Papers - SAKAI Go
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Electrochemical properties of anisotropic nickel hydroxide structures synthesized from nickel ammine complexes Reviewed
Naoki Matsunaga, Mariko Sugahara, Go Sakai
Journal of the Ceramic Society of Japan 122 ( 8 ) 613 - 617 2014.8
Language：English Publishing type：Research paper (scientific journal)
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Electrochemical and ESR Study on Pt-TiOx/C Electrocatalysts with Enhanced Activity for ORR Reviewed
Sakai G., Arai T., Matsumoto T., Ogawa T., Yamada M., Sekizawa K., Taniguchi T.
ChemElectroChem 1 ( 2 ) 366 - 370 2014.2
Language：English Publishing type：Research paper (scientific journal) Publisher：ChemElectroChem
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Pt-TiO x /C electrocatalysts possess specific activities for the oxygen reduction reaction of about 1.5times higher than that of conventional Pt/C. Electron-spin resonance spectra suggest that the specific activity of Pt-TiO x /C is related to the amount of ESR-active species.
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Sakai G., Sugahara M.
Journal of Applied Electrochemistry 42 ( 6 ) 367 - 374 2012.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Electrochemistry
Nanostructure control of β-Ni(OH) 2 was attempted by adopting hydrothermal treatment for the high specific surface area (high-SSA) β-Ni(OH) 2 in the presence of guanidine carbonate. β-Ni(OH) 2 nanosheets-linked structures could be synthesized from high-SSA β-Ni(OH) 2 owing to the strong effects of guanidine carbonate for keeping or enlarging SSA during hydrothermal treatment. The discharging capacities of the high-SSA sample showed the highest capacity above 80 % at 0.2C. However, the capacities were decreased with decreasing SSA of the β-Ni(OH) 2 prepared. It was also found that, at lower SSA, charging/discharging rates below 1C did not affect the discharging capacity, i.e., the almost same capacities for 0.2C and 1C. Cyclic voltammetry revealed that the electrochemical reactions for the charging/discharging were considered to be reversible and smooth at various scanning rates. The rate-determining step of the electrochemical reaction is considered to be regulated by the diffusion of the active species involved for the lower SSA samples. However, for the higher SSA sample (280 m 2 g -1 ) obtained at 200 °C in the presence of 1.0 × 10 -1 mol L -1 guanidine carbonate strongly indicates the effects of the rate of surface reaction or electronic conductivity on rate-determining step of charging/discharging of the material. © 2012 Springer Science+Business Media B.V.
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Synthesis of Ni(OH)2 nanostructures by the hydrothermal treatment in the presence of guanidine carbonate and their electrochemical properties Reviewed
Go Sakai, Mariko Sugahara
Journal of Applied Electrochemistry 42 367 - 374 2012.4
Language：English Publishing type：Research paper (scientific journal)
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Double layer capacitance of high surface area carbon nanospheres derived from resorcinol-formaldehyde polymers Reviewed
Daisuke Tashima, Eri Yamamoto, Nanami Kai, Daisuke Fujikawa, Go Sakai, Masahisa Otsubo, Tsuyoshi Kijima
Carbon 49 4848 - 4857 2011.11
Language：English Publishing type：Research paper (scientific journal)
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Tashima D., Yamamoto E., Kai N., Fujikawa D., Sakai G., Otsubo M., Kijima T.
Carbon 49 ( 14 ) 4848 - 4857 2011.11
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Carbon
Micro-mesoporous bimodal carbon nanospheres with high surface areas were synthesized by a combined use of surfactant templating technique and BaO 2 chemical activation one. Starting spherical nanopolymer/surfactant composites were prepared by the NaOH-catalyzed reaction of resorcinol (R) and formaldehyde (F) in the presence of cetyltrimethylammonium bromide (CTAB) as a core template and 1,3,5-trimethylbenzene (TMB) and tert-butanol (t-BuOH) as cosurfactants. After pretreatment with hydrochloric acid, the composite materials were calcined at 1000 °C in N 2 coexistent with varying weight ratios of BaO 2 to RF polymer ranging from 0 to 11. It produced micro-mesoporous bimodal carbon nanospheres of 124-143 nm diameter, with specific surface areas as high as 1884 m 2 g -1 or up to 3301 m 2 g -1 , in contrast to microporous ones with smaller surface areas obtained at low BaO 2 -loadings. The electrochemical double layer capacitance of the resulting nanocarbons in 0.5 M H 2 SO 4 showed a marked increase with specific surface areas, up to as high as 219 F g -1 for the highest surface area carbon material. © 2011 Elsevier Ltd. All rights reserved.
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Carbon-Supported Growth of Cross-Linked Platinum Nanowires by Surfactant Templating and Their Elecrochemical Characterization Reviewed
M. Uota, Y. Hayashi, A. Ohyama, H. Takemoto, R. Iriki, T. Kishishita, M. Shimoda, T. Yoshimura, H. Kawasaki, G. Sakai, T. Kijima
Journal of Nanoscience and Nanotechnology 10 ( 9 ) 5790 - 5795 2010.11
Language：English Publishing type：Research paper (scientific journal)
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Uota M., Hayashi Y., Ohyama K., Takemoto H., Iriki R., Kishishita T., Shimoda M., Takumi Y., Hideya K., Sakai G., Kijima T.
Journal of Nanoscience and Nanotechnology 10 ( 9 ) 5790 - 5795 2010.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Nanoscience and Nanotechnology
Platinum/carbon (Pt/C) composite materials were prepared by the hydrazine reduction of H 2 PtCI 6 confined to a mixed surfactant lytropic liquid crystal (LC)/C mixture with varying amounts of water. The reaction at relatively low water contentssuccessfully yielded cross-linked Pt nanowires with wire-widths of 2-5 nm. The novel Pt nanostructure is believed to be from poorly hydrated hexagonal domains formed together with layered domains by the phase separation of the precursory LC mixture in the presence of carbon. Electrochemical measurements using cyclic volutammetry and membrane electrode assemblies revealed that the cross-linked nanowired Pt/C composite exhibits fairly high electrocatalytic activity for oxygen reduction reaction, as well as a high performance as the cathode material for polymer electrolyte fuel cells. © 2010 American Scientific Publishers.
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Synthesis of b-Ni(OH)2 hexagonal plates and electrochemical behavior as a positive electrode material Reviewed
Go Sakai, Makoto Miyazaki, Tsuyoshi Kijima
Journal of The Electrochemical Society 157 A932 - A939 2010.8
Language：English Publishing type：Research paper (scientific journal)
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Sakai G., Miyazaki M., Kijima T.
Journal of the Electrochemical Society 157 ( 8 ) 2010.7
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society
Β-Ni (OH) 2 hexagonal plates were synthesized from the high specific surface area nickel hydroxide by adopting the solvothermal treatment, i.e., heat-treatment of nickel hydroxide in a closed vessel in the presence of the disperse phase. An aqueous ammonia solution was chosen as the disperse phase, and it was effective for producing unit cell derived hexagonal particles even at a relatively low temperature of around 80°C. A wide variety of sizes and specific surface areas of the hexagonal Β-Ni (OH) 2 could be available by choosing the solvothermal conditions such as amount and concentration of ammonia solution as the disperse phase as well as treatment temperature. The solvothermally synthesized hexagonal plates showed stable discharging behavior without serious deterioration in the discharging capacity when relatively high charge/discharge rates were adopted. It was speculated that there is a suitable specific surface area for the hexagonal particles to achieve a higher discharging capacity at high charge/discharge rates. © 2010 The Electrochemical Society.
DOI： 10.1149/1.3446847
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Synthesis of high-surface-area beta-Ni(OH)2 and its transformation into nanosheets and nanodisks by hydrothermal treatment Reviewed
Go Sakai, Makoto Miyazaki, Tsuyoshi Kijima
Journal of The Electrochemical Society 157 A480 - A486 2010.4
Language：English Publishing type：Research paper (scientific journal)
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Sakai G., Miyazaki M., Kijima T.
Journal of the Electrochemical Society 157 ( 4 ) 2010.3
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Electrochemical Society
We report here a simple method to synthesize an extremely high specific surface area (SSA) Β-Ni (OH) 2 by a rapid hydrolysis technique. The combination of nickel salt and a strong alkaline solution precipitated Β-Ni (OH) 2 with an extremely high SSA (beyond 200 m 2 /g up to 239 m 2 /g). Furthermore, the hydrothermal treatment of the as-precipitated nickel hydroxide at low temperatures, 100-120°C, was found to generate an aggregate of Β-Ni (OH) 2 nanosheets with high SSA around 190 m 2 g-1. A similar treatment at temperatures as high as 200°C led to the formation of Β-Ni (OH) 2 nanodisks with a low surface area of 39 m 2 g -1 . The discharging capacity of the as-precipitated high SSA Β-Ni (OH) 2 showed a strong dependence on the charging/discharging rate, with a fairly high capacity at a charging/discharging rate of 0.2C. The hydrothermally synthesized nanosheets and nanodisks showed relatively stable discharging characteristics over a wide range of charging/discharging rates ranging from 0.2 to 10C. Especially, the nanodisk material was found to stand the high rate charging/discharging and cause no deterioration in the discharging capacity, although the discharging capacity itself was low. © 2010 The Electrochemical Society.
DOI： 10.1149/1.3298456
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Electrocemical properties of the nickel hydroxide hexagonal plates as positive electrode material
Sakai Go, Miyazaki Makoto, Kijima Tsuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2010 ( 0 ) 1F33 - 1F33 2010
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
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Kijima T., Isayama T., Sekita M., Uota M., Sakai G.
Journal of Alloys and Compounds 485 ( 1-2 ) 730 - 733 2009.10
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds
Terbium (III)-doped yttrium oxysulfate Y 2 O 2 SO 4 :Tb 3+ was synthesized by the 1000 °C calcination of Tb 3+ -doped dodecylsulfate-templated yttrium oxide mesophases with straight-layered (S-type) and concentric-layered (C-type) structures. The Tb 3+ -doped oxysulfates exhibited luminescence bands including the 5 D 4 - 7 F 5 transition with a tendency in intensity to saturate or reach a maximum at 13-25 mol% Tb doping. The maximum intensity of Tb 3+ emission for the C-type-mesophase-mediated Y 2 O 2 SO 4 :Tb 3+ was 1.44 times stronger than that for the S-type-mesophase-mediated analogues, although the Eu 3+ emissions for C-type-mesophase-mediated Y 2 O 2 SO 4 :Eu 3+ was enhanced in intensity up to three times stronger than those for S-type-mesophase-mediated ones. It is suggested from FT-IR data that any specific deformation of sulfate groups is induced for both emission systems by the conversion of concentric dodecylsulfate-layers into straight sulfate-layers in the oxysulfate framework upon calcination. This leads to the enhanced emission for the Eu 3+ -doped system, whereas the emission of Tb 3+ in the same Y 2 O 2 SO 4 matrix is slightly enhanced because the electronic state of 4f 8 for Tb 3+ ion is insensitive to the change of the distribution of the surrounding negative-charged oxide ions. © 2009 Elsevier B.V. All rights reserved.
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Kijima T., Nagatomo Y., Takemoto H., Uota M., Fujikawa D., Sekiya Y., Kishishita T., Shimoda M., Yoshimura T., Kawasaki H., Sakai G.
Advanced Functional Materials 19 ( 4 ) 545 - 553 2009.2
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Advanced Functional Materials
Nanohole-structured single-crystalline Pt nanosheets have been synthesized by the borohydride reduction of Na 2 PtCl 6 confined to the lyotropic liquid crystals (LLCs) of polyoxyethylene (20) sorbitan monooleate (Tween 80) with or without nonaethylene-glycol (C 12 EO 9 ). The Pt nanosheets of around 4-10 nm in central thickness and up to 500 nm or above in diameter have a number of hexagonal-shaped nanoholes ∼1.8nm wide. High-resolution electron microscope images of the nanosheets showed atomic fringes with a spacing of 0.22 nm indicating that the nanosheets are crystallographically continuous through the nanoholed and non-holed areas. The inner-angle distributions for the hexagonal nanoholes indicate that the six sides of the nanoholes are walled with each two Pt (111 ), Pt (11̄1 ) and Pt (010) planes. The formation mechanism of nanoholed Pt nanosheets is discussed on the basis of structural and compositional data for the resulting solids and their precursory LLCs, with the aid of similar nanohole growth observed for a Tween 80 free but oleic acid-incorporated system. It is also demonstrated that the nanoholed Pt nanostructures loaded on carbon exhibit fairly high electrocatalytic activity for oxygen reduction reaction and a high performance as a cathode material for polymer-electrolyte fuel cells, along with their extremely high thermostability revealed through the effect of electronirradiation. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.
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Synthesis of Nanohole-Structured Single-Crystalline Platinum Nanosheets Using Surfactant-Liquid-Crystals and Their Electrochemical Characterization Reviewed
Tsuyoshi Kijima, Yu Nagatomo, Hirokatsu Takemoto, Masafumi Uota, Daisuke Fujikawa, Yuzo Sekiya, Teppei Kishishita, Keisuke Shimoda, Takumi Yoshimura, Hideya Kawasaki, Go Sakai
Advanced Functional Materials 19 545 - 553 2009.2
Language：English Publishing type：Research paper (scientific journal)
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Cathode properties of high-surface-area nickel hydroxide nanostructures
Sakai Go, Miyazaki Makoto, Matsunaga Mana, Kijima Tsuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2009 ( 0 ) 1H05 - 1H05 2009
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
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Synthesis and Characterization of Nanoshell Structured Carbon Nanospheres and Nanowires
Otsuka Akio, Matsumura Yuko, Kai Nanami, Iriki Ryosuke, Takemoto Hirokatsu, Sakai Go, Kijima Tsuyoshi
Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan 2009 ( 0 ) 2PF08 - 2PF08 2009
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
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Yoshimura T., Uota M., Kuwahara T., Fujikawa D., Kawasaki H., Sakai G., Kijima T.
Materials Research Bulletin 43 ( 5 ) 1282 - 1290 2008.5
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Research Bulletin
Using transmission electron microscopy (TEM) electron irradiation effects were studied for nanogroove-network structured single-crystalline and dendritic polycrystalline Pt nanosheets 50-60 nm in size. These two nanosheets with nearly the same average groove-width or dendritic spacing of 1.3-1.4 nm were prepared from the mixed and single surfactant liquid crystalline templates, respectively. On exposure to electron beam for 20 min at the acceleration voltage of 200 kV, the nanogrooved nanosheets were morphologically little affected, but the dendritic ones were transformed into less branched polycrystalline structures with spacings distributed around ∼1.7 nm. The shape transformation of the latter occurred by the combined mechanism of segmental migration and atomic diffusion. These observations indicate that the nanogrooved Pt nanosheets are highly stabilized by the grooved but crystallographically continuous Pt framework, leading to their extremely high thermo-resistance, in marked contrast to the polycrystalline dendritic structures constructed of crystallographically discontinuous linkages of nanoblocks. © 2007 Elsevier Ltd. All rights reserved.
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Abnormally Enhanced Eu3+ Emission in Y2O2SO4:Eu3+ Inherited from Their Precursory Dodecylsulfate-Templated Concentric-Layered Nanostructure Reviewed
T. Kijima, T. Shinbori, M. Sekita, M. Uota, G. Sakai
Journal of Luminescence 128 311 - 316 2008.4
Language：English Publishing type：Research paper (scientific journal)