2016 - 九州大学（kyushu university） · ‐ synthesis of novel alloy nanoparticles and phase...

2016 Japan‐Germany Joint Symposium on

Advanced Characterization of Nanostructured Materials for Energy and the Environment

June 27 ‐ 29, 2016

Hotel and Conference Center Mutterhaus Düsseldorf, Germany

The symposium aims at providing a forum for Japanese and German researchers interested in applying advanced methods of microscopy and spectroscopy, including aberration‐corrected and in situ electron microscopy, to different future directions of materials research for energy and the environment. The focus of the 2016 Joint Symposium will be on research aiming at developing new functional alloyed nanoparticles, especially also nanoparticles of metastable solid solution alloys. Topical areas will adress

‐ Synthesis of novel alloy nanoparticles and phase diagrams of binary or ternary metal alloys;

‐ Characterization and measurement of structural and physical properties by advanced TEM methods, synchrotron X‐ray scattering and neutron scattering techniques;

‐ Theoretical modeling of the stability and functional properties of the alloyed state;

‐ Applications of alloy nanomaterials in technologies for energy and the environment.

Initiatives to establish research collaborations and partnerships to support these important research directions are welcome.

Program Committee Prof. Syo Matsumura, Department of Applied Quantum Physics and The Ultramicroscopy Research Center, Kyushu University, Fukuoka 819‐0395, JAPAN [email protected]‐u.ac.jp Prof. Rafal E. Dunin‐Borkowski, Ernst Ruska‐Centre for Microscopy and Spectroscopy with Electrons, Research Centre Jülich, Germany rdb@fz‐juelich.de Prof. Wolfgang Jäger, Institute for Materials Science, Christian‐Albrechts‐University Kiel, Germany [email protected]‐kiel.de

Contact for participants from Japan Prof. Syo Matsumura Department of Applied Quantum Physics and The Ultramicroscopy Research Center, Kyushu University, Fukuoka 819‐0395, JAPAN [email protected]‐u.ac.jp

Local Organization and contact for participants from Germany / EU Ms. Ingrid Rische‐Radloff Secretary to Professor Dr. Rafal Dunin‐Borkowski Peter Grünberg Institute (PGI) PGI‐5: Microstructure Research and Ernst Ruska‐Centre for Microscopy and Spectroscopy with Electrons (ER‐C) Research Centre Jülich Wilhelm‐Johnen‐Straße D‐52425 Jülich, Germany Phone: +49 ‐ 2461 – 614274 Fax: +49 ‐ 2461 – 616444 Mobil : +49 ‐ 151 ‐ 155 62 524 Email: i.rische‐radloff@fz‐juelich.de Web: http://www.er‐c.org/centre/centre.htm

Venue Das Mutterhaus Hotel‐ und Tagungshaus GmbH Geschwister‐Aufricht‐Straße 1 40489 Düsseldorf Tel. 0211 – 61727‐1502 Fax 0211 – 61727‐1504 info@hotel‐mutterhaus.de

Schedule

Tuesday, 28 June, 2016 Lecture room : Caroline Fliedner Saal

9:00-9:40 Session 1 Welcome & Overview

9:40-10:50 Session 2 Synthesis

10:50-11:10 COFFEE BREAK Foyer

11.10-12.10 Session 3 Characterization - Electrons

12.10-14.00 LUNCH Friederike Fliedner Room

14.00-15.40 Session 3 Characterization – Neutrons & X-rays

15.40-16.00 COFFEE BREAK Foyer

16.00-16.50 Session 4 Catalysts and Storage Materials

16.50-18.30 Session 4 Theoretical Modeling

18.30-19.30 Poster Session

19.30- DINNER Friederike Fliedner Room

Wednesday, 29 June, 2016 Lecture room : Caroline Fliedner Saal

9:00-10:30 Session 5 In Situ TEM & Electron Holography


11:00-13:00 Session 6 Metallic Alloys and Catalysts

13:00-14:00 LUNCH Friederike Fliedner Room




17:30-18:30 Session 8 Oxides, Deforemation

18:30- Closing Remarks

19:30- DINNER Friederike Fliedner Room

Program

Tuesday, 28 June, 2016

9.00-9.40 Session 1 Welcome & Overview

9.00 - 9.10 OPENING Dunin-Borkowski (Forschungszentrum Jülich GmbH)

9.10 - 9.40 Elements strategy for new nano-materialsH. Kitagawa (Kyoto University)

p3

9.40-10.50 Session 2 Synthesis

9.40 - 10.00 Metal manoparticle@metal−organic framework for energy storage/conversionapplications H. Kobayashi (Kyoto University)

p4

10.00 -10.20 A route for phase control in metal nanoparticlesK. Kusada (Kyoto University)

p5

10.20 -10.50 Development of nanomaterials for efficient energy conversion and storageM. Yamauchi (Kyushu University)

p6


11.10-11.40 Session 3 Characterization - Electrons

11.10-11.40 High-resolution electron microscopy of metallic nanoparticlesS. Matsumura (Kyushu University)

p7

11.40-12.10 Electron microscopy studies on magnetic nanostructuresY. Murakami (Kyushu University)

p8


14.00-15.40 Session 3 Characterization – Neutrons & X-rays

14.00-14.30 Dynamics of hydrogen in palladium nanoparticlesO. Yamamuro (University of Tokyo)

p9

14.30-14.50 Neutron diffraction study on RuH nanoparticlesH. Akiba (University of Tokyo)

p10

14.50-15.20 Synchrotron X-ray characterization of atomic structures and electronic statesof newly synthesized nanoparticles O. Sakata (NIMS)

p11

15.20-15.40 XAFS investigations of palladium nano particles on hydrogen absorptionS. Yoshioka (Kyushu University)

p12


16.00-16.50 Session 4 Catalysts and Storage Materials

16.00-16.30 Characterization of multicomponent metal catalyst for energy andenvironment K. Nagaoka (Oita University)

p13

16.30-16.50 Pt doped Bi-metallic catalysts for energy and environmental reactionK. Sato (Kyoto University / Oita University)

p14

16.50-18.30 Session 4 Theoretical Modeling

16.50-17.20 Applications of computational chemistry to functional materials for futureenergy devices M. Koyama (Kyushu University)

p15

17.20-17.40 Density functional theory calculation of inhomogeneous nanomaterialsT. Ishimoto (Kyushu University)

p16

17.40-18.10 Stability mechanism of nano-alloy particles: Toward the theory of Inter-Element-Fusion Technology H. Nakanishi (NIT Akashi College)

p17

18.10-18.30 Reactivity mechanism in carbon due to metal effectsMary Clare S. Escano (University of Fukui)

p18

18.30-19.30 Poster Session

Size-controllable synthesis of PdRu solid-solution NPs for catalytic applications D.Wu (Kyoto university)

p37

Synthesis and characterization of novel rhodium compound Takuo Wakisaka (Kyoto university)

p38

Syntheses and physical properties of Ni and Pt nanoparticles coated with the metal-organic framework HKUST-1 Yoshimasa Aoyama (Kyoto university)

p39

Structural rearrangement of Pd nanocrystals driven by light-element doping Keigo Kobayashi (Kyoto university)

p40

Catalytic activity of metal-organic framework composites loading metal nanoparticles prepared through arc plasma deposition M. Sadakiyo (Kyushu University)

p41

Three dimensional elemental analysis of bimetallic nanoparticles T. Yamamoto (Kyushu University)

p42

RhCu nanoparticles: Electronic structure evolution versus composition alteration revealed by hard X-ray photoelectron spectroscopy. N. Mueller (Palina) (NIMS)

p43

Large-scale electronic state calculations of Ru-nanoparticles based on the observed structures Y. Nanba (Kyushu University)

p44

Surface structures of bimetallic systems: PdAg and PdRh R. Kishida (Osaka University)

p45

Surface effects on bimetallic alloys: Palladium-iridium case S. Menez Aspera (NIT Akashi College)

p46

Microstructural investigation of octahedral PtNiRh fuel cell catalyst nanoparticles Martin Gocyla (Forschungszentrum Jülich GmbH)

p47

Multimetallic nanostructures by galvanic replacement reaction Meital Shviro (Forschungszentrum Jülich GmbH)

p48

On the crystallography of silver nanoparticles with different shape Kateryna Loza (University of Duisburg-Essen)

p49


Wednesday, 29 June, 2016

9.00-10.30 Session 5 In Situ TEM & Electron Holography

9.00 - 9.30 In situ TEM of H storage materials Hendrik Willem Zandbergen (Delft University of Technology)

p19

9.30 -10.00 In situ off-axis electron holography of electrostatic potentials in working devices in the TEM Vadim Migunov (Forschungszentrum Jülich GmbH)

p20

10.00-10.30 In situ TEM of magnetic states in nanoscale materialsAndras Kovacs (Forschungszentrum Jülich GmbH)

p21


11.00-11.30 Session6 Metallic Alloys and Catalysts

11.00-11.30 Complex Metallic AlloysMichael Feuerbacher (Forschungszentrum Jülich GmbH)

p22

11.30-12.00 Growth and degradation of octahedral Pt-alloy nanoparticle catalystsMarc Heggen (Forschungszentrum Jülich GmbH)

p23

12.00-12.30 Quantitative compositional characterisation of fuel-cell catalysts using EDX ionisation cross sections Katherine MacArthur (Forschungszentrum Jülich GmbH)

p24

12.30-13.00 The dynamics of active metal catalysts revealed by in-situ electron microscopy Marc Willinger (Fritz Haber Institute of the Max-Planck-Society)

p25


14.00-16.00 Session7 Metallic Alloys and Catalysts

14.00-14.30 Atomic level characterization of novel hardening mechanisms in high-Mn-steels Joachim Mayer (RWTH Aachen University)

p26

14.30-15.00 On the phase stability of alloy nanoparticlesBernd Rellinghaus (IfW Dresden)

p27

15.00-15.30 Surface atomic structure of perovskite oxide nanocrystalsHongchu Du (Forschungszentrum Jülich GmbH)

p28

15.30-16.00 Metal hydrides for H storageClaudio Pistidda (Helmholtz Zentrum Geesthacht)

p29


16.30-17.30 Session7 Metallic Alloys and Catalysts (continued)

16.30-17.00 Interface segregation engineering studied by correlative atom probe tomography and electron microscopy Dierk Raabe (Max-Planck Institut)

p30

17.00-17.30 3D micro-structure of spindle-like lithium-titaniumphosphate (Li1Ti2(PO4)3) particles for lithium-ion batteries Roland Schierholz (Forschungszentrum Jülich GmbH)

p31

17.30-18.00 Session8 Oxides, Deformation

17.30-18.00 Towards controlled electro-chemistry of complex oxides in environmental transmission electron-microscopy Christian Jooss (University of Goettingen)

p32

18.00-18.30 BCC Cu-Cr alloy thin films studied by advanced S/TEMGerhard Dehm (MPI für Eisenforschung)

p33

18.30 Closing Remarks


Elements Strategy for New Nano-Materials

Hiroshi Kitagawa

Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, JAPAN E-mail : [email protected]

Atomic-level (solid-solution) alloying has the advantage of being able to continuously control chemical and physical properties of elements by changing compositions and/or combinations of constituent elements. However, solid-solution phases in alloys are limited to specific combinations of elements. Furthermore, most of the combinations have solid-solution phases in limited regions of composition and temperature. In our project, we will establish the inter-element-fusion science to create innovative functional materials where the immiscible metallic elements in the bulk state are mixing at the atomic level using nanotechnology [FIG]. We promote ambitious and challenging materials research with a multidisciplinary integration of physics, chemistry, engineering, and materials science [1]. References [1] Hiroshi Kitagawa, et al., Nature Chemistry, 8 (2016) 377, Advanced Materials, 28 (2016) 1129,

Accounts of Chemical Research, 48 (2015) 1551, Nature Materials, 13 (2014) 802, J. Am. Chem. Soc., 136 (2014) 1864, Chemical Society Reviews, 42 (2013) 6655, J. Am. Chem. Soc., 135 (2013) 5493, Nature Materials, 10 (2011) 291, Nature Materials, 9 (2010) 565, Nature Materials, 8 (2009) 476, Nature Chemistry, 1 (2009) 689, Nature Materials, 7 (2008) 41.

FIG. Schematic picture for elements strategy for new nano-materials.

3

Metal manoparticle@metal−organic framework for energy storage/conversion applications

Hirokazu Kobayashi

1. 1 Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku,

Kyoto, 606-8502, Japan 2 JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0012, Japan

E-mail (correspondence): [email protected] Metal-organic frameworks (MOFs) have received much interest because of the highly versatile nature of the material, which are constructed from organic ligands connecting metal ions into a crystalline framework structure. A recent progress in the field of MOFs has been made to develop multifunctional composite materials by including metal nanoparticles to synergize with the MOF for new applications. This is an important development because the MOF can serve many functions around the metal nanoparticle, acting as a stabilizer, a discrimination filter, a co-catalyst and even acting to alter the surface reactivity of the metal nanoparticles. Here we report Pd@copper(II) 1,3,5-benzenetricarboxylate (HKUST-1) as a novel hydrogen storage material. The HKUST-1 coating on Pd nanocrystals results in a remarkably enhanced hydrogen-storage capacity and speed in the Pd nanocrystals, originating from a charge transfer from Pd nanocrystals to HKUST-1.1 Another material, Cu@[Zr6O4(OH)4(BDC)6] (BDC = benzenedicarboxylate) (UiO-66) demonstrated higher activity for methanol synthesis from CO2 and H2, compared to Cu/γ-Al2O3. We will also present novel one-pot synthetic methods to produce composite materials including Ni@Ni2(dhtp) (H4dhtp=2,5-dihydroxyterephthalic acid) (MOF-74).2

References [1] G. Li, H. Kobayashi, J. M. Taylor, R. Ikeda, Y. Kubota, K. Kato, M. Takata, T. Yamamoto, S. Toh,

S. Matsumura, H. Kitagawa, Nature Materials, 13 (2014) 802. [2] M. Mukoyoshi, H. Kobayashi, K. Kusada, M. Hayashi, T. Yamada, M. Maesato, Jared M. Taylor, Y.

Kubota, K. Kato, M. Takata, T. Yamamoto, S. Matsumura, H. Kitagawa, Chem. Commun., 51 (2015) 12463.

FIG.1 Schematic view of Metal@MOF and EDX mappings of Pd@HKUST-1 (green; Pd element, red; Cu element composed of HKUST-1.

4

A Route for Phase Control in Metal Nanoparticles

Kohei Kusada1

1. Graduate School of Science, Kyoto University, Kyoto City, Kyoto, Japan E-mail (correspondence): [email protected]

Novel nanomaterials with unobtainable crystal structures in bulk state have been recently developed

and attracted attentions with unimagined properties different from conventional nanomaterials. This talk will introduce several examples of these materials including the synthesis and the catalytic properties and discuss the potential of “Phase control” as a new strategy to develop effective nanomaterials. There is unrevealed potential for nanomaterials whose crystal structures are unobtainable in the bulk

state. Properties of metals such as catalytic properties are influenced by their electronic structure and surface structure as reaction fields. Basically, these depend on the crystal structure of materials, and the crystal structure of materials is uniquely determined by constituent elements. If we could control the crystal structure of materials regardless of elemental species, we would be able to discover new aspect of elements. Therefore, to exploit full potential of the elements, it is considered that nanoparticles having novel phase become candidates for new functional materials. We have successfully synthesized phase-controlled nanomaterials with chemical reduction methods. [1] As the examples, PdRu solid-solution NPs and face centered-cubic (fcc)-Ru NPs will be discussed in this presentation. [2, 3] In bulk state, Pd and Ru cannot mix at the atomic level until melting points, also Ru adopts only hcp phase and fcc phase does not exist in the bulk state. These new materials showed unique catalytic properties compared with conventional materials. For example, since Rh is located between Ru and Pd in the periodic table of elements, the electronic structure of Pd0.5Ru0.5 solid-solution NPs is expected to be similar to that of Rh. Actually, obtained PdRu solid-solution NPs exhibited enhanced catalytic properties for many reactions such as CO oxidation and NOx reduction. Furthermore, fcc Ru exhibited higher catalytic activity for CO oxidation reaction than conventional hcp Ru. References [1] K. Kusada, H. Kitagawa, Advanced Materials, 28, 1129-1142 (2016). [2] K. Kusada, et al., J. Am. Chem. Soc., 136, 1864-1871 (2014). [3] K. Kusada, et al., J. Am. Chem. Soc., 135, 5493-5496 (2013)

FIG.1 Schematic illustration of novel metal NPs with crystal structures that are unobtainable in bulk state, but can be created through the phase control syntheses.

5

Development of nanomaterials for efficient energy conversion and storage

Miho Yamauchi1

1.International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) , Kyushu University E-mail (correspondence): [email protected]

The major impact of increasing CO2 concentration on climate change has been recognized. Thus, efficient utilization of renewable electricity is of increasing significant importance and development of various manner of its operation is required for our energetic and environmental sustainability [1, 2]. Recently, electric power storage in high-energy chemicals, called “energy carriers”, has received much attention for the efficient storage and on-demand supply of renewable electricity. Here, we demonstrate direct power charge using an alcohol/carboxylic acid redox couple as illustrated in FIG. 1 [3, 4]. Highly transportable glycolic acid, an alcoholic compound, was successfully produced by electroreduction of oxalic acid, a dicarboxylic acid, on ubiquitous TiO2 catalysts with high efficiency and selectivity (70-95% Faraday efficiency and >98% selectivity) under mild conditions in the potential region of -0.5 to -0.7 V vs. the RHE at 50 ºC. 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). The detailed observation of TiO2 catalysts using scanning TEM and eels techniques provided a mechanistic insight into this highly selective catalysis. Recently, we succeeded in the production of glycolic acid via the electrochemical reduction of oxalic acid and electrooxidation of water with the help of renewable light energy for the first time [5]. Furthermore, we succeeded in electric power generation via the selective electrooxidation of glycolic acid to oxalic acid without CO2 emission—specifically, carbon-neutral power generation. These results are the first experimental proof of concept for a carbon-neutral energy circulation system based on charging/discharging electric power using an alcohol/carboxylic acid redox couple [3, 4]. References [1] T. Matsumoto, M. Sadakiyo, M. L. Ooi, S. Kitano, T. Yamamoto, S. Matsumura, K. Kato, T.

Takeguchi, M. Yamauchi, Sci. Rep., 4 (2014), 5620. [2] T. Matsumoto, M. Sadakiyo, M. L. Ooi, T. Yamamoto, S. Matsumura, K. Kato, T. Takeguchi, N.

Ozawa, M. Kubo, M. Yamauchi,. Phys. Chem. Chem. Phys., 17 (2015), 11359-11366. [3] R. Watanabe, M. Yamauchi, M. Sadakiyo, R. Abe, T. Takeguchi, Energy Environ. Sci., 8 (2015),

1456-1462. [4] M. Yamauchi, N. Ozawa, M. Kubo, Chem. Rec., (2016), in press. [5] S. Kitano, M. Yamauchi, S. Hata, R. Watanabe, M. Sadakiyo, Green Chem., (2016) in press.

FIG. 1 Carbon-neutral power charge and discharge using the GC/OX redox couple. Grey, red and yellow spheres represent carbon, oxygen and hydrogen atoms, respectively.

6

High-resolution electron microscopy of metallic nanoparticles

Syo Matsumura1,2, Tomokazu Yamamoto1, Kohei Aso1 1. Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka Japan

2. The Ultramicroscopy Research Center, Kyushu University, Fukuoka Japan E-mail (correspondence): [email protected]

Cs-corrected scanning transmission electron microscopy (STEM) is widely used to observe atomic structures in various nanomaterials because sub-angstrom atomic resolution is routinely achieved. High-angle annular dark-field (HAADF) imaging in Cs-corrected STEM is advantageous to atomic resolution observation of crystalline nanoparticles, because the images are free from the background contrast from the supporting carbon film. However, the atom column positions imaged in STEM are inevitably influenced by instrumental instabilities, such as specimen drift and probe positioning irregularity. Recent advances in post processing of STEM images have overcome the instrumental instability issues, thereby enabling researchers to determine atomic positions with picometer-order precision [1]. In the present talk, we will demonstrate our recent achievements in detailed structural characterization of metallic nanoparticles, taking advantage of drift-compensated processing for HAADF-STEM images [2]. FIG. 1(a) shows an atomic-resolution HAADF-STEM image of a gold nanorod, which was obtained with a JEM-AccelARM200F operated at an acceleration voltage of 120 kV. A perfect regular array of atom columns appears in the nanorod. The upper-right and lower-left insets in FIG. 1(a) are close-up views of a center part of the nanorod in one frame scan and in 29 frames overlaid with cross-correlation, respectively. We are convinced that the drift-compensated operation by overlaying plural images significantly reduces the effect of shot noise and improves the signal-to-noise ratio in the resulting STEM image, enabling us to determine the atomic column positions precisely. It has been revealed that the statistical spread of regularity in the periodic positions of atomic columns in the middle part of the nanorod in the image is represented well by a 2D Gaussian function with the standard deviations, σx = 3.9 pm and σy = 3.7 pm. Thus the positions of atomic columns in this image are determined with a precision of ± 4 pm. FIG. 1(b) shows local atomic displacements larger than 10 pm with arrows in the left tip portion. The outward displacements toward the rod axis and inward contraction along the perpendicular short axis are recognized in FIG. 1(b) as a general tendency. References [1] A.B. Yankovich et al., Nature Communications, 5 (2014), 4155. [2] K. Aso, et al., Microscopy, 65 (2016), to be published.

FIG.1, HAADF-STEM image of a gold nanorod (a), close-up view of the left tip portion. Arrows indicate atomic displacements larger than 10 pm (b).

a

7

Electron Microscopy Studies on Magnetic Nanostructures

Yasukazu Murakami1,2

1. The Ultramicroscopy Research Center, Kyushu University, Fukuoka 819-0395, Japan 2. Dept. Appl. Quant. Phys. & Nuclear Eng., Kyushu University, Fukuoka 819-0395, Japan

E-mail (correspondence): [email protected] Electron holography can be a power tool for understanding of the relationship between electromagnetic interaction and self-assemble morphology in magnetic nanoparticles [1-3]. With reference to Fe3O4

nanoparticles (25 nm average size), which definitely show a ring-shaped self-assembly, our studies indicated significant fluctuations in the magnetic flux lines, as shown in Fig. 1 [3]. The fluctuations were reasonably explained by the magnetocrystalline anisotropy that was preserved in the nanoparticles. The results provide essential information on the micromagnetics of nanoparticles, in which the magnetic dipolar interaction competes with the magnetic anisotropy. In addition to the electron holography observations, we shall briefly discuss about recent in-situ TEM observations which examine the self-assemble morphology of Fe3O4 nanoparticles in liquid. References [1] R. E. Dunin-Borkowski et al., Science, 282 (1998) 1868. [2] A. Sugawara et al., Appl. Phys. Lett. 91 (2007) 262513. [3] Y. Takeno et al., Appl. Phys. Lett. 105 (2014) 183102

FIG.1 Self-assembled Fe3O4 nanoparticles. (a) TEM image, and electron holography observations revealing (b) electrostatic potential lines and (c) magnetic flux lines. Reprinted from Ref. 3.

8

Dynamics of Hydrogen in Palladium Nanoparticles

M. Kofu1,7, N. Hashimoto1,7, H. Akiba1,7, H. Kobayashi2,7, H. Kitagawa2,7, M. Tyagi3, W. Lohstroh4, K. Iida5, M. Nakamura6, O. Yamamuro1,7

1. Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan 2. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

3. NCNR, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA 4. Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching D-85747, Germany

5. CROSS Tokai, 162-1 Shirakata, Tokai, Naka, Ibaraki, 319-1106, Japan 6. J-PARC Center, 2-4 Shirakata, Tokai, Naka, Ibaraki, 319-1195, Japan

7. JST-ACCEL, 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan E-mail (correspondence): [email protected]

The nanometer-sized materials attract much attention since their physical and chemical properties are substentially different from those of bulk materials owing to their size and surface effects. We have studied thermal [1], structural [2] and dynamical properties of nanoparticles of palladium hydride (PdHx; 0 < x < 1), which may be the most well known metal hydride and has been remarked from not only basic scientific but also industrial points of view. In this workshop, we will present the quasielastic neutron scattering (QENS) and inelastic neutron scattering (INS) works on nanoparticles of palladium hydrides. Neutron scattering is a powerful method to explore the dynamics of H atoms in an atomic scale owing to a large scattering cross section for a H atom. The QENS experiments were performed on the HFBS at NCNR, NIST (USA) and TOFTOF at FRM II (Germany), and the INS experiment on 4SEASONS at MLF, J-PARC (Japan). Figure 1 shows the Arrhenius plot for the relaxation times determined by the QENS experiments. In PdH0.47 nanoparticles, we found a new faster relaxation in addition to the slower relaxation observed also in bulk PdH0.73. The activation energy of the new relaxation is much smaller than that of the slower relaxation. It is known that the slower relaxation is due to the jump motion among the octahedral (O) sites of the fcc lattice of Pd. We guess that the new relaxation is among the tetrahedral (T) sites which may be stabilized in the subsurface region, which is several Pd layers near the surface, by the surface and/or distortion effects of nanoparticles. This is consistent with the result of the INS experiment, i.e., a new excitation appeared at ca. 80 meV in addition to the excitation at ca. 68 mV which is known to be due to the vibration of the H atoms at the O-sites in the bulk Pd lattice. References [1] H. Akiba, H. Kobayashi, H. Kitagawa, M. Kofu, O. Yamamuro, Phys. Rev. B, 92 (2015) 064202. [2] H. Akiba, M. Kofu, H. Kobayashi, H. Kitagawa, K. Ikeda, T. Otomo, O. Yamamuro, J. Am. Chem.

Soc., submitted.

FIG 1. Arrhenius plot for the relaxation times for the motions of H atoms in bulk and nanoparticle palladium hydrides.

9

Neutron diffraction study on RuH nanoparticles

Hiroshi Akiba1,4, Maiko Kofu1,4, Kohei Kusada2,4, Hirokazu Kobayashi2,4, Hiroshi Kitagawa2,4, Kazutaka Ikeda3, Toshiya Otomo3, Osamu Yamamuro1,4

1. Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan 2. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

3. IMSS, High Energy Accelerator Research Organization, 203-1 Shirakata, Tokai, Ibaraki 319-1106, Japan 4. JST-ACCEL, 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan

E-mail (correspondence): [email protected] The nanometer-sized metals attract much attention since their structural, physical and chemical properties are substantially different from those of bulk metals owing to their size and surface effects. Bulk Ru takes an hcp structure and does not absorb hydrogen. Recently, Kusada et al. [1] succeeded to synthesize hcp and fcc nanoparticles separately and found that they absorb hydrogen gas as in the case of Pd. In this study, we have performed the neutron powder diffraction (NPD) experiments on the hydrides of Ru nanoparticles with an average diameter of ca. 3.8 nm to investigate the positions of hydrogen atoms in the Ru lattice. Figure 1 shows the NPD pattern of fcc-RuH0.2 nanoparticles measured at 300 K under 0.1 MPa of hydrogen gas. The composition was determined by a separate PCT measurement. We used a high intensity NPD instrument NOVA at J-PARC. This pattern is obtained after subtracting a large contribution of incoherent scattering from polyvinylpyrrolidone (PVP) which is used to avoid the adhesion between the nanoparticles. The Rietveld fitting based on the model, in which hydrogen atoms are located at the octahedral sites of the fcc lattice, is satisfactory as shown in Fig. 1. This is the first clear evidence that Ru nanoparticles accommodate hydrogen atoms owing to the nanometer size effect. The experiment on hcp-Ru nanoparticles is now going on. References [1] K. Kusada et al., J. Am. Chem. Soc., 135 (2013) 5493.

FIG. 1 Neutron powder diffraction pattern of fcc-RuH0.2 nanoparticles at 300 K under 0.1 MPa of hydrogen gas. The result of the Rietveld analysis is also shown. The inset shows the determined structure of the Ru hydride. Gray and red spheres show the Ru and H atoms, respectively; the occupancy of the H sites is 20%.

10

Synchrotron X-ray characterization of atomic structures and electronic states of newly synthesized nanoparticles

Osami Sakata,1,2,3,a) L. S. R. Kumara,1 Chulho Song1, Natalia Palina,1 Yanna Chen,1

Hirokazu Kobayashi,4 Kohei Kusada,4 and Hiroshi Kitagawa,4,5,6

1 Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, 679-5148, Japan 2 Synchrotron X-ray Group, Quantum Beam Unit, NIMS, 1-1-1 Kouto, 679-5148, Japan 3 Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan 4 Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan 5 Institute for Integrated Cell-Material Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan 6 INAMORI Frontier Research Center, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-3095, Japan

E-mail (correspondence): [email protected] We introduce two advanced synchrotron-based X-ray techniques which were utilized to investigate atomic and electronic structures of various nanoparticle (NP) samples. The first technique is hard X-ray photoelectron spectroscopy (HAXPES). The main advantages are (i) bulk sensitivity due to a large probing depth of about 20 nm and (ii) high energy resolution of about 240 meV for an incident energy at 6 keV. HAXPES data are discussed in terms of core level (CL) and valence band (VB) regions. CL data reveals chemical states of an element, while VB spectra represent density-of-state (DOS) occupied by electrons. In the hard X-ray regime, DOS can be decomposed into a sum of partial orbital-projected DOSs and atomic differential cross sections. The second technique is high-energy x-ray diffraction (HEXRD) with an incident energy of about 60 keV. Utilization of such high-energy X-rays enables access to a wide q-range intensity data in the reciprocal-lattice space. Combination of atomic pair distribution function (PDF) and reverse Monte Carlo (RMC) modeling allows us to model three dimensional atomic positions of all atoms in its sample model. Coordination number distribution and bond-angle distribution are typically obtained in a short to medium-range atomic-distance range in the real space. In addition, the Rietveld refinement analysis of the data also provides us with structural parameters including a space group, lattice parameters, domain size, lattice distortion, and static atomic displacement. We present recent experimental results of HAXPES performed at the NIMS beamline BL15XU and HEXRD done at the Japan Synchrotron Research Radiation Institute (JASRI) BL04B2, SPring-8. Samples that will be discussed are Ag-Rh [1], fcc-Ru, hcp-Ru, and Pd-Pt, Rh-Cu NPs and other related systems. The followings are parts of our results. Pd 3d5/2 CL HAXPES data reveal presence of PdX+ (oxygen-chemisorbed Pd atoms) states for Pd, Pd-Pt core/shell & solid-solution alloy NP. This indicates a formation of unique electronic states which can be linked to the intermetallic mixing during synthesis. In addition, the VB spectra of the solid-solution alloy NPs were not reproduced by the linear combination of Pd and Pt NPs. This discrepancy suggests possible presence of an unoccupied states near the Fermi edge. RMC models of the solid-solution alloy NPs show that the Pt and Pd atoms were randomly mixed at the atomic level. The coordination number distributions of Pd-Pd and Pt-Pd correlation are nearly same in the solid-solution alloy NP model. From the Rietveld refinement analysis of fcc- and hcp-Ru NPs, we argue that the enhancement of the CO oxidation activity in the fcc-Ru NPs may be caused by the lattice distortions of the close-packed planes and the static atomic displacements. [1] A. Yang, O. Sakata, K. Kusada, T. Yayama, H. Yoshikawa, T. Ishimoto, M. Koyama, H. Kobayashi, H. Kitagawa, Appl. Phys. Lett. 105, 153109 (2014)

11

XAFS Investigations of Palladium Nano Particles on Hydrogen Absorption

S. Yoshioka1,2, T. Yoshimoto1, T. Yamamoto1, K. Yasuda1, S. Matsumura1,2, K. Kamitani2, T. Sugiyama2, E. Kobayashi3, H. Kobayashi4, H. Kitagawa4

1 Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University 2 Research Center for Synchrotron Light Applications, Kyushu University

3 Kyushu Synchrotron Light Research Center 4Depertment of Chemistry, Kyoto University

E-mail (correspondence): [email protected]

High capacity of hydrogen absorption in palladium has been reported more than a hundred years before. Much interest has focused on the hydrogen positions in face-centered cubic (fcc) lattice Pd as well as the amount to be absorbed in the metal. Nanometer-sized particles show interesting chemical and physical properties which are different from bulk properties in many materials. Also for the nanoparticles of palladium there are drastic changes of the miscible gap in the hydrogen pressure-composition (PC) isothermal [1]. Therefore, Pd nanoparticles (NPs) are expected to show amazing hydrogen absorption properties. However, local structures of Pd nanoparticles on the hydrogen absorption/desorption process are not fully investigated. In this study, we have adopted Pd L3-edge X-ray absorption fine structure showing the excitation of electrons from the 2p to the 4d band. Moreover, in situ observations of the electronic structure around Pd of Pd nanoparticles have been performed in Pd-H system. Nanoparticle samples were synthesized by chemical reduction method. The Pd L3-edge (3.1 keV) XANES were performed at BL06 of Kyushu synchrotron light research center (SAGA-LS) in Japan. The Pd NPs and the bulk Pd as a standard were mounted in a custom-designed in situ reaction cell. Figure 1 presents the dynamical change of Pd L3-edge XANES spectra of the bulk Pd as function of hydrogen pressure. In the process of increasing hydrogen pressure, the absorption edge is shifted to higher energy and a new feature at 3180 eV is appeared at 40 kPa. These behaviours show the change of Pd electronic structure due to hydrogen absorption. On the other hand, in the process of pressure down, the absorption edge shift goes back at the original energy positon and the new peak is disappeared. The changes occur at 20 kPa. In the case of Pd NPs, the Pd L3-edge XANES spectra showed similar hysteresis but transition pressures were different from those of bulk Pd.

Reference [1] M. Yamauchi, et al., J. Phys. Chem. C, 112, 3294, (2008)

FIG.1 Pd L3-edge XANES spectra of the bulk Pd in increasing and decreasing hydrogen pressure.

12

Characterization of Multicomponent Metal Catalyst for Energy and Environment

Katsutoshi Nagaoka1

1. Oita University, Department of Applied Chemistry, 700 Dannoharu Oita City, Oita 870-1192E-mail (correspondence): [email protected]

Introduction We have created supported multicomponent catalysts and applied the catalysts to different kinds of heterogeneous reactions, such as synthesis gas production [1-3], ammonia decomposition [4], removal of air pollutants [5-7], and fine chemical synthesis [8]. In these researches, precise control of interaction and synergetic effects of hetero elements between metal-metal, metal-support and metal-dopant allows each reactant to optimize reaction kinetics, which have realized catalysts exhibiting higher activity, more excellent selectivity, and longer life time compared to conventional catalysts and further displaying unique functions[2, 3]. In the group work of CREST and ACCEL we applied immiscible Pdx-Ru1-x solid solution alloy nanoparticles to different kinds of reactions. At first CO oxidation [6] and NOx reduction were chosen because for these reactions Rh which is located in between Ru and Pd in periodic table is well known to be effective catalyst. Furthermore, it was also applied to liquid phase reactions such as Suzuki-Miyaura Cross-Coupling reaction [8].

Experimental PdxRu1-x NPs were synthesized by chemical reduction method using Pd and Ru precursors. The PdxRu1-

x NPs were loaded on γ-Al2O3 support via standard impregnation method. Activity tests for CO oxidation and NOx reduction were carried out with using fixed-bed reactors. Suzuki-Miyaura Cross-Coupling reaction was carried out in a batch type reactor.

Results and discussion Pd0.5-Ru0.5/γ-Al2O3 exhibited much higher CO oxidation activity than each monometallic catalyst, such as Pd/γ-Al2O3 and Ru/γ-Al2O3, and physical mixture of Pd and Ru supported on γ-Al2O3. Kinetic analysis revealed that CO poisoning over Pd/γ-Al2O3 and O poisoning over Ru/γ-Al2O3 were effectively retarded by alloying these elements. Furthermore, we have found that Pd0.5-Ru0.5/γ-Al2O3 showed better NOx reduction activity than Rh.

It was also disclosed that Pdx-Ru1-x-PVP showed excellent catalytic activity for Suzuki-Miyaura Cross-Coupling reaction compared with conventional Pd-PVP. Such high performance of Pdx-Ru1-x was rationalized with bi-functional mechanism, where aryl halide and boronic arene are activated both on Pd and Ru.

References [1] K. Nagaoka et al., ACS Catal., 3 (2013) 1564-1572. [2] K. Sato, et al., ChemCatChem, 6 (2014) 784-789. [Inside Cover] [3] K. Nagaoka, et al., ChemSusChem, 2 (2009) 1032-1035 [Cover]. [4] K. Nagaoka, et al., Int. J. Hydrogen Energy, 35 (2014) 20731-20735. [5] K. Sato, et al., ChemSusChem, 7 (2014) 3264-3267. [6] K. Kusada, et al., J.Am. Chem. Soc., 136 (2014) 1864-1871. [7] K. Kusada, et al., J. Am. Chem. Soc., 135 (2013) 5493-5496. [8] Md. S. Kutubi, et al., ChemCatChem, 23 (2015) 3887-3894.

13

Pt Doped Bi-metallic Catalysts for Energy and Environmental Reaction

Katsutohi Sato1,2

1. Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto, 615-8510, Japan2. Department of Applied Chemistry, Faculty of Engineering, Oita University, Oita, 870-1192, Japan


Platinum (Pt) is one of most the important noble metal for industrial application. Catalysts are major use of Pt because Pt shows excellent performance for several reactions. However Pt is very scares and expensive elements. Therefore development of an inexpensive and highly active catalysts including less amount of noble metal is strongly demanded in various areas. Based on this background, we have investigated preparation and application of bimetallic catalysts including several combinations of noble metals and non-noble metals. Combination of noble metal and non-noble metal is one of the potential strategies for reducing quantity of noble metal in the catalysts. In this presentation, we report Pt-Co bimetallic catalyst (Pt-Co/γ-Al2O3). Pt-Co/γ-Al2O3 have interesting fine structure and show good catalytic properties for energy and environmental reaction.

Pt-Co/γ-Al2O3 was prepared with wet impregnation method and following calcination at 450 ºC for 5 h. Obtained catalyst was treated at 850 ºC for 1 h under flowing H2. Loading amounts of Pt and Co were set to 0.1 and 1.0 wt%, respectively. γ-Al2O3 supported mono-metal catalysts, 0.1 wt% Pt/γ-Al2O3 and 1.0 wt% Co/γ-Al2O3, were prepared as reference by same procedure. In order to investigate fine structure of active site in Pt-Co/γ-Al2O3, XAFS, STEM-EDX, and FT-IR techniques were employed.

Pt LIII-edge XANES spectrum and EXAFS oscillations for Pt-Co/γ-Al2O3 and reference samples after reduction were observed. As shown in Fig. 1a, XANES spectra of Pt-Co/γ-Al2O3 and Pt/γ-Al2O3 were almost same. Furthermore, peak positions in these spectrums were similar to the positions in the spectrum of the Pt foil. In Fig. 1b, the shape of EXAFS oscillation of Pt/γ-Al2O3 was identical to that of Pt foil. On the other hand EXAFS oscillation of Pt-Co/γ-Al2O3 was completely different from that of Pt foil and Pt/γ-Al2O3. These results suggest that major parts of Pt species in Pt-Co/γ-Al2O3 were reduced to Pt0 and formed characteristic fine structure during H2 treatment at 850 ºC, probably Pt formed alloy with Co. The additional investigations by STEM-EDX and FT-IR also supported such the alloy formation. We applied Pt-Co/γ-Al2O3 for three way reaction for purification of automotive exhaust and found that Pt-Co/γ-Al2O3 shows better catalytic performance compared with reference mono metal catalysts.

FIG.1 Pt LIII-edge XANES and EXAFS for Pt-Co/γ-Al2O3 and reference samples after reduction.

14

Applications of Computational Chemistry to

Functional Materials for Future Energy Devises

Michihisa Koyama1,2

1. INAMORI Frontier Research Center, Kyushu University 2. International Institute for Carbon-Neutral Energy Research, Kyushu University

E-mail (correspondence): [email protected] Catalytic activity is determined by various factors such as materials, interface, morphology, and environment. Figure 1 shows a schematic of three design approaches for porous electrode systems. To rationally design catalysts, interplay between experimental and computational approaches are inevitable. Recent development of theoretical chemistry as well as computer science, one can expect that properties of bulk and ideal surfaces of materials are computational chemically investigated within a reasonable computational cost. The remaining challenges are the interface, microstructure, and bridging those three approaches. In the author’s research group, multi-scale, multi-physics simulation of porous electrode systems is challenged. Toward a rational design of functional porous materials, the structure observation at both m [1-2] and atomistic [3] scales and its incorporation into simulation are important. In this work, the state-of-the-art results of computational simulation taking into account the microscopy observations of solid oxide fuel cell anode will be introduced. References [1] S.-s. Liu et al., J. Microscopy, 261 (2016) 326. [2] S-S. Liu et al., Solid State Ionics, 262 (2014) 460. [3] S.-s. Liu et al., J. Electrochem. Soc., 162 (2015) F750. Acknowledgements The author is grateful for members of JST-CREST project “Multi-Scale and Multi-Physics Approach for Designing Materials and Microstructure of Solid Oxide Fuel Cell Electrodes”. The activities of INAMORI Frontier Research Center is supported by KYOCERA Co. Ltd.

FIG.1 Design approaches for functional porous electrode

nm mmμm

Material Design(～nm)

Alloy, Additive,New Material

Interface Design(100-1 nm)

Support, Triple Phase Boundary

High Surface Area,Pore Network

Microstructure(101nm～101μm)

15

Density Functional Theory Calculation of Inhomogeneous Nanomaterials

Takayoshi Ishimoto1, Michihisa Koyama1,2


E-mail (correspondence): [email protected] Palladium is well known as a hydrogen storage metal under the ambient temperature and pressure. Recently, hydrogen absorption properties of Pd nanoparticles and mixed metallic nanoparticles are studied [1,2]. Although it is regarded that the hydrogen occupies the octahedral site in Pd bulk [3], the absorption sites in Pd nanoparticle is unclear. Compared to Pd bulk and nanoparticle, the H/M and shape of pressure-composition temperature (PCT) curve are different. To understand the hydrogen absorption properties of nanoparticles, it is important to determine the absorption site of hydrogen in Pd nanoparticle. In this study, we analyzed the hydrogen absorption energy in Pd nanoparticle by using density functional theory. We used 405 atoms systems for Pd nanoparticles. In truncated-octahedral Pd405 system, 74 octahedral and 86 tetrahedral sites are considered as a hydrogen absorption sites. After geometry optimization of Pd405H, the partial vibrational frequency calculation was done to include the effect of zero-point vibrational energy of hydrogen in Pd405. All calculations are performed on the Vienna ab-initio simulation package (VASP) program under the GGA-PBE with projector augmented wave (PAW) method. The energy cutoff and k-points are 400 eV and 1 x 1 x 1, respectively. We first optimized the structure of Pd405. The volume of octahedral and tetrahedral sites in optimized Pd405 is shown in Fig. 1. The volume in Pd405 was smaller than bulk due to the Pd-Pd distance shortening in nanoparticle. This result indicates that the nanoparticle has inhomogeneous structure. Then, we put hydrogen in octahedral and tetrahedral sites. We clearly observed the possibility of hydrogen absorption in tetrahedral site as well as octahedral site in Pd405. Details are discussed in the presentation. Acknowledgement The activities of INAMORI Frontier Research Center are supported by Kyocera Corporation. All calculations were performed on the HA8000 computer system in the Research Institute for Information Technology, Kyushu University, Japan. References [1] M. Yamauchi et al., J. Phys. Chem. C, 112 (2008) 3294. [2] H. Kobayashi et al., J. Am. Chem. Soc., 132 (2010) 5576. [3] R. Caputo et al., Mol. Phys., 101 (2003) 1781. FIG.1 Volume of (a) octahedral and (b) tetrahedral sites after geometry optimization of Pd405. Dashed line is volume of Pd bulk. One example of octahedral and tetrahedral sites are also shown.

2.4

2.5

2.6

2.7

2.8

2.9

3

0 2 4 6 8 10 12

9.8

9.9

10

10.1

10.2

10.3

10.4

0 2 4 6 8 10 12

Distance from center (Å)

Volu

me (

Å3)

(a) Octahedral site (b) Tetrahedral site

Distance from center (Å)

16

Stability mechanism of nano-alloy particles:

Toward the theory of Inter-Element-Fusion Technology

Hiroshi Nakanishi1, Susan Meñez Aspera1, Ryo Kishida2, Koji Shimizu2, Kazuki Kojima2, Nguyen Hoang Linh2, Hideaki Kasai1,2,3

1. National Institute of Technology, Akashi College, JAPAN 2. Graduate School of Engineering, Osaka University, JAPAN

3. Institute of Industrial Science, the University of Tokyo, JAPAN E-mail: [email protected]

Alloys have been developed and used in a wide variety of applications. Some specific combination and

mixing ratio of metals give us the useful properties in our lives. In the case of bulk alloy, it has been known that possible combination of elements and their atomic mixing ratio are limited. And we could not access the material functions, which might be provided by such forbidden combinations or mixing ratios in bulk alloys. For example, Ru and Pd are immiscible at the atomic level in the bulk state. Recently, in the case of nanoparticle, PdxRu1–x solid solution is successfully achieved over the whole range of x, (0 < x < 1) [1]. We have been investigating the stability mechanism of such nano-alloy particles, with the aid of the density functional theory based first principles calculations. In FIG. 1, we show that the following properties of bulk alloy are reproduced by the first principles calculations. In this calculations, we use the AxB1–x (x=0.5) alloy models, which have 10 different mixing configurations of A and B atoms in their 2x2x2 fcc supercell and have different values of the nearest-neighbor Warren Cowley parameters (WCP) [2] from ca. -0.13 to 0.063. We estimate the stability by the alloying energy, which is defined as the difference between the cohesive energy of alloy system AB and the average cohesive energies of isolated pure systems A and B. Calculated alloying energies are negative values for Au-Ag and Pd-Ag, which are classified as solid solution case, and have no dependence on WCP. On the other hand, the phase separation cases such as Au-Ir and Ag-Rh, and the high temperature solid solution case such as Au-Rh, Pd-Ir, and Pd-Rh have their positive allying energies, which are decreased as WCP increases. On the basis of these results, we construct the alloy slab models in order to estimate the various surface effects on the stability of nano-alloy particles. In the symposium, we will discuss some surface effects on the alloy state stability of nano-alloy

particles based on our calculation results. And we will propose the condition to stabilize the alloy state in nano-particles.

References [1] K. Kusada, et al., J. Am. Chem. Soc., 136 (2014) 1864. [2] T. Abbas, et al., Mater. Sci. Poland, 25 (2007) 1161.

FIG.1. Bulk allowing energy as a function of the nearest-neighbor Warren Cowley parameter.

17

Reactivity mechanism in carbon due to metal effects

Mary Clare S. Escaño Tenure-Track Program for Innovative Research, University of Fukui

3-9-1 Bunkyo, Fukui, 910-8507, Japan E-mail (correspondence): [email protected]

Carbon in many forms can act as catalyst and as a support to metal nanoparticles. Even as a support, carbon still can catalyze reactions due to defects (vacancy, distortion, dopant). Typically, electronic states originating from the defects make the carbon reactive. The sole effect of metals on the reactivity of carbon has not been studied so far. In this work, the reactivity of carbon sheet (graphene) due to transition metal interaction is investigated. Ni(111) is used due to its epitaxial conformation with graphene, ruling out the effects of strain. Oxygen is used as a reactivity “probe” molecule due to its importance in many applications such as fuel cell, batteries, corrosion and oxidation. Density functional theory calculations with van der waals corrections are used to determine the adsorption and activation energies of O2 in comparison with free-standing graphene. The optimized graphene and Ni interface distance is ~2.06Å, however, the enhanced reactivity of the former can be noted (see FIG. 1). It is found that the metal shifted the spin-down electronic states of carbon towards higher energies such that hybridization with O2- electronic states is enhanced. Further details of the results and mechanism will be discussed in the symposium. References [1] M.C.S. Escaño , T.Q. Nguyen, H. Kasai. J. Phys. Chem. C 119 (2015) 26636. [2] M.C.S. Escaño , H. Nakanishi, H. Kasai. J. Phys. Chem. A 113 (2009) 14302.

FIG.1 (a) Potential energy of O2 dissociative adsorption on free-standing graphene (FSG) and graphene-Ni system (G-Ni). Energies and structures at the transition state (TS) and final state (FS) are given; (b) LDOS of FSG and (c)-(d) LDOS of G-Ni on two carbon atoms (C1, C2) in (1x1) unit cell.

18

In situ TEM of H storage materials

Hendrik Willem Zandbergen

Delft University of Technology, Netherland

19

In situ off-axis electron holography of electrostatic potentials in working devices in the TEM

Vadim Migunov1, Janghyun Jo2, Fengshan Zheng1, Mariya Neklyudova3, Helmut Soltner4, Martial Duchamp1, Henny W. Zandbergen3, Rafal E. Dunin-Borkowski1

1. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute,Forschungszentrum Jülich, Germany

2. Department of Materials Science and Engineering, Seoul National University, Seoul, Korea3. Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands

4. Central Institute of Engineering, Electronics and Analytics (ZEA-1), Forschungszentrum Jülich, GermanyE-mail (correspondence): [email protected]

The technique of off-axis electron holography in the transmission electron microscope (TEM), in combination with in situ electrical biasing, is a powerful tool for measuring the local electrostatic potential within and around a specimen with nm spatial resolution. It is useful for studying the effects of dopants and defects on electronic transport, resistive switching phenomena in both valence change and phase change materials [1], electron field emission, battery materials, electrical breakdown and sintering, as well as for studying the electric fields around atom probe tomography (APT) needles.

We have used electron holography and related in situ TEM techniques to study:

1) Resistive switching in thin films and nanoparticles of oxides (FIG.1, left);2) Breakdown and current-induced mass transport in InAs nanowires (FIG.1, middle);3) Electrostatic potentials around electricall biased field emitters and atom probe needles (FIG.1,

right) [2].We are also developing a method based on double exposure electron holography for studying time-resolved electromagnetic phenomena. The basis of the method and its future prospects will be discussed. We are grateful to Chris B. Boothroyd, Cory Czarnik, Christian Dwyer, Michael Farle, Anthony J. Kenyon, Andrew London, Adnan Mehonic, Anahita Pakzad, Giulio Pozzi, Urs Ramsperger and Oliver Schmidt for valuable contributions to this work.

References [1] A. Marchewka, et al., Sci. Rep. 4 (2014) 6975. DOI: 10.1038/srep06975. [2] V. Migunov et al., J. Appl. Phys. 117 (2015) 134301. DOI: 10.1063/1.4916609.

FIG.1 (left) Measured projected electrostatic potential of a TiO2 nanoparticle recorded during resistive switching in situ in the TEM. The yellow arrow indicates a minimum in potential at the interface between the nanoparticle and a gold counter-electrode. (middle) Electron hologram and projected electrostatic potential (inset) of a nanowire recorded during electric-current-induced mass transport, when a “bridge” forms in the middle. (right) Slice through a three-dimensional electrostatic potential recorded from an electrically biased APT needle on the assumption of cylindrical symmetry (shown as an overlaid amplitude image).

20

In situ TEM of magnetic states in nanoscale materials

András Kovács1, Zi-An Li2, Rafal E. Dunin-Borkowski1

1. Ernst-Ruska Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, Germany

2. Faculty of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, Germany E-mail (correspondence): [email protected]

Nanoscale magnetic materials are widely used in information recording, energy conversion and medical applications. The magnetic configuration in a nanomagnet is determined by magnetocrystalline anisotropy, shape anisotropy, exchange and magnetostatic energies, as well as on the kinetics of magnetic switching processes. Transmission electron microscopy (TEM) offers a variety of methods for imaging magnetic states in nanoscale materials, including the Fresnel mode of Lorentz TEM and off-axis electron holography. Here, we discuss recent results obtained from studies of magnetic states in nanocrystals, nanowires and nanotubes. For magnetic imaging, we record off-axis electron holograms using an aberration-corrected FEI Titan TEM equipped with an electrostatic biprism and a charged-couple device camera, with the sample imaged in magnetic-field-free conditions (in Lorentz mode) at 300 kV. We apply external magnetic fields to samples using the conventional microscope objective lens in order to study magnetization reversal processes. An example of different magnetic remanent states recorded from electrodeposited Co nanowires is shown in Fig. 1. [We are grateful to R. Pollard, D. Grundler, J. Arbiol, A. Fontcuberta i Morral and M. Pósfai for the provision of samples and valuable discussions].

FIG.1 In situ switching of magnetic states in electrodeposited Co nanowires. a) Bright-field TEM image. b-d) Magnetic induction maps of remanent states recorded using off-axis electron holography after applying a magnetic field of 50 mT, 150 mT and 1500 mT to the sample. The phase contour spacing is 0.2 rad. The BSWI in (b) marks the magnetic field direction.

21

Complex Metallic Alloys

M. Feuerbacher

Forschungszentrum Juelich GmbH, 52425 Juelich, Germany

E-mail (correspondence): [email protected] Complex metallic alloys (CMAs) represent a class of materials increasingly receiving scientific attention [1]. CMAs materials possess characteristic structural features substantially deviating from those of simple metals. They have large lattice constants and, correspondingly, a high number of atoms per unit cell, ranging from some ten to some thousand. Their local order is dominated by icosahedral-symmetric atom coordination, which does not occur in simple metals, and frequently, the ideal structures intrinsically include a substantial degree of disorder. These structural features open up the possibility for novel physical properties. In this talk, the current state of the field will be reviewed. We will address recent experimental progress in the investigation of the physical properties of various CMA materials. Basic scientific phenomena will be addressed, such as unexpected superconductivity, novel types of structural defects and deformation mechanisms [2], as well as application-related aspects, for example the use of CMAs as catalysts for the semihydrogenation of acytelene. References [1] K. Urban and M. Feuerbacher, J. Non Cryst. Sol., 334 - 335 (2004) 143. [2] M. Heggen, L. Houben, M. Feuerbacher, Nature Materials, 9 (2010) 332. FIG.1 The unit cell of β-Al-Mg, containing 1168 atoms

22

Growth and degradation of octahedral Pt-alloy nanoparticle catalysts

Marc Heggen1, Martin Gocyla

1, Lin Gan

2, Chun-Hua Cui

2, Stefan Rudi

2, Peter Strasser

2,

Rafal E. Dunin-Borkowski1

1. Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425

Jülich, Germany 2. The Electrochemical Energy, Catalysis, and Materials Science Laboratory, Department of Chemistry, TU

Berlin, 10623 Berlin, Germany


Shape control can be an effective approach for tuning the physical and chemical properties of

inorganic nanoparticles. Due to their extraordinary high activity for the oxygen-reduction-reaction

(ORR), recently, octahedral shaped Pt-Ni nanoparticles have become highly attractive fuel-cell

catalysts. A deep understanding on their atomic-scale structure, degradation behavior, and their

formation is a prerequisite for the rational design of advanced shaped nanoparticle catalysts with high

activity and long-term stability.

Using aberration-corrected HAADF-STEM combined with EELS and EDX, we reveal an

element-specific anisotropic growth mechanism of Pt-Ni nanooctahedra, where compositional

anisotropy couples to geometric anisotropy. During the solvothermal synthesis, a Pt-rich nucleus

evolves into precursor nanohexapods, followed by a slower step-induced deposition of Ni at the

concave hexapod surface forming the octahedral facets [1]. This compositional anisotropic of the

Pt-Ni octahedra leads to complex structural corrosive degradation patterns during the ORR

electrocatalysis. The Ni-rich (111) facets are preferentially etched, resulting first in concave octahedra

and finally a Pt-rich skeleton with less active facets remains [2]. In order to tune the atomic-scale

microstructure of the octahedra for an advanced long-term stability, we exemplify the effect of varied

growth conditions on the morphology and compositional segregation, by producing trimetallic PtNiCo

nanooctahedrons and by comparison of a “one-step” and a new developed "two-step" synthesis route

[3].

References

[1] Gan L, Cui CH, Heggen M, Dionigi F, Rudi S, Strasser P, Science 2014; 346: 1502.

[2] Cui CH, Gan L, Heggen M, Rudi S, Strasser P, Nature Materials 2013; 12: 765.

[3] Arán-Ais RM, et al., Nano Letters 2015; DOI: 10.1021/acs.nanolett.5b03057.

FIG.1 A microstructural study comprising high-resolution TEM, HAADF-STEM and EELS mapping

uncovers an element-specific compositionally anisotropic growth mechanism of octahedral PtNi

nanoparticles. The electron microscopy images and the respective models show the elemental

distribution of Pt (red) and Ni (green) alloy nanoparticles at different states of growth after 4, 8, 16,

and 42 hours of the solvothermal synthesis.

23

Quantitative Compositional Characterisation of Fuel-Cell Catalysts using EDX Ionisation Cross Sections

K. E. MacArthur1, T. J. A. Slater2, S. J. Haigh2, D Ozkaya3, P. D. Nellist4, S. Lozano-Perez4

1. Ernst Ruska Centre for Microscopy and Spectroscopy, Forschungszentrum, 52425 Jülich, Deutschland

2. School of Materials, The University of Manchester, Manchester, M13 9PL, UK 3. Johnson-Matthey Technology Centre, Sonning Common, Reading, UK

4. Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK E-mail (correspondence): [email protected]

The new generation of analytical electron microscopes with aberration correction and silicon drift detectors (SDDs) for energy dispersive X-ray (EDX) analysis open up immense possibilities for microanalysis at the nanometre and even subnanometre scales. The SDDs have increased solid angles of collection, which has led to higher counts rates, allowing for the acquisition of much higher, even atomic, resolution maps. Combining these new detectors with aberration correction in scanning transmission electron microscopy (STEM) allows for larger probe forming apertures to produce increased beam currents in much smaller probes, increasing the x-ray count rate still further. Such improvements in EDX analysis open huge possibilities for improved statistics and therefore quantification. This is especially important for catalyst particles where the amount of X-ray generation from is low due to the small sample mass. Here we apply a new method of EDX quantification designed especially for this new era of spectroscopy based on calculating partial ionization cross sections. This is a robust measure for quantification which is easy to compare to the scattering cross sections used for annular dark field (ADF) STEM quantification and ionisation edges in electron energy loss spectroscopy (EELS). Our quantification method is applied to alloy PtCo nanoparticles which have been acid leached to provide Pt enrichment or rather Co depletion at the particle surface. Such surface Co depletion is absent at the vertices of the more facetted nanoparticles. The leaching process demonstrates very little change in Co composition when investigating the whole particle but produces a localised surface depletion which can only be determined by the high resolution EDX quantification. References [1] K. E. MacArthur et al., Microsc. Microanal., 22 01 (2016) p71-81. [2] K. E. MacArthur et al., Mater. Sci. Tech. 32 3 (2016) p248-253

24

The Dynamics of Active Metal Catalysts Revealed by In Situ Electron Microscopy

Zhu-Jun Wang, Ramzi Farra, Jing Cao, Robert Schlögl, Marc Georg Willinger

Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany E-mail (correspondence): [email protected]

Conventional high-resolution imaging by electron microscopy plays an important role in the structural and compositional analysis of catalysts. However, since the observations are generally performed under vacuum and close to room temperature, the obtained atomistic details concern an equilibrium state that is of limited value when the active state of a catalyst is in the focus of the investigation. Since the early attempts of Ruska in 1942 [1], in situ microscopy has demonstrated its potential and, with the recent availability of commercial tools and instruments, led to a shift of the focus from ultimate spatial resolution towards observation of relevant dynamics.

During the last couple of years we have implemented commercially available sample holders for in

situ studies of catalysts in their reactive state inside a transmission electron microscope. In order to relate local processes that occur on the nanometer scale with collective processes that involve fast movement of a large amount of atoms, we have furthermore adapted an environmental scanning electron microscope (ESEM) for the investigation of surface dynamics on active catalysts. Using these two instruments, we are now able to cover a pressure range from 10-4 to 103 mbar and a spatial resolution ranging from the mm to the sub-nm scale. Presently we are investigating metal catalyzed CVD growth of graphene [2], as well as structural dynamics during oscillatory red-ox reactions. The observations are performed in real-time and under conditions in which the active state of the catalyst can be monitored. The latter is of upmost importance, since the key requirement is to observe relevant processes and dynamics that are related to catalytic function. The ability to directly image the active catalyst and associated morphological changes at high spatial resolution enables us to refine the interpretation of spatially averaged spectroscopic data that was obtained under otherwise similar reaction conditions, for example during near-ambient-pressure in situ XPS measurements [3]. It will be shown that the ability of observing the adaption of an active surface to changes in the chemical potential of the surrounding gas phase in real-time potentially offers new and direct ways of optimizing catalysts and applied reaction conditions.

References [1] E. Ruska, Kolloid-Zeitschrift, 100 (1942) 212-219 [2] Z.-J. Wang et al., ACS Nano, 9 (2015) 1506–1519 [3] R. Blume et al., PhysChemChemPhys, 16 (2014) 25989

25

Atomic Level Characterization of Novel Hardening Mechanisms in High-Mn-Steels

Joachim Mayer1,2, Maryam Beigmohamadi2, Marta Lipinska-Chwalek1,2 and James E.Wittig3

1. Central Facility for Electron Microscopy, RWTH Aachen University, Aachen, Germany

2. Ernst Ruska Centre, Forschungszentrum Jülich, Germany 3. Interdisciplinary Materials Science, Vanderbilt University, Nashville TN, 37235 USA


Recently developed high-manganese steels exhibit an exceptional combination of strength and ductility and show great promise for structural applications. Understanding the relationships between manganese and carbon content, microstructure, temperature, defect formation and strain-hardening behavior is critical for alloying, design, and further optimization of these steels. The present study investigates the influence of alloy content, temperature and deformation behavior on the microstructural evolution of an austenitic Fe-14Cr-16Mn-0.3C-0.3N alloy showing twinning induced plasticity (TWIP) and of a two-phase nanostructured Fe-30.5Mn-8Al-1.2C alloy exhibiting microband induced plasticity (MBIP). The twinning induced plasticity (TWIP) effect enables designing austenitic Fe-Mn-C based steels with >70% elongation at an ultimate tensile strength >1 GPa. These alloys are characterized by high strain hardening coefficients owing to the formation of twins and complex dislocation substructures which dynamically reduce the dislocation mean free path. Further insight in the strain hardening mechanisms can be gained by a conventional TEM analysis of highly strained samples of a stainless Fe-Cr-Mn-C-N steel [1]. The primary mechanical twins contribute to the strain-hardening by acting as obstacles to dislocations gliding on different slip systems, which shows mechanical twins and intersecting stacking faults after 0.21 logarithmic strain. Dislocation accumulation at the twin boundaries can be observed under diffraction conditions which make the dislocation arrangement visible. High resolution TEM and STEM images of the planar defects in the same alloy will be presented and detailed investigations revealed insight in the atomistic structure of the defects and the defect/dislocation interaction. The presented examples reveal that TEM investigations can give important insight in the deformation mechanisms and mechanical properties of the high-Mn alloys. In further HRTEM investigations, microband induced plasticity (MBIP) alloys with a composition of Fe-30.5Mn-8Al-1.2C were investigated after various heat treatments at 600°C. In the alloys, regularly spaced coherent precipitates of the κ-Phase were found, which cause the unique properties of these materials. In the TEM investigations, a regular arrangement of the cube- or brick-shaped nanoscale κ-carbide precipitates was observed. At higher magnifications, a coherent embedding of the precipitates in the austenitic matrix can be discerned. The specific thermal and mechanical properties of the alloys can be attributed to the mechanical strain introduced by the coherency at the matrix/precipitate interfaces. In further investigations, the microstructural evolution and the strain relaxation upon further annealing were investigated. References [1] L. Mosecker, D.T. Pierce, A. Schwedt, M. Beighmohamadi, J. Mayer, W. Bleck, J.E. Wittig, Materials Science & Engineering A 642 (2015) 71–83. [2] Finanial support from the German Research Foundation (DFG, SFB761) is gratefully acknowledged.

26

On the Phase Stability of Alloy Nanoparticles

B. Rellinghaus1, D. Pohl1, A. Surrey1,2, F. Schmidt1,3, S. Wicht1,3, S. Schneider1,2, L. Schultz1,

1. IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, D-01171 Dresden, Germany

2. TU Dresden, Institut für Festkörperphysik, D-01062 Dresden, Germany 3. TU Dresden, Institut für Werkstoffwissenschaft, D-01062 Dresden, Germany

E-mail (correspondence): [email protected] In nanoparticles, the surface-to-volume ratio is significantly enhanced over that of their bulk counterparts. Accordingly, the surface energy becomes relevant to the overall thermodynamic stability of the occurring phases. At sizes in the nanometer range, it effectively competes with cohesive, strain, grain boundary and twinning energies and thus contributes significantly to the total energy balance of the particle. Hence, both the morphology and structure of nanoparticles are increasingly affected by their surfaces. Specifically in alloy particles, differences in the surface (free) energies of their constituents may promote surface segregation. As a consequence, compounds that are known to form homogeneous alloys in the bulk may exhibit the tendency to segregate at small length scales. The talk will review our work on segregation phenomena in alloy nanoparticles. A particular focus will be laid on particles of binary metallic systems such as FePt, CuAu, FeNi, and AuFe, while elemental Au will serve as a reference material. The experimental HRTEM studies are corroborated by investigations using electron energy loss spectroscopy as well as Molecular Dynamics and Monte Carlo simulations. As for magnetic particles, the work highlights the necessity to not only determine structural details, but to also provide for quantitative magnetic information with ultimate resolution. It will be discussed, how Energy loss Magnetic Chiral Dichroism (EMCD) could pave the way towards this information, and how EMCD with electron vortex beams would allow for up to atomic resolution. References: [1] D. Pohl et al., Nano Lett. 14 (2014) 1776. [2] A. Surrey et al., Nano Lett. 12 (2012) 6071. [3] D. Pohl et al., Phys. Rev. Lett. 107 (2011) 185501. [4] B. Bieniek et al., J. Nanopart. Res. 13 (2011) 5935. [5] F. Schmidt et al., J. Nanopart. Res. 17 (2015) 170. [6] S. Schneider, submitted to Ultramicroscopy, (2016); arXiv:1605.03545 [cond-mat.mtrl-sci].

FIG.1 Left: Near-surface lattice relaxation in FePt icosahedra due to surface segregation of Pt as determined from aberration-corrected HR-TEM[1]. Inset: FePt model particle for MD simulations. Right: EMCD at the Fe-L3,2 absorption edge as measured in a section of an L10-FePt island on STO[6].

27

Surface atomic structure of perovskite oxide nanocrystals

Hongchu Du 1,2, Chun-Lin Jia1,3, Joachim Mayer1,2

1. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany

2. Central Facility for Electron Microscopy (GFE), RWTH Aachen University, Aachen, 52074, Germany 2. Peter Grünberg Institute, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany

E-mail (correspondence): [email protected] Monodisperse faceted nanocrystals, with controllable shapes and sizes, have been becoming increasingly important for applications in catalysis, gas sensing, and energy conversion. Such highly shape sensitive and selective physical and chemical properties inherently stem from the atomic and electronic structures on the faceted surfaces. For elemental nanocrystals, the atomic structure on the surfaces is determined by the geometric shape itself. However, for compound materials such as alloys and complex oxides, the compositional segregation and different terminating lattice planes on the surfaces have to be taken into account. In order to understand the unique property and growth mechanism of these nanocrystals, atomic details on the faceted surfaces need to be studied on the atomic level. In this work, we report on detailed studies of monodisperse {1 0 0}-faceted nanocubes of SrTi1−xZrxO3 (x = 0.25 to 0.5). The surface atomic structure of the monodisperse faceted nanocrystals is determined by means of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). On the basis of the structural features on the faceted surfaces, a deeper insight into the growth mechanisms could be obtained. References [1] H.Du et al., Chem. Mater., 28 (2016) 650. [2] H. Du. et al., J. Mater. Chem., 17 (2007) 4605.

FIG.1 a) Sketch of a layerwise growth process for a {1 0 0} facet of the perovskite ABO3 structure presuming a faster growth rate for the AO layer (green) than that for the BO2 layer (blue). The gray, yellow, and red symbols indicate the possible atom sites for the BO2 layer growth in the order of increasing preference. Oxygen was omitted in the model for clarity. (b) HAADF-STEM image of a SrTi0.75Zr0.25O3 nanocube with a growth step. (c) HAADF-STEM image overlaid with color-scale two-dimensional Gaussian peaks from fitting the intensity distribution of each column.

28

Metal hydrides for H storage

Claudio Pistidda,a Thomas Klassen,a,b Fahim Karimi,a Ulrike Bösenberg,a Gagik Barkhordarian,a Christian Bonatto Minella,a Martin Dornheim,a

aInstitute of Materials Research, Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research, Geesthacht, Germany

bInstitute of Materials Technology, Helmut Schmidt University, University of the Federal Armed Forces Hamburg, Germany


The use of fossil fuels as energy supply is growing increasingly problematic both from the point of view of environmental emissions and energy sustainability. As an alternative to fossil fuels, hydrogen is widely regarded as a key element for a potential energy solution. In this respect, hydrogen storage technology is considered a key roadblock towards the use of H2 as energy carrier. Among the methods available to store hydrogen, solid-state storage appears to be the most attractive alternative.

Recently, based on the unexpected kinetic effects of the MgB2, Barkhordarian et al. and Vajo et al. reported on the possibility to reversibly store hydrogen (up to 11 wt.%) in tetrahydroborates when mixed with MgH2. As confirmed by the numerous works published in the last years, this discovery ignited new interest in this class of hydrides as potential hydrogen storage material. In particular the systems LiBH4-MgH2, Ca(BH4)2-MgH2 and NaBH4-MgH2 have been subject of intensive investigations. However, In spite of a significantly lowered reaction enthalpy and thus high thermodynamic driving force for desorption, due to kinetic constrains hydrogen release from these systems still requires temperatures above 250°C.

Transmission electron microscopy (TEM) is a powerful tool for analysing and understanding the relationship between structure, morphology and the limiting reactions associated with complex metal hydrides. In this work an overview of reaction mechanisms, thermodynamic properties, material structure and sorption behaviour of nanocrystalline LiBH4-MgH2, Ca(BH4)2-MgH2 and NaBH4-MgH2 is given

References [1] G. Barkhordarian et al., Journal of Alloys and Compounds 440 (2007) L18-L21. [2] J.J. Vajo JJ et al., The Journal of Physical Chemistry B.108 (2004) 13977-83. [3] U. Bösenberg et al., Acta Materialia 58 (2010) 3381-3389. [4] M. Dornheim, T. Klassen, Encyclopedia of Electrochem. Power Sources (2009) 459-472. [5] F. Karimi et al., Journal of Applied Crystallography 47(2014) 67-75.

29

Interface Segregation Engineering studied by Correlative Atom Probe Tomography and Electron Microscopy

M. Herbig1, A. Stoffers1,2, M. Kuzmina1, B. Gault1, C. Liebscher1, O. Cojocaru-Mirédin2, I. Povstugar3,

S. Sandlöbes4, D. Ponge1, C. Scheu1, G. Dehm1, M. Yao1, P.-P. Choi5, D. Raabe1

1 Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straβe 1, 40237 Düsseldorf, Germany 2 I Physikalisches Institut IA, RWTH Aachen University, Sommerfeldstraße 14, 52074 Aachen, Germany

2 Analytik (ZEA-3), Research Centre Jülich, Wilhelm-Johnen-Straße, 52428 Jülich, Germany 4 Institut für Metallkunde und Metallphysik, RWTH Aachen University, Kopernikusstr. 14, 52074 Aachen, Germany

5 Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Daejeon 305-338, Republic of Korea E-mail (correspondence): [email protected]

We present recent progress in correlative methods for the joint analysis of nanostructured samples by Atom Probe Tomography (LEAP 3000, LEAP 5000) and Electron Microscopy (Cs corrected Titan Themis). Measurements are conducted on the same Atom Probe sample tips and in some cases atomic resolution is reached [1-3]. Examples from functional and structural materials are presented including segregation effects in multicrystalline silicon solar cells and their relation to cell efficiency, superalloys for advanced turbines and high strength steels (Fig. 1). References [1] M. Kuzmina et al., Science 349 (2015) 1080. [2] M. Herbig et al., Phys. Rev. Lett. 112 (2014) 126103. [3] W. Guo et al., Phys. Rev. Lett. 113 (2014) 035501.

FIG.1 Examples of correlative TEM-APT imaging [1-3]: Left: Nanostructured Fe-C steel with 7 GPa strength. Right: Linear Complexions in an Fe-Mn alloy.

30

3D micro-structure of spindle-like lithium-titaniumphosphate (Li1Ti2(PO4)3) particles for lithium-ion batteries

Roland Schierholz1, Shicheng Yu1, Hermann Tempel1, Hans Kungl1 and Rüdiger-A.

1. Institute of Energy and Climate Research: Fundamental Electrochemistry (IEK-9), Forschungszentrum Jülich GmbH - Jülich - GERMANY

Aim of our research is an all solid state lithium ion battery consisting of phosphate materials in NASICON structure. As an Electrolyte we use Li1+xAlxTi2-x(PO4)3 (LATP) and as Electrode materials Li3-xV2(PO4)3 (LVP) and Li1+xTi2(PO4)3 (LTP). The presentation will focus on the study of these materials by electron microscopy techniques, especially particles of LiTi2(PO4)3 (LTP). Those particles were synthesized using oxalic acid as solubilizer for the titanium source, surfactant and carbon source during a one-pot solvothermal process. The carbon source is used to create a thin carbon coating to increase the electric conductivity. From these particles and reference particles synthesized by sol-gel method electrode sheets were prepared and compared. Electrochemical characterization reveals higher rate stability for the electrodes containing the spindle like particles synthesized in the solvothermal process. While the sol-gel powder has inhomogeneous particle size distribution and morphology, for the solvothermal route most of particles show an interesting spindle-like morphology with sizes about 5 μm. We believe that the electrochemical behavior is related to the particle morphology and therefore performed a detailed study of the micro-structure in three dimensions of the spindle like particles in order to understand the forming mechanism. We will present the volume reconstructed from "slice and view" experiments and combine this with more detailed investigations of the crystallographic structure in the TEM and the local chemistry by STEM-analysis. By this we could prove that the particles contain pores, are not single phase and the whole morphology is formed by sub-particles of approximately 300 nm size, which can be seen in Figure 1.

FIG.1 Transmission electron microscope image of a FIB Lamella prepared from a LiTi2(PO4)3-particle.

31

Towards controlled electro-chemistry of complex oxides in environmental transmission electron-microscopy

Stephanie Mildner1, Daniel Mierwaldt1, Vladimir Roddatis1, Thilo Kramer1, Marco Beleggia2,

Christian Jooss1,

1Inst. of Materials Physics, Univ. of Goettingen, Friedrich-Hund-Platz 1, 37077 Goettingen, Germany 2Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.

Presenting author email address: [email protected] Environmental TEM is an excellent as well as challenging tool for gaining insight into the atomic and electronic structure of electro-catalysts under operating conditions. Several electro-chemical reactions such as oxidation/reduction processes of electrodes, heterogeneous gas phase catalysis of water splitting/oxygen evolution and electro-chemical corrosion processes of materials have been studied in some pioneering experiments. These experiments often reveal a strong change of the electrode specimens in contact with environmental gas species due to the impact of the electron beam. We show that even for electron doses well below beam damage the inelastic scattering of the high-energy electrons induce electric potentials in the studied samples influencing the electrical state of the catalyst. We show by systematic experiments and theoretical studies, how beam-induced potentials depend on several parameters, such as electron flux, electric conductivity and geometry of samples and how to disentangle them from radiation damage. In addition, the electric potential distribution within and around samples can be controlled by dedicated electrical TEM sample holders. To illustrate how this can be achieved, we present the results of bias-controlled electro-chemical oxygen evolution experiments using manganite electrodes. We can correlate trends in O2 evolution activity and defect chemistry in the active state to doping induced changes of the electronic band structure in A-site doped manganites. Further experimental and theoretical challenges for the development of controlled electro-chemistry studies in transmission electron microscopes such as analysis of reaction products and control of clean chemical environments will be addressed. References S. Raabe, D. Mierwaldt, J. Ciston, M. Uijttewaal, H. Stein, J. Hoffmann, Y. Zhu, P. Blöchl, and Ch. Jooss, Adv. Funct. Mater. 22 (2012) 3378–3388. S. Mildner M. Beleggia, D. Mierwaldt Th. W. Hansen, J. B. Wagner, S. Yazdi, T. Kasama, J. Ciston, Y. Zhu, and Ch. Jooss, J. Phys. Chem. C, 119 (2015) 5301–5310. Ch. Jooss, S. Mildner, M. Beleggia, D. Mierwaldt, V. Roddatis, Handbook chapter in “Controlled Atmosphere Transmission Electron Microscopy - Principles and Practice”, edited by Jakob Birkedal Wagner and Thomas Willum Hansen, Springer 2015.

32

BCC Cu-Cr Alloy Thin Films Studied by Advanced S/TEM

T. Harzer, C. Liebscher, R. Raghavan, G. Dehm

Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany E-mail (correspondence): [email protected]

Cu thin films are widely used in microelectronic devices due to their excellent electrical and thermal conductivity. However, repeated exposure to temperature fluctuations can cause thermo-mechanical fatigue [1] and failure of the devices. Increasing the yield strength of Cu-based thin films would be the remedy to decrease the susceptibility to thermal fatigue. In this study, supersaturated Cu-Cr solid solutions were fabricated by physical vapor deposition with the aim to create thermally (meta-)stable nanocrystalline Cu-based thin films with exceptional strength. The microstructure evolution, thermal stability, and mechanical performance are analyzed by analytical and in situ TEM studies as well as micro-compression testing inside the SEM. The studies revealed that alloy films with 66 at.% Cu and 34 at.% Cr form nanocrystalline films (Fig. 1a-c) with a bcc crystal structure [2]. The films remain globally single-phase bcc and nanocrystalline at temperatures up to 300°C, while at 400°C a decomposition into fcc and bcc phases is observed. The microcompression testing of the alloyed film revealed excellent strength at elevated temperature and an anomalous increase in strength after aging at 300°C (Fig. 1d) [3]. References [1] W. Heinz et al., Microelectronic Eng., 137 (2015) 5. [2] T. Harzer et al., Acta Mater., 83 (2015) 318. [3] R. Raghavan et al., Acta Mater., 93 (2015) 175.

FIG.1 STEM-HAADF image (a) of the Cu66Cr34 alloy film revealing chemical modulations on a grain to grain level but also (b) inside individual bcc grains. (c) The nanolayered elemental partitioning is confirmed by EDX maps. d) Microcompression testing reveals a moderate reduction in strength for temperatures up to 300°C. Annealing the sample at 300°C leads to an unexpected increase in the room temperature strength (see curve --- 25°C//300°C); stress-strain curve taken from [3].

33

Size-controllable synthesis of PdRu solid-solution NPs for catalytic applications

Dongshuang Wu,1 Kohei Kusada,1 and Hiroshi Kitagawa1

1. Graduate School of Science, Kyoto University, Japan.E-mail: [email protected]

Very recently, PdRu non-equilibrium solid-solution nanoparticles (NPs) have been developed as effective catalysts in various reactions, such as CO oxidation and formic acid oxidation. [1, 2] The chemical and physical properties of solid-solution NPs are significantly affected by the constituent elements, their ratio, and the particle size. Although, in the research on the PdRu catalyst, the effect of metal composition has been reported so far, there is no report on the size effects. Since Pd and Ru are two immiscible metals in their bulk form, it is difficult to simultaneously control the metal composition and size of the PdRu solid-solution NPs. Herein, fixing the Pd/Ru molar ratio at 1:1, we successfully synthesized PdRu solid-solution NPs from 2 to 15 nm with narrow size distribution via a simple one-pot reaction (FIG.1). The as-prepared PdRu NPs were employed as catalysts for certain catalytic reactions. The relationship between size and catalytic activity is discussed.

References [1] Kusada, K.; Kitagawa, H.; et al., J. Am. Chem. Soc. 136 (2014) 1864. [2] Wu, D.; Cao, M.; Shen, M.; Cao, R.; ChemCatChem, 6 (2014) 1731.

FIG.1 TEM images of Pd0.5Ru0.5 solid-solution nanoparticles with size of a) 2.0, b) 5.0, c) 11.1, d) 15.5 nm, e) powder X-ray diffraction patterns (λ = 0.5876(4) Å).

37

Synthesis and Characterization of Novel Rhodium Compound

Takuo Wakisaka1, Kohei Kusada1, Tomokazu Yamamoto2, Satoru Yoshioka2, Toshiki Higashihara2, Syo Matsumura2, Yoshiki Kubota3, Hiroshi Kitagawa1

1. Division of Chemistry, Graduate School of Science, Kyoto University

2. Department of Applied Quantum Physics and Nuclear Engineering, Graduate School of Engineering, Kyushu University

3. Department of Physical Science, Graduate School of Science, Osaka Prefecture University E-mail: [email protected]

Although various materials have been created by combining available elements, the number of combinations of the elements that are mixed easily is limited. Recently, novel solid-solution alloys that do not exist in the bulk state have been developed by nanosize effect, which tap the unrealized potential for nano-materials [1]. However the alloy combinations with noble metals and light elements have not been fully developed yet, since most of noble metals do not form carbide or nitride. A few experimental examples were reported so far, which were synthesized at high temperature or high pressure [2][3]. Here, we report the first example of rhodium carbide and its synthesis using liquid-phase reaction under ambient conditions. The synthesis of rhodium carbide was succeeded by controlling speed of reduction and a carbon supply. The structure of this compound was characterized by powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) measurements (FIG.1). Energy dispersive X-ray (EDX) spectroscopy revealed that carbon atoms homogeneously existed in the whole particle (FIG.2). The electronic state of this compound was investigated by X-ray absorption fine structure (XAFS) measurement, and it was totally different from that of metallic rhodium. References [1] K. Kusada and H. Kitagawa, Adv. Mater. 28 (2016) 1129. [2] E. Gregoryanz et al., Nat. Mater. 3 (2004) 294. [3] NRS. Kumar et al., J. Phys. Condens. Matter 24 (2012) 362202.

FIG.1 High-resolution TEM image and the structural model

FIG.2 HAADF-STEM image and STEM-EDX map images

38

Syntheses and Physical Properties of Ni and Pt Nanoparticles Coated with

the Metal-organic Framework HKUST-1

Y. Aoyama1, H. Kobayashi1, T. Yamamoto2,3, S. Matsumura2,3, Y. Kubota4, H. Kitagawa1 1 Division of Chemistry, Graduate School of Science, Kyoto University,

Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto-shi, Kyoto, 606-8502, Japan 2 Department of Applied Quantum Physics and Nuclear Engineering and

3 The Ultramicroscopy Research Center, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan

4 Department of Physical Science, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan

[email protected]

Hybrid materials composed of metal nanoparticles and metal–organic frameworks (MOFs) have increasingly received attention in recent years because of their potential multi-functionality, such as material and energy conversion applications. Very recently, we reported Pd nanocrystals covered with the MOF, copper(II) 1,3,5-benzenetricarboxylate (HKUST-1) as a novel highly-efficient hydrogen storage material.1 The hybrid material (Pd@HKUST-1) showed doubly enhanced hydrogen storage capacity and speed, compared to the bare Pd nanocrystals. The enhancement of hydrogen storage ability of Pd@HKUST-1 is considered to originate from a charge transfer from Pd to HKUST-1. The synergistic property of Pd and HKUST-1 promotes us to develop other hybrid material systems with HKUST-1. In this study, we focus on Ni and Pt where the constituent elements belong to the same 10 group of Pd as metal nanoparticles for hybrid materials with HKUST-1. The hybrids, Ni@HKUST-1 and Pt@HKUST-1 were synthesized by a liquid phase method. Ni and Pt nanoparticles were covered with HKUST-1 by stirring nanoparticles with the precursors of HKUST-1 in ethanol. The powder X-ray diffraction (XRD) patterns of Ni@HKUST-1 and Pt@HKUST-1 consisted of two kinds of Ni or Pt and HKUST-1 diffractions. The crystal sizes of Ni and Pt were estimated to be 3.4 nm and 4.6 nm from the Le Bail fitting, respectively. The transmission electron microscope (TEM) images revealed that the Ni or Pt nanoparticles were monodispersed (Figure). The electron structure changes were investigated with X-ray photoelectron spectroscopy (XPS). Their hydrogen storage properties and magnetism were investigated and are presented. References [1] G. Li, H. Kobayashi, H. Kitagawa, et al., Nature Materials, 2014, 13, 802.

FIG.1 TEM images of Ni@HKUST-1 and Pt@HKUST-1.

39

Structural rearrangement of Pd nanocrystals driven by light-element doping

Keigo Kobayashi1, Hirokazu Kobayashi1, Tomokazu Yamamoto2 , Mitsuhiko Maesato1, Syo Matsumura2 , Hiroshi Kitagawa1

1. Division of Chemistry, Graduate School of Science, Kyoto University 2. Graduate School of Engineering, Kyushu University


It is known that metal nanoparticles exhibit different structure or chemical and physical properties from those in bulk metals. For examples, ruthenium (Ru) nanoparticles were reported to form a face-centered cubic (fcc) structure although the bulk metal has only hexagonal close-packed (hcp) structure1. In addition, Palladium (Pd) and Ru, which are immiscible in the bulk state, were mixed homogeneously at the atomic level by the nanosize effect2. To date, novel solid-solution alloy nanoparticles have been mainly developed by the combination of transition metals, but there are few reports on the alloy nanoparticles composed of transition metal and light element. Here we demonstrate novel nanostructured Pd-boron (Pd-B) alloy. At first, PVP-coated Pd nanocubes enclosed by {100} facets, were prepared in a water-based system, as reported previously.3 Then, B doping was performed by adding borane-tetrahydrofuran complex solution into the obtained Pd nanocubes under inert condition. The powder X-ray diffraction (PXRD) pattern and transmission electron microscopy revealed that Pd nanocubes have fcc structure and the mean diameter is about 12 nm. After B doping into the Pd nanocubes, the diffraction pattern dramatically changed from fcc to a hcp lattice pattern. Interestingly, the cubic morphology and the mean diameter were maintained before/after the B doping. In order to investigate the elemental distribution of Pd and B in Pd–B alloy nanocube, we performed electron energy loss spectroscopy (EELS) mapping. The EELS mapping demonstrated that Pd and B are mixed homogeneously in the nanocube. So far, there has been no report on hcp Pd-B alloy compound in bulk state. Our result provides the first example of hcp Pd-B alloy. To investigate the electronic state of the hcp Pd-B alloy nanocubes in detail, we performed X-ray photoelectron spectroscopy.

References [1] K. Kusada et al., J. Am. Chem. Soc., 135 (2013) 5493-5496. [2] K. Kusada et al., J. Am. Chem. Soc., 136 (2014) 1864-1871. [3] B. Lim et al., Adv. Funct. Mater., 19 (2009) 189-200.

FIG. (a)PXRD pattern and (b)EELS mapping image of synthesized Pd-B nanoparticles

Pd C

B Overlay

(a) (b)

40

Catalytic activity of metal–organic framework composites loading metal nanoparticles prepared through arc plasma deposition

Masaaki Sadakiyo,1 Shotaro Yoshimaru,2 Miho Yamauchi1,2

1. International Institute for Carbon-Neutral Energy Research, Kyushu University, Moto-oka 744, Nishi-ku,

Fukuoka, Japan 2. Department of Chemistry, Faculty of Science, Kyushu University, Moto-oka 744, Nishi-ku, Fukuoka, Japan

Functionalization of porous metal–organic frameworks (MOFs) is a current topic in materials

chemistry. We present a new approach for facile preparation of M/MOFs through an arc plasma deposition (APD) method. We succeeded in gram-scale preparation of M/MOFs including various metal NPs such as Pt, Pd, and Ru on various MOF supports such as ZIF-8, MIL-101, Zn-MOF-74, and UiO-66-NH2 without any chemicals in the same way. The resulting samples were characterized using scanning transmission microscope (STEM) observations, STEM-EDS analysis, X-ray powder diffraction, ICP-AES, and so on. Applicability of the samples to catalysis was also examined.

M/MOFs (M = Pt, Pd, Ru; MOFs = ZIF-8, MIL-101, Zn-MOF-74, UiO66-NH2) were prepared by irradiation of arc plasma shots. Figure 1 shows STEM images of Pt/ZIF-8 (0.82 wt% metal loading), Pd/ZIF-8 (0.79 wt%), Ru/ZIF-8 (0.93 wt%), and blank ZIF-8. Each sample had well-dispersed small NPs on the crystal of ZIF-8 except for the blank ZIF-8, indicating that the deposited metal species automatically formed small NPs. Average diameters (dav) of the deposited metal NPs in Pt/ZIF-8, Pd/ZIF-8, and Ru/ZIF-8 were estimated to be similar values of 1.8 ± 0.3, 2.0 ± 0.4, and 2.1 ± 0.6 nm, respectively. This result clearly shows that various metal NPs can be easily deposited over the MOF supports with the APD method and that the particle sizes are hardly dependent on the metal element. STEM-EDS analyses revealed that these NPs were located on the surface of MOF crystals.

To confirm the connectivity between the deposited NPs and MOFs, and the applicability of the M/MOF composites to heterogeneous catalysis, we conducted a formic acid decomposition reaction, which requires the presence of basic groups such as –NH2 or –N(CH2)2 adjacent to Pd NPs to enhance the catalytic activity.1 Pd/UiO-66-NH2 prepared through the APD showed higher catalytic activity than Pd-PVP/UiO-66-NH2 loading PVP-coated Pd NPs, while the amount of Pd is almost the same. This result confirms that the surface of MOF is not decomposed during the APD experiment and that metal NPs deposited through the APD have a direct contact with the MOF, confirming that M/MOFs are expected to provide specific reaction fields forming around the NPs through the spatial or chemical interaction with MOF supports.

(1) K. Mori, M. Dojo, H. Yamashita, ACS Catal., 2013, 3, 1114–1119.

Figure 1. STEM images of (a) blank ZIF-8, (b)

Pt/ZIF-8, (c) Pd/ZIF-8, and (d) Ru/ZIF-8.

41

Three dimensional elemental analysis of bimetallic nanoparticles

Tomokazu Yamamoto 1, Koji Shigematsu1, Syo Matsumura1,2

1. Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan 2. The Ultramicroscopy Research Center, Kyushu University, Fukuoka, Japan

E-mail (correspondence): [email protected] Bimetallic nanoparticles have been extensively investigated for a wide range of applications. The information about local compositions in nanoparticles are essential to understand thier chemical and physical properties. The recent advance in energy dispersive x-ray (EDX) detector systems for a transmission electron microscope (TEM), such as improvements of x-ray collection efficiency due to multiple detectors, enables us to perform more quantitative elemental analysis of nanoparticles in shorter acquisition time compared with that by conventional systems. The x-ray collection efficiency improvement is also expected to possibilities of 3D elemental analysis such as STEM-EDX tomography. In recent years, STEM-EDX tomography for nanomaterials have been investigated by several groups using FEI Titan series with the Super-X EDX detector system composed of four silicon drift detectors (SDDs) [1, 2]. The problems in application of STEM-EDX tomography are collection efficiency change due to holder shadowing, x-ray absorption corrections, which depend on specimen tilting angle, and a choice of reconstruction techniques for a noisy small data set. In the present study, we show the x-ray detection efficiency of the dual 100 mm2 SDD system in a JEOL JEM-ARM200F with a HR-type OL pole piece when using a JEOL standard high-tilt tomography holder and discuss a methodology for STEM-EDX tomography of bimetallic nanoparticles (FIG.1).

References [1] P. Burdet et al., Ultramicroscopy, 160 (2016) 118. [2] T.J.A. Slater et al., Ultramicroscopy, 162 (2016) 61.

FIG.1 A tilt series of elemental maps for Pd/Pt core-shell nanoparticles. The each acquisition of elemental maps was performed with the acquisition time of 30 min and the probe current of 25 pA at the acceleration voltage of 200 kV.

42

RhCu Nanoparticles: Electronic Structure Evolution versus Composition Alteration Revealed by Hard X-ray Photoelectron Spectroscopy.

Natalia Palina,1 Osami Sakata,1,2 L. S. R. Kumara,1 Hirokazu Kobayashi,3,4 Kohei Kusada,3 Tokutaro Komatsu,5 and Hiroshi Kitagawa,3,4,6

1 Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, 679-5148, Japan 2 Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan

3 Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan 4 Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan

5School of Medicine, Nihon University 30-1, Oyaguchi Kami-cho, Itabashi-ku, Tokyo 173-8610 Japan 6 INAMORI Frontier Research Center, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-3095, Japan

E-mail (correspondence): [email protected] and [email protected]

In this study, advanced synchrotron radiation (SR) based characterisation techniques were utilized to assess changes in electronic structure of extremely small 1-1.5 nm solid solution RhCu alloy nanoparticles (NPs). Rh and RhCu alloy NPs have been investigated as cost-effective candidates for CO oxidation catalysts, namely CO removal from car exhaust or for preventing CO poisoning in fuel cell systems. RhCu nanoparticles with a narrow size distribution were prepared by chemical reduction method. The Hard X-ray Photoelectron Spectroscopy (HAXPES) core level (CL) and valence band (VB) spectra of RhCu NPs with various composition were recorded ex-situ at the NIMS (National Institute for Materials Science) contract undulator beamline, BL15XU of SPring-8, Japan. Our characterisation reveals, that for pure Rh and Rh-rich alloy NPs formation of rhodium surface oxide with non-integer oxidation state (Rh(3-+) is main factor which leads to the improvement of catalytic activity. Whereas, for alloy NPs with comparable Rh:Cu ratio a decreased fraction of catalytically active Rh (3-)+ oxide is compensated by charge transfer from Cu to Rh, hence ensuring a negligible change in the catalytic activities of those as compared to Rh-rich and pure Rh NPs. We demonstrate capability of SR-based characterisation to access, understand and possibly control physical properties of novel functional nanoscale materials.

FIG.1 Rh 3d and Cu 2p3/2 CL HAXPES spectra, (a) and (b) respectively, of reference Rh and Cu powder (solid and dashed lines, respectively), Rh NPs (red square scatters), Rh1.53Cu0.47 (green circle scatters), Rh1.06Cu0.94 (magenta triangle scatters) and Rh0.50Cu0.50 (blue diamond scatters) alloy NPs. The change in the electronic structure can be understood as concurrent reduction of Rh and oxidation of Cu.

315 310 305

Rh(1)+307.48 eV

Rh(3)+312.35 eV

Rh3+313.3 eV

Rh0312.1 eV

Rh3+308.5 eV

Rh(0) powder bulk Rh NP's (1.0 nm) Rh

1.53Cu

0.47 (1.2 nm)

Rh1.06

Cu0.94

(1.4 nm)

Rh0.5

Cu0.5

(1.5 nm)

CP

S

BE [eV]

Rh0307.3 eV

(a)

938 937 936 935 934 933 932 931 930 929

(b)

Cu powder Ref

Rh1.53

Cu0.47

(1.2 nm)

Rh1.06

Cu0.94

(1.4 nm)

Rh0.5

Cu0.5

(1.5 nm)

CP

S

BE [eV]

Cu2+933.45 eV

Cu0932.4 eV

43

Large-scale electronic state calculations of Ru nanoparticles

based on the observed structures

Yusuke Nanba1, Takayoshi Ishimoto1, Michihisa Koyama1,2


E-mail (correspondence): [email protected] Transition-metal nanoparticles may exhibit not only the same crystalline structure as the bulk state but also the different one. Recently, Kusada et al. synthesized both ruthenium-nanoparticles (Ru-NPs) with hexagonal close packed (hcp) and face-centered cubic (fcc) structures[1], although the ruthenium-metal in the bulk state shows the hcp structure. The catalytic activity for the CO oxidation of the Ru-NP supported on γ-Al2O3 are dependent on the particle size and shape of the Ru-NP. Revealing the electronic structure of the Ru-NP with the realistic particle size and shape is important to understand the interesting property variation. In this study, we performed density functional theory (DFT) calculations of the Ru-NPs with various sizes and shapes. The models were based on the observation of the high-resolution transmission electron microscopy[1]. The shape of the hcp Ru-NP is similar to a barrel with (0001) and (11-21) surfaces, while that of the fcc Ru-NP is a decahedral structure with a {111} facet. For comparison, icosahedral and truncated octahedral structures were also prepared. The diameters of the Ru-NPs are more than 3 nm, which indicates that more than 1000 atoms are necessary to reproduce the realistic particle. Figure 1 shows the models of the Ru-NPs with more than 1000 Ru atoms. The DFT calculations were performed by using Vienna Ab Initio Simulation Package (VASP). The exchange and correlation terms were treated by generalized gradient approximation with Perdew-Burke-Ernzerhof functional. The cutoff energy was 400 eV and k-point was 1╳1╳1. We used cohesive energy to evaluate the stability of Ru-NP with four structures[2]. In large particle size, the cohesive energy of the hcp Ru-NP is the lowest, which is consistent with that the hcp structure is stable in the bulk state. With decreasing particle size, the cohesive energy of the icosahedral fcc Ru-NP becomes lower than that of the hcp Ru-NP. The surface energies forming the (0001) and (11-21) surfaces of the hcp structure are higher than that forming the (111) surface of the fcc one. With decreasing particle size, the surface ratio to NP increases and the cohesive energy of the hcp Ru-NP becomes high more rapidly than that of the icosahedral fcc Ru-NP. Thus, it was found that the particle size gives a large influence on the stability for the shape of the Ru-NP. The activities in INAMORI Frontier Research Center are supported by KYOCERA. This work was supported by JST-ACCEL and all calculations were performed on CX400 and HA8000 computer systems in Research Institute for Information Technology, Kyushu University. References [1] K. Kusada et al., J. Am. Chem. Soc., 135 (2013) 5493. [2] P. Nava et al., Phys. Chem. Chem. Phys., 5 (2003) 3372. FIG.1 Models of Ru-NPs with fcc and hcp structures.

44

Surface structures of bimetallic systems: PdAg and PdRh

Ryo Kishida1, Susan Meñez Aspera2, Hiroshi Nakanishi2, and Hideaki Kasai2,3,4

1. Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan 2. National Institute of Technology, Akashi College, Japan, Akashi, Hyogo 674-8501, Japan

3. Center for International Affairs, Osaka University, Suita, Osaka 565-0871, Japan 4. Institute of Industrial Science, The University of Tokyo, Meguro, Tokyo 153-8505, Japan

Email: [email protected] Alloying of metals has been extensively studied and attracted considerable attention due to their possibilities for designing functional materials with various combinations and compositions of the constituents. Recently, the limitation of the thermodynamically allowed combinations and compositions in the macroscopic solid-solution phases is being overcome because of the establishment of techniques for realizing stable alloy systems in a nano-particle form [1]. However, the physical origins of the nanonization effects on the stabilization have not been clarified. Detailed analyses of electronic structures and an appropriate model that simply describes the stability of the nano-particles are necessary for the theoretical prediction and design of functional materials in future. In this study, we investigate two bimetallic alloy systems, PdAg and PdRh. Pd and Ag are known to soluble whereas Pd and Rh are soluble at room temperature [1]. We employ first principles calculation based on the density functional theory for the electronic state calculations. Considering that nano-particles exhibit high surface area relative to the case of the bulk systems, we focus on the effects of surface in the structure. Thus, slab models are used to evaluate the local structures of nano-particles, and compared with the corresponding bulk systems (FIG. 1). As stable low index surfaces, (001) and (111) surfaces are used in this calculation. The configurations of the alloy constituents are randomly placed. Our comparative study reveals the energetic differences between alloy systems and pure systems at various lattice constants, both in bulks and slab models. The detailed results and discussion will be presented at the symposium. References [1] K. Kusada et al., J. Am. Chem. Soc., 132 (2010) 15896. FIG.1 Super cell structures of (001) surface (slab model) and bulk of PdAg alloy system. 10 different random configurations are used in this calculation.

45

Surface Effects on Bimetallic Alloys: Palladium-Iridium Case

Susan Meñez Aspera1, Koji Shimizu2, Kazuki Kojima2, Ryo Kishida2, Nguyen Hoang Linh2, Hiroshi Nakanishi1, and Hideaki Kasai1,3,4

1. National Institute of Technology, Akashi College, Akashi Hyogo 674-8501, Japan 2. Department of Applied Physics, Osaka University, 2-1 Yamadaoka Suita, Osaka 565-0871, Japan

3. Institute of Industrial Science, The University of Tokyo, Meguro, Tokyo 153-8505, Japan 4. Center for International Affairs, Osaka University, 2-1 Yamadaoka Suita, Osaka 565-0871, Japan


Interest in the properties and behavior of binary transition metal alloys have been shown from the numerous studies to date. Owing to the wide variety of possible combinations and promising applications, research on different ways and conditions for synthesis is still a relevant and interesting field of research. Recent advancement in nanoparticle science shows that binary transition metal nano-alloy particle shows remarkable properties different from that of its bulk form [1,2]. This provided the motivation to unravel the mysteries behind atomic behavior at the nano-particle size and further the advancement in materials design. In this study, we used density functional theory (DFT)-based calculation and analysis to determine the material properties and possible promising applications of nano-particle-sized binary transition metal alloy. To sample, we used the binary alloy PdIr, which is known to be miscible only at high temperature, i.e., at low temperature the two constituent atoms are known to separate in the bulk form [3]. One of the distinct properties of nano-particle are its larger surface area as compared with its bulk form. We therefore assumed that this is one of the major factors that contribute to the atomic interaction within the surface, and consequently, for nano-particle size, also within its bulk [4]. We therefore analyzed the effect of surface on the binary transition metal alloy PdIr. Our results show that surface effects have large factors in the formation of nano-particle alloy. And depending on the type of atom at the surface and the type of surface, tendency for surface segregation has drastic effects. For low index surfaces, surfaces such as the (001) and (111) were analyzed to determine tendency for atomic movement for highly mixed surface atoms. Surfaces with similar type of atoms have less energy for formation, where surfaces with Pd atoms at the surface are more stable. Further discussions and details on the mechanism will be presented at the conference. References [1] K. Kusada et al., J. Am. Chem. Soc., 132 (2010) 15896. [2] A. Yang et al., Appl. Phys. Lett., 105 (2014) 153109. [3] S.N Tripathi et al., J. Phase Equilibria, 12 (1991) 603. [4] H. Nakanishi et al., J. Phys. Soc. Jpn., in preparation.

46

Microstructural investigation of octahedral PtNiRh fuel cell catalyst nanoparticles

Martin Gocyla1*, Marc Heggen1, Vera Beermann2, Stefanie Kühl2, Rafal E. Dunin-Borkowski1, Peter

Strasser2 1Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute,

Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. 2Electrochemical Energy, Catalysis and Material Science Laboratory, Department of Chemistry, Chemical

Engineering Division, Technical University of Berlin, 10623 Berlin, Germany. Email (correspondence): [email protected]

The use of advanced octahedral PtNi catalysts with high oxygen reduction reaction (ORR) activities [1-4] and the use of PtNi alloys with high ethanol oxidation reaction (EOR) activities [5] have been severaltimes reported in the past years. PtNi nanooctahedra with extremely high catalytic activities are well established and exceeding those of Pt benchmark catalysts by up to 30 times [6], as a result of the presence of (111) facets. Nevertheless one of the key challenges in the development of such shaped catalysts is to improve long-term stability, i.e., to prevent the loss of the octahedral shapes of the nanoparticles during long-term electrochemical cycling. Previous work by the group of Strasser has shown that the ORR on octahedral PtNi catalysts leads to the preferential leaching of Ni from the particle surfaces and to the loss of highly active (111)-oriented surfaces, leading to a strong degradation in catalytic activity [7]. These and other theoretical and experimental studies have provided evidence for the strong dependence of catalytic performance on structure and composition and underlined the importance of careful atomic scale microstructural and compositional analysis as a basis for the rational design of active and stable catalysts. Here, we present a detailed microstructural study of well-defined stable octahedral-shaped PtNiRh alloy nanoparticle catalysts and correlate the elemental distribution in the particles with their shape stability after electrochemical potential cycling. The particles are investigated using high-angle annular dark field (HAADF) imaging in probe-corrected FEI Titan scanning transmission electron microscopes (STEMs) combined with atomic-scale compositional analysis using energy-dispersive X-ray spectroscopy in an FEI TITAN ChemiSTEM equipped with a Super-X detector. HAADF images of representative octahedral particles show before and after electrochemical potential cycling even after long-term electrochemical potential cycling (30000 cycles), the octahedral shape is still retained. By using a newly modified synthesis route that involves the use of oleylamine, oleic acid and W(CO)6, stable Rh-doped PtNi alloy particles that keep their octahedral shape and high catalytic activity even after long-term cycling are obtained [1,3].

[1] J. Zhang, H. Yang, J. Fang, S. Zou, Nano Letters, 10 (2010), 638. [2] C. Cui, L. Gan, H.-H. Li, S.-H. Yu, M. Heggen, P. Strasser, Nano Letters, 12 (2012), 5885-5889. [3] S.-I. Choi, S. Xie, M. Shao, J.H. Odell, N. Lu, H.-C. Peng, L. Protsailo, S. Guerrero, J. Park, X. Xia, J. Wang, M.J. Kim, Y. Xia, Nano Letters, 13 (2013), 3420-3425. [4] L. Gan, C. Cui, M. Heggen, F. Dionigi, S. Rudi, P. Strasser, Science, 346 (2014), 1502-1506. [5] D. Soundararajan, J. H. Park, K. H. Kim, J. M. Ko, Current Applied Physics, 12 (2012), 854-859. [6] P. Strasser, Science 349 (2015), 379-380. [7] C. Cui, L. Gan, M. Heggen, S. Rudi, P. Strasser, Nature Materials, 12 (2013), 765-771.

47

Multimetallic Nanostructures by Galvanic Replacement Reaction

Meital Shviro1,2, Shlomi Polani1, Martin Gocyla2, Marc Heggen2 and David Zitoun1

1. Bar Ilan University, Department of Chemistry and Bar Ilan Institute of Nanotechnology and AdvancedMaterials (BINA), Ramat Gan 52900, ISRAEL

2. Ernst Ruska-Centre (ER-C) and Peter Grünberg Institute (PGI-5), Forschungszentrum Jülichm. [email protected]

Metallic nanoparticles have been the center of focus of an intense scientific research activity in the past few years due to their potential application in plasmonics, catalysis and sensing. Pt–Ni–Au alloys have been prepared through a two-step reaction with the synthesis of NiPt octahedral and cuboctahedral templates followed by a galvanic replacement reaction by Au(III). Metal etching presents an efficient method to yield hollow particles to investigate Au diffusion in the metallic Pt–Ni framework through macroscopic (X-ray diffraction and SQUID magnetic measurement) and microscopic (HRTEM and STEM) measurements. The hollow particles retain the shape of the original nanocrystals. The nucleation of Au is found to be induced preferentially on the tip of the polyhedral nanocrystals while the etching of Ni starts from the facets leaving hollow octahedral particles consisting of 2 nm thick edges. In the presence of oleylamine, the Au tip grows and yields a heterogeneous dimer hollow-NiPt/Au. Without oleylamine, the Au nucleation is followed by Au diffusion in the Ni/Pt framework to yield a hollow single crystal Pt–Ni–Au alloy. The Pt–Ni–Au alloyed particles display a superparamagnetic behavior at room temperature.

References [1] M. Shviro, S. Polani and D. Zitoun, Nanoscale, 2015, 7, 13521 Hollow octahedral and cuboctahedral nanocrystals of ternary Pt–Ni–Au alloys

Fig: Bright-field transmission electron microscopy (TEM) of PtNi4.8 octahedral (left) and cuboctahedral nanocrystals (right).

20 nm

20nm

48

On the Crystallography of Silver Nanoparticles with Different Shape

K. Loza 1, J. Helmlinger 1, O. Prymak 1, M. Gocyla 2, M. Heggen 2, M. Epple 1

1. Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-

Essen, Universitaetsstr. 5-7, 45117 Essen, Germany 2. Ernst Ruska-Center and Peter Grünberg Institute, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

E-mail (correspondence): [email protected] Silver nanoparticles are well known for their interesting optical, biological, and electronic properties. There are many possible applications, ranging from catalysis over photonics, medical research, imaging and sensing by surface-enhanced Raman spectroscopy to energy storage and conversion. The particle properties not only depend on their size, but also on their morphology, therefore a shape-controlled synthesis of silver nanoparticles is of special interest. Silver nanoparticles with different shapes but comparable size and identical surface functionalization were prepared, i.e. spheres, platelets, cubes, and rods. The crystallographic properties of silver nanoparticles with different form were derived from X-ray powder diffraction and electron microscopy. The preferred crystallographic orientation (texture) as obtained by X-ray powder diffraction, including pole figure analysis, and high resolution transmission electron microscopy showed the crystallographic nature of the spheres (almost no texture), the cubes (terminated by {100} faces), the platelets (terminated by {111} faces), and the rods (grown from pentagonal twins along [110] and terminated by {100} faces).

FIG.1 Representative scanning electron micrograph (left) and (200) pole figure (right) of cubic Ag nanoparticles. The cubes show a distinct preferred orientation on the sample holder.

49

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