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Journal Articles

Origin of the enhancement of electrocatalytic activity and durability of PtRu alloy prepared from a hetero binuclear Pt-Ru complex for methanol oxidation reactions

Okawa, Yukihisa*; Masuda, Takuya*; Uehara, Hiromitsu*; Matsumura, Daiju; Tamura, Kazuhisa; Nishihata, Yasuo; Uosaki, Kohei*

RSC Advances (Internet), 3(35), p.15094 - 15101, 2013/09

 Times Cited Count:8 Percentile:60.65(Chemistry, Multidisciplinary)

Journal Articles

Structure of Pt(111)/ionomer membrane interface and its bias-induced change in membrane electrode assembly

Masuda, Takuya*; Fukumitsu, Hitoshi*; Kondo, Toshihiro*; Naohara, Hideo*; Tamura, Kazuhisa; Sakata, Osami*; Uosaki, Kohei*

Journal of Physical Chemistry C, 117(23), p.12168 - 12171, 2013/06

 Times Cited Count:12 Percentile:54.85(Chemistry, Physical)

The structure of the perfluorosulfonated ionomer (PFSI)/Pt(111) interface in a membrane electrode assembly (MEA)-like configuration of a polymer electrolyte membrane (PEM) fuel cell, that is, a vacuum evaporated Pt layer/PEM(Nafion membrane)/PFSI(adhesion Nafion layer)/Pt(111) single crystal, and its bias-induced change were investigated by surface X-ray scattering measurement at an atomic level. Crystal truncation rod measurement shows that PFSI adsorbed on the Pt(111)-(1$$times$$1) surface without bias. When the Pt(111) electrode was positively biased to form Pt oxide, the PFSI layer was detached from the Pt surface and oxygen atoms penetrated into the Pt lattice.

Journal Articles

Role of cerium oxide in the enhancement of activity for the oxygen reduction reaction at Pt-CeO$$_{x}$$ nanocomposite electrocatalyst; An in situ electrochemical X-ray absorption fine structure study

Masuda, Takuya*; Fukumitsu, Hitoshi*; Fugane, Keisuke*; Togasaki, Hirotaka*; Matsumura, Daiju; Tamura, Kazuhisa; Nishihata, Yasuo; Yoshikawa, Hideki*; Kobayashi, Keisuke*; Mori, Toshiyuki*; et al.

Journal of Physical Chemistry C, 116(18), p.10098 - 10102, 2012/05

 Times Cited Count:87 Percentile:6.1(Chemistry, Physical)

In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L$$_{3}$$ and Ce L$$_{3}$$ edges of the Pt-CeO$$_{x}$$/C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L$$_{3}$$ edge of the conventional Pt/C catalyst in oxygen-saturated H$$_{2}$$SO$$_{4}$$ solution to clarify the role of CeO$$_{x}$$ in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt-CeO$$_{x}$$ nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeO$$_{x}$$ layer, of which Ce$$^{3+}$$ was oxidized to Ce$$^{4+}$$ instead of Pt at the Pt oxide formation potential.

Journal Articles

In situ electrochemical, electrochemical quartz crystal microbalance, scanning tunneling microscopy, and surface X-ray scattering studies on Ag/AgCl reaction at the underpotentially deposited Ag bilayer on the Au(111) electrode surface

Uosaki, Kohei*; Morita, Jun*; Katsuzaki, Tomoko*; Takakusagi, Satoru*; Tamura, Kazuhisa; Takahashi, Masamitsu; Mizuki, Junichiro; Kondo, Toshihiro*

Journal of Physical Chemistry C, 115(25), p.12471 - 12482, 2011/06

 Times Cited Count:12 Percentile:55.46(Chemistry, Physical)

Ag/AgCl reaction at the Ag bilayer, which was underpotentially prepared on a Au(111) surface, was investigated using electrochemical quartz crystal microbalance (EQCM), scanning tunneling microscopy (STM), surface X-ray scattering (SXS), and electrochemical techniques. When the potential was scanned positively from -200 mV, the Cl$$^{-}$$ ion was adsorbed on the Au(111) electrode surface around 0 mV, and then the phase transition of the adsorbed Cl$$^{-}$$ ion layer from random orientation to ($$sqrt{3}$$ $$times$$ $$sqrt{3}$$) structure took place at around +130 mV. The Ag bilayer and Cl$$^{-}$$ ions were oxidatively reacted to form the AgCl monolayer with ($$sqrt{13}$$ $$times$$ $$sqrt{13}$$) $$R$$13.9$$^{circ}$$ structure around +200 mV, accompanied with the formation of AgCl monocrystalline clusters on the AgCl monolayer surface. The structure of the AgCl monolayer on the Au(111) surface was changed from ($$sqrt{13}$$ $$times$$ $$sqrt{13}$$)R13.9$$^{circ}$$ structure to (4$$times$$4) structure around +500 mV.

Journal Articles

Orientation dependence of Pd growth on Au electrode surfaces

Takahashi, Masamitsu; Tamura, Kazuhisa; Mizuki, Junichiro; Kondo, Toshihiro*; Uosaki, Kohei*

Journal of Physics; Condensed Matter, 22(47), p.474002_1 - 474002_9, 2010/12

 Times Cited Count:13 Percentile:44.17(Physics, Condensed Matter)

Journal Articles

Partial stripping of Ag atoms from silver bilayer on a Au(111) surface accompanied with the reductive desorption of hexanethiol SAM

Kondo, Toshihiro*; Tamura, Kazuhisa; Takakusagi, Satoru*; Kitamura, Ken*; Takahashi, Masamitsu; Mizuki, Junichiro; Uosaki, Kohei*

Journal of Solid State Electrochemistry, 13(7), p.1141 - 1145, 2009/07

 Times Cited Count:5 Percentile:85.11(Electrochemistry)

The interfacial structures of Ag bilayer prepared by underpotential deposition on Au(111) were determined by STM and SXS before and after oxidative adsorption and after desorption of a SAM of C$$_{6}$$SH in alkaline ethanol solution. While no structural change was observed after oxidative formation of C$$_{6}$$SH SAM on the Ag/Au(111) in an ethanol solution containing 20 mM KOH and 0.1 mM C$$_{6}$$SH, some of the Ag atoms in the bilayer were stripped when the SAM was reductively desorbed.

Journal Articles

Structure of Au(111) and Au(100) single-crystal electrode surfaces at various potentials in sulfuric acid solution determined by in situ surface X-ray scattering

Kondo, Toshihiro*; Morita, Jun*; Hanaoka, Kazuya*; Takakusagi, Satoru*; Tamura, Kazuhisa; Takahashi, Masamitsu; Mizuki, Junichiro; Uosaki, Kohei*

Journal of Physical Chemistry C, 111(35), p.13197 - 13204, 2007/09

 Times Cited Count:64 Percentile:12.43(Chemistry, Physical)

Potential-dependent surface structures of Au(111) and Au(100) single-crystal electrodes in a 50 mM H$$_{2}$$SO$$_{4}$$ solution were investigated at an atomic level using in situ surface X-ray scattering (SXS) techniques. It was confirmed that both the Au(111) and Au(100) surfaces were reconstructed with an attached submonolayer of an oxygen species, most probably water, at 0 V (vs Ag/AgCl). Results at +0.95 V supported a previously suggested model for both the Au(111) and the Au(100) electrodes that, based on infrared and scanning tunneling microscopy measurements, the surfaces were a (1$$times$$1) structure with the coadsorbed sulfate anion and hydronium cation (H$$_{3}$$O$$^{+}$$). At +1.05 V, where a small amount of an anodic current flowed, adsorption of a monolayer of oxygen species was observed on both surfaces.

Journal Articles

A Novel spectroelectrochemical cell for in situ surface X-ray scattering measurements of single crystal disk electrodes

Kondo, Toshihiro*; Tamura, Kazuhisa*; Takahashi, Masamitsu; Mizuki, Junichiro; Uosaki, Kohei*

Electrochimica Acta, 47(19), p.3075 - 3080, 2002/07

 Times Cited Count:30 Percentile:40.23

A nwely designed spectroelectrochemical cell was constructed for surface X-ray scattering (SXS) to study single crystal electrodes. Electrochemical characteristics of a specific face of a single crystal electrode can be investigated in the meniscus mode, adn SXS measurement can be easily carried out using the spectroelectrochemical cell. The usefulness of the present cell was demonstrated by studying the electrochemical deposition of Pd thin layers on Au(111) and Au(001) that require precise amounts of Pd deposits.

Journal Articles

Evidence for the diffusion of Au atoms into the Te UPD layer formed on a Au(111) substrate

Kawamura, Hiroyuki; Takahashi, Masamitsu; Hojo, Nobuhiko*; Miyake, Masao*; Murase, Kuniaki*; Tamura, Kazuhisa*; Uosaki, Kohei*; Awakura, Yasuhiro*; Mizuki, Junichiro; Matsubara, Eiichiro*

Journal of the Electrochemical Society, 149(2), p.C83 - C88, 2002/02

 Times Cited Count:6 Percentile:76.75(Electrochemistry)

The structure of a Te layer formed on a Au(111) substrate by underpotential deposition (UPD) in an electrolytic solution has been studied using in-situ surface X-ray diffraction technique. The measurements were carried out for a series of samples which were kept at UPD potential for 4 to 59 hours. The results revealed that the Te UPD layer is unstable. The top layer is analyzed to consist of the UPD Te atoms and Au atoms which diffuse from the Au(111) substrate. Also, the Te UPD layer does not have the structure with periodicity reported in previous works, such as (√3×√3)R30° after ample time elapses. Stripping voltammetry for the Te UPD layer shows that the interaction between Te and Au increases with time, supporting the finding that the top layer is a mixture of Te and Au.

Journal Articles

Growth process of Pd thin layers on Au electrode surfaces

Takahashi, Masamitsu; Mizuki, Junichiro; Tamura, Kazuhisa*; Kondo, Toshihiro*; Uosaki, Kohei*

Shinku, 44(3), P. 375, 2001/03

no abstracts in English

Journal Articles

Pseudomorphic growth of Pd monolayer on Au(111) electrode surface

Takahashi, Masamitsu; Hayashi, Yukio; Mizuki, Junichiro; Tamura, Kazuhisa*; Kondo, Toshihiro*; Naohara, Hideo*; Uosaki, Kohei*

Surface Science, 461(1-3), p.213 - 218, 2000/08

 Times Cited Count:69 Percentile:7.39

no abstracts in English

Oral presentation

Investigation of oxygen reduction reaction (ORR)on Pt-CeO$$_{x}$$ model interface for polymer electrolyte fuel cells

Fugane, Keisuke*; Mori, Toshiyuki*; Masuda, Takuya*; Uosaki, Kohei*; Yamamoto, Shunya; Maekawa, Yasunari

no journal, , 

no abstracts in English

Oral presentation

Effect of electrochemical pre-treatment and interface structure between Pt and CeO$$_{x}$$ for improvement of oxygen reduction reaction activity on Pt-CeO$$_{x}$$ model electro catalysis

Fugane, Keisuke*; Mori, Toshiyuki*; Wu, Y. Y.*; Yamamoto, Shunya; Maekawa, Yasunari; Yoshikawa, Hideki*; Yamashita, Yoshiyuki*; Ueda, Shigenori*; Vladimir, M.*; Suzuki, Akira*; et al.

no journal, , 

no abstracts in English

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