研究者詳細 - 近藤　寛

論文 - 近藤　寛

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Operando Observations of a Manganese Oxide Electrocatalyst for Water Oxidation Using Hard/Tender/Soft X-ray Absorption Spectroscopy

Tsunekawa S., Yamamoto F., Wang K.H., Nagasaka M., Yuzawa H., Takakusagi S., Kondoh H., Asakura K., Kawai T., Yoshida M.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 124 （ 43 ） 23611 - 23618 2020年10月

ISSN 19327447

A layered manganese oxide catalyst containing K+ cations [K/MnOx catalyst] was developed, and its ability to efficiently decompose water was demonstrated. Operando hard/tender/soft X-ray absorption fine structure (XAFS) techniques were used to investigate the function of the K/MnOx catalyst under working conditions. The Mn valency depended on the potential and the amount of K+ cation adsorption. Mn K-edge (hard X-ray) XAFS measurements for the K/MnOx catalyst suggested that the Mn in the catalyst was an Mn3+ species with an octahedral δ-MnO2 structure at a lower electrode potential, which changed reversibly to an Mn4+ species with a δ-MnO2 structure at higher potential during oxygen evolution. A similar result was obtained from operando O K-edge (soft X-ray) XAFS. The chemical state of K species was analyzed using operando K K-edge (tender X-ray) XAFS, which indicated that K+ cations were intercalated with hydrated states in the δ-MnO2 layers. These operando XAFS results demonstrated that the layered δ-MnO2 containing hydrated K+ cations functioned as efficient oxygen evolution electrocatalysts because of the presence of Mn3+ reaction sites.

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In situ AP-XPS analysis of a Pt thin-film sensor for highly sensitive H<inf>2</inf>detection

Toyoshima R., Tanaka T., Kato T., Uchida K., Kondoh H.

Chemical Communications （Chemical Communications） 56 （ 70 ） 10147 - 10150 2020年09月

ISSN 13597345

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Promotional Effect of la in the Three-Way Catalysis of La-Loaded Al<inf>2</inf>O<inf>3</inf>-Supported Pd Catalysts (Pd/La/Al<inf>2</inf>O<inf>3</inf>)

Jing Y., Cai Z., Liu C., Toyao T., Maeno Z., Asakura H., Hiwasa S., Nagaoka S., Kondoh H., Shimizu K.I.

ACS Catalysis （ACS Catalysis） 10 （ 2 ） 1010 - 1023 2020年01月

La-loaded Al2O3 (La/Al2O3) is a practical support for three-way catalysis (TWC) reactions. Although it has been reported that the addition of La to Al2O3 results in improved thermal stability to retain high specific surface areas, its effect on the catalytic reduction of NOx (DeNOx) has not been studied systematically. Herein, we describe the role of La in La/Al2O3-supported Pd catalysts (Pd/La/Al2O3) for TWC reactions. For that purpose, we employed various in situ spectroscopic studies, including infrared (IR), X-ray absorption fine structure (XAFS), and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in combination with density functional theory (DFT) calculations. The obtained results revealed that Pd0 species supported on La/Al2O3 are more electron-deficient compared to those on pristine Al2O3 without La(Pd/Al2O3). Kinetic studies using powdered catalysts revealed that the addition of La suppresses the poisoning effect by CO during the DeNOx reactions. In addition to the catalytic tests with powdered catalysts, monolithic honeycomb forms of the catalysts were prepared and employed for TWC reactions, which showed that Pd/La/Al2O3 exhibits higher DeNOx activity than Pd/Al2O3. In this study, we also reexamined the effective loading amount of La, which has traditionally been ∼3-5 wt % of La for TWC processes in order to retain the high specific surface area of the La/Al2O3 supports. Our investigations showed that an increased La loading (15 wt %) is even more effective for the DeNOx reactions tested in this study due to the higher reactivity toward NO and the greater suppression of the poisoning effect of CO. The developed catalyst Pd/La(15)/Al2O3 has also been tested in a commercial vehicle and has been evaluated on a practical driving mode test cycle (LA-4; city cycle of U.S. Federal and California), where it showed a better catalytic performance than the conventionally used Pd/La(3-5)/Al2O3 catalysts. Our study suggests that the loading amount of La in Pd/La/Al2O3 catalysts needs to be adjusted depending on the application systems, considering not only the support stability (surface areas) but also the promotional effect in the TWC process.

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Operando observations of reactive metal–Oxide structure formation on the Pt<inf>3</inf>Ni(111) surface at near-ambient pressure

Kim J., Doh W.H., Kondoh H., Mase K., Gallet J.J., Bournel F., Mun B.S., Park J.Y.

Journal of Electron Spectroscopy and Related Phenomena （Journal of Electron Spectroscopy and Related Phenomena） 238 2020年01月

ISSN 03682048

The formation of interfacial metal–oxide structures on the Pt3Ni(111) bimetallic surface was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques at near-ambient pressure (NAP). Direct observation of surface images clearly shows the occurrence of surface segregation of the sub-surface Ni depending on the surrounding gas-phase conditions. Especially, the prepared topmost Pt-skin layer of the Pt3Ni(111) is altered by Ni oxide segregation that makes an interfacial Pt-NiO1−x nanostructure with dissociated oxygen. This metal–oxide interface could provide active sites for more-efficient carbon monoxide (CO) conversion processes under mixed CO/O2 gas environments; the associated specific chemical binding energy was identified using NAP-XPS. The combined operando observations from the NAP-STM and NAP-XPS on the Pt3Ni(111) surface reveal that the interfacial metal–oxide structure is strongly correlated with the origin of the enhanced catalytic activity at thermodynamic equilibrium.

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Improvement in cobalt phosphate electrocatalyst activity toward oxygen evolution from water by glycine molecule addition and functional details

Yamada K., Hiue T., Ina T., Wang K., Kondoh H., Sakata Y., Lee Y.L., Kawai T., Yoshida M.

Analytical Sciences （Analytical Sciences） 36 （ 1 ） 35 - 40 2020年

ISSN 09106340

Electrochemical water splitting using renewable energy shows promise for the development of sustainable hydrogen production methods. The process requires a highly active electrocatalyst for oxygen evolution to improve the overall water splitting efficiency. The present study showed that oxygen evolution improved dramatically upon the addition of glycine to cobalt phosphate, when the glycine was added to the electrolyte solution during electrodeposition. The functionality of the organic molecules was investigated using in situ UV-vis absorption, in situ X-ray absorption fine structure, and in situ infrared (IR) absorption spectroscopy in the attenuated total reflection mode. The results demonstrated that the glycine molecules assembled cobalt oxide clusters composed of CoO6 (CoOOH) octahedrons a few nanometers in diameter upon the electrodeposition of cobalt catalysts. This suggests that the cobalt-glycine catalyst can decompose water to oxygen gas efficiently, because the number of cobalt oxide clusters increased as active reaction sites upon the addition of glycine molecules.

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Orientation-Dependent Hindrance to the Oxidation of Pd-Au Alloy Surfaces

Toyoshima R., Amemiya K., Mase K., Kondoh H.

Journal of Physical Chemistry Letters （Journal of Physical Chemistry Letters） 9249 - 9254 2020年

Oxidation of monometallic Pd and bimetallic Pd3Au alloy surfaces are observed by in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at an elevated pressure (100 mTorr O2 ambient). It is directly evidenced that the alloying with Au hinders the surface oxidation of Pd3Au surfaces compared with monometallic Pd surfaces. Remarkably, the oxidation behavior is clearly different between Pd3Au(111) and (100) surfaces. The (100) surface has a relatively Pd-rich surface composition, and the surface oxide layer is formed, whereas the (111) surface has a Au-rich composition, and the surface oxidation is quite limited. A combined approach of experimental and theoretical techniques reveals that Pd/Au surface composition and atomic arrangement are key factors determining the oxidation behavior.

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Adsorption state of NO on Ir(111) surfaces under excess O <inf>2</inf> coexisting condition

Ikeda H., Koike Y., Shiratori K., Ueda K., Shirahata N., Isegawa K., Toyoshima R., Masuda S., Mase K., Nito T., Kondoh H.

Surface Science （Surface Science） 685 1 - 6 2019年07月

ISSN 00396028

Iridium (Ir) exhibits a good efficiency for reduction of NO under excess O 2 coexisting conditions at temperatures higher than 250 °C. On the other hand, the advantage is lost at lower temperatures below 250 °C under O 2 existence, compared to any other platinum group metals. In this study, adsorption behavior of NO on Ir(111) single-crystal surfaces under excess O 2 coexisting conditions at the temperatures from room temperature to 250 °C has been studied by in-situ X-ray Photoelectron Spectroscopy (XPS). It is revealed that the coexisting O 2 induces formation of a high-density chemisorbed atomic oxygen (O) phase and the atomic O phase suppresses adsorption of NO at on-top sites significantly, which suggests that the suppression of NO adsorption causes a decrease in the ability of NO reduction at the lower temperatures.

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Influence of Surface Orientation on Electrochemical Properties of Boron-Doped Diamond

Ivandini T.A., Watanabe T., Matsui T., Ootani Y., Iizuka S., Toyoshima R., Kodama H., Kondoh H., Tateyama Y., Einaga Y.

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 123 （ 9 ） 5336 - 5344 2019年03月

ISSN 19327447

To study the influence of crystal orientation on the electrochemical properties of boron-doped diamond (BDD), electrodes comprising (100) and (111) homoepitaxial single-crystal layers of BDD were investigated and these were compared with a thin polycrystalline BDD electrode. The BDD samples with similar amounts of boron of around 1020 cm-3 and resistivity of around 6 × 10-3 ? cm were prepared. Evaluation of the electrochemical reactivity of each of the samples with both H- and O-terminated surfaces showed that polycrystalline BDD was the most reactive, whereas the (111) samples proved to be more reactive than the (100) ones for single-crystal BDD. Moreover, considering the results of first-principles molecular dynamics simulations, it is proposed that surface transfer doping is the dominating factor for H-terminated surfaces, whereas the degree of band bending and the thickness of the space-charge layer are the dominating factors for O-terminated surfaces.

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Operando study of Pd(100) surface during CO oxidation using ambient pressure x-ray photoemission spectroscopy

Yu Y., Kim D., Lim H., Kim G., Koh Y.E., Kim D., Ueda K., Hiwasa S., Mase K., Bournel F., Gallet J.J., Rochet F., Crumlin E.J., Ross P.N., Kondoh H., Noh D.Y., Mun B.S.

AIP Advances （AIP Advances） 9 （ 1 ） 2019年01月

The surface chemical states of Pd(100) during CO oxidation were investigated using ambient pressure x-ray photoelectron spectroscopy and mass spectroscopy. Under the reactant ratio of CO/O 2 = 0.1, i.e. an oxygen-rich reaction condition, the formation of surface oxides was observed with the onset of CO oxidation reaction at T = 525 K. As the reactant ratio (CO/O 2 ) increased from 0.1 to 1.0, ∼ 90 % surface oxides remains on surface during the reaction. Upon the formation of surface oxides, the core level shift of oxygen gas phase peak was observed, indicating that change of surface work function. As CO oxidation takes places, i.e. making a transition from CO covered surface to the oxidic surface, the work functions of surface oxide on Pd(100) and Pt(110) display opposite behavior.

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Formation of carbonate on Ag(111) under exposure to ethylene and oxygen gases evidenced by near ambient pressure XPS and NEXAFS

Isegawa K., Ueda K., Hiwasa S., Amemiya K., Mase K., Kondoh H.

Chemistry Letters （Chemistry Letters） 48 （ 2 ） 159 - 162 2019年

ISSN 03667022

The active oxygen species for ethylene epoxidation on Ag surfaces has been a long-standing issue. We conducted in situ observations of Ag(111) surfaces under exposure to ethylene and oxygen gases with near ambient pressure (NAP) X-ray photo-electron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Combined results of these spectroscopies evidence that a carbonate species with a flat-lying configuration is formed on the Ag(111) surface at 370500 K under exposure to the NAP gas mixture of ethylene and oxygen.

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Operando NAP-XPS Observation and Kinetics Analysis of NO Reduction over Rh(111) Surface: Characterization of Active Surface and Reactive Species

Ueda K., Isegawa K., Amemiya K., Mase K., Kondoh H.

ACS Catalysis （ACS Catalysis） 8 （ 12 ） 11663 - 11670 2018年12月

NO reduction by CO on Rh(111) was investigated by near-ambient pressure X-ray photoelectron spectroscopy, mass spectrometry, and kinetic analysis. Under exposure to NO + CO mixed gases and with heating the surface from room temperature to 450 °C, NO dissociation and NO reduction reaction start simultaneously independent of gas pressure ratio of NO/CO, which indicates that NO dissociation triggers this reaction. From kinetic analyses based on observed adsorbate coverages under reaction conditions, the following two points are suggested: (i) NOhollow is a reactive species for N2 and N2O formation via N + NO reaction. (ii) At low temperatures, the N + NO reaction is dominant for N2 production, whereas above around 400 °C, the N + N reaction becomes dominant, which leads to an increase in N2 selectivity at the higher temperatures. Compared with the NO + CO reaction on Ir(111) surfaces, which exhibits a high N2 selectivity, the adsorption site of reactive NO and the availability of vacant surface sites could be key factors for the lower N2 selectivity for Rh(111).

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Adsorbate-driven reactive interfacial Pt-NiO<inf>1−</inf>x nanostructure formation on the Pt<inf>3</inf>Ni(111) alloy surface

Kim J., Park W.H., Doh W.H., Lee S.W., Noh M.C., Gallet J.J., Bournel F., Kondoh H., Mase K., Jung Y., Mun B.S., Park J.Y.

Science Advances （Science Advances） 4 （ 7 ） 2018年07月

The origin of the synergistic catalytic effect between metal catalysts and reducible oxides has been debated for decades. Clarification of this effect, namely, the strong metal-support interaction (SMSI), requires an understanding of the geometric and electronic structures of metal-metal oxide interfaces under operando conditions. We show that the inherent lattice mismatch of bimetallic materials selectively creates surface segregation of subsurface metal atoms. Interfacial metal-metal oxide nanostructures are then formed under chemical reaction environments at ambient pressure, which thus increases the catalytic activity for the CO oxidation reaction. Our in situ surface characterizations using ambient-pressure scanning tunneling microscopy and ambient-pressure x-ray photoelectron spectroscopy exhibit (i) a Pt-skin layer on the Pt-Ni alloyed surface under ultrahigh vacuum, (ii) selective Ni segregation followed by the formation of NiO1−x clusters under oxygen gas, and (iii) the coexistence of NiO1−x clusters on the Pt-skin during the CO oxidation reaction. The formation of interfacial Pt-NiO1−x nanostructures is responsible for a highly efficient step in the CO oxidation reaction. Density functional theory calculations of the Pt3Ni(111) surface demonstrate that a CO molecule adsorbed on an exposed Pt atom with an interfacial oxygen from a segregated NiO1−x cluster has a low surface energy barrier of 0.37 eV, compared with 0.86 eV for the Pt(111) surface.

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Chemical state changes of Nafion in model polymer electrolyte fuel cell under oxygen/hydrogen gas atmosphere observed by S-K XANES spectroscopy

Isegawa K., Kim D., Kondoh H.

RSC Advances （RSC Advances） 8 （ 67 ） 38204 - 38209 2018年

Changes in the chemical states of the sulfonic groups of Nafion in a model polymer electrolyte fuel cell under an oxygen/hydrogen gas atmosphere were studied using sulfur K-edge XANES spectroscopy. First, the chemical state changes in the sulfonic acid groups of both cathode and anode electrodes due to humidity under oxygen/hydrogen gas flow were observed. Reversible spectral changes ascribed to the hydration and dehydration of the sulfonic acid group were observed at both electrodes. This result is similar to the experimental results obtained without introducing oxygen (helium/hydrogen). On the anode, some of the sulfonic acid groups were decomposed to atomic sulfur adsorbed on platinum (Sad) and the amount increased with time. On the cathode, the formation of Sad was suppressed under the oxygen atmosphere. Next, the effects of oxygen gas introduction onto Sad were examined. Sad was at once formed on both electrodes under dry conditions without an oxygen supply. By supplying oxygen gas, Sad on the cathode disappears. Therefore, the catalyst of the cathode has the ability to recover against the poisoning Sad, while that on the anode accumulates.

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Element selective oxidation on Rh-Pd bimetallic alloy surfaces

Kondoh H., Toyoshima R., Shirahata N., Hoda A., Yoshida M., Amemiya K., Mase K., Mun B.

Physical Chemistry Chemical Physics （Physical Chemistry Chemical Physics） 20 （ 45 ） 28419 - 28424 2018年

ISSN 14639076

The interactions between oxygen and Rh-Pd bimetallic alloy surfaces were investigated using surface sensitive experimental techniques and density functional theory calculations. The alloy surfaces were oxidized under 10-5 Torr and 100 mTorr oxygen upon heating above 250 °C. A thin Rh oxide layer was preferentially formed on a Rh1Pd9(100) surface, while a thin Pd oxide layer was formed on a Rh1Pd9(111) surface, though the Rh oxide is thermodynamically more stable irrespective of the surface orientation. Chemical analyses revealed that the initial Rh fraction for the (111) surface was significantly lower than that for the (100) surface, which suggests that the oxidized element on the surface is kinetically selected depending on the near surface initial composition.

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Dehydration Pathway for the Dissociation of Gas-Phase Formic Acid on Pt(111) Surface Observed via Ambient-Pressure XPS

近藤寛

Journal of Physical Chemistry C （Journal of Physical Chemistry C） 122 （ 4 ） 2064 - 2069 2017年12月

共著, 査読有り, ISSN 19327447

While model studies of surface science under ultrahigh vacuum (UHV) have made significant contributions to understanding electrochemistry, many issues related to electrochemical phenomena still remain unanswered due to the extreme environmental differences between UHV and liquid conditions. Electrochemical formic acid (HCOOH) oxidation is one such example. While the dehydration step in the indirect oxidation pathway (HCOOH → H2O + COad → 2H+ + 2e- + CO2) is observed in the electrochemical oxidation of formic acid on Pt(111) surface, the surface science studies conducted in UHV condition reported the complete HCOOH dissociation to H2 and CO2 on Pt(111) surface with no adsorbed CO at room temperature. A dehydration mechanism may also exist in gas-phase HCOOH dissociation in some conditions different from UHV, but it has not been demonstrated with a surface science method due to pressure limitations. Using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), we observed the dehydration mechanism of gas-phase HCOOH in unprecedented high pressure environment for the first time. This study is a demonstration of reconciling the disagreement between electrocatalysis and surface science by bridging the environment gap.

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Catalytic CO oxidation over Pd70Au30(111) alloy surface: spectroscopic evidence for Pd ensemble dependent activity

近藤寛

Chem. Commun. （The Royal Society of Chemistry） 53 12657 - 12660 2017年11月

共著, 査読有り

Chemical states of surface oxygen during CO oxidation on Pt(110) surface revealed by ambient pressure XPS

近藤寛

J. Phys.: Condens. Matter. （IOP） 29 464001-(1) - 464001-(6) 2017年10月

研究論文（学術雑誌）, 共著, 査読有り

Ambient pressure phase transitions over Ir(111): At the onset of CO oxidation

近藤寛

J. Phys.: Condens. Matter. （IOP） 29 444002-(1) - 444002-(10) 2017年10月

研究論文（学術雑誌）, 共著, 査読有り

Operando Observation of NO Reduction by CO on Ir(111) Surface Using NAP-XPS and Mass Spectrometry: Dominant Reaction Pathway to N2 Formation under Near Realistic Conditions

近藤寛

J. Phys. Chem. C （American Chemical Society） 121 （ 3 ） 1763 - 1769 2017年01月

査読有り

Integration of Active Nickel Oxide Clusters by Amino Acids for Water Oxidation

近藤寛

J. Phys. Chem. C （American Chemical Society） 121 （ 1 ） 255 - 260 2016年12月

査読有り

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