Kazumichi Yanagisawa

High Pseudocapacitance in FeOOH/rGO Composites with Superior Performance for High Rate Anode in Li-Ion Battery

Capacitive storage has been considered as one type of Li-ion storage with fast faradaic surface redox reactions to offer high power density for electrochemical applications. However, it is often limited by low extent of energy contribution during the charge/discharge process, providing insufficient influences to total capacity of Li-ion storage in electrodes. In this work, we demonstrate a pseudocapacitance predominated storage (contributes 82% of the total capacity) from an in-situ pulverization process of FeOOH rods on rGO (reduced graphene oxide) sheets for the first time. Such high extent of pseudocapacitive storage in the FeOOH/rGO electrode achieves high energy density with superior cycling performance over 200 cycles at different current densities (1135 mAh/g at 1 A/g and 783 mAh/g at 5 A/g). It is further revealed that the in-situ pulverization process is essential for the high pseudocapacitance in this electrode, because it not only produces a porous structure for high exposure of tiny FeOOH crystallites to electrolyte but also maintains stable electrochemical contact during ultrahigh rate charge transfer with high energy density in the battery. The utilization of in-situ pulverization in an Fe-based anode to realize high surface pseudocapacitance with superior performance may inspire future design of electrode structures in Li-ion batteries.

Effects of ionic conduction on hydrothermal hydrolysis of corn starch and crystalline cellulose induced by microwave irradiation

This study investigated the effects of ionic conduction of electrolytes under microwave field to facilitate hydrothermal hydrolysis of corn starch and crystalline cellulose (Avicel), typical model biomass substrates. Addition of 0.1M NaCl was effective to improve reducing sugar yield by 1.61-fold at unit energy (kJ) level. Although Avicel cellulose was highly recalcitrant to hydrothermal hydrolysis, addition of 0.1M MgCl2 improved reducing sugar yield by 6.94-fold at unit energy (kJ). Dielectric measurement of the mixture of corn starch/water/electrolyte revealed that ionic conduction of electrolytes were strongly involved in facilitating hydrothermal hydrolysis of polysaccharides.

Facile microwave-assisted fabrication of WC-Al2O3 composite powder from WO3-Al-C mixture

Abstract A facile and cheap method for the fabrication of WC-Al2O3 composite powder was proposed. Thermodynamic calculations indicate that aluminothermic reduction of WO3 in WO3:xAl:(4–1.5x)C mixture is accompanied by a great deal of heat, so carbothermic reduction reaction (endothermic) becomes activated in the system. By substitution of aluminum with carbon, the formation of unwanted W2C phase can be prevented because of less thermodynamic stability at lower temperatures. For the verification of the proposed reaction mechanism, various WO3:xAl:(4–1.5x)C mixtures (1.1≤x≤2) were heat-treated in a domestic microwave oven. The results showed that the type of reaction is self-propagating high temperature synthesis (SHS) when 1.4≤x≤2. Lower amount of Al in WO3:xAl:(4–1.5x)C mixtures results in a higher formation of WC. A W2C-free WC-Al2O3 composite was obtained by continuation of microwave heating in an isolated atmosphere, after the occurrence of SHS reaction in a mixture containing 1.4 mol of Al. Results also showed that when x≤1.3, type of reaction becomes gradual, which in turn brings about the incompleteness reaction and residue of initial reagents.

Synthesis of nanocrystalline TiB2 powder from TiO2, B2O3 and Mg reactants through microwave-assisted self-propagating high-temperature synthesis method

In this research work, microwave-assisted self-propagating high-temperature synthesis (SHS) process was employed for the fabrication of titanium diboride (TiB2) compound from TiO2–B2O3–Mg mixtures. Thermodynamic evaluations of this system and its relevant subsystems revealed that TiB2–MgO composite powder can be easily produced by a SHS reaction. However, experimental results of a TiO2 : B2O3 : 5Mg mixture heated in a domestic oven showed the formation of some intermediate compounds such as Mg3B2O6, presumably due to some degree of Mg loss. The optimum amount of Mg in TiO2 : B2O3 : xMg mixtures, yielding the highest amount of TiB2 phase, was found to be around 7 mol, i.e., 40 mol% more than the stoichiometric amount. Experimental results revealed that a pure TiB2 compound could be obtained by leaching the unwanted by-products in an HCl acid solution. Scanning electron microscopic observations and Scherrer calculations showed that the produced TiB2 contains sub-micron (150–200 nm) particles, where each particle consists of a number of nanosized (32 nm) crystallites.

Synthesis and characterization of glycolate precursors to MTiO3 (M = Ni2+, Co2+, Zn2+)

Abstract Novel glycolate precursors to metal titanates MTiO3 (M = Ni2+, Co2+, Zn2+) were synthesized by heating metal acetate and titanium isopropoxide in ethylene glycol up to 190 °C during distilling the water to avoid hydrolysis of precursors. These glycolate precursors were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), thermal analysis (TG-DTA), and scanning electron microscopy (SEM). The obtained three isostructural glycolate precursors were containing metal (Ni, Co, Zn), titanium, and ethylene glycol with a ratio of 1:1:4. The crystal growth processes of three precursors were different from each other. These precursors revealed homogeneous and well-defined rod-like structure with 0.5–3.0 μm in thickness and 4–20 μm in length. The obtained metal titanates were consisted of microrods with 0.4–1.5 μm in thickness and 2–15 μm in length.

Synthesis of WC powder through microwave heating of WO3–C mixture

A simple, easy, and low-cost process for the fabrication of tungsten carbide (WC) powder through microwave heating of WO3–C mixtures was developed. Thermodynamic calculations and experimental investigations were carried out for WO3–C and W–C systems, and a formation mechanism was proposed. In the results, for the synthesis of WC, the use of over stoichiometric amount of C together with a specially assembled experimental setup (which effectively retains heat in the system) is necessary. The WC powder is successfully obtained by heating WO3:5C mixture for 900 s in a domestic microwave oven.

Catalytic Hydrolysis of Polysaccharides Derived from Fast-Growing Green Macroalgae

Green macroalgae, such as Ulva spp., has a higher growth rate than terrestrial lingocellulosic biomass, which often leads to serious environmental issues such as green tide. So, it is a promising feedstock for biorefineries. Hiraoka produced Ulva with reproducible compositions and sizes by our original cultivation method. The macroalgae contained approximately 35u2005wtu2009% of a soluble polysaccharide called ulvan, which is a sulfated glucuronorhamnan polysaccharide. The catalytic conversion of extracted ulvan was performed under hydrothermal conditions at 130u2009°C by using solid acid catalysts. The Amberlystu200570 catalyst has a stable structure and gave monosaccharides in quantitative yield, predominantly in the form of rhamnose. The Amberlystu200570 catalyst showed higher activity than sulfonated activated‐carbon (AC‐SO3H) in the hydrothermal conversion of ulvan, although Amberlystu200570 showed lower catalytic activity than AC‐SO3H in the hydrolysis of starch.