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Nanomaterials & Self-Organization

Nanotechnology brings innovations to the society in wide fields of energy/environment, information/communication, etc., by adding novel functions to materials by controlling their structures at nanometer-scale. We are trying to establish the base of materials nanotechnology.

Let us think about the future clean energy systems. For large-scale electric power generation by solar cells, efficient use of high purity silicon is the key. We are trying to improve the efficiency several-ten times by making highly-crystalline films in one minute instead of bulk substrates. Transparent electrodes are important for both solar cells (yielding electricity from light) and display & lighting devices (generating lights from electricity). We try to replace rare-metal-based oxide semiconductors with carbon nanotubes or graphene. Nanotube-silicon hybrids are promising to realize Li ion batteries of larger capacities for (hybrid) electric vehicles. In this way, nanotechnology can bring innovations widely even with abundant carbon and silicon elements, and contributes to sustainable technological society.

But nanomaterials can never be made in macro-scale if we artificially manipulate atoms/molecules one-by-one. Self-organization, i.e. spontaneous formation of materials from numerous atoms/molecules, is the key. We are trying to understand the processes of chemical reactions of atoms/molecules, formation of nanostructures, and evolution of higher-order structures fundamentally. Based on the fundamental understandings with flexible thinking and idea, we are proposing and developing novel processes for nanomaterials and their devices.

Carbon Nanotubes

Carbon nanotubes (CNTs) are a unique 1D nanomaterial as thin as ~nm and as long as ~mm. They have good electrical conductivity, high tensile strength, thermal and chemical stability similarly with inorganic materials, and have small mass, flexibility, and compatibility with printing process similarly with organic materials. Thus, many applications have been proposed for them.
On the other hand, as their price (higher than gold) shows, their fabrication process is still under development and their practical applications are very much limited. Chemistry & engineering should lead the innovations for their production and manufacturing. We have developed rapid growth process of millimeter-long single-wall CNTs and are trying to realize their practical production. Please click here for details.
We are developing mass-production processes of CNTs by utilizing three-dimensional space of reactors, and direct fabrication of various devices by growing CNTs on device substrates. We have also started the synthesis of boron nitride nanotubes (BNNTs) having similar structure as CNTs and insulative property.
    (3D Synthesis)
  • Mochen LI (PD): Fluidized-bed synthesis of long CNTs.
  • Xiaoxu HUANG (D1): Synthesis of high-quality CNTs by floating catalyst CVD and application to CNT-Si heterojunction solar cells.
  • Katsuya NAMIKI (M2): Continuous production of single-wall CNTs and their fibers by floating catalyst CVD method.
  • Yohei MAEDA (M2): Development of gas-phase continuous production process of carbon nanoparticle-nanotube hybrids.
  • Risa MAEDA (M2): Quick wet preparation of catalysts on ceramic powders and fluidized-bed synthesis of long CNTs.
  • Masahiro YOSHIDA (M2): In situ dry preparation of catalysts on ceramic powders and fluidized-bed synthesis of long CNTs.
  • Kaisheng FENG (M1): Continuous gas-phase synthesis of CNTs by floating supported catalyst.
  • Zihao ZHANG (M1): Enhanced production of single-wall CNTs and their yarns by floating catalyst CVD method.
  • Ryoya OTAHARA (B4): Gas-phase synthesis of CNTs by high-density floating catalyst.
  • Bozhi CHEN (B4): Fluidized-bed synthesis of small-diameter carbon nanotubes using flame-synthesized nanopowder catalyst.

  • (2D Synthesis & Applications)
  • Michiko EDO (M2): Combinatorial screening of binary metal catalyst for chirality controlled synthesis of CNTs.
  • Sae KITAGAWA (M2): Fabrication of self-organized CNT spike arrays for electron emitter application.
  • Toshihiro SATO (M2): Understanding and engineering of catalytic growth of long CNTs on substrates.
  • Mayu ASAKA (M1): On-aluminum synthesis, morphology control, and heat-transfer application of CNTs.
  • Rei NAKAGAWA (M1): Catalysts and mechanisms for vertically aligned growth of long CNTs.
  • Mengju YANG (M1): On-substrate synthesis of millimeter-tall, large-diameter single-wall CNTs.
  • Tomohiro SEI (B4): Synthesis of long BNNTs.
  • Hiromu TAKAHASHI (B4): Synthesis of long BNNTs.
  • Pengfei CHEN (B4): Activation of alkane for CVD synthesis of CNTs.

Rapid SWCNT growth
Larger Movie.

Continuous production by fluidized bed: Movie

Soft Films and Solar Cells

Strong chemical bonds make bulk materials stable and mechanically hard. Whereas CNTs and BNNTs, one dimensional materials with strong chemical bonds and a-few-nm diameters, are stable yet mechanically soft. They easily form self-supporting, sponge-like films owing to the large specific surface areas, strong van der Waals interaction, and high aspect ratio for interwoven structure. When we integrate materials into devices, it is important how to make connections between materials. Our goal is to connect the interfaces as we like using these soft nanomaterials.
By the way, promoting the use of natural/renewable energy is essential to realize sustainable society. Japan has once been the leader for the solar cell technology and industry, however, we are now behind the world innovating this field. It is now widely recognized that renewable energy such as solar and wind powers are cheaper than nuclear and fire powers, there still remain vast areas with no electric power supply. Whether shall we install and use coal power plant or levelized renewable energy? The future will be much different. Various types of solar cells have been extensively researched, but the bulk crystalline silicon solar cells still account for >90% owing to their balanced cost, performance, reliability, and stability. Aiming at further cost reduction, we are developing a rapid vapor deposition process of highly crystalline Si films at >10 times larger area than the conventional Si substrates in 1 minute. We are also working on a simple cell fabrication process coating the Si film with CNTs and/or organic conductors. And we started technology assessment of their environmental, energy, and economical aspects.
  • Rongbin XIE (D1): Simple fabrication of silicon solar cells based on heterojunction with carbon nanomaterials.
  • Naoya ISHIJIMA (M2): Rapid vapor deposition of crystalline Si films and simple fabrication of flexible solar cells by coating Si with CNTs.
  • Kei OHASHI (M2): Investigation of catalyst metals for direct synthesis of graphene on SiO2 substrates by etching-precipitation method.
  • Yuki KANAZAWA (M1): Filling polymer sheet with high-density, vertically-aligned carbon fibers for thermal interface materials.
  • Satoru KAWAKAMI (LD1/M1): Hybridization of nanofibers with metal particles for anisotropic conductive films.
  • Mizuki MORI (B4): Novel synthesis method of free-standing graphene films.
  • Minami SUTO (B4): Rapid fabrication of large-grain Si films for solar cells.
  • Hideaki TANAKA (B4): Removing metals from CNTs and BNNTs by dry process.
  • Seven MUNAKATA (B4): Creation of metal aerogel by in-gas evaporation for connection of solid interfaces.

1-min-epitaxy and lift-off of Si films for solar cells

Electrochemical materials and processes for energy

Energy devices must be produced at low cost and installed at large scale in order to contribute to the sustainable energy and environmental systems.
We are developing next-generation, high energy and power density rechargeable batteries via rapid, high-yield fabrication process using low-cost sources. Self-supporting, sponge-like films of single-wall and few-wall CNTs can be easily obtained by dispersion and filtration. For example, 0.1 mm-thick paper of our few-wall CNTs by fluidized-bed CVD is as light as 0.3 mg/cm3 and 3 mg/cm2, has a 80-90% porosity and 100 S/cm electrical conductivity. Differently from the conventional electrodes fabricated by coating active materials on heavy current collectors of Cu or Al foils with binder and conductive fillers, we are developing light-weight, high-capacity electrodes by capturing various active materials in the CNT papers.
Especially, Si has a huge theoretical capacity 10-times as large as the current graphite anode, however is suffering from the degradation due to the volumetric change during charge-discharge cycles. Vapor deposition is a common method in basic research in preparing thin films slowly and carefully under ultrahigh vacuum. But it enables rapid, low-cost fabrication of aluminum thin films for gas barriers in snack packaging in industry. We elevate the vapor pressure of the evaporation source by heating it to a temperature much higher than the melting point, deposit the vapor on substrates at lower temperature, and realize several micrometer-thick porous films quickly in 1 minute. We are applying this method also for various metals to realize high-performance battery electrodes via simple, low-cost processes.
Hydrogen is expected as a clean secondary energy, which does not emit CO2 upon usage. Renewable energy is getting cheaper drastically, and large-scale production of CO2-free hydrogen is expected in future. However, breakthrough still is needed in its storage and transportation for their efficient use for production of energy and chemicals. Various technologies such as hydrogen storage alloys and hydrogen carriers have been researched, in which the chemical conversion of hydrogen via interfacial reaction is important. We are developing new materials by hybridization of hydrogen storage alloys and electrocatalysts with carbon nanotubes, and apparatuses and processes based on those materials.
  • Keisuke HORI (D2): Development of high-capacity lithium secondary batteries by capturing high-capacity cathode and anode materials in CNT sponge films.
  • Go YAMAGATA (M2): CNT-based hybrid electrodes of transition metal oxides for cathodes of Li ion batteries.
  • Tatsuya TOMINAGA (M2): On-foil growth, structure control, and battery application of vertically-aligned CNTs.
  • Yuta HASHIZUME (M2): Rapid vapor deposition of self-supporting Si/metal/Si films and their application to lithium secondary battery anodes.
  • Kentaro KANEKO (M1): Creation of nanotube-based separator and cathode/separater/anode unit for secondary batteries.
  • Tomotaro MAE (B4): Fast synthesis of Si nanoparticles and development of Si-CNT hybrid anode for lithium secondary battery.
  • Yuichi YOSHIE (B4): Peformance improvement of CNT-based Li-S battery.

  • (Electrochemistry)
  • Yusuke KOHASE (M1): Nanoparticle catalyst supported on CNT sponge films for electrolysis of aqueous ammonia for hydrogen recovery.
  • Natsuho AKAGI (B4): Electrolysis of liquid ammonia for hydrogen recovery.
  • Miho OKITSU (B4): Simple yet highly-sensitive, CNT-based sensor.
  • Kosuke KAJIWARA (B4): Alloy-CNT composite for efficient hydrogen storage.
  • Takafumi KUSAKABE (B4): High-capacity electrochemical capacitor based on Ni(OH)2-CNT hybrid films.
  • Neel PATIL (B4): Energy-efficient catalytic production of hydrogen from ammonia.

1-min deposition of porous Si films for Li ion batteries

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Noda-Hanada Laboratory,
Department of Applied Chemistry,
School of Advanced Science and Engineering,
Waseda University,
3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan