Faculty Profiles - Yamakata Akira

Papers - Yamakata Akira

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Surface-enhanced infrared absorption spectroscopic studies of adsorbed nitrate, nitric oxide, and related compounds 1: Reduction of adsorbed NO on a platinum electrode Reviewed

Kou Nakata, Akinori Okubo, Katsuaki Shimazu, Akira Yamakata, Shen Ye, Masatoshl Osawa

LANGMUIR 24 ( 8 ) 4352 - 4357 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Surface-enhanced infrared absorption spectroscopy (SEIRA) was used to examine the adsorption state of nitrogen monoxide (nitric oxide, NO) and the reduction of the adsorbed species. The SEIRA spectra gave two distinct bands at 1723-1733 and 1575-1607 cm(-1) with an additional weak band at 1656-1676 cm(-1) at 0.20 V, the frequencies of which are slightly dependent on the surface coverage. The former two bands are attributed to the on-top and bridged NO, respectively. While the on-top NO stably remained on the surface in the potential range of 0.05-0.60 V, the bridged NO decreased in its intensity with increasing electrode potential. The reduction of the adsorbed NO obeys first-order kinetics with respect to the adsorbed NO. The rate constants are 2.24 +/- 0.03 and 0.24 +/- 0.09 s(-1) at -0.10 V for the on-top and bridged NO, respectively. Tafel slopes obtained from the potential dependence of the rate constant indicate that the rate-determining step is the first electron-transfer process.

DOI： 10.1021/la703394z

Surface-enhanced infrared absorption spectroscopic studies of adsorbed nitrate, nitric oxide, and related compounds 2: Nitrate ion adsorption at a platinum electrode Reviewed

Kou Nakata, Yota Kayama, Katsuaki Shimazu, Akira Yamakata, Shen Ye, Masatoshi Osawa

LANGMUIR 24 ( 8 ) 4358 - 4363 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The adsorbed species formed from the nitrate ion were examined using surface-enhanced infrared absorption spectroscopy (SEIRAS). The main band was observed at 1547-1568cm(-1) at 0.2 V in 0.01 M NaNO3 + 0.1 MHClO4. Although this band is close to that assigned to the adsorbed NO in the literature, it is assigned to the N=O stretching vibration of the chelating bidentate form of nitrate for the following reasons. (i) Nitrate gives a single band, while NO has three bands independent of the coverage. (ii) The band intensity remained constant in the potential range from 0.1 to 0.6 V. while that of the bridged NO at around 1600 cm(-1) decreased in this range. (iii) The rate constants for the reduction and/or desorption at negative potentials are about 3 times higher than those of the bridged NO. (iv) The adsorbed species from nitrate is replaced with CO more easily than the bridged NO.

DOI： 10.1021/la703476m

Structure of water at the electrified platinum-water interface: A study by surface-enhanced infrared absorption spectroscopy Reviewed

Masatoshi Osawa, Minoru Tsushima, Hirokazu Mogami, Gabor Samjeske, Akira Yamakata

JOURNAL OF PHYSICAL CHEMISTRY C 112 ( 11 ) 4248 - 4256 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode is used to examine the structure of water on a polycrystalline Pt electrode in H2SO4 and HClO4 as a function of applied potential. The electrode surface covered with CO is used as the reference in recording spectra, which enables us to obtain the absolute infrared spectrum of the interfacial water layer (monolayer or bilayer) in contact with the surface with negligible interference from the bulk water. The spectrum of the interfacial water is largely different from that of bulk water and changes around the potential of zero charge of the electrode. The spectral changes are ascribed to the potential-dependent reorientation of water molecules from a weakly hydrogen-bonded oxygen-up orientation at the negatively charged surface to a strongly hydrogen-bonded nearly flat orientation at the positively charged surface in agreement with theoretical simulations reported in the literature. Clear experimental evidence of the formation of a stable ice-like structured water on the positively charged surface is reported.

DOI： 10.1021/jp710386g

表面増強赤外吸収分光法による電極界面の超高速ダイナミクスの追跡 Reviewed

山方啓, 大澤雅俊

Electrochemistry 電気化学および工業物理化学 : denki kagaku 76 ( 3 ) 208 - 213 2008.3

固液界面の水分子の構造とエネルギー移動ダイナミクス Reviewed

山方啓

分光研究 57 ( 1 ) 23 - 24 2008

Time-resolved infrared absorption study of nine TiO2 photocatalysts Reviewed

Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi

CHEMICAL PHYSICS 339 ( 1-3 ) 133 - 137 2007.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Electron kinetics of nine TiO2 catalysts were compared in a microsecond time domain. Each catalyst was band-gap excited with an UV light pulse, and electron-induced absorption of mid infrared light was observed as a function of time delay. The probability of electron-hole recombination in the bulk, electron attachment to adsorbed oxygen, and hole attachment to adsorbed methoxy species was estimated. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemphys.2007.05.010

How the Molecules Reach the Reaction Center? Reviewed

YAMAKATA AKIRA

触媒 = Catalysts & Catalysis 48 ( 8 ) 611 - 611 2006.12

Laser-induced potential jump at the electrochemical interface probed by picosecond time-resolved surface-enhanced infrared absorption spectroscopy Reviewed

A Yamakata, T Uchida, J Kubota, M Osawa

JOURNAL OF PHYSICAL CHEMISTRY B 110 ( 13 ) 6423 - 6427 2006.4

Language：English Publisher：AMER CHEMICAL SOC

Picosecond time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS) has been used for the first time to examine the potential jump at the electrochemical interface induced by a visible pulse irradiation. The potential dependent shift of the C-O stretching vibration of CO adsorbed on a Pt electrode was utilized to monitor the potential jump. A 6-cm(-1) red-shift was observed with a time delay of similar to 200 ps with respect to a visible pump-pulse irradiation (532 nm, 35 ps duration, 3 mJ cm(-2)). The observed red-shift is ascribed to the heating of the in-plane frustrated translational mode of CO and the negative shift of potential. These two contributions can be separated with the aid of the transient of the background reflectivity of the electrode surface. The heating of water layers near the surface is mainly responsible for the potential jump through the orientation change of water molecules. This method is promising as a tool to examine ultrafast electrode dynamics.

DOI： 10.1021/jp060387d

Adsorbed structures of 4,4 '-bipyridine on Cu(111) in acid studied by STM and IR Reviewed

YX Diao, MJ Han, LJ Wan, K Itaya, T Uchida, H Miyake, A Yamakata, M Osawa

LANGMUIR 22 ( 8 ) 3640 - 3646 2006.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The adsorption of 4,4'-bipyridine (BiPy) on Cu(111) has been investigated in 0.1 M HClO4 by cyclic voltammetry, electrochemical scanning tunneling microscopy (STM), and surface-enhanced infrared adsorption spectroscopy (SEIRAS). Cyclic voltammetry showed the double layer region extending from -0.2 to 0.26 V and a pair of redox waves superposing on hydrogen evolution wave at more negative potentials. Diprotonated BiPy, BiPyH22+, is adsorbed flat on the Cu(111) (1 x 1) surface and forms a well-ordered monolayer with a (3 x 4) symmetry in the double-layer potential region. At more negative potential, BiPyH22+ is reduced to its monocation radical, BiPyH2 center dot+, and forms another well-ordered structure in which the radicals are stacked in molecular rows with a face-to-face self-dimer as the building unit. The SEIRA spectra of both BiPyH22+ and BiPyH2 center dot+ are dominated by gerade modes which should be IR-inactive for the centrosymmetric species. The breakdown of the selection rule of IR absorption is ascribed to the vibronic coupling associated with charge transfer between BiPyH22+ and the surface and between the radicals.

DOI： 10.1021/la052765w

Study on photogenerated charge carriers dynamics in sulfur-doped titanium dioxide by transient IR absorption Reviewed

Kan Takeshita, Akira Yamakata, Taka-aki Ishibashi, Hiroshi Onishi, Kazumoto Nishijima, Teruhisa Ohno

J. photochem. Photobiol. B. Chemistry 117 269 - 275 2006.4

Transient IR absorption study of charge carriers photogenerated in sulfur-doped TiO2 Reviewed

K Takeshita, A Yamakata, T Ishibashi, H Onishi, K Nishijima, T Ohno

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 177 ( 2-3 ) 269 - 275 2006.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Sulfur-doped TiO2 was prepared by two methods; one was simple oxidation annealing of TiS2, the other was mixing of titanium isopropoxide and thiourea. These two sulfur-doped TiO2, preparations showed fairly different photocatalytic activity under visible light. The dynamics of photogenerated charge carriers were studied by the transient absorption measurement in the region of mid-IR. In both samples, excitation by 532 nm pulse led to photocarrier generation to the same extent. Nevertheless, the reactivity of the photocarriers was totally different. Photogenerated electrons and holes transferred to reactant gas in the latter sample, whereas they did not in the former sample. We attributed the different carrier behavior to the difference in the distribution of S atoms or particle size. These observations can explain the difference in capability of photocatalysis under visible light. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2005.06.006

Potential oscillations in galvanostatic electrooxidation of formic acid on platinum: A time-resolved surface-enhanced infrared study Reviewed

G Samjeske, A Miki, S Ye, A Yamakata, Y Mukouyama, H Okamoto, M Osawa

JOURNAL OF PHYSICAL CHEMISTRY B 109 ( 49 ) 23509 - 23516 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The mechanism of temporal potential oscillations that occur during galvanostatic formic acid oxidation on a Pt electrode has been investigated by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS). Carbon monoxide (CO) and formate were found to adsorb on the surface and change their coverages synchronously with the temporal potential oscillations. Isotopic solution exchange (from (HCOOH)-C-13 to (HCOOH)-C-12) and potential step experiments revealed that the oxidation of formic acid proceeds dominantly through adsorbed formate and the decomposition of formate to CO2 is the rate-determining step of the reaction. Adsorbed CO blocks the adsorption of formate and also suppresses the decomposition of formate to CO2, which raises the potential to maintain the applied current. The oxidative removal of CO at a high limiting potential increases the coverage of formate and accelerates the decomposition of formate, resulting in a potential drop and leading to the formation of CO. This cycle repeats itself to give the sustained temporal potential oscillations. The oscillatory dynamics can be explained by using a nonlinear rate equation originally proposed to explain the decomposition of formate and acetate on transition metal surfaces in UHV.

DOI： 10.1021/jp055220j

Time-Resolved IR Absorption Study on Solid Surfaces Reviewed

YAMAKATA AKIRA, OSAWA MASATOSHI

触媒 = Catalysts & Catalysis 47 ( 5 ) 334 - 340 2005.8

Time-resolved infrared absorption study of photochemical reactions over metal oxides Reviewed

A Yamakata, T Ishibashi, K Takeshita, H Onishi

TOPICS IN CATALYSIS 35 ( 3-4 ) 211 - 216 2005.7

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER/PLENUM PUBLISHERS

The present account describes how photochemical reactions over metal oxides are traced by time-resolved infrared (IR) absorption spectroscopy. The ac-coupled amplification of the IR signal allows detection of transient absorbance changes as small as 10(-6) with a time resolution of 50 ns. Band-gap excited electrons in TiO2 and NaTaO3 present a structureless absorption of IR light from 3000 to 1000 cm(-1). Reaction-perturbed decay of this absorption evidences the assignment to photoexcited electrons, not to holes. The efficiency of the water splitting reaction on NaTaO3-based catalysts correlates with the quantity of electrons detected by the IR absorption. A short-lived intermediate state of 2-propanol oxidation on TiO2 is identified by its vibrational band at 1640 cm(-1) superposed on the structureless absorption of electrons. Ru dye (N3) on a TiO2 film is irradiated with a 532-nm light pulse to simulate dye-sensitized solar cells. The neutralization rate of dye cations and the decay rate of electrons injected in the film are quantified, leading to a three-state model which describes the relaxation of injected electrons. These results demonstrate the ability of this method in tracing photochemical kinetics over metal oxides.

DOI： 10.1007/s11244-005-3826-0

Carrier dynamics in TiO2 and Pt/TiO2 powders observed by femtosecond time-resolved near-infrared spectroscopy at a spectral region of 0.9-1.5 mu m with the direct absorption method Reviewed

K Iwata, T Takaya, H Hamaguchi, A Yamakata, TA Ishibashi, H Onishi, H Kuroda

JOURNAL OF PHYSICAL CHEMISTRY B 108 ( 52 ) 20233 - 20239 2004.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Femtosecond time-resolved near-infrared spectra of TiO2 and Pt/TiO2 powders are measured at the wavelength region of 0.9-1.5 mum with the direct absorption method. Broad absorption bands of charge carriers, mainly free and trapped electrons, are observed for TiO2 and Pt/TiO2. The absorption band shape changes with a time constant of 160 A after the photoirradiation, which most probably reflects the trapping of the generated free electrons. Population decay curves of the carriers after 1 ps, obtained for three different pump light powers, are well-explained by the second-order decay kinetics with a common second-order rate constant, indicating nongeminate recombination of the electron-hole pairs. When Pt is loaded to TiO2, an additional decaying process of 2.3 ps is observed. This decay component represents the transfer of generated electrons from TiO2 to Pt, which is consistent with the known increase of overall catalytic activities by the Pt cocatalyst.

DOI： 10.1021/jp047531k

In situ surface-enhanced infrared study of hydrogen bond pairing of complementary nucleic acid bases at the electrochemical interface Reviewed

Y Sato, H Noda, F Mizutani, A Yamakata, M Osawa

ANALYTICAL CHEMISTRY 76 ( 18 ) 5564 - 5569 2004.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Surface-enhanced infrared absorption spectroscopy with a Kretschmann-type attenuated total reflection configuration has been used to study hydrogen-bonded pairing between 6-amino-8-purinethiol, a thiol-derivatized adenine, immobilized on a gold electrode surface, and thymidine, a complimentary base derivative of adenine, in 0. 1 M NaClO4 aqueous solution as a function of applied potential. 6-Amino-8-purinethiol is adsorbed on a gold surface via a sulfur atom to form a S-Au bond. Nearly half of the adsorbed molecules are protonated, and the long axis of the adenine moiety is tilted from the surface normal at open circuit potential. As the potential increases, the acid-base equilibrium is shifted toward the unprotonated form and the adenine moiety is reoriented toward a nearly perpendicular configuration. The hydrogen bond interaction between the adsorbed 6-amino-8purinethiol with thymidine in solution is greatly affected by the protonation and orientation of the adenine moiety and is controllable by the applied potential. Due to steric hindrance, an adenine-thymine-type hydrogen bond pair is formed only at potentials more positive than 0. 1 V (vs SCE) where the unprotonated adenine moiety is perpendicularly oriented.

DOI： 10.1021/ac049303s

Effect of annealing temperature on back electron transfer and distribution of deep trap sites in dye-sensitized TiO2, studied by time-resolved infrared spectroscopy Reviewed

K Takeshita, Y Sasaki, M Kobashi, Y Tanaka, S Maeda, A Yamakata, TA Ishibashi, H Onishi

JOURNAL OF PHYSICAL CHEMISTRY B 108 ( 9 ) 2963 - 2969 2004.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The effect of annealing temperature on electron dynamics in Ru complex-sensitized TiO2 films was studied by highly sensitive measurement of transient IR absorption. The amount of electron injection and the back electron transfer rate were not influenced to a large extent by annealing temperature, but the distribution of deep trap sites was considerably influenced. The difference in solar cell efficiency due to annealing temperature was mainly attributed to the difference in the nature of deep trap sites. By extending the probe light window from the mid-IR (1000-4000 cm(-1)) to the near-IR (-10000 cm(-1)) region, we investigated deep trap sites directly and found that electrons in deep trap sites have absorption in the near-IR region whose peak locates around 7500 cm(-1). As a whole, the electron dynamics in the films annealed at higher than 400 degreesC were considerably different compared with those in the films annealed at lower than 400 degreesC.

DOI： 10.1021/jp035416o

Photodynamics of NaTaO3 catalysts for efficient water splitting Reviewed

A Yamakata, T Ishibashi, H Kato, A Kudo, H Onishi

JOURNAL OF PHYSICAL CHEMISTRY B 107 ( 51 ) 14383 - 14387 2003.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Electrons photoexcited in catalysts based on NaTaO3 were observed by time-resolved infrared (IR) absorption spectroscopy. The electrons excited by 266-nm pump pulse exhibited a monotonic absorption of mid-IR light. The recombination kinetics of the excited electrons with holes was monitored in a vacuum as a function of time delay ranging from 100 ns to 1 s. When the Na content and La dopant were optimized to achieve high activity in the steady-state reaction of water splitting, the recombinative decay was hindered to increase the amount of electrons. The electrons were transferred to NiO ultrafine particles, loaded as a cocatalyst, within 1 mus following the pulse excitation. Exposing the catalysts to water vapor affected the electron decay and efficient electron transfer to water via the cocatalyst was evidenced.

DOI： 10.1021/jp036473k

Effects of water addition on the methanol oxidation on Pt/TiO2 photocatalyst studied by time-resolved infrared absorption spectroscopy Reviewed

A Yamakata, TA Ishibashi, J Onishi

JOURNAL OF PHYSICAL CHEMISTRY B 107 ( 36 ) 9820 - 9823 2003.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The reaction kinetics of electrons photoexcited in a Pt/TiO2 catalyst were observed by time-resolved infrared absorption in the presence of methanol-water vapor mixtures. The recombinative decay of the electrons was completed in microseconds on the catalyst exposed to a vacuum. The decay was suspended in the catalyst exposed to pure methanol vapor due to an effective hole-consuming reaction by adsorbed methoxy species. The suspension was released as partial water pressure was increased, indicating that the holes reacted with the methoxy species without the aid of adsorbed water or hydroxyl species. The excess electrons remaining in the catalyst were consumed by adsorbed water in a time domain of 0.1 s. The water-induced promotion of the methanol oxidation reaction described in the literature was interpreted with these results.

DOI： 10.1021/jp034997e

Time-Resolved Infrared Absorption Study of Reaction Intermediate on Pt/TiO_2 Photocatalyst Reviewed

YAMAKATA Akira, ISHIBASHI Taka-aki, ONISHI Hiroshi

J. Surf. Sci. Soc. Jpn. 24 ( 9 ) 563 - 567 2003.9

Language：Japanese Publisher：The Surface Science Society of Japan

Oxidation of 2-propanol to acetone on a Pt/TiO<Sub>2</Sub> photocatalyst by UV pulse irradiation was observed by time-resolved IR spectroscopy (TR-IR). The hole transfer to the 2-propanol, which triggers the oxidation, was completed within 0.5 μs. Transient vibrational spectra showed a new band at 1640 cm<Sup>−1</Sup>, which appeared immediately after the irradiation. This band gradually transformed to a band at 1700 cm<Sup>−1</Sup>, which was assigned to the C=O stretching mode of acetone, the product of 2-propanol oxidation. Thus, the band at 1640 cm<Sup>−1</Sup> was suggested to be the reaction intermediate that transforms to acetone. We discussed the origin of this band using density functional calculation, and an acceptable agreement was obtained with the anion radical of acetone adsorbed on the catalyst.

DOI： 10.1380/jsssj.24.563

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