九州大学 研究者情報
論文一覧
山内 美穂(やまうちみほ) データ更新日:2024.06.03

教授 /  先導物質化学研究所 分子集積化学部門


原著論文
1. Mingxu Sun, Jiamin Cheng, Miho Yamauchi, Gas diffusion enhanced electrode with ultrathin superhydrophobic macropore structure for acidic CO2 electroreduction, Nature Communications, 10.1038/s41467-024-44722-4, 15, 1, 491-1-491-9, 2024.01, AbstractCarbon dioxide (CO2) electroreduction reaction (CO2RR) offers a promising strategy for the conversion of CO2 into valuable chemicals and fuels. CO2RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO2 diffusion due to the absence of hydroxide that facilitates the CO2 diffusion in an acidic environment. Here, we design an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO2RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density $$( {j}_{ { { { m{C } } } }_{2+ } })$$ of −1.6 A cm−2 for multicarbon products (C2+), and $$ {j}_{ { { { { { m{C } } } } } }_{2+ } }$$ of −0.34 A cm−2 when applying dilute 25% CO2. In a highly acidic environment, C2+ formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide..
2. Nada H A Besisa, Ki-Seok Yoon, Miho Yamauchi, In situ electrochemical regeneration of active 1,4-NADH for enzymatic lactic acid formation via concerted functions on Pt-modified TiO2/Ti, Chemical Science, 10.1039/d3sc04104b, 2024.01, Nicotinamide adenine dinucleotide (NAD+) and its reduced form (NADH) are key cofactors serving as essential hydrogen accepters and donors to facilitate energy and material conversions under mild conditions. We demonstrate direct electrochemical conversion....
3. T. G. Noguchi, D. S. R. Rocabado, Y. Kojo, A. Oyabe, T. Ishimoto, M. Yamauchi, Definitive Adsorption States of Intermediates on Ru Nanocatalysts for Progress of Ammonia Synthesis Discovered by Modulation Excitation Spectroscopy under Reaction Conditions, J. Catal., doi.org/10.1016/j.jcat.2023.07.020 J. Catal., 426, 301-307 (2023)., 426, 301-307, 2023.10.
4. T. Fukushima, M. Higashi, M. Yamauchi, Carbon-neutral energy cycle via highly selective electrochemical reactions using biomass derivable organic liquid energy carriers, Bull. Chem. Soc. Jpn., doi:10.1246/bcsj.20230172 , 2023.10.
5. Tomohiro Goroh Noguchi, David S. Rivera Rocabado, Yuki Kojo, Atsushi Oyabe, Takayoshi Ishimoto, Miho Yamauchi, Definitive adsorption states of intermediates on Ru nanocatalysts for progress of ammonia synthesis discovered by modulation excitation spectroscopy under reaction conditions, Journal of Catalysis, 10.1016/j.jcat.2023.07.020, 426, 301-307, 2023.10.
6. A. Anzai, M. Higashi, M. Yamauchi, Direct electrochemical CO2 conversion using oxygen-mixed gas on a Cu network cathode and tailored anode, Chem. Comm., doi.org/10.1039/D3CC03298A, 59, 11188-11191, 2023.08.
7. Miho Yamauchi, Hikaru Saito, Toshiki Sugimoto, Shogo Mori, Susumu Saito, Sustainable organic synthesis promoted on titanium dioxide using coordinated water and renewable energies/resources, Coordination Chemistry Reviews, 10.1016/j.ccr.2022.214773, 472, 214773-214773, 2022.12.
8. Mingxu Sun, Aleksandar Staykov, and Miho Yamauchi, Understanding the Roles of Hydroxide in CO2 Electroreduction on a Cu Electrode for Achieving Variable Selectivity, ACS Catal., doi.org/10.1021/acscatal.2c03650, 12, 14856-14863, 2022.11.
9. Xuemei Liao, Mengdie Guo, Wei Tang, Changwen Liu, Wei Luo, Lei Tan, Tomohiro G. Noguchi, Miho Yamauchi, Yonghui Zhao, Xiaopeng Li, Bimetallic single atom promoted α-MnO2 for enhanced catalytic oxidation of 5-hydroxymethylfurfural, Green Chemistry, doi.org/10.1039/d2gc01769e, 24, 21, 8424-8433, 2022.10.
10. K. Fukutani, J. Yoshinobu, M. Yamauchi, T. Shima, S. Orimo, Hydrogenomics: Efficient and Selective Hydrogenation of Stable Molecules Utilizing Three Aspects of Hydrogen, Catalysis Letters, 10.1007/s10562-021-03750-1, 152, 6, 1583-1597, 2022.06.
11. Kohei Aso, Hirokazu Kobayashi, Shotaro Yoshimaru, Xuan Quy Tran, Miho Yamauchi, Syo Matsumura, Yoshifumi Oshima, Singular behaviour of atomic ordering in Pt-Co nanocubes starting from core-shell configurations, Nanoscale, 10.1039/d2nr01982e, 14, 27, 9842-9848, 2022.06, The ordered structure of platinum–cobalt (Pt–Co) alloy nanoparticles has been studied actively because the structure influences their magnetic and catalytic properties. On the Pt–Co alloy’s surface, Pt atoms preferentially segregate....
12. Akihiko Anzai, Ming-Han Liu, Kenjiro Ura, Tomohiro G. Noguchi, Akina Yoshizawa, Kenichi Kato, Takeharu Sugiyama, Miho Yamauchi, Cu Modified TiO2 Catalyst for Electrochemical Reduction of Carbon Dioxide to Methane, Catalysts, 10.3390/catal12050478, 12, 5, 478-478, 2022.04, Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%..
13. Sho Kitano, Tomohiro G. Noguchi, Masamichi Nishihara, Kazutaka Kamitani, Takeharu Sugiyama, Satoru Yoshioka, Tetsuya Miwa, Kazunari Yoshizawa, Aleksandar Staykov, Miho Yamauchi, Heterointerface Created on Au‐Cluster‐Loaded Unilamellar Hydroxide Electrocatalysts as a Highly Active Site for the Oxygen Evolution Reaction, Advanced Materials, 10.1002/adma.202110552, 34, 16, 2110552-2110552, 2022.03, AbstractThe oxygen evolution reaction (OER) is a critical element for all sorts of reactions that use water as a hydrogen source, such as hydrogen evolution and electrochemical CO2 reduction, and novel design principles that provide highly active sites on OER electrocatalysts push the limits of their practical applications. Herein, Au‐cluster loading on unilamellar exfoliated layered double hydroxide (ULDH) electrocatalysts for the OER is demonstrated to fabricate a heterointerface between Au clusters and ULDHs as an active site, which is accompanied by the oxidation state modulation of the active site and interfacial direct OO coupling (“interfacial DOOC”). The Au‐cluster‐loaded ULDHs exhibit excellent activities for the OER with an overpotential of 189 mV at 10 mA cm−2. X‐ray absorption fine structure measurements reveal that charge transfer from the Au clusters to ULDHs modifies the oxidation states of trivalent metal ions, which can be active sites on the ULDHs. The present study, supported by highly sensitive spectroscopy combining reflection absorption infrared spectroscopy and modulation‐excitation spectroscopy and density functional theory calculations, indicates that active sites at the interface between the Au clusters and ULDHs promote a novel OER mechanism through interfacial DOOC, thereby achieving outstanding catalytic performance..
14. David S. Rivera Rocabado, Mika Aizawa, Tomohiro G. Noguchi, Miho Yamauchi, Takayoshi Ishimoto, Uncovering the Mechanism of the Hydrogen Poisoning on Ru Nanoparticles via Density Functional Theory Calculations, Catalysts, 10.3390/catal12030331, 12, 3, 331-331, 2022.03, Although hydrogen plays a crucial role in ammonia synthesis, very little is known about its poisoning of Ru catalysts. In this study, density functional theory calculations of H2 and N2 dissociations, and H atom binding on Ru153 were performed to provide a fundamental understanding of hydrogen poisoning. Because of the kinetic dominance of the H2 dissociation over N2 (vertically or horizontally adsorbed) splitting, the dissociated H atoms block the active sites required for horizontal (less energetically demanding dissociation) N2 adsorption to occur either from the gas phase or after its geometrical transformation from being adsorbed vertically. Additionally, the dissociated H atoms withdraw electrons from the surface, which reduces the ability of the neighboring Ru atoms to donate electrons for N2 activation, hindering its dissociation and suppressing ammonia synthesis..
15. Kenshi Matsumoto, Ryota Sato, Yasutomi Tatetsu, Ryo Takahata, Seiji Yamazoe, Miho Yamauchi, Yuji Inagaki, Yoichi Horibe, Masaki Kudo, Takaaki Toriyama, Mitsunari Auchi, Mitsutaka Haruta, Hiroki Kurata, Toshiharu Teranishi, Inter-element miscibility driven stabilization of ordered pseudo-binary alloy, Nature Communications, 10.1038/s41467-022-28710-0, 13, 1, 2022.02, Abstract

An infinite number of crystal structures in a multicomponent alloy with a specific atomic ratio can be devised, although only thermodynamically-stable phases can be formed. Here, we experimentally show the first example of a layer-structured pseudo-binary alloy, theoretically called Z3-FePd3. This Z3 structure is achieved by adding a small amount of In, which is immiscible with Fe but miscible with Pd and consists of an alternate L10 (CuAu-type)-PdFePd trilayer and Pd–In ordered alloy monolayer along the c axis. First-principles calculations strongly support that the specific inter-element miscibility of In atoms stabilizes the thermodynamically-unstable Z3-FePd3 phase without significantly changing the original density of states of the Z3-FePd3 phase. Our results demonstrate that the specific inter-element miscibility can switch stable structures and manipulate the material nature with a slight composition change..
16. A. Chapman, E. Ertekin, M. Kubota, A. Nagao, K. Bertsch, A. Macadre, T. Tsuchiyama, T. Masamura, S. Takaki, R. Komoda, M. Dadfarnia, B. Somerday, A, Staykov, J. Sugimura, Y. Sawae, T. Morita, H. Tanaka, K. Yagi, V. Niste, P. Saravanan, S. Onitsuka, K-S. Yoon, S. Ogo, T. Matsushima, G. Tumen-Ulziil, D. Klotz, D. H. Nguyen,G. Harrington, C. Adachi, H. Matsumoto, L. Kawati, Y. Takahashi, N. Kosem, T. Ishihara, M. Yamauchi,B. B. Saha,M. A. Islam, J. Miyawaki, H. Sivasavkaran,M. Kohno, S. Fujikawa, R. Selyanchyn, T. Tsuji, Y. Higashi, R. Kirchheim,P. Sofronis, Achieving a Carbon Neutral Future through Advanced Functional Materials and Technoligies, Bull. Chem. Soc. Jpn., doi.org/10.1246/bcsj.20210323, 95, 1, 73-103, 2022.01.
17. David S. Rivera Rocabado, Tomohiro G. Noguchi, Shio Hayashi, Nobutaka Maeda, Miho Yamauchi, Takayoshi Ishimoto, Adsorption States of N2/H2 Activated on Ru Nanoparticles Uncovered by Modulation–Excitation Infrared Spectroscopy and Density Functional Theory Calculations, ACS Nano, 10.1021/acsnano.1c07825, 15, 12, 20079-20086, 2021.12.
18. Hiroto Eguchi, Takashi Kobayashi, Teppei Yamada, David S.Rivera Rocabado, Takayoshi Ishimoto, Miho Yamauchi, Inversely polarized thermo-electrochemical power generation via the reaction of an organic redox couple on a TiO2/Ti mesh electrode, Scientific Reports, 10.1038/s41598-021-93269-7, 11, 1, 2021.12, Abstract

We demonstrate thermo-electrochemical (TEC) conversion using a biocompatible redox couple of lactic acid and pyruvic acid on earth-abundant TiO2. The TEC cell exhibited a positive Seebeck coefficient of 1.40 mV K−1. DFT calculations figured out that the adsorption of intermediate species and protons on TiO2 controls both the redox reaction and current polarity..
19. Xuemei Liao, Yonghui Zhao, Changwen Liu, Xiaopeng Li, Yu Sun, Kenichi Kato, Miho Yamauchi, Zheng Jiang, Low temperature surface oxygen activation in crystalline MnO2 triggered by lattice confined Pd single atoms, Journal of Energy Chemistry, 10.1016/j.jechem.2021.03.012, 62, 136-144, 2021.11, Tuning the coordination environment is the research axis of single atom catalysts (SACs). SACs are commonly stabilized by various defects from support. Here, we report a lattice confined Pd SAC using MnO as support. Compared with the Pd clusters anchored on the surface, the lattice confined Pd single atoms allows spontaneous exaction of surrounding lattice oxygen at room temperature when employed in CO oxidation. The MnO supported Pd SAC exhibited a high turnover frequency of 0.203 s at low reaction temperature, which is higher than that of recently reported Pd SACs. Theoretical calculations also confirmed the confined monatomic Pd activate lattice oxygen with an ultralow energy barrier. Our results illustrate that the unique coordination environment of single atom provided by lattice confinement is promising to boost the activity of SACs. 2 2 −1.
20. Miho Yamauchi, Inorganic Nanocatalysts for Hydrogenation Reactions Contributable to a Sustainable Material Supply, Chemistry Letters, 10.1246/cl.210454, 50, 11, 1901-1908, 2021.11.
21. J. Cheng, P. Ganesan, Z. Wang, M. Zhang, G. Zhang, N. Maeda, J. Matsuda, M. Yamauchi, B. Chi, N. Nakashima, Bifunctional electrochemical properties of La0.8Sr0.2Co0.8M0.2O3−δ (M = Ni, Fe, Mn, and Cu): efficient elemental doping based on a structural and pH-dependent study, Materials Advances, 10.1039/d1ma00632k, 3, 272-281, 2021.10, Perovskite oxides with a low cost and high catalytic activity are considered as suitable candidates for the oxygen evolution reaction (OER)/oxygen reduction reaction (ORR), but most of them favour only either the ORR or the OER..
22. Hiroto Eguchi, Kenichi Kato, Gergely Juhasz, Miho Yamauchi, Selectivity enhancement in the electrochemical reduction of oxalic acid over titanium dioxide nanoparticles achieved by shape and energy-state control, Catalysis Science and Technology, 10.1039/d1cy01239h, 11, 23, 7592-7597, 2021.09, The morphology of TiO2 nanoparticles has a substantial impact on the product selectivity in an electrochemical reduction reaction..
23. Norihiro Oshime, Kenji Ohwada, Kento Sugawara, Tomohiro Abe, Reiji Yamauchi, Tetsuro Ueno, Akihiko Machida, Tetsu Watanuki, Shintaro Ueno, Ichiro Fujii, Satoshi Wada, Ryota Sato, Toshiharu Teranishi, Miho Yamauchi, Kenji Ishii, Hidenori Toyokawa, Koichi Momma, Yoshihiro Kuroiwa, Bragg coherent diffraction imaging allowing simultaneous retrieval of three-dimensional shape and strain distribution for 40–500 nm particles, Japanese Journal of Applied Physics, 10.35848/1347-4065/ac148b, 60, SF, SFFA07-SFFA07, 2021.08.
24. Miho Isegawa, Aleksandar Staykov, Miho Yamauchi, Proton-Coupled Electron Transfer in Electrochemical Alanine Formation from Pyruvic Acid: Mechanism of Catalytic Reaction at the Interface between TiO2 (101) and Water, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.1c01304, 125, 23, 12603-12613, 2021.06.
25. Shotaro Yoshimaru, Masaaki Sadakiyo, Nobutaka Maeda, Miho Yamauchi, Kenichi Kato, Jenny Pirillo, Yuh Hijikata, Support Effect of Metal-Organic Frameworks on Ethanol Production through Acetic Acid Hydrogenation, ACS Applied Materials and Interfaces, 10.1021/acsami.1c01100, 13, 17, 19992-20001, 2021.05, We present a systematic study on the support effect of metal-organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH2, UiO-66-NH2, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH2 and MIL-125-NH2) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH2 showed a remarkably high EtOH yield (31% at 200 °C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO2, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH2 support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH..
26. Mengmeng Liu, Shang Hu, Yaojia Zhang, Chuyi Zhao, Wenqian Jiang, Chunhong Qi, Xiaohang Zhu, Pengpeng Qiu, Yu Sun, Kenichi Kato, Yonghui Zhao, Xiaopeng Li, Miho Yamauchi, Wei Luo, Atomistic Site Control of Pd in Crystalline MnO2 Nanofiber for Enhanced Electrocatalysis, Advanced Materials Interfaces, 10.1002/admi.202002060, 8, 8, 2021.04, Oxides supported precious metals have wide applications in (electro-)catalysis. Although single atom dispersion is known as the most efficient metal utilization strategy, the dependence of the catalytic activity on different sites consisted of various anchoring sites for single atoms is largely unknown. Here, the electrocatalytic activities of crystalline α-MnO with atomistic Pd locating at different sites including substitutional, tunnel, and surface-bound sites are first predicted, and then experimentally validated by applying different synthetic methods including hydrothermal reaction and impregnation-calcination. The quantum chemistry calculations together with experimental characterization suggest that substitutional Pd/MnO possesses higher activity than the other samples due to the favorable geometric and electronic structures. Substitutional Pd can work synergistically with vicinal Mn sites toward cleavage of O-O bonds. This work provides a comprehensive understanding on the impact of atomistic anchoring site and advances the reliable control over the electrocatalytic performance of oxide-supported single atoms. 2 2.
27. Sho Kitano, Mei Lee Ooi, Tomokazu Yamamoto, Syo Matsumura, Miho Yamauchi, Catalytic Roles and Synergetic Effects of Iron-Group Elements on Monometals and Alloys for Electrochemical Oxidation of Ammonia, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20210007, 94, 4, 1292-1299, 2021.04.
28. Takashi Fukushima, Miho Yamauchi, Electrosynthesis of glycine from bio-derivable oxalic acid, Journal of Applied Electrochemistry, 10.1007/s10800-020-01428-x, 51, 1, 99-106, 2021.01, Abstract: Electrochemical hydrogenation of non-fossil resources to produce value added chemicals has great potential to contribute to realization of sustainable material supply. We previously demonstrated that TiO catalyzed electrochemical reduction of biomass-derivable α-keto acid in the presence of NH or NH OH affords amino acids. In this work, we focused on oxalic acid, which is producible by chemical degradation of agro wastes, as a starting material for the electrosynthesis of an amino acid. We examined the electrocatalytic properties of various materials, including Cu, Pt, Ti foils, calcined Al, Co, Mo, Nb, Ni, Ti, V, W, Zr foils, and some TiO catalysts, by conducting linear sweep voltammetry (LSV) measurements, and found that Mo and Ti foil calcined at 450 °C show favorable catalytic features for the one-step glycine electrosynthesis from oxalic acid and NH OH. Electrochemical reduction of oxalic acid at an applied potential of − 0.7 V using calcined Ti foil resulted in formation of glycine and glyoxylic acid oxime, i.e., intermediate of the glycine formation, with moderate Faradaic efficiency of 28 and 28%, respectively. Graphic abstract: [Figure not available: see fulltext.] 2 3 2 2 2.
29. Nating Yang, Yonghui Zhao, Hao Zhang, Weikai Xiang, Yuhan Sun, Shuai Yang, Yu Sun, Gaofeng Zeng, Kenichi Kato, Xiaopeng Li, Miho Yamauchi, Zheng Jiang, Tong Li, Sintering Activated Atomic Palladium Catalysts with High-Temperature Tolerance of ∼1,000°C, Cell Reports Physical Science, 10.1016/j.xcrp.2020.100287, 2, 1, 2021.01, Sintering-induced aggregation of active metals is a major cause of catalyst deactivation. Catalysts that can operate above 800°C are rare. Here, we report an unusual noble metal catalyst with sintering-induced activation at temperatures up to 1,000°C. The catalyst consists of atomically dispersed palladium embedded in a reducible SnO support designated for lean methane combustion. High temperature reaction simultaneously causes favorable changes of palladium ensemble state combining synergistically with lattice oxygen activation. Such changes lead to at least one order of magnitude improvement of the intrinsic reactivity, which compensates the surface area loss. Extensive characterizations such as atom probe tomography, X-ray absorption spectroscopy, and isotope tracking together with theoretical calculations illustrate the structure and surface chemistry changes and their impacts on the reaction mechanism. The catalyst also shows notable long-term stability and facile regeneration after poisoning. Our work may provide new insights into designing active and thermally stable catalysts. 2.
30. Junfang Cheng, Manabu Higashi, Nobutaka Maeda, Junko Matsuda, Miho Yamauchi, Naotoshi Nakashima, CO2-free energy circulation system—Polymer electrolyte alcohol electro-synthesis cell with a low iridium content anode based on in situ growth method, Electrochimica Acta, 10.1016/j.electacta.2020.137078, 361, 2020.11, Alcohol is considered as a potential CO -free energy carrier to replace hydrogen because of its high energy density, appropriate chemical stability and low-cost production. In this study, we describe the development of a simple in situ growth method to prepare a binder free IrO -Ti anode with a very low IrO loading amount (
31. Haojie Zhang, Yonghui Zhao, Yu Sun, Qing Xu, Ruoou Yang, Hao Zhang, Chao Lin, Kenichi Kato, Xiaopeng Li, Miho Yamauchi, Zheng Jiang, A novel self-assembly approach for synthesizing nanofiber aerogel supported platinum single atoms, Journal of Materials Chemistry A, 10.1039/d0ta03207g, 8, 30, 15094-15102, 2020.08, A great challenge in catalyst engineering is precisely assembling and positioning nanoscale active metals at desired locations while constructing robust functional architectures. This article presents a novel approach for constructing macroscopic Ag-doped manganese oxide aerogels (up to 2 L) while homogeneously incorporating active Pt single atoms (Pt/Ag-MnO2) based on a solution-solid-solid (SSS) mechanism. AgOx seeds were identified as key species for triggering the octopus-like growth of MnO2 nanofibers and inserting Ag and Pt into the MnO2 crystalline framework. The interconnection and entanglement among nanofibers allowed the formation of mechanically strengthened hierarchical structures, leading to one of the most robust manganese-based aerogels to date. Impressively, the Pt/Ag-MnO2 aerogel also possessed promising selectivity and stability toward the electrocatalytic oxygen reduction reaction, with Pt showing a high mass activity of 1.6 A/(mgPt) at 0.9 V vs. RHE. Experimental characterization and theoretical calculation confirmed Pt single atoms to be located at substitutional lattice sites, which reduced the overall oxygen reduction barriers. Our approach suggests that SSS or other analogous nanofiber or nanowire growth strategies are powerful in controlling structural formation over the entire range of length scales while being applicable to fabricating single-atom catalysts..
32. Takashi Fukushima, Manabu Higashi, Sho Kitano, Takeharu Sugiyama, Miho Yamauchi, Multiscale design for high-performance glycolic acid electro-synthesis cell: Preparation of nanoscale-IrO2-applied Ti anode and optimization of cell assembling, Catalysis Today, 10.1016/j.cattod.2019.03.071, 351, 12-20, 2020.07, Performance of a polymer electrolyte alcohol electrosynthesis cell (PEAEC) using a glycolic acid (GC)/oxalic acid (OX) redox couple was enhanced via the multiscale approach, i.e., increase of reaction rate on an anode by employing nanometer-scale (nanoscale) IrO catalysts and increase of selectivity for GC production via optimization of cell structures, i.e., a millimeter-scale approach. We prepared nanoscale IrO anode catalyst, which is mixture of IrO nanoparticles (d = 3.7 ± 1.8 nm) and their agglomerates (d
33. Jun Yang, Junfang Cheng, Jie Tao, Manabu Higashi, Miho Yamauchi, Naotoshi Nakashima, Wrapping Multiwalled Carbon Nanotubes with Anatase Titanium Oxide for the Electrosynthesis of Glycolic Acid, ACS Applied Nano Materials, 10.1021/acsanm.9b01357, 2, 10, 6360-6367, 2019.10, [URL], The construction of an efficient electrocatalyst is of significant importance for electrochemical devices. In this study, a facile preparation method is developed to wrap pristine multiwalled carbon nanotubes (MWNTs) by an anatase TiO layer with the assistance of pyridine-based polybenzimidazole (PyPBI) The factors dominating the morphology of the obtained MWNT/PyPBY/TiO products, involving the employment of PyPBI and the post-treatment method, are investigated in detail. Furthermore, a self-standing electrode film is prepared via a filtration route. The electrode film is composed of a MWNT/PyPBI/TiO catalyst layer and a MWNT current collecting layer. The resultant electrocatalysts and electrode film with the MWNT/PyPBI/TiO catalyst are evaluated for the electroreduction of oxalic acid (OX) to glycolic acid (GC). By using the optimized electrode film with the MWNT/PyPBI/TiO catalyst, the conversion rate of OX and the selectivity of GC reach 51.2% and 38.7%, respectively. 2 2 2 2 2.
34. Junfang Cheng, Jun Yang, Sho Kitano, Gergely Juhasz, Manabu Higashi, Masaaki Sadakiyo, Kenichi Kato, Satoru Yoshioka, Takeharu Sugiyama, Miho Yamauchi, Naotoshi Nakashima, Impact of Ir-Valence Control and Surface Nanostructure on Oxygen Evolution Reaction over a Highly Efficient Ir-TiO2 Nanorod Catalyst, ACS Catalysis, 10.1021/acscatal.9b01438, 9, 8, 6974-6986, 2019.08, [URL], Iridium oxide (IrOx)-based materials are the most suitable oxygen evolution reaction (OER) catalysts for water electrolysis in acidic media. There is a strong demand from industry for improved performance and reduction of the Ir amount. Here, we report a composite catalyst, IrOx-TiO2-Ti (ITOT), with a high concentration of active OH species and mixed valence IrOx on its surface. We have discovered that the obtained ITOT catalyst shows an outstanding OER activity (1.43 V vs RHE at 10 mA cm-2) in acidic media. Moreover, no apparent potential increase was observed even after a chronopotentiometry test at 10 mA cm-2 for 100 h and cyclic voltammetry for 700 cycles. We proposed a detailed OER mechanism on the basis of the analysis of the in situ electrochemical X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements as well as density functional theory (DFT) calculations. All together, we have concluded that controllable Ir-valence and the high OH concentration in the catalyst is crucial for the obtained high OER activity..
35. Junfang Cheng, Jun Yang, Sho Kitano, Gergely Juhasz, Manabu Higashi, Masaaki Sadakiyo, Kenichi Kato, Satoru Yoshioka, Takeharu Sugiyama, Miho Yamauchi, Naotoshi Nakashima, Impact of Ir-Valence Control and Surface Nanostructure on Oxygen Evolution Reaction over a Highly Efficient Ir-TiO2 Nanorod Catalyst, ACS Catalysis, 10.1021/acscatal.9b01438, 9, 8, 6974-6986, 2019.08, Iridium oxide (IrO )-based materials are the most suitable oxygen evolution reaction (OER) catalysts for water electrolysis in acidic media. There is a strong demand from industry for improved performance and reduction of the Ir amount. Here, we report a composite catalyst, IrO -TiO -Ti (ITOT), with a high concentration of active OH species and mixed valence IrO on its surface. We have discovered that the obtained ITOT catalyst shows an outstanding OER activity (1.43 V vs RHE at 10 mA cm ) in acidic media. Moreover, no apparent potential increase was observed even after a chronopotentiometry test at 10 mA cm for 100 h and cyclic voltammetry for 700 cycles. We proposed a detailed OER mechanism on the basis of the analysis of the in situ electrochemical X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements as well as density functional theory (DFT) calculations. All together, we have concluded that controllable Ir-valence and the high OH concentration in the catalyst is crucial for the obtained high OER activity. x x 2 x -2 -2.
36. Hadi Razavi-Khosroshahi, Sara Mohammadzadeh, Mirabbos Hojamberdiev, Sho Kitano, Miho Yamauchi, Masayoshi Fuji, BiVO 4 /BiOX (X = F, Cl, Br, I) heterojunctions for degrading organic dye under visible light, Advanced Powder Technology, 10.1016/j.apt.2019.04.002, 30, 7, 1290-1296, 2019.07, The accumulation of organic pollutants in surface water, groundwater, and even drinking water has raised as a serious issue in recent decades. Semiconductor-based photocatalysis has emerged as a green and sustainable approach to find remediate solutions for environmental and energy issues. However, the fast recombination rate of photogenerated charge carriers reduces the photocatalytic efficiency of photocatalysts. In this study, a hydrothermal synthesis method is proposed for preparing four types of p–n heterojunctions, BiVO /BiOX (X = F, Cl, Br, I). BiVO is an n-type semiconductor and BiOX is a p-type semiconductor. Photocatalytic activity tests showed that the BiVO /BiOF has the best photocatalytic performance under visible light, and photoluminescence spectra confirmed the lowest recombination rate of photogenerated charge carriers for BiVO /BiOF as compared with others. 4 4 4 4.
37. Shenglin Ni, Haojie Zhang, Yonghui Zhao, Xiaopeng Li, Yu Sun, Jin Qian, Qing Xu, Peng Gao, Dekun Wu, Kenichi Kato, Miho Yamauchi, Yuhan Sun, Single atomic Ag enhances the bifunctional activity and cycling stability of MnO2, Chemical Engineering Journal, 10.1016/j.cej.2019.02.084, 366, 631-638, 2019.06, Heterogeneous electrocatalyst with single atom feature has attracted great interests. Although significant progress has been made on constructing and understanding carbon supported single atom electrocatalysts (SAECs), few attentions has been paid to metal oxide supported SAECs. The effect of single atom in enhancing electrocatalytic activity and stability of metal oxides has been poorly understood. Here, we reported MnO nanowires loaded with single atomic Ag (Ag-MnO ) that can simultaneously catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The incorporation of Ag into the crystal framework of α-MnO provided multiple benefits including an improved conductivity and a substantial increase in both lattice distortion and oxygen vacancies. As a result, Ag-MnO outperformed α-MnO in oxygen electrocatalysis and showed ∼3-fold enhancement in kinetic current density. The Zinc air battery containing the Ag-MnO displayed a high discharge peak power of 273.2 mW cm , an energy density of 915.4 Wh kg and an outstanding rate performance. The Zinc air battery (ZAB) stably operated up to 3200 cycles of charge-discharge. Such excellent rechargeability can be ascribed to the promoted crystal phase transformation from α-MnO to δ-MnO that is beneficial for OER due to the presence of atomic Ag. 2 2 2 2 2 2 Zn 2 2 −2 −1.
38. H. Razavi-Khosroshahi,* S. Mohammadzadeh, M. Hojamberdiev, S. Kitano, M. Yamauchi, M. Fuji, Visible Light Active Bi3TaO7 Nanosheets for Water Splitting, Dalton Trans., 2019.05.
39. Kenichi Kato, Yoshihito Tanaka, Miho Yamauchi, Koji Ohara, Takaki Hatsui, A statistical approach to correct x-ray response non-uniformity in microstrip detectors for high-accuracy and high-resolution total-scattering measurements, Journal of Synchrotron Radiation, 10.1107/S1600577519002145, 26, 3, 762-773, 2019.05, An unbiased approach to correct X-ray response non-uniformity in microstrip detectors has been developed based on the statistical estimation that the scattering intensity at a fixed angle from an object is expected to be constant within the Poisson noise. Raw scattering data of SiO glass measured by a microstrip detector module was found to show an accuracy of 12σ at an intensity of 10 photons, where σ is the standard deviation according to the Poisson noise. The conventional flat-field calibration has failed in correcting the data, whereas the alternative approach used in this article successfully improved the accuracy from 12σ to 2σ . This approach was applied to total-scattering data measured by a gapless 15-modular detector system. The quality of the data is evaluated in terms of the Bragg reflections of Si powder, the diffuse scattering of SiO glass, and the atomic pair distribution function of TiO nanoparticles and Ni powder. 2 PN PN PN PN 2 2 6.
40. K. Edalati,* Q. Wang,* H. Eguchi, H. Razavi-Khosroshahi, H. Emami, M. Yamauchi, M. Fuji, Z. Horita, Impact of TiO2-II Phase Stabilized in Anatase Matrix by High Pressure Torsion on Electrocatalytic Hydrogen Production, Mater. Res. Lett., 2019.04.
41. Kenichi Yatsugi, Toshitaka Ishizaki, Kunio Akedo, Miho Yamauchi, Composition-controlled synthesis of solid-solution Fe–Ni nanoalloys and their application in screen-printed magnetic films, Journal of Nanoparticle Research, 10.1007/s11051-019-4497-2, 21, 3, 2019.03, [URL], Screen printing is attracting attention as a method for manufacturing magnetic components such as on-chip transformers and inductors. Fe–Ni alloys, which have high saturation magnetizations and permeabilities, are suitable as magnetic materials for screen-printed high-frequency devices. Here, we demonstrate the fabrication of a screen-printed film comprising solid-solution Fe–Ni nanoalloys, which can achieve enhanced permeability and reduced eddy-current losses in high-frequency regions. The Fe–Ni nanoalloys were prepared by chemical reduction using sodium borohydride as a reducing reagent followed by hydrogen reduction. X-ray diffraction measurements, electron microscopy, and inductively coupled plasma spectroscopy revealed that well-mixed Fe Ni nanoalloys (x = 40, 21.5, and 10) with grain sizes of ~ 10 nm were synthesized. The obtained nanoalloys showed high saturation magnetizations comparable to bulk alloys. The screen-printed film using the Fe Ni nanoalloy exhibited the highest permeability of the nanoalloy films. The eddy-current loss was suppressed by the synthesis of nanoscale-grained nanoalloys. The permeability was sufficiently high for application in transformers and inductors. x 100−x 21.5 78.5.
42. K. Ghuman, K. Tozaki, M. Sadakiyo, S. Kitano, T. Oyabe, M. Yamauchi, Tailoring Widely Used Ammonia Synthesis Catalysts for H and N Poisoning Resistance, Phys. Chem. Chem. Phys., 2019.01.
43. Xuemei Liao, Jindou Hou, Ya Wang, Hao Zhang, Yu Sun, Xiaopeng Li, Siyang Tang, Kenichi Kato, Miho Yamauchi, Zheng Jiang, An active, selective, and stable manganese oxide-supported atomic Pd catalyst for aerobic oxidation of 5-hydroxymethylfurfural, Green Chemistry, 10.1039/c9gc01674k, 21, 15, 4194-4203, 2019.01, [URL], Here we report for the first time a Pd-MnO2 catalyst with a single-atom feature that can convert 5-hydroxylmethyfurfural (HMF) into the important bioplastic building block 2,5-furandicarboxylic acid (FDCA) with a high yield of 88% in aqueous solution using O2 as an oxidant at ambient pressure. Pd-MnO2 shows higher activity in the productivity of FDCA (100.91 mmol h-1 gPd-1) than its Pd nanoparticle counterpart (45.57 mmol h-1 gPd-1) and state-of-the-art Pd-based catalysts. Pd-MnO2 displays promising recyclability with no degradation after five catalytic runs. Experimental and theoretical results suggest that the single-atom Pd sites that have enhanced binding affinity to HMF and their surrounding sites on the MnO2 support work synergistically toward HMF oxidation..
44. M. Yamauchi, S. Hata, H. Eguchi, S. Kitano, T. Fukushima, M. Higashi, M. Sadakiyo, K. Kato, Catalytic enhancement on Ti-Zr complex oxide particles for electrochemical hydrogenation of oxalic acid to produce an alcoholic compound by controlling electronic states and oxide structures, Catalysis Science and Technology, 10.1039/c9cy01541h, 9, 23, 6561-6565, 2019.01, [URL], Ti1-xZrxO2 complex oxide particles with 0.02 ≤ x ≤ 0.1 show superior catalytic performances for the direct power storage into glycolic acid via electroreduction of oxalic acid. The atomic pair distribution function analysis of X-ray total scatterings suggested that structural periodicity is the key factor for the catalytic enhancement..
45. Masaaki Sadakiyo, Shinichi Hata, Takashi Fukushima, Gergely Juhász, Miho Yamauchi, Electrochemical hydrogenation of non-aromatic carboxylic acid derivatives as a sustainable synthesis process
From catalyst design to device construction, Physical Chemistry Chemical Physics, 10.1039/c8cp07445c, 21, 11, 5882-5889, 2019.01, [URL], Electrochemical hydrogenation of a carboxylic acid using water as a hydrogen source is an environmentally friendly synthetic process for upgrading bio-based chemicals. We systematically studied electrochemical hydrogenation of non-aromatic carboxylic acid derivatives on anatase TiO 2 by a combination of experimental analyses and density functional theory calculations, which for the first time shed light on mechanistic insights for the electrochemical hydrogenation of carboxylic acids. Development of a substrate permeable TiO 2 cathode enabled construction of a flow-type electrolyser, i.e., a so-called polymer electrode alcohol synthesis cell (PEAEC) for the continuous synthesis of an alcoholic compound from a carboxylic acid. We demonstrated the highly efficient and selective conversion of oxalic acid to produce glycolic acid, which can be regarded as direct electric power storage into an easily treatable alcoholic compound..
46. Takashi Fukushima, Miho Yamauchi, Electrosynthesis of amino acids from biomass-derivable acids on titanium dioxide, Chemical Communications, 10.1039/c9cc07208j, 55, 98, 14721-14724, 2019.01, [URL], Seven amino acids were electrochemically synthesized from biomass-derivable α-keto acids and NH2OH with faradaic efficiencies (FEs) of 77-99% using an earth-Abundant TiO2 catalyst. Furthermore, we newly constructed a flow-Type electrochemical reactor, named a "polymer electrolyte amino acid electrosynthesis cell", and achieved continuous production of alanine with an FE of 77%..
47. Takashi Fukushima, Sho Kitano, Shinichi Hata, Miho Yamauchi, Carbon-neutral energy cycles using alcohols, Science and Technology of Advanced Materials, 10.1080/14686996.2018.1426340, 19, 1, 142-152, 2018.12, [URL], We demonstrated carbon-neutral (CN) energy circulation using glycolic acid (GC)/oxalic acid (OX) redox couple. Here, we report fundamental studies on both catalyst search for power generation process, i.e. GC oxidation, and elemental steps for fuel generation process, i.e. OX reduction, in CN cycle. The catalytic activity test on various transition metals revealed that Rh, Pd, Ir, and Pt have preferable features as a catalyst for electrochemical oxidation of GC. A carbon-supported Pt catalyst in alkaline conditions exhibited higher activity, durability, and product selectivity for electrooxidation of GC rather than those in acidic media. The kinetic study on OX reduction clearly indicated that OX reduction undergoes successive two-electron reductions to form GC. Furthermore, application of TiO catalysts with large specific area for electrochemical reduction of OX facilitates the selective formation of GC. 2.
48. W. Xiang, Y. Zhao, Z. Jiang, X. Li, H. Zhang, Y. Sun, Z. Ning, F. Du, P. Gao, J. Qian, K. Kato, M. Yamauchi, Y. Sun, Palladium Single Atoms Supported by Interwoven Carbon Nanotube and Manganese Oxide Nanowire Networks for Enhanced Electrocatalysis, J. Mater. Chem. A, 2018.10.
49. Nobuki Ozawa, Shigeki Chieda, Yuji Higuchi, Tatsuya Takeguchi, Miho Yamauchi, Momoji Kubo, First-principles calculation of activity and selectivity of the partial oxidation of ethylene glycol on Fe(0 0 1), Co(0 0 0 1), and Ni(1 1 1), Journal of Catalysis, 10.1016/j.jcat.2018.03.017, 361, 361-369, 2018.05, [URL], To recycle ethylene glycol (HOCH CH OH) fuel in alkaline fuel cells, active and selective catalysts for partially oxidizing HOCH CH OH to glycolic acid (HOCH COOH) and oxalic acid ((COOH) ) are required at the anode; in other words, complete oxidation of HOCH CH OH to CO prevents ethylene glycol recycling. We investigate catalyst activity and selectivity for oxidizing HOCH CH OH to HOCH COOH on Fe(0 0 1), Co(0 001), and Ni(1 1 1) via first-principles calculations. We calculate the oxidation reaction path from HOCH CH OH to HOCH COOH without C–C bond dissociation to avoid CO generation. Partial oxidation of HOCH CH OH to HOCH COOH without C–C bond dissociation proceeds as follows: O–H bond dissociation of HOCH CH OH to generate HOCH CH O; C–H bond dissociation of HOCH CH O to generate HOCH CHO; C–H bond dissociation of HOCH CHO to generate HOCH CO; and OH addition to HOCH CO to generate HOCH COOH. The activation energies for O–H bond dissociation of HOCH CH OH and C–H bond dissociation of HOCH CH O and HOCH CHO on Fe(0 0 1) are 20.2, 22.8, and 35.2 kcal/mol, respectively, which are the lowest of the three surfaces. Thus, Fe(0 0 1) is most active. To determine the selectivity, we compare the bond dissociation activation energies. The activation energies for C–C bond dissociation of HOCH CH OH and HOCH CH O on Fe(0 0 1) (66.7 and 39.5 kcal/mol, respectively) are higher than those for O–H bond dissociation of HOCH CH OH (20.2 kcal/mol) and C–H bond dissociation of HOCH CH O (22.8 kcal/mol), implying that the O–H bond of HOCH CH OH and C–H bond of HOCH CH O dissociate before the C–C bond dissociation during oxidation on Fe(0 0 1). In contrast, the activation energies for C–H and C–C bond dissociation of HOCH CHO (35.2 and 32.8 kcal/mol, respectively) are similar. The C–H and C–C bonds therefore dissociate during HOCH CHO oxidation. On Co(0 0 0 1) and Ni(1 1 1), the activation energies for C–C bond dissociation of HOCH CH O and HOCH CHO are lower than those for their C–H bond dissociation. Therefore, Fe(0 0 1) is more active and selective than Co(0 0 0 1) and Ni(1 1 1) for the partial oxidation of HOCH CH OH to HOCH COOH. 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2.
50. H. Kobayashi, M. Yamauchi, R. Ikeda, T. Yamamoto, S. Matsumura, H. Kitagawa, Double enhancement of hydrogen storage capacity of Pd nanoparticles by 20 at% replacement with Ir, Chem. Sci., 2018.05.
51. Masaaki Sadakiyo, Shinichi Hata, Xuedong Cui, Miho Yamauchi, Electrochemical Production of Glycolic Acid from Oxalic Acid Using a Polymer Electrolyte Alcohol Electrosynthesis Cell Containing a Porous TiO2 Catalyst, Scientific Reports, 10.1038/s41598-017-17036-3, 7, 1, 2017.12, [URL], A liquid flow-Type electrolyser that continuously produces an alcohol from a carboxylic acid was constructed by employing a polymer electrolyte, named a polymer electrolyte alcohol electrosynthesis cell (PEAEC). Glycolic acid (GC, an alcoholic compound) is generated on anatase TiO catalysts via four-electron reduction of oxalic acid (OX, a divalent carboxylic acid), accompanied with water oxidation, which achieves continuous electric power storage in easily stored GC. Porous anatase TiO directly grown on Ti mesh (TiO /Ti-M) or Ti felt (TiO /Ti-F) was newly fabricated as a cathode having favourable substrate diffusivity. A membrane-electrode assembly composed of the TiO /Ti-M, Nafion 117, and an IrO supported on a gas-diffusion carbon electrode (IrO /C) was applied to the PEAEC. We achieved a maximum energy conversion efficiency of 49.6% and a continuous 99.8% conversion of 1 M OX, which is an almost saturated aqueous solution at room temperature. 2 2 2 2 2 2 2.
52. Miho Yamauchi, Sho Kitano, Masaaki Sadakiyo, Inorganic nanocatalysts for the electronic power circulation using alcohol/carboxylic acid redox couples, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 254, 2017.08.
53. Sho Kitano, Masaaki Sadakiyo, Kenichi Kato, Miho Yamauchi, Hiroyuki Asakura, Tsunehiro Tanaka, Keiji Hashimoto, Hiroshi Kominami, Effects of the structure of the Rh3+modifier on photocatalytic performances of an Rh3+/TiO2photocatalyst under irradiation of visible light, Applied Catalysis B: Environmental, 10.1016/j.apcatb.2016.12.047, 205, 340-346, 2017.01, [URL], For a rhodium ion-modified TiO2(Rh3+/TiO2) photocatalyst responding to visible light, control of the structure of the Rh3+modifier and effects of the structures of the Rh3+modifier on photocatalytic activities were examined. A TiO2support was pre-calcined to maintain crystallinity and specific surface area during post-calcination, and the structure of the Rh3+modifier for Rh3+/TiO2was changed by post-calcination without causing changes in the crystallinity and specific surface area of the TiO2support. In mineralization of acetone under irradiation of visible light, the photocatalytic activities of the post-calcined Rh3+/TiO2showed a volcano-like tendency as a function of post-calcination temperature. The results of this study showed that an atomically isolated structure of the Rh3+modifier was preferable for high activities and that aggregation of the Rh species led to a decrease in the activities..
54. Sichao Ma, Masaaki Sadakiyo, Minako Heim, Raymond Luo, Richard T. Haasch, Jake I. Gold, Miho Yamauchi, Paul J.A. Kenis, Electroreduction of carbon dioxide to hydrocarbons using bimetallic Cu-Pd catalysts with different mixing patterns, Journal of the American Chemical Society, 10.1021/jacs.6b10740, 139, 1, 47-50, 2017.01, [URL], Electrochemical conversion of CO holds promise for utilization of CO as a carbon feedstock and for storage of intermittent renewable energy. Presently Cu is the only metallic electrocatalyst known to reduce CO to appreciable amounts of hydrocarbons, but often a wide range of products such as CO, HCOO , and H are formed as well. Better catalysts that exhibit high activity and especially high selectivity for specific products are needed. Here a range of bimetallic Cu-Pd catalysts with ordered, disordered, and phase-separated atomic arrangements (Cu :Pd = 1:1), as well as two additional disordered arrangements (Cu3Pd and CuPd3 with Cu :Pd = 3:1 and 1:3), are studied to determine key factors needed to achieve high selectivity for Cl or C2 chemicals in CO reduction. When compared with the disordered and phase-separated CuPd catalysts, the ordered CuPd catalyst exhibits the highest selectivity for Cl products (>80%). The phase-separated CuPd and Cu3Pd achieve higher selectivity (>60%) for C2 chemicals than CuPd3 and ordered CuPd, which suggests that the probability of dimerization of Cl intermediates is higher on surfaces with neighboring Cu atoms. Based on surface valence band spectra, geometric effects rather than electronic effects seem to be key in determining the selectivity of bimetallic Cu-Pd catalysts. These results imply that selectivities to different products can be tuned by geometric arrangements. This insight may benefit the design of catalytic surfaces that further improve activity and selectivity for CO reduction. 2 2 2 2 at at at at 2 2 -.
55. Hadi Razavi-Khosroshahi, Kaveh Edalati, Ji Wu, Yuki Nakashima, Makoto Arita, Yoshifumi Ikoma, Masaaki Sadakiyo, Yuji Inagaki, Aleksandar Tsekov Staykov, Miho Yamauchi, Zenji Horita, Masayoshi Fuji, High-pressure zinc oxide phase as visible-light-active photocatalyst with narrow band gap, Journal of Materials Chemistry A, 10.1039/c7ta05262f, 5, 38, 20298-20303, 2017.01, [URL], Wide band gap of pure ZnO with wurtzite crystal structure (3.1-3.4 eV) limits its photocatalytic activity to the ultraviolet (UV) region of solar spectrum. High-pressure rocksalt polymorph of ZnO can theoretically show narrow band gap; however, the rocksalt phase is unstable at ambient pressure. Herein, rocksalt phase with large fractions of oxygen vacancies is successfully stabilized at ambient conditions by inducing plastic strain in pure ZnO under 6 GPa using the High-Pressure Torsion (HPT) method. Formation of rocksalt phase reduces the band gap of ZnO to 1.8 eV, which is in good agreement with the first-principles calculations, and significantly improves the photocatalytic activity under visible light..
56. Masaaki Sadakiyo, Takahiro Kuramoto, Kenichi Kato, Miho Yamauchi, Introduction of an amino group on zeolitic imidazolate framework through a ligand-exchange reaction, Chemistry Letters, 10.1246/cl.170323, 46, 7, 1004-1006, 2017.01, [URL], We newly synthesized an amino-functionalized zeolitic imidazolate framework (ZIF), [Zn{(dmamIM)n(mIM)m}2] (dmamIM-: 2-[(dimethylamino)methyl]imidazolate; mIM-: 2- methylimidazolate), through a ligand-exchange reaction using an amino-functionalized ligand, dmamIM-, and ZIF-8 as a mother framework. Original ligand of ZIF-8, mIM-, was partially replaced with the dmamIM-under various solvothermal conditions. The crystal structures of resultant specimens were analyzed by Rietveld method combined with maximum entropy method using synchrotron X-ray powder diffraction patterns. Porous characters of the compound were examined using adsorption measurements and alternate-current impedance measurements. The ligand exchange was found to occur as an equilibrium reaction in the reaction solutions. The reaction rate deeply depends on the types of solvents and the introduced ligands are homogeneously distributed on the sodalite-type framework..
57. Shotaro Yoshimaru, Masaaki Sadakiyo, Aleksandar Tsekov Staykov, Kenichi Kato, Miho Yamauchi, Modulation of the catalytic activity of Pt nanoparticles through charge-transfer interactions with metal-organic frameworks, Chemical Communications, 10.1039/c7cc02829f, 53, 50, 6720-6723, 2017.01, [URL], We employed metal-organic framework (MOF) supports to modulate the electronic states of loaded Pt nanoparticles (NPs) in their composite catalysts (Pt/MOFs). Pt NPs were homogenously deposited on four MOFs characterized with different electronic states (Zn-MOF-74, Mg-MOF-74, HKUST-1, and UiO-66-NH2). Theoretical and experimental studies demonstrated that a charge-transfer interaction between Pt NPs and MOFs is a critical factor for controlling the catalytic activity of Pt NPs supported on MOFs..
58. Miho Yamauchi, T Kuramoto, Masaaki Sadakiyo, Crystal structure of poly[tris (μ-2-dimethylaminomethyl imidazolato) nitratodizinc(II)], 2016.11, Crystal structure of poly[tris (μ-2-dimethylaminomethyl imidazolato) nitratodizinc(II)].
59. Miho Yamauchi, 北野 翔, 秦 慎一, 渡邉 亮太, Masaaki Sadakiyo, Kenichi Kato, Masaki Takaka, Hydrogenation of oxalic acid using light-assisted water electrolysis for the production of an alcoholic compound, Green Chem., 18, 3700-3706, 2016.10, Hydrogenation of oxalic acid using light-assisted water electrolysis for the production of an alcoholic compound.
60. Miho Yamauchi, S. Ma, Masaaki Sadakiyo, R. Luoa, P. Kenis, One-step electrosynthesis of ethylene and ethanol from CO2 in an alkaline electrolyzer, J. Power Sources, 310, 219-228, 2016.10, One-step electrosynthesis of ethylene and ethanol from CO2 in an alkaline electrolyzer.
61. Miho Yamauchi, Nobuki Ozawa, Momoji Kubo, Experimental and Quantum Chemical Approaches to Develop Highly Selective Nanocatalysts for CO2-free Power Circulation, Chemical Record, 10.1002/tcr.201600047, 16, 5, 2249-2259, 2016.10, [URL], Renewable electricity must be utilized to usefully suppress the atmospheric CO2 concentration and slow the progression of global warming. We have thus proposed a new concept involving CO2-free electric power circulation systems via highly selective electrochemical reactions of alcohol/carboxylic acid redox couples. Design concepts for nanocatalysts able to catalyze highly selective electrochemical reactions are provided from both experimental and quantum mechanical perspectives..
62. Miho Yamauchi, Nobuki Ozawa, Momoji Kubo, Experimental and Quantum Chemical Approaches to Develop Highly Selective Nanocatalysts for CO2-free Power Circulation, Chemical Record, 10.1002/tcr.201600047, 16, 5, 2249-2259, 2016.10, Renewable electricity must be utilized to usefully suppress the atmospheric CO concentration and slow the progression of global warming. We have thus proposed a new concept involving CO -free electric power circulation systems via highly selective electrochemical reactions of alcohol/carboxylic acid redox couples. Design concepts for nanocatalysts able to catalyze highly selective electrochemical reactions are provided from both experimental and quantum mechanical perspectives. 2 2.
63. Hadi Razavi-Khosroshahi, Kaveh Edalati, Masashige Hirayama, Hoda Emami, Makoto Arita, Miho Yamauchi, Hidehisa Hagiwara, Shintaro Ida, Tatsumi Ishihara, Etsuo Akiba, Zenji Horita, Masayoshi Fuji, Visible-Light-Driven Photocatalytic Hydrogen Generation on Nanosized TiO2-II Stabilized by High-Pressure Torsion, ACS Catalysis, 10.1021/acscatal.6b01482, 6, 8, 5103-5107, 2016.08, Photocatalytic activity of pure TiO is limited to ultraviolet (UV) light due to the wide bandgap of anatase and rutile phases. The bandgap of high-pressure phases of TiO can theoretically coincide with visible light, but these phases are unstable at ambient pressure. In this work, the high-pressure TiO -II (columbite) phase with large fractions of oxygen vacancies was stabilized by inducing plastic strain to anatase under 6 GPa. The material could absorb visible light as a consequence of bandgap narrowing by â14 0.7 eV. Formation of nanosized TiO -II enhanced the hydrogen generation efficiency under visible light, and the efficiency improved after removing the oxygen vacancies by annealing. 2 2 2 2.
64. Miho Yamauchi, Masaaki Sadakiyo, Shotaro Yoshimaru, H. Kasai, K. Kato, M. Takata, A new approach for the facile preparation of metal-organic framework composites directly contactingwith metal particles through ark plasma deposition, Chem. Comm., 52, 8385-8388, 2016.05, A new approach for the facile preparation of metal-organic framework composites directly contactingwith metal particles through ark plasma deposition.
65. Kenichi Kato, Hidetaka Kasai, Akihiro Hori, Masaki Takata, Hiroshi Tanaka, Susumu Kitagawa, Akira Kobayashi, Nobuki Ozawa, Momoji Kubo, Hidekazu Arikawa, Tatsuya Takeguchi, Masaaki Sadakiyo, Miho Yamauchi, Superionic Conduction in Co-Vacant P2-NaxCoO2 Created by Hydrogen Reductive Elimination, Chemistry - An Asian Journal, 10.1002/asia.201600370, 11, 10, 1537-1541, 2016.05, The layered P2-Na MO (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2-Na CoO created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm at 25 °C. Using in situ synchrotron X-ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na (H O) Co O . Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co-stoichiometric compound Na (H O) CoO does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity. Migration routes: Na (H O) Co O obtained by hydrogen reductive elimination has been found to exhibit superionic conductivity at room temperature. Disordered structures observed at the Na sites 1 and 3 imply the diffusion channels of conducting ion species. In molecular dynamics simulations using the experimental model, H and O delivered from H O appear to migrate between the sites 2 and 3 and 1 and 2, respectively, forming a double honeycombed sublattice. x 2 x 2 0.61 3 0.18 0.93 2 x 3 y 2 x 3 y 1-δ 2 3 -1.
66. Kenichi Kato, Hidetaka Kasai, Akihiro Hori, Masaki Takata, Hiroshi Tanaka, Susumu Kitagawa, Akira Kobayashi, Nobuki Ozawa, Momoji Kubo, Hidekazu Arikawa, Tatsuya Takeguchi, Masaaki Sadakiyo, Miho Yamauchi, Superionic Conduction in Co-Vacant P2-NaxCoO2 Created by Hydrogen Reductive Elimination (Chem. Asian J. 10/2016), Chemistry – An Asian Journal, 10.1002/asia.201600589, 11, 10, 1465, 2016.05.
67. Sichao Ma, Masaaki Sadakiyo, Raymond Luo, Minako Heima, Miho Yamauchi, Paul J.A. Kenis, One-step electrosynthesis of ethylene and ethanol from CO2 in an alkaline electrolyzer, Journal of Power Sources, 10.1016/j.jpowsour.2015.09.124, 301, 219-228, 2016.01, Electroreduction of CO has potential for storing otherwise wasted intermittent renewable energy, while reducing emission of CO into the atmosphere. Identifying robust and efficient electrocatalysts and associated optimum operating conditions to produce hydrocarbons at high energetic efficiency (low overpotential) remains a challenge. In this study, four Cu nanoparticle catalysts of different morphology and composition (amount of surface oxide) are synthesized and their activities towards CO reduction are characterized in an alkaline electrolyzer. Use of catalysts with large surface roughness results in a combined Faradaic efficiency (46%) for the electroreduction of CO to ethylene and ethanol in combination with current densities of ∼200 mA cm , a 10-fold increase in performance achieved at much lower overpotential (only
68. Sichao Ma, Masaaki Sadakiyo, Raymond Luo, Minako Heima, Miho Yamauchi, Paul J.A. Kenis, One-step electrosynthesis of ethylene and ethanol from CO2Journal of Power Sources, 10.1016/j.jpowsour.2015.09.124, 301, 219-228, 2016.01, Electroreduction of CO has potential for storing otherwise wasted intermittent renewable energy, while reducing emission of CO into the atmosphere. Identifying robust and efficient electrocatalysts and associated optimum operating conditions to produce hydrocarbons at high energetic efficiency (low overpotential) remains a challenge. In this study, four Cu nanoparticle catalysts of different morphology and composition (amount of surface oxide) are synthesized and their activities towards CO reduction are characterized in an alkaline electrolyzer. Use of catalysts with large surface roughness results in a combined Faradaic efficiency (46%) for the electroreduction of CO to ethylene and ethanol in combination with current densities of ∼200 mA cm , a 10-fold increase in performance achieved at much lower overpotential (only
69. Masaaki Sadakiyo, Minako Heima, Tomokazu Yamamoto, Syo Matsumura, Masashi Matsuura, Satoshi Sugimoto, Kenichi Kato, Masaki Takata, Miho Yamauchi, Preparation of solid-solution type Fe-Co nanoalloys by synchronous deposition of Fe and Co using dual arc plasma guns, Dalton Transactions, 10.1039/c5dt02815a, 44, 36, 15764-15768, 2015.08, We succeeded in the efficient preparation of well-dispersed Fe-Co nanoalloys (NAs) using the arc plasma deposition method. Synchronous shots of dual arc plasma guns were applied to a carbon support to prepare the solid-solution type Fe-Co NAs having an approximately 1 : 1 atomic ratio. The alloy structures with and without a reductive thermal treatment under a hydrogen atmosphere were examined using X-ray powder diffraction, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray analysis, high resolution STEM, and magnetic measurements, suggesting that highly crystalline spherical particles of ordered B2-type Fe-Co NAs form by the thermal treatment of the deposited grains..
70. R. Watanabe, M. Yamauchi, M. Sadakiyo, R. Abe, T. Takeguchi, CO2-free electric power circulation via direct charge and discharge using the glycolic acid/oxalic acid redox couple, Energy and Environmental Science, 10.1039/c5ee00192g, 8, 5, 1456-1462, 2015.05, The establishment of an efficient electric power distribution method is the key to realising a sustainable society driven by renewable-energy-based electricity, such as solar photovoltaics, wind turbine, and wave electricity, in view of supply instability. Here, we demonstrate an electric power circulation method that does not emit CO and is based on the glycolic acid (GC)/oxalic acid (OX) redox couple. Direct electric power storage in GC ensures considerably high energy density storage and good transportability through OX electroreduction with significantly high selectivity (>98%) using pure anatase-type titania (TiO ) spheres under mild conditions in the potential region of -0.5 to -0.7 V vs. the RHE at 50 °C. The most desirable characteristic of this electroreduction is the suppression of hydrogen evolution even in acidic aqueous media (Faraday efficiency of 70-95%, pH 2.1). We also successfully generated power without CO emissions via selective electrooxidation of GC with an alkaline fuel cell. 2 2 2.
71. Takeshi Matsumoto, Masaaki Sadakiyo, Mei Lee Ooi, Tomokazu Yamamoto, Syo Matsumura, Kenichi Kato, Tatsuya Takeguchi, Nobuki Ozawa, Momoji Kubo, Miho Yamauchi, Atomically mixed Fe-group nanoalloys: Catalyst design for the selective electrooxidation of ethylene glycol to oxalic acid, Physical Chemistry Chemical Physics, 10.1039/c5cp00954e, 17, 17, 11359-11366, 2015.05, We demonstrate electric power generation via the electrooxidation of ethylene glycol (EG) on a series of Fe-group nanoalloy (NA) catalysts in alkaline media. A series of Fe-group binary NA catalysts supported on carbon (FeCo/C, FeNi/C, and CoNi/C) and monometallic analogues (Fe/C, Co/C, and Ni/C) were synthesized. Catalytic activities and product distributions on the prepared Fe-group NA catalysts in the EG electrooxidation were investigated by cyclic voltammetry and chronoamperometry, and compared with those of the previously reported FeCoNi/C, which clarified the contributory factors of the metal components for the EG electrooxidation activity, C2 product selectivity, and catalyst durability. The Co-containing catalysts, such as Co/C, FeCo/C, and FeCoNi/C, exhibit relatively high catalytic activities for EG electrooxidation, whereas the catalytic performances of Ni-containing catalysts are relatively low. However, we found that the inclusion of Ni is a requisite for the prevention of rapid degradation due to surface modification of the catalyst. Notably, FeCoNi/C shows the highest selectivity for oxalic acid production without CO2 generation at 0.4 V vs. the reversible hydrogen electrode (RHE), resulting from the synergetic contribution of all of the component elements. Finally, we performed power generation using the direct EG alkaline fuel cell in the presence of the Fe-group catalysts. The power density obtained on each catalyst directly reflected the catalytic performances elucidated in the electrochemical experiments for the corresponding catalyst. The catalytic roles and alloying effects disclosed herein provide information on the design of highly efficient electrocatalysts containing Fe-group metals. This journal is.
72. M. Yamauchi, K. Okubo, T. Tsukuda, K. Kato, M. Takata, S. Takeda, Hydrogen-Induced Structural Transformation of AuCu Nanoalloys Probed by Synchrotron X-ray Diffraction Techniques, Nanoscale, DOI: 10.1039/c3nr06327e, 6, 8, 4067-4071, 2014.08.
73. Masaaki Sadakiyo, Masaru Kon-No, Katsutoshi Sato, Katsutoshi Nagaoka, Hidetaka Kasai, Kenichi Kato, Miho Yamauchi, Synthesis and catalytic application of PVP-coated Ru nanoparticles embedded in a porous metal-organic framework, Dalton Transactions, 10.1039/c4dt00996g, 43, 29, 11295-11298, 2014.08, A hybrid catalyst consisting of polymer-coated Ru nanoparticles (Ru-PVP, PVP: poly(N-vinyl-2-pyrrolidone)) embedded in a porous metal-organic framework of ZIF-8 (Ru-PVP@ZIF-8) was synthesized by the crystallization of ZIF-8 in a methanol solution of Ru-PVP. The structural properties of Ru-PVP@ZIF-8 were examined by N gas adsorption, infrared spectra, and X-ray powder diffraction measurements. We successfully identified the most appropriate pretreatment conditions for surface activation of the Ru nanoparticles in the catalyst. The pretreated Ru-PVP@ZIF-8 was applied for a CO oxidation reaction with H gas feeds. Ru-PVP@ZIF-8 was found to exhibit higher catalytic activities and higher CO selectivity than those observed on a carbon-supported Ru-PVP (Ru-PVP/C), implying that the pores of the ZIF-8 provide a more suitable environment for the reaction with O and CO gases. This journal is © the Partner Organisations 2014. 2 2 2 2.
74. Takeshi Matsumoto, Masaaki Sadakiyo, Mei Lee Ooi, Sho Kitano, Tomokazu Yamamoto, Syo Matsumura, Kenichi Kato, Tatsuya Takeguchi, Miho Yamauchi, CO2-free power generation on an iron group nanoalloy catalyst via selective oxidation of ethylene glycol to oxalic acid in alkaline media, Scientific Reports, 10.1038/srep05620, 4, 5620-5620, 2014.07, An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO -free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO , produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C 2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4 V vs. the reversible hydrogen electrode (RHE), without CO generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system. 2 2 2.
75. M. Yamauchi, K. Okubo, T. Tsukuda, K. Kato, M. Takata, S. Takeda, Hydrogen-induced structural transformation of AuCu nanoalloys probed by synchrotron X-ray diffraction techniques, Nanoscale, 10.1039/c3nr06327e, 6, 8, 4067-4071, 2014.04, In situ X-ray diffraction measurements reveal that the transformation of a AuCu nanoalloy from a face-centered-cubic to an L1 structure is accelerated under a hydrogen atmosphere. The structural transformation rate for the AuCu nanoalloy under hydrogen above 433 K was found to be 100 times faster than that in a vacuum, which is the first quantitative observation of hydrogen-induced ordering of nanoalloys. © the Partner Organisations 2014. 0.
76. Miho Yamauchi, Minako Heima, Masaaki Sadakiyo, Development of Nanoalloy Catalysts for Realization of Carbon-Neutral Energy Cycles, Mater. Sci. Forum., 10.4028/www.scientific.net/MSF.783-786, 783-786, 2046-2050, 2014.03, Increase of CO2 concentration in the atmosphere is one of reasons for the global warming. Development of energy circulation systems, which do not emit CO2 in the atmosphere, is an emergent issue for present-generation scientists [1]. As an answer, we have proposed a new type of energy circulation system, namely, carbon-neutral energy (CN) cycle. With a practical application in mind, three limitations are imposed on the CN cycle; (1) no CO2 emissions, (2) utilization of liquid fuels and (3) minimizing the use of precious metal catalysts. In anticipation of a practical use in the near future, an alkaline fuel cell will be adapted for the CN cycle where non-platinum catalysts can work. For our purpose, electric power will be generated by partial oxidation of alcohols to carboxylic acids.[2] In view of ease in handling, fuels having a high boiling point (b.p.) are favorable for the CN cycles. To this end, glycol (EG) of which b.p. is 470 K an ideal candidate as a fuel. In this case, an oxidized product of EG can be oxalic acid. Compared to the energy obtained by the complete oxidation of EG into CO2, we can derive ca. 80 % of energy even in the partial oxidation of EG to oxalic acid, implying that the EG/oxalic cycle possibly works as an energy cycle. We herein show an example of selective EG oxidation catalysts working in alkaline conditions.
In the previous reports, Pd-based catalysts are found to show remarkably high activities for alcohol oxidation in the alkaline media.[3,4] In this study, Cu-Pd nanoalloy catalysts are synthesized and applied to the EG electrooxidation in the alkaline conditions..
77. Miho Yamauchi, Hydrogen-related Properties of Metal and Alloy Nanoparticles, 10.7566/JPSCP.2.010305, 2, 010305-010305, 2014.03, Transition metals exhibit strong interaction with hydrogen regardless of their chemical form. Metal particles in the nanometer range, i.e., metal nanoparticles (NPs), have unique properties, which are different from those of their bulk counterparts, resulting from their large surface fractions and specific electronic states, depending on the particle size. It is natural, therefore, that hydrogen storage properties vary depending on the metal size. In this paper, I discuss nano-size effects on hydrogen storage in metal NPs by taking an example of Pd NPs, which bulk store hydrogen in their lattices, using Pd NPs as an example[1]
The other target materials in our study are bimetallic nanoalloys (NAs), which have great potential as novel catalysts because their reactivities can be controlled by changing the composition and elemental distributions in the particles. Considering the electronegativity of hydrogen, 2.2, which is close to those of the late transition metals, 1.8—2.6, various transition-metal NAs are expected to show significant affinities to hydrogen through a moderate metallic bonds; this probably influences the metal structure. In our study, hydrogen treatment was used to change the structures of NAs. Recently, we observed hydrogen-enhanced ordering of the CuPd NAs.[2] Here, I review our works on hydrogen-related properties of metal and alloy NPs..
78. Masaaki Sadakiyo, Hidetaka Kasai, Kenichi Kato, Masaki Takata, Miho Yamauchi, Design and synthesis of hydroxide ion-conductive metal-organic frameworks based on salt inclusion, Journal of the American Chemical Society, 10.1021/ja410368j, 136, 5, 1702-1705, 2014.02, We demonstrate a metal-organic framework (MOF) design for the inclusion of hydroxide ions. Salt inclusion method was applied to an alkaline-stable ZIF-8 (ZIF = zeolitic imidazolate framework) to introduce alkylammonium hydroxides as ionic carriers. We found that tetrabutylammonium salts are immobilized inside the pores by a hydrophobic interaction between the alkyl groups of the salt and the framework, which significantly increases the hydrophilicity of ZIF-8. Furthermore, ZIF-8 including the salt exhibited a capacity for OH ion exchange, implying that freely exchangeable OH ions are present in the MOF. ZIF-8 containing OH ions showed an ionic conductivity of 2.3 × 10 S cm at 25 C, which is 4 orders of magnitude higher than that of the blank ZIF-8. This is the first example of an MOF-based hydroxide ion conductor. © 2014 American Chemical Society. - - - -8 -1.
79. Md Jafar Sharif, Miho Yamauchi, Shoichi Toh, Syo Matsumura, Shin Ichiro Noro, Kenichi Kato, Masaki Takata, Tatsuya Tsukuda, Enhanced magnetization in highly crystalline and atomically mixed bcc Fe-Co nanoalloys prepared by hydrogen reduction of oxide composites, Nanoscale, 10.1039/c2nr33467d, 5, 4, 1489-1493, 2013.02, Fe Co nanoalloys (NAs) with 20 ≤ x ≤ 80 were prepared by hydrogen reduction of Fe-Co oxide nano-composites, which were composed of mixed phases (or domains) of Fe O and CoO. In situ X-ray diffraction (XRD) measurements using synchrotron radiation clearly showed development of a solid-solution Fe-Co phase by hydrogen reduction from the oxide composites. High-resolution transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM and powder XRD revealed that Fe-Co NAs form a single crystal structure and the two elements are mixed homogeneously. The saturation magnetization depends on the size and metal composition and shows the highest value (250 emu g ) for the Fe Co NA in the size range of 30-55 nm, which is comparable to that of the Fe Co bulk alloy (245 emu g ). This high magnetization is attributable to high crystallinity and homogeneous mixing of constituent atoms, which are attained by thermal treatment of oxide phases under a hydrogen atmosphere. © 2013 The Royal Society of Chemistry. x 100-x 2 3 70 30 70 30 -1 -1.
80. Atsunori Kamegawa, Asaya Fujita, Miho Yamauchi, Masuo Okada, New useful function of hydrogen in materials, J. Alloys Compd., 10.1016/j.jallcom.2013.03.225, 580, S401-S405, 2013.01.
81. Hirokazu Kobayashi, Hitoshi Morita, Miho Yamauchi, Ryuichi Ikeda, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Masaki Takata, Shoichi Toh, Syo Matsumura, Nanosize-induced drastic drop in equilibrium hydrogen pressure for hydride formation and structural stabilization in Pd-Rh solid-solution alloys, Journal of the American Chemical Society, 10.1021/ja305031y, 134, 30, 12390-12393, 2012.08, We have synthesized and characterized homogeneous solid-solution alloy nanoparticles of Pd and Rh, which are immiscible with each other in the equilibrium bulk state at around room temperature. The Pd-Rh alloy nanoparticles can absorb hydrogen at ambient pressure and the hydrogen pressure of Pd-Rh alloys for hydrogen storage is dramatically decreased by more than 4 orders of magnitude from the corresponding pressure in the metastable bulk state. The solid-solution state is still maintained in the nanoparticles even after hydrogen absorption/desorption, in contrast to the metastable bulks which are separated into Pd and Rh during the process. © 2012 American Chemical Society..
82. Prasenjit Maity, Songhai Xie, Miho Yamauchi, Tatsuya Tsukuda, Stabilized gold clusters: From isolation toward controlled synthesis, Nanoscale, 10.1039/c2nr30900a, 4, 14, 4027-4037, 2012.07, Bare metal clusters with fewer than ∼100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of the art of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy. © 2012 The Royal Society of Chemistry..
83. Kobayashi, Hirokazu, Morita, Hitoshi, Miho Yamauchi, Ikeda, Ryuichi, Kitagawa, Hiroshi, Kubota, Yoshiki, Kato, Kenichi, Takata, Masaki, Toh, Shoichi, Matsumura, Syo, Nanosize-Induced Drastic Drop in Equilibrium Hydrogen Pressure for Hydride Formation and Structural Stabilization in Pd-Rh Solid-Solution Alloys, 134, 12390-12393, 2012.06.
84. Prasenjit Maity, Tomonari Wakabayashi, Nobuyuki Ichikuni, Hironori Tsunoyama, Songhai Xie, Miho Yamauchi, Tatsuya Tsukuda, Selective synthesis of organogold magic clusters Au54(C≡CPh)26, Chemical Communications, 10.1039/c2cc18153c, 48, 49, 6085-6087, 2012.05, Organogold clusters Au (C Ph) were selectively synthesized by reacting polymer-stabilized Au clusters (1.2 ± 0.2 nm) with excess phenylacetylene in chloroform. © 2012 The Royal Society of Chemistry. 54 2 26.
85. Hirokazu Kobayashi, Miho Yamauchi, Hiroshi Kitagawa, Finding hydrogen-storage capability in iridium induced by the nanosize effect, Journal of the American Chemical Society, 10.1021/ja302021d, 134, 16, 6893-6895, 2012.04, We report nanosize-induced hydrogen storage in Ir, which does not absorb hydrogen in its bulk form. The mean diameter of the obtained Ir nanoparticles was estimated as 1.5 ± 0.5 nm by transmission electron microscopy. Hydrogen storage was confirmed by solid-state H NMR and hydrogen pressure-composition isotherm measurements. © 2012 American Chemical Society. 2.
86. M. Jakir Hossain, Hironori Tsunoyama, Miho Yamauchi, Nobuyuki Ichikuni, Tatsuya Tsukuda, High-yield synthesis of PVP-stabilized small Pt clusters by microfluidic method, Catalysis Today, 10.1016/j.cattod.2011.10.008, 183, 1, 101-107, 2012.03, Monodisperse PVP-stabilized Pt nanoparticles (PtNPs) with an average diameter of 1.4 ± 0.3 nm were efficiently produced via the complete reduction of Pt ions by BH in a micromixer. Because of microfluidic mixing, hydrolytic decomposition of BH by the PtNPs formed in the initial stage of the reaction was suppressed, and hence, the PtNP yield was higher than that in the conventional batch mixing. The results of various spectroscopic analyses including EXAFS, FTIR of CO and XPS revealed that the microfluidically synthesized PtNPs were negatively charged and had a high population of edges and vertices on their surface. © 2011 Elsevier B.V. 4+ - - 4 4.
87. Prasenjit Maity, Hironori Tsunoyama, Miho Yamauchi, Songhai Xie, Tatsuya Tsukuda, Organogold clusters protected by phenylacetylene, Journal of the American Chemical Society, 10.1021/ja209236n, 133, 50, 20123-20125, 2011.12, A new class of monolayer-protected Au clusters with Au-C covalent bonds (organogold clusters) was synthesized by ligating phenylacetylene (PhC-μCH) to PVP-stabilized Au clusters. Matrix-assisted laser desorption ionization mass spectrometry revealed for the first time a series of stable compositions of the organogold (Au:C Ph) clusters. © 2011 American Chemical Society. 2.
88. Hirokazu Kobayashi, Hitoshi Morita, Miho Yamauchi, Ryuichi Ikeda, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Masaki Takata, Nanosize-induced hydrogen storage and capacity control in a non-hydride-forming element: Rhodium, Journal of the American Chemical Society, 10.1021/ja2027772, 133, 29, 11034-11037, 2011.07, We report the first example of nanosize-induced hydrogen storage in a metal that does not absorb hydrogen in its bulk form. Rhodium particles with diameters of
89. Miho Yamauchi, Tatsuya Tsukuda, Production of an ordered (B2) CuPd nanoalloy by low-temperature annealing under hydrogen atmosphere, Dalton Transactions, 10.1039/c0dt01632b, 40, 18, 4842-4845, 2011.05, CuPd (1/1) nanoalloys composed of disordered body-centered-cubic crystals (crystal size = 1.6 nm) were prepared by synchronous reduction of Cu and Pd precursor ions with NaBH . In situ XRD measurement revealed that Cu and Pd atoms in the CuPd nanoalloys are arranged into an ordered B2 structure under exposure to H (5 kPa) at 373 K. Ordering of Cu and Pd atoms over a longer distance (up to 3.6 nm) was achieved by annealing the nanoalloys for a longer time under a H atmosphere. © 2011 The Royal Society of Chemistry. 4 2 2.
90. Miho Yamauchi, Ryu Abe, Tatsuya Tsukuda, Kenichi Kato, Masaki Takata, Highly selective ammonia synthesis from nitrate with photocatalytically generated hydrogen on CuPd/TiO2, Journal of the American Chemical Society, 10.1021/ja106285p, 133, 5, 1150-1152, 2011.02, Body-centered-cubic type CuPd nanoalloys were synthesized by a chemical reduction method. Photocatalytic hydrogen evolution and nitrate reduction were simultaneously examined over CuPd nanoalloys deposited on TiO (CuPd/TiO ). The efficiency of hydrogen evolution over CuPd/TiO was better than that over Pd/TiO . As for nitrate reduction, ammonia was selectively (78%) produced with hydrogen generated photocatalytically over CuPd/TiO . The continuous generation of nascent hydrogen atoms on the surface of the CuPd nanoalloy, where Cu and Pd are homogeneously mixed, led to the high selectivity for ammonia. © 2011 American Chemical Society. 2 2 2 2 2.
91. T. Takeguchi, H. Arikawa, M. Yamauchi, and R. Abe, Selective Ethylene Glycol Oxidation Reaction for Carbon Neutral Energy Cycle System, ECS Transactions, 41, 1755-1759, 2011.01.
92. Kohei Kusada, Miho Yamauchi, Hirokazu Kobayashi, Hiroshi Kitagawa, Yoshiki Kubota, Hydrogen-storage properties of solid-solution alloys of immiscible neighboring elements with Pd, Journal of the American Chemical Society, 10.1021/ja107362z, 132, 45, 15896-15898, 2010.11, Rh and Ag are the elements neighboring Pd, which is well known as a hydrogen-storage metal. Although Rh and Ag do not possess hydrogen-storage properties, can Ag-Rh alloys actually store hydrogen? Ag-Rh solid-solution alloys have not been explored in the past because they do not mix with each other at the atomic level, even in the liquid phase. We have used the chemical reduction method to obtain such Ag-Rh alloys, and XRD and STEM-EDX give clear evidence that the alloys mixed at the atomic level. From the measurements of hydrogen pressure-composition isotherms and solid-state H NMR, we have revealed that Ag-Rh solid-solution alloys absorb hydrogen, and the total amount of hydrogen absorbed reached a maximum at the ratio of Ag:Rh = 50:50, where the electronic structure is expected to be similar to that of Pd. © 2010 American Chemical Society. 2.
93. Hirokazu Kobayashi, Miho Yamauchi, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Masaki Takata, Atomic-level Pd-Pt alloying and largely enhanced hydrogen-storage capacity in bimetallic nanoparticles reconstructed from core/shell structure by a process of hydrogen absorption/desorption, Journal of the American Chemical Society, 10.1021/ja1013163, 132, 16, 5576-5577, 2010.04, We have achieved the creation of a solid-solution alloy where Pd and Pt are homogeneously mixed at the atomic level, by a process of hydrogen absorption/desorption as a trigger for core (Pd)/shell (Pt) nanoparticles. The structural change from core/shell to solid solution has been confirmed by in situ powder X-ray diffraction, energy dispersive spectra, solid-state H NMR measurement, and hydrogen pressure-composition isotherms. The successfully obtained Pd-Pt solid-solution nanoparticles with a Pt content of 8-21 atom % had a higher hydrogen-storage capacity than Pd nanoparticles. Moreover, the hydrogen-storage capacity of Pd-Pt solid-solution nanoparticles can be tuned by changing the composition of Pd and Pt. © 2010 American Chemical Society. 2.
94. M. Okada, A. Kamegawa, J. Nakahigashi, A. Yamaguchi, A. Fujita, M. Yamauchi, New function of hydrogen in materials, Mater. Sci. Eng. B, doi.org/10.1016/j.mseb.2010.02.004, 173, 253-259, 2010.01.
95. Miho Yamauchi, Hirokazu Kobayashi, Hiroshi Kitagawa, Hydrogen storage mediated by Pd and Pt nanoparticles, ChemPhysChem, 10.1002/cphc.200900289, 10, 15, 2566-2576, 2009.10, The hydrogen storage properties of metal nanoparticles change with particle size. For example, in a palladium-hydrogen system, the hydrogen solubility and equilibrium pressure for the formation of palladium hydride decrease with a decrease in the particle size, whereas hydrogen solubility in nanoparticles of platinum, in which hydrogen cannot be stored in the bulk state, increases. Systematic studies of hydrogen storage in Pd and Pt nanoparticles have clarified the origins of these nanosize effects. We found a novel hydrogen absorption site in the hetero-interface that forms between the Pd core and Pt shell of the Pd/Pt core/shell-type bimetallic nanoparticles. It is proposed that the potential formed in the hetero-interface stabilizes hydrogen atoms rather than interstitial in the Pd core and Pt shells. These results suggest that metal nanoparticles a few nanometers in size can act as a new type of hydrogen storage medium. Based on knowledge of the nanosize effects, we discuss how hydrogen storage media can be designed for improvement of the conditions of hydrogen storage. © 2009 Wiley-VCH Verlag GmbH &Co. KGaA..
96. Rie Makiura, Takayuki Yonemura, Teppei Yamada, Miho Yamauchi, Ryuichi Ikeda, Hiroshi Kitagawa, Kenichi Kato, Masaki Takata, Size-controlled stabilization of the superionic phase to room temperature in polymer-coated AgInanoparticles, Nature Materials, 10.1038/nmat2449, 8, 6, 476-480, 2009.06, Solid-state ionic conductors are actively studied for their large application potential in batteries and sensors. From the view of future nanodevices, nanoscaled ionic conductors are attracting much interest. Silver iodide (AgI) is a well-known ionic conductor for which the high-temperature α-phase shows a superionic conductivity greater than 1 1 cm 1 (ref.6). Below 147 C, α-AgI undergoes a phase transition into the poorly conducting Β- and γ-polymorphs, thereby limiting its applications. Here, we report the facile synthesis of variable-size AgI nanoparticles coated with poly-N-vinyl-2-pyrrolidone (PVP) and the controllable tuning of the α- to Β-/γ-phase transition temperature (Tc). Tc shifts considerably to lower temperatures with decreasing nanoparticle size, leading to a progressively enlarged thermal hysteresis. Specifically, when the size approaches 10-11 nm, the α-phase survives down to 30 Cthe lowest temperature for any AgI family material. We attribute the suppression of the phase transition not only to the increase of the surface energy, but also to the presence of defects and the accompanying charge imbalance induced by PVP. Moreover, the conductivity of as-prepared 11 nm Β-/γ-AgI nanoparticles at 24 C is 1.5×10 2 1 cm 1 the highest ionic conductivity for a binary solid at room temperature. The stabilized superionic phase and the remarkable transport properties at a practical temperature reported here suggest promising applications in silver-ion-based electrochemical devices. © 2009 Macmillan Publishers Limited. All rights reserved..
97. Atsunori Kamegawa, Jun Nakahigashi, Akira Yamaguchi, Asaya Fujita, Miho Yamauchi, Hiroshi Kitagawa, Masuo Okada, Hydrogen-induced new functions in sub-nano lattice matter, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.73.141, 73, 3, 141-150, 2009.03, This paper includes some results of "Hydrogen-Induced New Functions in Sub-Nano Lattice Matters" accomplished by MEXT's program "Elements strategy Project". In the 21st century, the era concerning about environment, this research achieve- ment utilizing hydrogen as the technology for strengthening alloys will be expected to make a breakthrough in the metal heat- treatment and processing technology as the new environmental conscious process. Hydrogen heat-treatments for grain-size refinements of alloys were performed. The grain size of Cu-3 mass%Ti alloy turned into about 20~50 nm after hydrogenation and dehydrogenation treatment. Moreover, grain-size refined Ti-based alloy showed large super-elastic elongation. On the other hand, hydrogen induced functions in the alloys were also investigated. Hydrogen transmitting films with Pd nanogranular parti- cles dispersed in ceramic material were developed as attachment of metal-hydride switchable mirrors. Metamagnetism transition temperature (Tc) could be increased by hydrogen introduction in La (Fe Si ) Pd/Pt core-shell type nano-particles were also investigated. © 2009 The Japan Institute of Metals. x 1-x.
98. K. Kobayashi, M. Yamauchi, R. Ikeda, H. Kitagawa, Atomic-Level Pd-Au Alloying and Controllable Hydrogen-Absorption Properties in Size-Controlled Nanoparticles Synthesized by Hydrogen Reduction Method, Chem. Commun., 4806–4808, 2009.01.
99. Hirokazu Kobayashi, Miho Yamauchi, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Takata Masaki, On the Nature of Storng Hydrogen Trapping Inside Pd Nanoparticles, Journal of the American Chemical Society, 130巻6号1828-1829, 2008.05.
100. Miho Yamauchi, Ryuichi Ikeda, Hiroshi Kitagawa, Masaki Takata, Nanosize effects on hydrogen storage in palladium, Journal of Physical Chemistry C, 10.1021/jp710447j, 112, 9, 3294-3299, 112巻9号:3294-3299, 2008.03, The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ± 0.4 and 7.0 ± 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the two-phase state. By analyzing the isotherms, we quantitatively determined the heat of formation (ΔH ) and the entropy change (ΔS ) in the hydride formation of the nanoparticle. ΔH and ΔS for the 2.6 ± 0.4 nm diameter Pd nanoparticle were -34.6 ± 0.61 kJ(H mol) and -83.1 ± 1.8 J(H mol) K , whereas for the 7.0 ± 0.9 nm diameter Pd nanoparticles the values were -31.0 ± 1.8 kJ(H mol) and -67.3 ± 5.1 J(H mol) K , respectively. These quantities gave us a prospective picture of hydrogen absorption in Pd nanoparticles and the peculiarities in the formation of a single nanometer-sized hydride. © 2008 American Chemical Society. α-β α-β α-β α-β 2 2 2 2 -1 -1 -1 -1 -1 -1.
101. Hirokazu Kobayashi, Miho Yamauchi, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Masaki Takata, Hydrogen absorption in the core/shell interface of Pd/Pt nanoparticles, Journal of the American Chemical Society, 10.1021/ja078126k, 130, 6, 1818-1819, 130巻、6号、1818-1819, 2008.02, We have investigated the hydrogen absorption behavior of Pd/Pt nanoparticles with a core/shell-type structure. From the results of the hydrogen pressure-composition (PC) isotherm and solid-state H NMR measurements, it was revealed that the Pd/Pt nanoparticles can absorb hydrogen, and most of the absorbed hydrogen atoms are situated around the interfacial region between the Pd core and the Pt shell of the Pd/Pt nanoparticles, indicating that the core/shell boundary plays an important role in the formation of the hydride phase of the Pd/Pt nanoparticles. Copyright © 2008 American Chemical Society. 2.
102. Hirokazu Kobayashi, Miho Yamauchi, Hiroshi Kitagawa, Yoshiki Kubota, Kenichi Kato, Masaki Takata, On the nature of strong hydrogen atom trapping inside Pd nanoparticles, Journal of the American Chemical Society, 10.1021/ja7102372, 130, 6, 1828-1829, 2008.02, We have investigated the hydrogen absorption/desorption hysteresis by means of in situ powder X-ray diffraction (XRD) and solid-state H NMR to clarify the location of hydrogen, surface or body, and its chemical form, molecular, atomic, or as hydride. The present results point out that strongly trapped hydrogen atoms exist inside the Pd nanoparticles due to a strong Pd-H bond formation and are stabilized in the lattice of Pd nanoparticles, compared to bulk Pd. Copyright © 2008 American Chemical Society. 2.
103. Masafumi Nakaya, Masayuki Kanehara, Miho Yamauchi, Hiroshi Kitagawa, Toshiharu Teranishi, Hydrogen-induced crystal structural transformation of FePt nanoparticles at low temperature, Journal of Physical Chemistry C, 10.1021/jp072201w, 111, 20, 7231-7234, 111, 7231-7234 (2007), 2007.05, The hydrogen-induced crystal structural transformation of FePt nanoparticles from a chemically disordered face-centered-cubic (fee) structure to a chemically ordered L structure was first demonstrated at around 300°C. The hydrogen treatment at low temperature led to not complete but considerable suppression of the nanoparticle coalescence. The obtained L -FePt nanoparticles exhibited ferromagnetic property with large coercivity at room temperature. The ordering degree of FePt nanoparticles was dependent on both the hydrogen pressure and treatment time. © 2007 American Chemical Society. 10 10.
104. 山内 美穂, 北川 宏, Pdナノ粒子の水素吸蔵特性, 九州大学低温センターだより, 10.15017/14766, 1, 3-7, 2007.03.
105. Miho Yamauchi, Hiroshi Kitagawa, Hydrogen absorption of the polymer-coated Pd nanoparticle, Synthetic Metals, 10.1016/j.synthmet.2005.07.296, 153, 1-3, 353-356, 153, 353-356 (2005), 2005.09, Mono-dispersed palladium nanoparticles, which were coated with polymer, were prepared and their hydrogen absorption properties were investigated. The averaged diameter of the prepared particles was estimated to be 2.6 ± 0. 4 nm from a TEM photograph. By measurement of hydrogen pressure-composition isotherms, the hydrogen solubility of the Pd particles was determined to be 0.5 H per Pd. In the isotherms, plateau-like region was observed in the temperature rang of 303 to 393 K, indicating the coexistence of solid solution and hydride phases in the Pd nanoparticles in this temperature range. © 2005 Published by Elsevier B.V..
106. M.Fujishima, M. Yamauchi, R. Ikeda, T. Kubo, K. Nakasuji andH. Kitagawa, Powder XRD and Solid-State 2H NMR Studies on RAP-Protected Palladium Nanoparticle (RAP=Rubeanic-Acid Polymer), Solid State Phenom, 10.4028/3-908451-18-3.107, 111, 107-110, 111, 107-110 , (2006), 2005.07.
107. Miho Yamauchi, Shin'ichi Ishimaru, Ryuichi Ikeda, Two-dimensional self-diffusion of alkylammonium ions located in the interlayer space of tetrasilicicfluormica, Journal of Physical Chemistry A, 10.1021/jp035874x, 108, 5, 717-720, 108(5), 717-720, 2004.02, A layered clay mineral, tetrasilicicfluonnica intercalated with spherical, planar, and rodlike alkylammonium ions, was prepared. Two-dimensional dynamic properties of intercalated ions were investigated by solid-state H and H NMR and electrical conductivity measurements. From these measurements, all intercalation compounds were revealed to show two-dimensional (2-D) cationic self-diffusion between mica layers. The 2-D self-diffusion could be characterized by comparing shapes of intercalated ions and their occupancies in the interlayer space. The activation energies for the 2-D self-diffusion in the present intercalation compounds were found to be smaller than those for three-dimensional cationic diffusion in bulk crystals. 1 2.
108. M. Yamauchi, S. Ishimaru, and R. Ikeda, Dynamics of n-alkylammonium ions intercalated in saponite, Journal of Physical Chemistry A, 76(12), 2301-2305, 2004.01.
109. Miho Yamauchi, Yasuaki Takazaki, Zhiyong Yang, Takashi Kawamura, Ryuichi Ikeda, A 1H NMR study on the electronic state of a chloride-bridged tetrakis(acetamidato)dirhodium complex, Chemistry Letters, 10.1246/cl.2004.110, 33, 2, 110-111, 33(2), 110-111, 2004.02, A temperature dependence of H NMR spin-lattice relaxation time in a zig-zag chain of chloride-bridged tetrakis(acetamidato)dirhodium was measured. The observed H relaxation was well explained by the fluctuation of the magnetic dipolar interaction between proton and paramagnetic electron spins, where each unpaired spin is coupled by the one-dimensional antiferromagnetic interaction above 35 K. The slight change of the electronic state in the Rh dimer was observed below 35 K. 1 1.
110. M. Yamauchi, H. Kitagawa, Hydrogen Absorption in Size-Controlled Pt Nanoparticle, Chemical Engineering Transactions, 8, 159-163, 8, 159-163 (2005), 2005.05.
111. Takayoshi Ishimoto, Masanori Tachikawa, Miho Yamauchi, Hiroshi Kitagawa, Hiroaki Tokiwa, Umpei Nagashima, Isotope effect in hydrogen/deuterium-absorbing Pd nanoparticles revealed by X-ray powder diffraction and by a multi-component MO method, Journal of the Physical Society of Japan, 10.1143/JPSJ.73.1775, 73, 7, 1775-1780, 73(7), 1775-1780 (2004), 2004.07, The isotope effect in Pd nanoparticles that absorb hydrogen or deuterium (i.e., H/D isotope effect) was studied experimentally and theoretically. First, the geometries (i.e., lattice parameters) of such Pd nanoparticles exposed to hydrogen or deuterium gas were measured by using X-ray powder diffraction to determine the lattice parameters. Then, the geometrical and electronic relaxations of Pd H and Pd D (n = 1-6) clusters, which modeled Pd nanoparticles exposed to hydrogen or deuterium gas, were calculated by using a multi-component molecular orbital (MC_MO) method, which uses first principles of quantum mechanics to account for the quantum effect of proton/deuteron. Experimental results from the diffraction patterns show that the bond distances of Pd nanoparticles exposed to hydrogen gas (and thus had absorbed hydrogen) were about 0.005 Å longer than those of exposed to deuterium gas. These results were confirmed by analytical results from the MC_MO calculation for Pd H and Pd D clusters. Therefore, the local geometrical changes due to the H/D isotope effect control the geometrical changes of the entire nanoparticle. Both the experimental and analytical results also show that the nanoparticle (cluster) size influences the extent of the H/D isotope effect on the geometrical changes. Based on the analytical results, the electronic charge densities are only slightly influenced by the H/D isotope effect. © 2004 The Physical Society of Japan. n n n n - - - -.
112. Emi Shinohara, Miho Yamauchi, Shin'ichi Ishimaru, Ryuichi Ikeda, Structures and dynamics of n-dodecyltrimethylammonium ions intercalated into sodium octosilicate and tetrasilicicfluoromica, Journal of Physics Condensed Matter, 10.1088/0953-8984/15/43/009, 15, 43, 7253-7259, 2003.11, Structures and dynamics of n-dodecyltrimethylammonium ions intercalated into sodium octosilicate and tetrasilicicfluoromica were studied by powder x-ray diffraction, and C CP/MAS and H NMR measurements. In the octosilicate, cations form a 2D-crystalline state in which long axes of intercalated alkylammonium ions were shown to be inclined to silicate layers and polymethylene chains (-CH -) take the all-trans conformation. On the other hand, in the tetrasilicicfluoromica, cations form disordered arrangements with random conformations of alkyl-chains, considered to be in a 2D-amorphous state. Based on the NMR results, the dynamic behaviour of these ions in 2D space is discussed. 13 1 2 n.
113. Miho Yamauchi, Shin'ichi Ishimaru, Ryuichi Ikeda, Two-dimensional Molecular Motions of Guanidinium Ions Confined in the Interlayer Space of Tetrasilicicfluormica, Chemistry Letters, 10.1246/cl.2003.976, 32, 10, 976-977, 2003.10, Dynamic behavior of guanidinium ions with the planar structure in the two-dimensional interlayer space of tetrasilicic-fluormica was investigated by the solid NMR method. Above 300 K, guanidinium ions were found to perform the two-dimensional self-diffusion with their molecular plane parallel to the clay layers..
114. Shin'ichi Ishimaru, Miho Yamauchi, Ryuichi Ikeda, A new semiconducting organic-inorganic nanocomposite, 1,5-diaminonphthalene-saponite intercalation compound, Solid State Communications, 10.1016/S0038-1098(03)00353-3, 127, 1, 57-59, 127(1), 57-59, 2003.06, We synthesized a new intercalation compound, 1,5-diaminonaphathalene(DAN)-saponite where intercalated DAN molecules were shown to have a formal charge of +0.67 The measurement of optical diffuse reflectance spectra revealed the formation of electronic bands with a gap of ca. 1 eV suggesting semiconducting behaviour of this system. From ESR measurements, the radical formation in DAN-saponite was confirmed and the spin concentration was determined to be 1 spin per 200 and 300 DAN-molecules at 290 and 7.9 K, respectively. This temperature dependence of the spin density also implies the semiconductive nature of DAN-saponite. © 2003 Elsevier Science Ltd. All rights reserved..
115. T. Ishimoto, M. Tachikawa, M. Yamauchi, H. Kitagawa, H. Tokiwa, U. Nagashima, Analysis of isotope effect of hydrogen-absorbing Pd ultra-fine particle by X-ray powder diffraction and first principle multi-component MO calculation, Chemical Physics Letters, 10.1016/S0009-2614(03)00414-7, 372, 3-4, 503-507, 2003.04, The isotope effect for the geometrical and electronical relaxations of the hydrogen/deuterium-absorbing ultra-fine particles of Pd has been investigated using an X-ray powder diffraction, which shows that the bond distances of Pd H are longer about 0.005 Å than those of Pd D. Also, the first principle multi-component molecular orbital (MC MO) calculation, which takes account of the quantum effect of proton/deuteron, has been employed for the optimization of Pd H and Pd D (n=4,6). The H/D isotope effect of MC MO calculation is good agreement with those of the X-ray powder diffraction and shows a little relaxation of the electronic charge densities. © 2003 Elsevier Science B.V. All rights reserved. n n n n - -.
116. Shin'ichi Ishimaru, Miho Yamauchi, Ryuichi Ikeda, Dynamics of Interlayer Cations in Tetramethylammonium-Saponite Studied by 1H, 2H NMR, and Electrical Conductivity Measurements, Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences, 10.1515/zna-1998-10-1116, 53, 10-11, 903-908, 53a, 903-908 (1998)., 1998.11, We observed H and H NMR spectra, H NMR spin-lattice relaxation times, and electrical conductivities of water-saturated and anhydrous tetramethylammonium(TMA)-saponites between 100 and 415 K. The very weakly bound cations produced narrow H and H NMR lines observed in both specimens down to 150 K. The temperature dependence of the H NMR spin-lattice relaxation times in the water-saturated and anhydrous samples gave asymmetric minima attributable to the heterogeneous overall rotation and self-diffusion of the cations. The inhomogeneity of the cationic motions in the anhydrous TMA-saponite was greater than in the water-saturated one. From measurements of the electrical conductivity of anhydrous TMA-saponite a large anisotropic cation-diffusivity was concluded. © 1998, Verlag der Zeitschrift für Naturforschung. All rights reserved. 1 2 1 1 2 1.
117. Miho Yamauchi, Shin'ichi Ishimaru, Ryuichi Ikeda, Dynamics of two-dimensionally arranged n-octylammonium ions intercalated into tetrasilicicfluormica, Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences, 10.1515/zna-1999-1213, 54, 12, 755-760, 54a, 755-760, 1999.12, The dynamic behaviour of n-octylammonium ions intercalated into tetrasilicicfluormica was investigated by measuring H and H solid state NMR spectra and H spin-lattice relaxation times. X-Ray diffraction measurements revealed that the cations are arranged with the long axis parallel to the clay sheet. Uniaxial rotation of cations was found to take place above ca. 200 K among non-equivalent potential wells made by clay sheets. As a new type of 2-D motion mode, whole cationic in-plane tumbling in the 2-D layer seems to be excited above ca. 450 K. The obtained results are compared with those previously reported on saponite of an analogous structure. 1 2 1.
118. M. Yamauchi, S. Ishimaru, and R. Ikeda, Dynamics of n-Octylammonium Ions Intercalated in Saponite, Mol. Cryst. Liq. Cryst.,, 341, 315-320, 2000.01.
119. M. Yamauchi, A. B. Koudriavtsev, R. Ikeda, Z. Yang, and T. Kawamura, Spin Polarization in Infinite Zigzag Chains of [Rh2(HNCOCH3)4Cl]n, Mol. Cryst. Liq. Cryst., doi.org/10.1080/713738627, 379, 321-326, 379, 321-326, 2002.01.
120. T. Ishimoto, M. Tachikawa, M. Yamauchi, H. Kitagawa, H. Tokiwa, and U. Nagashima, Isotope Effect of Hydrogen-Absorbing Pd Ultrafine Particle -X-ray Powder Diffraction and Multi-Component MO Method-, Chem. Phys. Lett., 372(3,4), 503-507, 2003.01.

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