Kyushu University Academic Staff Educational and Research Activities Database
Researcher information (To researchers) Need Help? How to update
Miho Yamauchi Last modified date:2024.05.18



Graduate School


E-Mail *Since the e-mail address is not displayed in Internet Explorer, please use another web browser:Google Chrome, safari.
Homepage
https://kyushu-u.elsevierpure.com/en/persons/miho-yamauchi
 Reseacher Profiling Tool Kyushu University Pure
https://yamauchi-lab.com/
HTML of Yamauchi Lab .
Phone
092-802-6454
Fax
092-802-6454
Academic Degree
Ph. D
Country of degree conferring institution (Overseas)
No
Field of Specialization
Solid-state physical chemistry, Solid-state NMR, Nano materials, Catalysis, Hydrogen storage
Total Priod of education and research career in the foreign country
00years06months
Outline Activities
We are developing novel nanometer-sized materials for highly efficient material/energy conversions.
Research
Research Interests
  • Development of highly selective nanoalloy catalysts for realization of carbon neutral energy cycles
    keyword : carbon neutral, catalysis, nanoalloys, hydrogen, ethylene glycol, ammonia
    2012.01Size dependencies of hydrogen storage in Pd nanoparticles.
Academic Activities
Papers
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 (CO<sub>2</sub>) electroreduction reaction (CO<sub>2</sub>RR) offers a promising strategy for the conversion of CO<sub>2</sub> into valuable chemicals and fuels. CO<sub>2</sub>RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO<sub>2</sub> diffusion due to the absence of hydroxide that facilitates the CO<sub>2</sub> 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 CO<sub>2</sub> diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO<sub>2</sub>RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density $$( {j}_{ { { { m{C } } } }_{2+ } })$$ of −1.6 A cm<sup>−2</sup> for multicarbon products (C<sub>2+</sub>), and $$ {j}_{ { { { { { m{C } } } } } }_{2+ } }$$ of −0.34 A cm<sup>−2</sup> when applying dilute 25% CO<sub>2</sub>. In a highly acidic environment, C<sub>2+</sub> formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide..
2. 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.
3. 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.
4. 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.
5. 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.
6. 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%..
7. 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 CO<sub>2</sub> 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<sup>−2</sup>. 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..
8. 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..
9. 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.
10. 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..
11. 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.
12. 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.
13. 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.
14. 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
15. 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 (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..
16. 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.
17. 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, 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..
18. 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, 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..
19. 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, 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%..
20. 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, 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.
21. 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.
22. 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, 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.
23. 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, 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 -.
24. 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, 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..
25. 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.
26. 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.
27. 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 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..
28. 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.
29. 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
30. 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
31. 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..
32. 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.
33. 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.
34. 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.
35. 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.
36. 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..
37. 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..
38. 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.
39. 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.
40. 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.
41. 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..
42. 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..
43. 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.
44. 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.
45. 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.
46. 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
47. 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.
48. 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.
49. 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.
50. 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.
51. 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..
52. 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.
53. 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.
54. 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.
55. 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.
56. 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.
57. M. Yamauchi, H. Kitagawa, Hydrogen Absorption in Size-Controlled Pt Nanoparticle, Chemical Engineering Transactions, 8, 159-163, 8, 159-163 (2005), 2005.05, [URL].
58. 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.
59. 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.
60. 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.