野田　優

掲載種別：研究論文（学術雑誌）

掲載種別：研究論文（学術雑誌）

掲載種別：研究論文（学術雑誌）

ISSN：00086223

概要：© 2018 Elsevier Ltd Millimeter-tall vertically aligned carbon nanotubes (VA-CNTs) were grown directly on Al substrates. Atmospheric pressure chemical vapor deposition is performed at 600 °C, which is well below the melting point of Al (660 °C), using Fe catalyst and C 2 H 2 as a highly reactive carbon feedstock. The CNT height was sensitive to the C 2 H 2 concentration and 0.06 vol% was optimum for balanced growth rate and catalyst lifetime, yielding 0.06 mm-tall VA-CNTs in 2 h. The CO 2 addition at 1.8 vol% to the C 2 H 2 /Ar gas significantly enhanced the CNT growth, yielding 1.1 mm-tall VA-CNTs in 12 h. CO 2 shows this remarkable effect when added in large excess to C 2 H 2 , differently from the well-known method of “small addition of water.” Moreover, the resulting VA-CNTs showed electrical contact with the Al sheets with resistance of ≤0.7 Ω cm −2 . The effect of CO 2 is systematically studied and discussed.

掲載種別：研究論文（学術雑誌）

掲載種別：研究論文（学術雑誌）

概要：© 2018 The Royal Society of Chemistry. Although lithium-sulfur (Li-S) batteries are a promising secondary power source, it still faces many technical challenges, such as rapid capacity decay and low sulfur utilization. The loading of sulfur and the weight percentage of sulfur in the cathode usually have a significant influence on the energy density. Herein, we report an easy synthesis of a self-supporting sulfur@graphene oxide-few-wall carbon nanotube (S@GO-FWCNT) composite cathode film, wherein an aluminum foil current collector is replaced by FWCNTs and sulfur particles are uniformly wrapped by graphene oxide along with FWCNTs. The 10 wt% FWCNT matrix through ultrasonication not only provided self-supporting properties without the aid of metallic foil, but also increased the electrical conductivity. The resulting S@GO-FWCNT composite electrode showed high rate performance and cycle stability up to ∼385.7 mA h g electrode -1 after 500 cycles and close to ∼0.04% specific capacity degradation per cycle, which was better than a S@GO composite electrode (353.1 mA h g electrode -1 ). This S@GO-FWCNT composite self-supporting film is a promising cathode material for high energy density rechargeable Li-S batteries.

ISSN：20507488

概要：© The Royal Society of Chemistry 2018. Hybrid supercapacitors, which combine the advantages of supercapacitors and rechargeable batteries, have the potential to meet the demands of both high-energy and -power in electrochemical energy storage systems. However, the energy density of the hybrid supercapacitors has been limited because of the low capacity of the activated carbon cathode. Here we introduce a high-capacity carbon cathode containing plenty of oxygen functional groups that are redox-active towards both Li- and Na-ions. This functional carbon has an ultra-thin two-dimensional structure that has significant advantages in utilizing the redox reactions. The functional carbon cathode can exhibit very high capacities of ∼250 mA h g -1 in Li-cells and ∼210 mA h g -1 in Na-cells. A hybrid supercapacitor consisting of the two-dimensional functional carbon cathode with a commercial level loading density of ∼9.3 mg cm -2 and a Si-based anode delivers a high-energy density of ∼182 W h kg -1 at a high-power density of 1 kW kg -1 .

ISSN：03787753

概要：© 2017 Elsevier B.V. Rapid gas-evaporation method is proposed and developed, which yields Si nanoparticles (SiNPs) in a few seconds at high yields of 20%–60% from inexpensive and safe bulk Si. Such rapid process is realized by heating the Si source to a temperature ≥2000 °C, much higher than the melting point of Si (1414 °C). The size of SiNPs is controlled at tens to hundreds nanometers simply by the Ar gas pressure during the evaporation process. Self-supporting films are fabricated simply by co-dispersion and filtration of the SiNPs and carbon nanotubes (CNTs) without using binders nor metal foils. The half-cell tests showed the improved performances of the SiNP-CNT composite films as anode when coated with graphitic carbon layer. Their performances are evaluated with various SiNP sizes and Si/CNT ratios systematically. The SiNP-CNT film with a Si/CNT mass ratio of 4 realizes the balanced film-based capacities of 618 mAh/g film , 230 mAh/cm 3 , and 0.644 mAh/cm 2 with a moderate Si-based performance of 863 mAh/g Si at the 100th cycle.

概要：© 2017 American Chemical Society. Epitaxial copper (Cu) films yield graphene with superior quality but at high cost. We report 1-3 μm thick epitaxial Cu films prepared on c plane sapphire substrates in 10-30 s, which is much faster than that of the typical sputtering method. Such rapid deposition is realized by vapor deposition using a Cu source heated to 1700-1800 °C, which is much higher than its melting point of 1085 °C. Continuous graphene films, either bilayer or single-layer, are obtained on the epitaxial Cu by chemical vapor deposition and transferred to carrier substrates. The sapphire substrates can be reused five to six times maintaining the quality of the epitaxial Cu films and graphene. The mechanisms and requirements are discussed for such quick epitaxy of Cu on reused sapphire, which will enable high-quality graphene production at lower cost.

ISSN：00086223

概要：© 2016 Elsevier LtdFlame-synthesized (CoO)x(Al2O3)1-x spinel nanopowders with primary particles of ∼20 nm were used to grow small diameter carbon nanotubes (CNTs). The nanopowders with x ≤ 0.35 grew few CNTs whereas that with x = 0.65 grew CNTs efficiently. Low crystalline and large-diameter multi-wall CNTs grew by annealing and chemical vapor deposition (CVD) at 800 °C for ∼10 min, whereas single-wall CNTs with high crystallinity (G-band to D-band intensity ratio of 20–100 by Raman spectroscopy) grew by annealing and CVD at ≥1000 °C for ∼10 s. The excess Co in the spinel reduced and segregated to form multiple Co nanoparticles on the surface of the single primary alumina nanoparticles in ∼10 s, yielding SWCNTs in ∼10 s. Such flame synthesized nanopowders, reduced and activated by H2, provide CNTs from C2H2, all in ten-second time scale, and as such are promising for practical, high-through-put production of small-diameter CNTs.

ISSN：18820778

概要：© 2017 The Japan Society of Applied Physics.Hole doping into carbon nanotubes can be achieved. However, the doped nanotubes usually suffer from the lack of air and moisture stability, thus, they eventually lose their improved electrical properties. Here, we report that a salt of the two-coordinate boron cation Mes2B+ (Mes: 2,4,6-trimethylphenyl group) can serve as an efficient hole-doping reagent to produce nanotubes with markedly high stability in the presence of air and moisture. Upon doping, the resistances of the nanotubes decreased, and these states were maintained for one month in air. The hole-doped nanotube films showed a minimal increase in resistance even upon humidification with a relative humidity of 90%.

ISSN：17545692

概要：© The Royal Society of Chemistry 2017.Self-polymerized dopamine is a versatile coating material that has various oxygen and nitrogen functional groups. Here, we demonstrate the redox-active properties of self-polymerized dopamine on the surface of few-walled carbon nanotubes (FWNTs), which can be used as organic cathode materials for both Li- and Na-ion batteries. We reveal the multiple redox reactions between self-polymerized dopamine and electrolyte ions in the high voltage region from 2.5 to 4.1 V vs. Li using both density functional theory (DFT) calculations and electrochemical measurements. Free-standing and flexible hybrid electrodes are assembled using a vacuum filtration method, which have a 3D porous network structure consisting of polydopamine coated FWNTs. The hybrid electrodes exhibit gravimetric capacities of ∼133 mA h g-1 in Li-cells and ∼109 mA h g-1 in Na-cells utilizing double layer capacitance from FWNTs and multiple redox-reactions from polydopamine. The polydopamine itself within the hybrid film can store high gravimetric capacities of ∼235 mA h g-1 in Li-cells and ∼213 mA h g-1 in Na-cells. In addition, the hybrid electrodes show a high rate-performance and excellent cycling stability, suggesting that self-polymerized dopamine is a promising cathode material for organic rechargeable batteries.

掲載種別：研究論文（学術雑誌）

概要：Crumpled graphene is known to have a strong aggregation-resistive property due to its unique 3D morphology, providing a promising solution to prevent the restacking issue of graphene based electrode materials. Here, we demonstrate the utilization of redox-active oxygen functional groups on the partially reduced crumpled graphene oxide (r-CGO) for electrochemical energy storage applications. To effectively utilize the surface redox reactions of the functional groups, hierarchical networks of electrodes including r-CGO and functionalized few-walled carbon nanotube (f-FWNT) are assembled via vacuum-filtration process, showing a 3D porous structure. These composite electrodes are employed as positive electrodes in Li-cells, delivering high gravimetric capacity up to ~170 mAh/g with significantly enhanced rate-capability compared to the electrodes consisting of conventional 2D reduced graphene oxide and f-FWNT. These results highlight the importance of microstructure design coupled with oxygen chemistry control, for maximizing the surface redox reactions on the functionalized graphene based electrodes.

ISSN：03787753

概要：© 2016 Elsevier B.V. All rights reserved. Herein, we propose lithium ion batteries (LIBs) without binder or metal foils, based on a three-dimensional carbon nanotube (CNT) current collector. Because metal foils occupy 20-30 wt% of conventional LIBs and the polymer binder has no electrical conductivity, replacing such non-capacitive materials is a valid approach for improving the energy and power density of LIBs. Adding only 1 wt% of few-wall CNTs to the active material enables flexible freestanding sheets to be fabricated by simple dispersion and filtration processes. Coin cell tests are conducted on full cells fabricated from a 99 wt% LiCoO2-1 wt% CNT cathode and 99 wt% graphite-1 wt% CNT anode. Discharge capacities of 353 and 306 mAh ggraphite -1 are obtained at charge-discharge rates of 37.2 and 372 mA ggraphite -1, respectively, with a capacity retention of 65% at the 500th cycle. The suitability of the 1 wt% CNT-based composite electrodes for practical scale devices is demonstrated with laminate cells containing 50 × 50 mm2 electrodes. Use of metal combs instead of metal foils enables charge-discharge operation of the laminate cell without considerable IR drop. Such electrodes will minimize the amount of metal and maximize the amount of active materials contained in LIBs.

掲載種別：研究論文（学術雑誌）

概要：We developed a film deposition method which yielded continuous polycrystalline Si films with large lateral grain sizes of over 100 μm and thicknesses of ∼10 μm in 1 min on growth substrates other than silicon wafers in a single-step process. The silicon source is heated to ∼2000 °C, much higher than the melting point of Si, which enables a high deposition rate. Controlling the temperature of the growth substrate, initially above and later below the melting point of Si, allows the seamless lateral to vertical growth of crystalline silicon grains. Thermally and chemically stable substrates of quartz glass and alumina with a 0.1 μm-thick amorphous carbon layer were effective; liquid silicon wetted well by forming a thin SiC interlayer while substrates stayed stable. Such large-grain polycrystalline silicon films synthesized rapidly in 1 min may be used for low-cost, stable and flexible thin film photovoltaic cells.

掲載種別：研究論文（学術雑誌）

概要：To overcome the tradeoff between the gravimetric capacitance and loading density of pseudocapacitive MnO2, we electrodeposited MnO2 nanoparticles on the carbon nanotube (CNT) surfaces in 18–37 μm-thick self-supporting CNT papers. We examined the electrodeposition conditions including constant potential, constant current, and potential pulses, and obtained MnO2–CNT hybrid electrodes containing MnO2 nanoparticles uniformly deposited at 60–90 wt% with an expanded CNT matrix. The MnO2–CNT hybrid electrode with a thickness of 62 μm, density of 1.09 g cm−3, areal mass of 6.75 mg cm−2, and 82 wt% MnO2 load showed a total gravimetric capacitance of 120 and 51 Ftotal gelectrode−1, volumetric capacitance of 131 and 56 Ftotal cm−3 and areal capacitance of 0.81 and 0.34 Ftotal cm−2 at scan rates of 2 and 200 mV s−1, respectively. The large thickness, moderately high mass density, and fairly conductive CNT matrix realized such high values of gravimetric, areal and volumetric capacitances that are important for practical devices.

ISSN：20403364

概要：© 2016 The Royal Society of Chemistry. Biomass derived carbon materials have been widely used as electrode materials; however, in most cases, only electrical double layer capacitance (EDLC) is utilized and therefore, only low energy density can be achieved. Herein, we report on redox-active carbon spheres that can be simply synthesized from earth-abundant glucose via a hydrothermal process. These carbon spheres exhibit a specific capacity of ∼210 mA h gCS -1, with high redox potentials in the voltage range of 2.2-3.7 V vs. Li, when used as positive electrode in lithium cells. Free-standing, flexible composite films consisting of the carbon spheres and few-walled carbon nanotubes deliver high specific capacities up to ∼155 mA h gelectrode -1 with no obvious capacity fading up to 10000 cycles, proposing to be promising positive electrodes for lithium-ion batteries or capacitors. Furthermore, considering that the carbon spheres were obtained in an aqueous glucose solution and no toxic or hazardous reagents were used, this process opens up a green and sustainable method for designing high performance, environmentally-friendly energy storage devices.

概要：© The Royal Society of Chemistry 2016.Carbon nanotube (CNT)-silicon (Si) heterojunction solar cells are fabricated with surface-textured Si substrates. Using a dilute alkaline solution, common etchant in the Si solar cell industry, we formed a pyramidal texture on the Si substrate surface. The texture effectively enhances the absorption of the incident light, improving the short-circuit current density by ∼1.3-fold, up to 33.1 mA cm-2. We fabricated CNT-Si solar cells with a power conversion efficiency (PCE) of 10.4% without any anti-reflective coatings or doping of the CNTs. Moreover, the CNT films were prepared from commercialized CNT agglomerates by a mild solution-based process, which is well suited for the fabrication of CNT-Si solar cells with large area. We also achieved a PCE of 9.57% for a flat cell with careful removal of surfactant from and doping by nitric acid of the CNT films. These findings suggest that with the combination of surface-textured Si and solution-processed CNT films, efficient and low-cost CNT-Si solar cells may be realized.

ISSN：00189383

概要：© 2015 IEEE. A flexible organic-light-emitting diode (OLED) with capability to show 16 million colors is fabricated on plastic barrier-film substrate, which can produce arbitrary shape with arbitrary colors, suitable for artistic expressions. Independently controlled red, green, and blue light-emitting layers are stacked vertically, so that no visible structure can be observed even with magnifiers from right-in-front measurement. In the past, large voltage drop of intermediate electrode was preventing this approach to be applied to actual electronic devices. However, according to the surface mobility control using Fick's law analysis, low sheet resistance 7.34 ω/on plastic film is developed, so that 7.17-cm2 area emission is successfully achieved. With optical length optimization for each color stack, more than 100% color reproduction in National Television Committee Standard is achieved by stack design. The device can be used for colored illumination, as well as for organic-light-emitting display pixels for three times emission than the conventional pixel design. The device is fabricated on plastic substrate, so that the polychromatic OLED device is manufacturable with roll-to-roll production line.

ISSN：0021-4922

概要：To achieve denser and taller carbon nanotube (CNT) arrays on Cu foils, catalyst and chemical vapor deposition (CVD) conditions were carefully engineered. CNTs were grown to ∼50 µm using Fe/TiN/Ta catalysts in which Ta and TiN acted as diffusion barriers for Cu and Ta, respectively. A tradeoff was found between the mass density and height of the CNT arrays, and CNT arrays with a mass density of 0.30 g cm⁻³and height of 45 µm were achieved under optimized conditions. Thermal interface materials (TIMs) with CNT array/Cu foil/CNT array structures showed decreasing thermal resistance from 86 to 24 mm²K W⁻¹with increasing CNT array mass densities from 0.07–0.08 to 0.19–0.26 g cm⁻³for Cu and Al blocks with surfaces as rough as 20–30 µm. The best CNT/Cu/CNT TIMs showed thermal resistance values comparable to that of a typical indium sheet TIM.