinesterase immobilized in F127-MST is a practical sensor with high sensitivity, reusability, and storage stability.

Enhancement of activity and stability of the formaldehyde dehydrogenase by immobilizing onto phenyl-functionalized mesoporous silica.

Formaldehyde dehydrogenase (FDH, molecular size of 8.6 nm × 8.6 nm × 19.0 nm) was immobilized on seven types of mesoporous silica (MPS), whose pores were from 2.4 to 31.2 nm sized, and their catalytic activities were evaluated by oxidation of formaldehyde. Among MPSs, FDH immobilized on MPS-4 (pore size of 12.3 nm) showed the best catalytic activity. Enhancement of catalytic activity was obtained by immobilizing onto MPS, whose pore (mesopore) size was similar to the molecular size of FDH. In addition, FDH was immobilized on five types of organo-functionalized MPS-4. Results from assays of enzyme activity showed that FDH immobilized on phenyl-functionalized MPS-4 (MPS-4-Ph) had higher activity than FDH immobilized on non-functionalized one. Immobilized FDH on MPS-4-Ph was active for low formaldehyde concentration form 6.0 µM and more sensitive than conventional formaldehyde detectors. Stability of FDH activity was also evaluated under the various conditions, in which protein denaturation could occur by solvent treatment, such as methanol or sodium dodecyl sulfate. As a result, FDH stability was strongly improved by the immobilization on MPS materials. Further investigation using tryptophan fluorescence and circular dichroism (CD) indicated that the high-order structure of the FDH did not alter upon binding to the non-functionalized MPS surface. On the other hand, FDH immobilized on functionalized-MPS was changed by hydrophobic interaction or covalent binding. Consequently, substrate affinity was improved by the change in the structure of FDH and then the orientation of the active site.

Simple methods for tuning the pore diameter of mesoporous carbon.

The organic-organic self-assembly method with Resorcinol (R)/Formaldehyde (F) and Pluronic F127 has been employed to synthesize mesoporous carbon (MC). The pore diameter of the MC has been tuned from 7 to 12.5 nm by changing the molar ratio of carbon sources to surfactant and polymerization time.

Direct fabrication of aligned metal composite carbon nanofibers on copper substrate at room temperature and their field emission property.

Direct growth of aligned metal composite carbon nanofibers (MCNFs) was achieved by a highly reproducible room temperature growth process on cost effective electrically conductive copper (Cu) substrate without any catalyst. The direct fabrication of MCNFs on electrically conductive substrate might offer new perspectives in the field of field emission displays (FEDs).

Fabrication of ion-induced carbon-cobalt nanocomposite fibers: effect of cobalt supply rate.

Graphite surfaces were irradiated by argon (Ar+) ions at 1 keV with a simultaneous cobalt (Co) supply at room temperature. Various kinds of carbon nanocomposites, such as nanocones with and without single nanofibers on their tops, nanorods and fish-scale-like nanoprotrusions, were formed depending on Co supply rates. It has been observed that with increasing the Co supply rate the formation of nanoprotrusions without nanofibers became prominent. Both nanofibers and nanoprotrusions were surely composed of carbon and Co, as confirmed by energy-dispersive X-ray analysis. The cobalt carbon nanocomposite fibers (CCNFs), -1.5 microm in average length, were grown on the top of the nanocones at the Co supply rate of 1.0 nm/min. The field electron emission characteristics of CCNFs thus grown indicated that there is an optimum parameter for the CCNF growth to achieve the better emission performance than that of pristine Ar(+)-induced carbon nanofibers.

Fabrication and morphological control of ion-induced zinc nanostructures.

An efficient method for the fabrication of zinc (Zn) nanostructures (nanoneedles and nanofibers) of controllable density and morphology without any catalyst, hazardous chemicals or external heat supply has been investigated. By varying the ion irradiation time and the ion current density, morphological control and the density of Zn nanostructures were successfully achieved using a fast and viable ion irradiation technique. Scanning (SEM) and transmission electron microscopy (TEM) results revealed that the sputtered surface was almost entirely covered with densely distributed conical and needle-like protrusions with linear shaped (sometimes curved) nanostructures (such as nanoneedles and nanofibers) with diameters and lengths of about 20-50 nm and several hundred nanometers, respectively. Detailed analysis of selected area electron diffraction (SAED) patterns with TEM analysis indicates that the Zn nanofibers were polycrystalline in nature. A possible mechanism of the formation of Zn nanostructures is briefly discussed. These aligned arrays of Zn nanoneedles/nanofibers could be a promising material for the fabrication of zinc oxide nanostructures by subsequent oxidation of Zn nanostructures and their future application in nanodevices. Thus, it is believed that this ion irradiation technique could open up a new approach for the fabrication of many kinds of nanomaterials of controllable density.

Transparent and flexible field electron emitters based on the conical nanocarbon structures.

The fabrication of conical nanocarbon structures (CNCSs) on a transparent and flexible nafion substrate at room temperature using an ion irradiation technique and their application toward field emission displays (FEDs) have been demonstrated. The main advantage of this technique is that CNCSs can be fabricated directly on the transparent substrate while retaining the transparency of the substrate. A scanning electron microscopy (SEM) image revealed that the sputtered surface was entirely covered with CNCSs with a calculated numerical density of 6 x 10(6) /mm(2). Such nafion based CNCSs have proved to be an effective electron emitter with turn-on and threshold fields of 6.1 and 9.5 V/mum, respectively. The field enhancement factor was estimated to be 1020 from the Fowler-Nordheim (F-N) plot. Thus the room temperature fabricated CNCSs based on transparent and flexible nafion substrate would be very promising for future flexible (roll-up) and transparent FEDs.

Preparation of a self-standing mesoporous carbon membrane with perpendicularly-ordered pore structures.

A self-standing mesoporous carbon membrane (sOMC) with perpendicularly-ordered pore structures was prepared through a simple synthetic method; the pores with a diameter of 8 nm were well ordered over a large area and perpendicularly-oriented to the surface without any external field; in the formation of this ordered structure, the drying process is key, and a porous alumina support is important to induce drying.

Sequential metal ion assembly in cyclic phenylazomethine.

[reaction: see text] Cyclic phenylazomethines with methylene spacers (CPA-M) are obtained by dehydration of diamine with diketone. During the titration of CPA-M 4mer with FeCl(3), we observe two consecutive isosbestic points in the UV-vis spectra. We conclude that complexation occurs in two consecutive steps. Our analysis suggests that the stepwise metal ion assembly is caused by a difference in the basicity of the imine conformers. Metal ion binding first occurs at the Z imines followed by coordination to the E imine. Finally, metal ion assembly in this compound can be controlled electrochemically.

Metal ion assembly in macromolecules.

Self-assembled organic-inorganic hybrid nano-materials have recently received much attention due to their novel and original functions, including new electronic, optical, magnetic, and catalytic properties. Especially, reactions in organic-metallic hybrid materials are closely related to biological reactions, such as the reactions in metal-containing protein, and the controlled metal ions assembly into organic polymers becomes very important. In the first part of this review, recent progresses in two types of organic-inorganic hybrid nano-materials (Organic compounds [character: see text] inorganic mesoporous materials and Metal ions [character: see text] organic polymer) are summarized. In the latter parts, dendrimer-metal complexes, examples of nature-mimetic materials, are introduced, and their controlled metal assembly in dendrimer and their application are reviewed.

Crystal chemistry of the gold (I) trimer, Au(3)(NC(5)H(4))(3): formation of hourglass figures and self-association through aurophilic attraction.

X-ray crystallography reveals that individual molecules of Au(3)(NC(5)H(4))(3) self-associate through aurophilic interactions into two distinct structural motifs that involve both extended chains of molecules connected by pairwise Au.Au contacts and individual Au.Au contacts and discrete dimers linked by pairwise Au.Au contacts. The colorless or pale yellow crystals are remarkable for the formation of a distinct hourglass shape within the crystals that develops after months of standing in the atmosphere or after immersion in 4 M hydrochloric acid for a few days. The hourglass figures appear to result from the deposition of gold and are unusual in being formed by a chemical reaction within a crystal rather than as a result of dying the crystal during growth.