論文2020

名前をで表記しているメンバーは当研究室の学生・院生、で表記しているメンバーは当研究室の教員です。

原著論文

  1. Pemika Teabnamang, Wathanyu Kao-ian, Mai Thanh Nguyen, Tetsu Yonezawa, Rongrong Cheacharoen, Soorathep Kheawhom
    “High Capacity Dual-electrolyte Aluminum-air Battery with Circulating Methanol Anolyte”
    Energies, 13(9), 2275 (2020).
    DOI: 10.3390/en13092275 (Published 5 May 2020). 【Open Access】

    Abstract: Nevertheless, a critical issue limiting their practical application is corrosion of aluminum (Al) anode in an alkaline aqueous electrolyte, which results from hydrogen evolution reaction (HER). To effectively solve the corrosion issue, dissolution of Al anode should be carried out in a nonaqueous electrolyte. However, the main cathodic reaction, known as oxygen reduction reaction (ORR), is sluggish in such a nonaqueous electrolyte. A dual-electrolyte configuration with an anion exchange membrane separator allows AABs to implement a nonaqueous anolyte along with an aqueous catholyte. Thus, this work addresses the issue of anode corrosion in an alkaline Al–air flow battery via a dual-electrolyte system. The battery configuration consisted of an Al anode | anolyte | anion exchange membrane | catholyte | air cathode. The anolytes were methanol solutions containing 3 M potassium hydroxide (KOH) with different ratios of water. An aqueous polymer gel electrolyte was used as the catholyte. The corrosion of Al in the anolytes was duly investigated. The increase of water content in the anolyte reduced overpotential and exhibited faster anodic dissolution kinetics. This led to higher HER, along with a greater corrosion rate. The performance of the battery was also examined. At a discharge current density of 10 mA·cm−2, the battery using the anolyte without water exhibited the highest specific capacity of 2328 mAh/gAl, producing 78% utilization of Al. At a higher content of water, a higher discharge voltage was attained. However, due to greater HER, the specific capacity of the battery decreased. Besides, the circulation rate of the anolyte affected the performance of the battery. For instance, at a higher circulation rate, a higher discharge voltage was attained. Overall, the dual-electrolyte system proved to be an effective approach for suppressing anodic corrosion in an alkaline Al–air flow battery and enhancing discharge capacity.

  2. Ryan Dula Corpuz, Lyn Marie De Juan-Corpuz, Mai Thanh Nguyen, Tetsu Yonezawa, Heng-Liang Wu, Anongnat Somwangthanaroj, Soorathep Kheawhom
    “Binder-Free α-MnO2 Nanowires on Carbon Cloth as Cathode Material for Zinc-ion Batteries”
    International Journal of Molecular Sciences, 21(9), 3113 (2020). 【Open Access】
    DOI: 10.3390/ijms21093113 (Published 28 April 2020)

    Abstract: Recently, rechargeable zinc-ion batteries (ZIBs) have gained a considerable amount of attention due to their high safety, low toxicity, abundance, and low cost. Traditionally, a composite manganese oxide (MnO2) and a conductive carbon having a polymeric binder are used as a positive electrode. In general, a binder is employed to bond all materials together and to prevent detachment and dissolution of the active materials. Herein, the synthesis of α-MnO2 nanowires on carbon cloth via a simple one-step hydrothermal process and its electrochemical performance, as a binder-free cathode in aqueous and nonaqueous-based ZIBs, is duly reported. Morphological and elemental analyses reveal a single crystal α-MnO2 having homogeneous nanowire morphology with preferential growth along {001}. It is significant that analysis of the electrochemical performance of the α-MnO2 nanowires demonstrates more stable capacity and superior cyclability in a dimethyl sulfoxide (DMSO) electrolyte ZIB than in an aqueous electrolyte system. This is because DMSO can prevent irreversible proton insertion as well as unfavorable dendritic zinc deposition. The application of the binder-free α-MnO2 nanowires cathode in DMSO can promote follow-up research on the high cyclability of ZIBs.

  3. Ikumi Akita, Yohei Ishida, and Tetsu Yonezawa
    “Atomic-scale Imaging of a Free-standing Monolayer Clay Mineral Nanosheet using Scanning Transmission Electron Microscopy”
    The Journal of Physical Chemistry Letters, in press.
    DOI:10.1021/acs.jpclett.0c00758 (Published (web) 5 April 2020)

    Abstract: Although aberration-corrected scanning transmission electron microscope (STEM) enables the atomic-scale visualization of ultrathin 2D materials such as graphene, imaging of electron-beam sensitive 2D materials with structural complexity is an intricate problem. We here report the first atomic-scale imaging of a free-standing monolayer clay mineral nanosheet via the annular dark field (ADF) STEM. The monolayer clay nanosheet was stably observed under optimal conditions, and we confirmed that the hexagonal contrast pattern with a pore of ∼4 Å corresponds to the atomic structure of clay mineral that consisted of adjacent Si, Al, Mg, and O atoms by comparison with simulations. The findings offer the usefulness of ADF–STEM techniques for the atomic scale imaging of clay minerals and various 2D materials having electron-beam sensitivity and structural complexity than few-atom-thick graphene analogues.

  4. Shilei Zhu, Dan Deng, Mai Thanh Nguyen, Yuen-ting Rachel Chau, Cheng-Yen Wen, Tetsu Yonezawa
    “Synthesis of Au@Cu2O Core-Shell Nanoparticles with Tunable Shell Thickness and Their Degradation”
    Langmuir, 36(13), 3386-3392 (2020).
    DOI: 10.1021/acs.langmuir.0c00382 (Published (web) 16 Mar 2020)

    Abstract: Metal@semiconductor core-shell nanoparticles (NPs) are widely used in photocatalysts, sensors and optical applications thanks to the unique metal-semiconductor interface and integration of the properties from both core and shell materials. Although many efforts have been paid on the precise synthesis of Au@Cu2O core-shell structures, the chemical stability of Au@Cu2O aqueous suspensions are not mentioned in any published research, which is of great significance in many related applications. Herein, we report the synthesis of Au@Cu2O core-shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV-Vis absorption properties are found to be tunable with Cu2O thickness in the range of 2~40 nm. Furthermore, the chemical stability of Au@Cu2O core-shell nanoparticle suspensions in ethanol-water mixed solvents are investigated. It was found that ethanol-water mixed solvents with high water content are more likely to deteriorate the stability of Au@Cu2O NPs by oxidizing Cu2O to CuO. The results from this work may provide useful information for the preparation of metal@Cu2O water-based suspensions which are expected to be used for the SERS, photocatalyst or photothermal applications.

  5. Hsin-hui Huang, Takeshi Nagashima, Tetsu Yonezawa, Yasutaka Matsuo, Soon Hock Ng, Saulius Juodkazis, Koji Hatanaka
    “Giant enhancement of THz wave emission under double pulse excitation of thin water flow”
    Applied Sciences, 10(6), 2031 (2020). (12 pp.)【Open Access】
    DOI: 10.3390/app10062031 (Published 17 Mar 2020)

    Abstract: Simultaneous measurements of THz wave and hard X-ray emission from thin and flat water flow when irradiated by double femtosecond laser pulses (800 nm, 35 fs/transform-limited, 0.5 kHz, delay times up to 15 ns) were carried out. THz wave measurements by time-domain spectroscopy and X-ray detection by Geiger counters were performed at the transmission and the reflection sides of the flow. THz wave emission spectra show their dynamic peak shifts toward the low frequency with the highest intensity enhancements more than 1.5×103 times in |E|2 accumulated over the whole spectrum range of 0–3 THz at the delay time of 4.7 ns between the two pulses. On the other hand, X-ray intensity enhancements are limited to about 20 times at 0 ns under the same experimental conditions. The mechanisms for the spectral changes and the intensity enhancements in THz wave emission are discussed from the viewpoint of laser ablation on the water flow induced by the pre-pulse irradiation.

  6. Lianlian Deng, Mai Thanh Nguyen, Jinming Shi, Yuen-ting Rachel Chau, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Naoyuki Hashimoto, and Tetsu Yonezawa*
    “Highly Correlated Size and Composition of Pt/Au Alloy Nanoparticles via Magnetron Sputtering onto Liquid”
    Langmuir, 36(12), 3004-3015 (2020).
    DOI: 10.1021/acs.langmuir.0c00152 (Published (web) 9 Mar 2020)

    Abstract: Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloy with the face-centered cubic (fcc) structure. In addition, particle sizes, composition, and shape are strongly correlated but can be tailored by appropriate variation of sputtering parameters. No individual particle but large agglomerates with partially alloy structure formed at Pt content less than 16 at.%. Highly dispersed NPs with no agglomeration were observed in PEG when Pt atomic percentage is more than 26 at.%. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment as well as computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of cluster, and the interaction between different metal atoms and PEG molecule.

  7. Hsin-Hui Huang, Yuen-ting Rachel Chau, Tetsu Yonezawa,* Mai Thanh Nguyen, Shilei Zhu, Dan Deng, Takeshi Nagashima, Koji Hatanaka*
    “THz Wave Emission From ZnTe Nano-Colloidal Aqueous Dispersion Irradiated by Femtosecond Laser”
    Chemistry Letters, 49(6), 597-600 (2020).
    DOI: 10.1246/cl.200055 (Published (web) 12 Mar 2020)

    Abstract: THz wave emission from ZnTe nano-colloidal aqueous dispersion flow (the particle size is 5-nm in diameter, the flow thickness is 17 μm) with two different particle densities (1.60 mmol/L and 1.07 mmol/L) was measured by time-domain spectroscopy (TDS) under femtosecond laser irradiation (>35 fs/transform-limited, 800 nm, horizontally-polarized, 0.5 kHz) in air. Intensity increase and peak shift in the TDS signal wave-form if compared with distilled water indicate that THz wave emission is induced in ZnTe nano-particles in the aqueous dispersion.

  8. Ikumi Akita, Yohei Ishida, and Tetsu Yonezawa
    “COUNTING THE LAYER NUMBER OF FREE-STANDING MONTMORILLONITE NANOSHEETS USING ANNULAR DARK FIELD SCANNING TRANSMISSION ELECTRON MICROSCOPY”
    Clay Science21(3), 41-45 (2019).【Open Access】
    DOI: 10.11362/jcssjclayscience.23.3_41 (Published 1 Mar 2020)

    Abstract: In this report, we demonstrate the direct determination of the layer number of free-standing montmorillonite (MMT) nanosheets using annular dark field (ADF) scanning transmission electron microscopy (STEM). The layer number of the free-standing MMT nanosheets deposited on a holey carbon-coated grid was successfully counted to range from monolayer to four layers by the difference in the ADF contrast. Meanwhile, counting of the layer numbers was difficult using conventional TEM and bright field STEM due to the low contrast. Therefore, ADF–STEM can potentially be applied to further investigate the clay nanosheets and their molecular complexes by the atomic scale imaging for a deeper understanding of clay-nanosheet-based chemistry.

  9. Yuen-ting Rachel Chau, Mai Thanh Nguyen, Mingbei Zhu, Arnaud Romier, Tomoharu Tokunaga, and Tetsu Yonezawa*
    “Synthesis of compositional tunable Pd-Cu alloy nanoparticles by double target sputtering”
    New Journal of Chemistry, 44(12), 4704-4712 (2020).
    DOI: 10.1039/D0NJ00288G (Published (web) 5 Feb 2020)

    Abstract: In this work, we introduce a green synthesis technique, double-target sputtering into a liquid polymer – polyethylene glycol (PEG, M. W. = 600), to synthesize palladium-copper (Pd-Cu) alloy nanoparticles (NPs) dispersed in PEG. The composition of Pd and Cu in the alloy NPs can be controlled and varied by applying different sputtering currents for Pd and Cu targets. The particle sizes of Pd-Cu NPs are maintained in the range of 2.3-2.4 nm for various Pd-Cu compositions. Oxidation issues and crystallinity enhancement are discussed.

    裏表紙採用,Cover illustration is also published.

  10. Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Cheng-Yen Wen, and Tetsu Yonezawa*
    “In situ TEM observation of liquid-state Sn nanoparticles vanishing in SiO2 structure: a potential synthetic tool for controllable morphologies from core-shell to yolk-shell and hollow structures”
    Nanoscale Advances, 2(4), 1456-1464 (2020).【Open Access】
    DOI: 10.1039/C9NA00782B (Publsihed (web) on 3 Feb 2020)

    Abstract: Precise design of hollow nanostructure can be realized via various approaches that developed in last two decades, endowing the nanomaterials with unique structures and outstanding performances, showing their talents in a broad range of fields. Herein, we demonstrate the formation of SnO2@SiO2 hollow nanostructures, for the first time, by interaction between liquid state Sn cores and SiO2 shell structure inside Sn@SiO2 core-shell nanoparticles with real-time observation via in situ transmission electron microscopy (TEM). Based on the in situ results, a designed transformation of nanoparticle structure from core-shell Sn@SiO2 to yolk-shell Sn@SiO2 and hollow SnO2@SiO2 is demonstrated, showing the controllable structure from core-shell Sn@SiO2 nanoparticles via fixing liquid state Sn inside SiO2 shell which has a certain Sn containing capacity. The present approach expands the toolbox for the design and preparation of yolk-shell and hollow nanostructure, thus provides us a new strategy in fabrication of more complicated nanostructures.

  11. Laksanaporn Poolnapol, Wathanyu Kao-ian, Anongnat Somwangthanaroj, Falko Mahlendorf, Mai Thanh Nguyen, Tetsu Yonezawa, and Soorathep Kheawhom
    “Silver Decorated Reduced Graphene Oxide as Electrocatalyst for Zinc–Air Batteries”
    Energies, 13(2), 462 (2020). 【Open Access】
    DOI:10.3390/en13020462 (Published on 17 January 2020) 

    Abstract: Due to their low cost and very high energy density, zinc–air batteries (ZABs) exhibit high potential for various energy applications. The electrochemical performance of the air-cathode has a decisive impact on the discharge performance of ZABs because the sluggish oxygen reduction reaction (ORR) kinetics increase the overpotential of the air-cathode and hence the performance of ZABs. In this work, reduced graphene oxide decorated with silver nanoparticles (AgNP/rGO) is synthesized using simultaneous reduction of graphene oxide and silver ions. Different amounts of silver loading are examined for the synthesis of AgNP/rGO. The synthesized AgNP/rGO samples are analyzed using a rotating disk electrode in order to investigate ORR activity. Then, the synthesized AgNP/rGO electrocatalyst is applied on a tubular designed zinc–air battery in order to study the performance of the zinc–air battery. Results demonstrate that AgNP/rGO is an efficient and cost-effective ORR electrocatalyst for its practical application in ZABs.

総説・解説

  1. 米澤 徹
    「濃厚分散系としての導電インク・ペーストの作製ならびに微細構造検証」【総説】
    日本接着学会誌56(5), (2020).(印刷中)
  2. 松原正樹・蟹江澄志・米澤 徹
    「高分子修飾微粒子・ナノ粒子の熱的構造制御」
    材料表面5(1), 11-17 (2020).
    Masaki Matsubara,* KIyoshi Kanie, and Tetsu Yonezawa
    “Thermal Structure Control of Polymer-Modified Fine Particles and Nanoparticles”
    Accounts of Materials & Science Research5(1), 11-17 (2020).
    Link (Published (web) 30 Jan 2020)

    Abstract: Polymer-modified inorganic fine particles and nanoparticles have a great possibility of developing synergistic functions that cannot be achieved with inorganic materials and organic materials themselves, because polymers exhibit thermally unique behavior. We have focused on these unique thermal behaviors of polymers and designed chemical structures of polymers in terms of the functions required for hybrid materials. In this account paper, low-temperature sintering and sintered structure of Cu fine particles and temperature-dependent self-organized structure of organic-inorganic dendrimers are briefly reviewed. A new preparation method of polymer-modified fine particles by SI-ATRP will also be discussed.