1
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Sánchez-Grande A, Nguyën HC, Lauwaet K, Rodríguez-Fernández J, Carrasco E, Cirera B, Sun Z, Urgel JI, Miranda R, Lauritsen JV, Gallego JM, López N, Écija D. Electrically Tunable Reactivity of Substrate-Supported Cobalt Oxide Nanocrystals. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2106407. [PMID: 35064636 DOI: 10.1002/smll.202106407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 12/15/2021] [Indexed: 06/14/2023]
Abstract
First-row transition metal oxides are promising materials for catalyzing the oxygen evolution reaction. Surface sensitive techniques provide a unique perspective allowing the study of the structure, adsorption sites, and reactivity of catalysts at the atomic scale, which furnishes rationalization and improves the design of highly efficient catalytic materials. Here, a scanning probe microscopy study complemented by density functional theory on the structural and electronic properties of CoO nanoislands grown on Au(111) is reported. Two distinct phases are observed: The most extended displays a Moiré pattern (α-region), while the less abundant is 1Co:1Au coincidental (β-region). As a result of the surface registry, in the β-region the oxide adlayer is compressed by 9%, increasing the unoccupied local density of states and enhancing the selective water adsorption at low temperature through a cobalt inversion mechanism. Tip-induced voltage pulses irreversibly transform α- into β-regions, thus opening avenues to modify the structure and reactivity of transition metal oxides by external stimuli like electric fields.
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Affiliation(s)
| | - Huu Chuong Nguyën
- Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Tarragona, 43007, Spain
| | | | | | | | | | - Zhaozong Sun
- Interdisciplinary Nanoscience Center, Aarhus University, Aarhus C, DK-8000, Denmark
| | | | - Rodolfo Miranda
- IMDEA Nanociencia., Madrid, 28049, Spain
- Dep. Física de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, Madrid, 28049, Spain
| | - Jeppe V Lauritsen
- Interdisciplinary Nanoscience Center, Aarhus University, Aarhus C, DK-8000, Denmark
| | - José M Gallego
- Instituto de Ciencias Materiales - CSIC, Cantoblanco, Madrid, 28049, Spain
| | - Nuria López
- Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Tarragona, 43007, Spain
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2
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Hein D, Wartner G, Bergmann A, Bernal M, Roldan Cuenya B, Seidel R. Reversible Water-Induced Phase Changes of Cobalt Oxide Nanoparticles. ACS NANO 2020; 14:15450-15457. [PMID: 33103880 DOI: 10.1021/acsnano.0c06066] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Cobalt oxides have been identified as highly active catalysts for the electrochemical water splitting and oxygen evolution reaction. Using near-ambient pressure resonant photoelectron spectroscopy, we studied changes in the metal-oxygen coordination of size-selected core-shell CoOx nanoparticles induced by liquid water. In dry conditions, the nanoparticles exhibit an octahedrally coordinated Co2+ core and a tetrahedrally coordinated Co2+ shell. In the presence of liquid water, we observe a reversible phase change of the nanoparticle shell into octahedrally coordinated Co2+ as well as partially oxidized octahedrally coordinated Co3+. This is in contrast to previous findings, suggesting an irreversible phase change of tetrahedrally coordinated Co2+ after the oxygen evolution reaction conditioning. Our results demonstrate the appearance of water-induced structural changes different from voltage-induced changes and help us to understand the atomic scale interaction of CoOx nanoparticles with water in electrochemical processes.
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Affiliation(s)
- Dennis Hein
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany
| | - Garlef Wartner
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany
| | - Arno Bergmann
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany
| | - Miguel Bernal
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany
- Department of Physics, Ruhr-University Bochum, 44780 Bochum, Germany
| | - Beatriz Roldan Cuenya
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany
| | - Robert Seidel
- Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany
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3
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Xiang F, Schmitt T, Raschmann M, Schneider MA. Adsorption and self-assembly of porphyrins on ultrathin CoO films on Ir(100). BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2020; 11:1516-1524. [PMID: 33094085 PMCID: PMC7554680 DOI: 10.3762/bjnano.11.134] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 09/22/2020] [Indexed: 06/11/2023]
Abstract
Porphyrins represent a versatile class of molecules, the adsorption behavior of which on solid surfaces is of fundamental interest due to a variety of potential applications. We investigate here the molecule-molecule and molecule-substrate interaction of Co-5,15-diphenylporphyrin (Co-DPP) and 2H-tetrakis(p-cyanophenyl)porphyrin (2H-TCNP) on one bilayer (1BL) and two bilayer (2BL) thick cobalt oxide films on Ir(100) by scanning tunneling microscopy (STM) and density functional theory (DFT). The two substrates differ greatly with respect to their structural and potential-energy landscape corrugation with immediate consequences for adsorption and self-assembly of the molecules studied. On both films, an effective electronic decoupling from the metal substrate is achieved. However, on the 1BL film, Co-DPP molecules are sufficiently mobile at 300 K and coalesce to self-assembled molecular islands when cooled to 80 K despite their rather weak intermolecular interaction. In contrast, on the 2BL film, due to the rather flat potential landscape, molecular rotation is thermally activated, which effectively prevents self-assembly. The situation is different for 2H-TCNPP, which, due to the additional functional anchoring groups, does not self-assemble on the 1BL film but forms self-assembled compact islands on the 2BL film. The findings demonstrate the guiding effect of the cobalt oxide films of different thickness and the effect of functional surface anchoring.
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Affiliation(s)
- Feifei Xiang
- Solid State Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - Tobias Schmitt
- Solid State Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - Marco Raschmann
- Solid State Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
| | - M Alexander Schneider
- Solid State Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
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4
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Kersell H, Hooshmand Z, Yan G, Le D, Nguyen H, Eren B, Wu CH, Waluyo I, Hunt A, Nemšák S, Somorjai G, Rahman TS, Sautet P, Salmeron M. CO Oxidation Mechanisms on CoOx-Pt Thin Films. J Am Chem Soc 2020; 142:8312-8322. [DOI: 10.1021/jacs.0c01139] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Heath Kersell
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Zahra Hooshmand
- Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
| | - George Yan
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States
| | - Duy Le
- Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
| | - Huy Nguyen
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States
| | - Baran Eren
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Cheng Hao Wu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Iradwikanari Waluyo
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Adrian Hunt
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Slavomír Nemšák
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Gabor Somorjai
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Talat S. Rahman
- Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
| | - Philippe Sautet
- Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United States
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Miquel Salmeron
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Materials Science and Engineering, University of California, Berkeley, California 94720, United States
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5
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De Santis M, Bailly A, Coates I, Grenier S, Heckmann O, Hricovini K, Joly Y, Langlais V, Ramos AY, Richter C, Torrelles X, Garaudée S, Geaymond O, Ulrich O. Epitaxial growth and structure of cobalt ferrite thin films with large inversion parameter on Ag(001). ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2019; 75:8-17. [PMID: 32830773 DOI: 10.1107/s2052520618016177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 11/14/2018] [Indexed: 06/11/2023]
Abstract
Cobalt ferrite ultrathin films with the inverse spinel structure are among the best candidates for spin filtering at room temperature. High-quality epitaxial CoFe2O4 films about 4 nm thick have been fabricated on Ag(001) following a three-step method: an ultrathin metallic CoFe2 alloy was first grown in coherent epitaxy on the substrate and then treated twice with O2, first at room temperature and then during annealing. The epitaxial orientation and the surface, interface and film structure were resolved using a combination of low-energy electron diffraction, scanning tunnelling microscopy, Auger electron spectroscopy and in situ grazing-incidence X-ray diffraction. A slight tetragonal distortion was observed, which should drive the easy magnetization axis in-plane due to the large magneto-elastic coupling of such a material. The so-called inversion parameter, i.e. the Co fraction occupying octahedral sites in the ferrite spinel structure, is a key element for its spin-dependent electronic gap. It was obtained through in situ resonant X-ray diffraction measurements collected at both the Co and Fe K edges. The data analysis was performed using FDMNES, an ab initio program already extensively used to simulate X-ray absorption spectroscopy, and shows that the Co ions are predominantly located on octahedral sites with an inversion parameter of 0.88 (5). Ex situ X-ray photoelectron spectroscopy gives an estimation in accordance with the values obtained through diffraction analysis.
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Affiliation(s)
- Maurizio De Santis
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Aude Bailly
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Ian Coates
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Stéphane Grenier
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Olivier Heckmann
- LMPS, Université de Cergy-Pontoise, Neuville/Oise, Cergy-Pontoise 95031, France
| | - Karol Hricovini
- LMPS, Université de Cergy-Pontoise, Neuville/Oise, Cergy-Pontoise 95031, France
| | - Yves Joly
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | | | - Aline Y Ramos
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Christine Richter
- LMPS, Université de Cergy-Pontoise, Neuville/Oise, Cergy-Pontoise 95031, France
| | - Xavier Torrelles
- Institut de Ciència de Materials de Barcelona (ICMAB), CSIC, Bellaterra, Barcelona 08193, Spain
| | - Stéphanie Garaudée
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Olivier Geaymond
- Institut Néel, Université Grenoble Alpes, CNRS, Grenoble INP, Grenoble 38042, France
| | - Olivier Ulrich
- INAC/MEM, Université Grenoble Alpes, CEA, Grenoble 38054, France
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6
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Roca AG, Golosovsky IV, Winkler E, López-Ortega A, Estrader M, Zysler RD, Baró MD, Nogués J. Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1703963. [PMID: 29479814 DOI: 10.1002/smll.201703963] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 01/19/2018] [Indexed: 06/08/2023]
Abstract
Although cubic rock salt-CoO has been extensively studied, the magnetic properties of the main nanoscale CoO polymorphs (hexagonal wurtzite and cubic zinc blende structures) are rather poorly understood. Here, a detailed magnetic and neutron diffraction study on zinc blende and wurtzite CoO nanoparticles is presented. The zinc blende-CoO phase is antiferromagnetic with a 3rd type structure in a face-centered cubic lattice and a Néel temperature of TN (zinc-blende) ≈225 K. Wurtzite-CoO also presents an antiferromagnetic order, TN (wurtzite) ≈109 K, although much more complex, with a 2nd type order along the c-axis but an incommensurate order along the y-axis. Importantly, the overall magnetic properties are overwhelmed by the uncompensated spins, which confer the system a ferromagnetic-like behavior even at room temperature.
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Affiliation(s)
- Alejandro G Roca
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, E-08193, Barcelona, Spain
| | - Igor V Golosovsky
- National Research Center "Kurchatov Institute", B.P. Konstantinov, St. Petersburg Nuclear Physics Institute, 188300, Gatchina, Russia
| | - Elin Winkler
- Centro Atómico Bariloche, CNEA-CONICET, 8400, S.C. de Bariloche, Río Negro, Argentina
| | | | - Marta Estrader
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, E-08193, Barcelona, Spain
| | - Roberto D Zysler
- Centro Atómico Bariloche, CNEA-CONICET, 8400, S.C. de Bariloche, Río Negro, Argentina
| | - María Dolors Baró
- Departament de Física, Universitat Autònoma de Barcelona, 08193, Bellaterra, Cerdanyola del Vallès, Spain
| | - Josep Nogués
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, E-08193, Barcelona, Spain
- ICREA, Pg. Lluís Companys 23, E-08010, Barcelona, Spain
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7
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Mohr S, Schmitt T, Döpper T, Xiang F, Schwarz M, Görling A, Schneider MA, Libuda J. Coverage-Dependent Anchoring of 4,4'-Biphenyl Dicarboxylic Acid to CoO(111) Thin Films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4178-4188. [PMID: 28402643 DOI: 10.1021/acs.langmuir.7b00465] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We investigated the adsorption behavior of 4,4'-biphenhyl dicarboxylic acid (BDA) on well-ordered CoO(111) films grown on Ir(100) as a function of coverage and temperature using time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) in combination with density functional theory (DFT) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. To compare the binding behavior of BDA as a function of the oxide film thickness, three different CoO(111) film thicknesses were explored: films of about 20 bilayers (BLs) (approximately 5 nm), 2 BLs, and 1 BL. The two carboxylic acid groups of BDA offer two potential anchoring points to the oxide surface. At 150 K, intact BDA adsorbs on 20 BL thick oxide films in planar geometry with the phenyl rings aligned parallel to the surface. With decreasing oxide film thickness, we observe an increasing tendency for deprotonation and the formation of flat-lying BDA molecules anchored as dicarboxylates. After saturation of the first monolayer, intact BDA multilayers grow with molecules aligned parallel to the surface. The BDA multilayer desorbs at around 360 K. Completely different growth behavior is observed if BDA is deposited above the multilayer desorption temperature. Initially, doubly deprotonated dicarboxylates are formed by adopting a flat-lying orientation. With increasing exposure, however, the adsorbate layer transforms into upright standing monocarboxylates. A sharp OH stretching band (3584 cm-1) and a blue-shifted CO stretching band (1759 cm-1) indicate weakly interacting apical carboxylic acid groups at the vacuum interface. The anchored monocarboxylate phase slowly desorbs in a temperature range of up to 470 K. At higher temperature, a flat-lying doubly deprotonated BDA is formed, which desorbs and decomposes in a temperature range of up to 600 K.
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Affiliation(s)
- Susanne Mohr
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Tobias Schmitt
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Tibor Döpper
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Feifei Xiang
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Matthias Schwarz
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Andreas Görling
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - M Alexander Schneider
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
| | - Jörg Libuda
- Lehrstuhl für Physikalische Chemie II, ‡Lehrstuhl für Festkörperphysik, §Lehrstuhl für Theoretische Chemie, and ∥Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany
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8
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Fester J, Walton A, Li Z, Lauritsen JV. Gold-supported two-dimensional cobalt oxyhydroxide (CoOOH) and multilayer cobalt oxide islands. Phys Chem Chem Phys 2017; 19:2425-2433. [DOI: 10.1039/c6cp07901f] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Synthesis and characterization of layered cobalt oxides for model studies of electrochemical water splitting catalysts.
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Affiliation(s)
- Jakob Fester
- Interdisciplinary Nanoscience Center (iNANO)
- Aarhus University
- 8000 Aarhus C
- Denmark
| | - Alex Walton
- Interdisciplinary Nanoscience Center (iNANO)
- Aarhus University
- 8000 Aarhus C
- Denmark
| | - Zheshen Li
- ISA
- Aarhus University
- 8000 Aarhus C
- Denmark
| | - Jeppe V. Lauritsen
- Interdisciplinary Nanoscience Center (iNANO)
- Aarhus University
- 8000 Aarhus C
- Denmark
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9
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Xu T, Schwarz M, Werner K, Mohr S, Amende M, Libuda J. Structure-Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic Acid on Co3O4(111), CoO(100), and CoO(111). Chemistry 2016; 22:5384-96. [PMID: 26934313 DOI: 10.1002/chem.201504810] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Indexed: 12/21/2022]
Abstract
We have performed a model study to explore the influence of surface structure on the anchoring of organic molecules on oxide materials. Specifically, we have investigated the adsorption of phthalic acid (PA) on three different, well-ordered, and atomically defined cobalt oxide surfaces, namely 1) Co3O4(111), 2) CoO(111), and 3) CoO(100) on Ir(100). PA was deposited by physical vapor deposition (PVD). The formation of the PA films and interfacial reactions were monitored in situ during growth by isothermal time-resolved IR reflection absorption spectroscopy (TR-IRAS) under ultrahigh vacuum (UHV) conditions. We observed a pronounced structure dependence on the three surfaces with three distinctively different binding geometries and characteristic differences depending on the temperature and coverage. 1) PA initially binds to Co3O4(111) through the formation of a chelating bis-carboxylate with the molecular plane oriented perpendicularly to the surface. Similar species were observed both at low temperature (130 K) and at room temperature (300 K). With increasing exposure, chelating mono-carboxylates became more abundant and partially replaced the bis-carboxylate. 2) PA binds to CoO(100) in the form of a bridging bis-carboxylate for low coverage. Upon prolonged deposition of PA at low temperature, the bis-carboxylates were converted into mono-carboxylate species. In contrast, the bis-carboxylate layer was very stable at 300 K. 3) For CoO(111) we observed a temperature-dependent change in the adsorption mechanism. Although PA binds as a mono-carboxylate in a bridging bidentate fashion at low temperature (130 K), a strongly distorted bis-carboxylate was formed at 300 K, possibly as a result of temperature-dependent restructuring of the surface. The results show that the adsorption geometry of PA depends on the atomic structure of the oxide surface. The structure dependence can be rationalized by the different arrangements of cobalt ions at the three surfaces.
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Affiliation(s)
- Tao Xu
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax
| | - Matthias Schwarz
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax
| | - Kristin Werner
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax
| | - Susanne Mohr
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax
| | - Max Amende
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax
| | - Jörg Libuda
- Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany), Fax. .,Erlangen Catalysis Resource Center and Interdisciplinary Center Interface Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany.
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10
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Otto S, Fauster T. Two-photon photoemission from CoO layers on Ir(1 0 0). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:055001. [PMID: 26789862 DOI: 10.1088/0953-8984/28/5/055001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Two-photon photoelectron spectroscopy is used to study the unoccupied electronic states of cobalt oxide layers on Ir(1 0 0). For thicker layers of (1 0 0) orientation the conduction band minimum is found 2 eV above the Fermi level. Layers with (1 1 1) orientation and thickness ≤4 bilayers show a peak around 3.4 eV energy and no evidence for the conduction band minimum. This is attributed to the metallic character of thin CoO(1 1 1) layers.
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Affiliation(s)
- Sebastian Otto
- Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstrasse 7, D-91058 Erlangen, Germany
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11
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Walton AS, Fester J, Bajdich M, Arman MA, Osiecki J, Knudsen J, Vojvodic A, Lauritsen JV. Interface controlled oxidation states in layered cobalt oxide nanoislands on gold. ACS NANO 2015; 9:2445-2453. [PMID: 25693621 DOI: 10.1021/acsnano.5b00158] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Layered cobalt oxides have been shown to be highly active catalysts for the oxygen evolution reaction (OER; half of the catalytic "water splitting" reaction), particularly when promoted with gold. However, the surface chemistry of cobalt oxides and in particular the nature of the synergistic effect of gold contact are only understood on a rudimentary level, which at present prevents further exploration. We have synthesized a model system of flat, layered cobalt oxide nanoislands supported on a single crystal gold (111) substrate. By using a combination of atom-resolved scanning tunneling microscopy, X-ray photoelectron and absorption spectroscopies and density functional theory calculations, we provide a detailed analysis of the relationship between the atomic-scale structure of the nanoislands, Co oxidation states and substrate induced charge transfer effects in response to the synthesis oxygen pressure. We reveal that conversion from Co(2+) to Co(3+) can occur by a facile incorporation of oxygen at the interface between the nanoisland and gold, changing the islands from a Co-O bilayer to an O-Co-O trilayer. The O-Co-O trilayer islands have the structure of a single layer of β-CoOOH, proposed to be the active phase for the OER, making this system a valuable model in understanding of the active sites for OER. The Co oxides adopt related island morphologies without significant structural reorganization, and our results directly demonstrate that nanosized Co oxide islands have a much higher structural flexibility than could be predicted from bulk properties. Furthermore, it is clear that the gold/nanoparticle interface has a profound effect on the structure of the nanoislands, suggesting a possible promotion mechanism.
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Affiliation(s)
- Alex S Walton
- †Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000 Aarhus C, Denmark
| | - Jakob Fester
- †Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000 Aarhus C, Denmark
| | - Michal Bajdich
- ‡SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 San Hill Road, Menlo Park, California 94025, United States
| | - Mohammad A Arman
- §Division of Synchrotron Radiation Research, Department of Physics, Lund University, 221 00 Lund, Sweden
| | - Jacek Osiecki
- ⊥MAX IV Laboratory, Lund University, 221 00 Lund, Sweden
| | - Jan Knudsen
- §Division of Synchrotron Radiation Research, Department of Physics, Lund University, 221 00 Lund, Sweden
- ⊥MAX IV Laboratory, Lund University, 221 00 Lund, Sweden
| | - Aleksandra Vojvodic
- ‡SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, 2575 San Hill Road, Menlo Park, California 94025, United States
| | - Jeppe V Lauritsen
- †Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000 Aarhus C, Denmark
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12
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Lamirand AD, Soares MM, De Santis M, Ramos AY, Grenier S, Tolentino HCN. Strain driven monoclinic distortion of ultrathin CoO films in the exchange-coupled CoO/FePt/Pt(0 0 1) system. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:085001. [PMID: 25604708 DOI: 10.1088/0953-8984/27/8/085001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The structure and strain of ultrathin CoO films grown on a Pt(0 0 1) substrate and on a ferromagnetic FePt pseudomorphic layer on Pt(0 0 1) have been determined with in situ and real time surface x-ray diffraction. The films grow epitaxially on both surfaces with an in-plane hexagonal pattern that yields a pseudo-cubic CoO(1 1 1) surface. A refined x-ray diffraction analysis reveals a slight monoclinic distortion at RT induced by the anisotropic stress at the interface. The tetragonal contribution to the distortion results in a ratio [Formula: see text], opposite to that found in the low temperature bulk CoO phase. This distortion leads to a stable Co(2+) spin configuration within the plane of the film.
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Affiliation(s)
- Anne D Lamirand
- Université Grenoble Alpes, Institut Néel, F-38042 Grenoble, France. CNRS, Institut Néel, F-38042 Grenoble, France
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13
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Mehl S, Ferstl P, Schuler M, Toghan A, Brummel O, Hammer L, Schneider MA, Libuda J. Thermal evolution of cobalt deposits on Co3O4(111): atomically dispersed cobalt, two-dimensional CoO islands, and metallic Co nanoparticles. Phys Chem Chem Phys 2015; 17:23538-46. [DOI: 10.1039/c5cp03922c] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cobalt deposition onto Co3O4(111) leads to formation of atomically dispersed cobalt species, which form ordered two-dimensional oxide islands upon annealing.
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Affiliation(s)
- S. Mehl
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - P. Ferstl
- Lehrstuhl für Festkörperphysik
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - M. Schuler
- Lehrstuhl für Festkörperphysik
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - A. Toghan
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
- Chemistry Department
| | - O. Brummel
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - L. Hammer
- Lehrstuhl für Festkörperphysik
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - M. A. Schneider
- Lehrstuhl für Festkörperphysik
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - J. Libuda
- Lehrstuhl für Physikalische Chemie II
- Friedrich-Alexander-Universität Erlangen-Nürnberg
- 91058 Erlangen
- Germany
- Erlangen Catalysis Resource Center
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14
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Electrosynthesis of Co/PPy nanocomposites for ORR electrocatalysis: a study based on quasi-in situ X-ray absorption, fluorescence and in situ Raman spectroscopy. Electrochim Acta 2014. [DOI: 10.1016/j.electacta.2014.05.098] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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15
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Lu A, Chen Y, Zeng D, Li M, Xie Q, Zhang X, Peng DL. Shape-related optical and catalytic properties of wurtzite-type CoO nanoplates and nanorods. NANOTECHNOLOGY 2014; 25:035707. [PMID: 24356716 DOI: 10.1088/0957-4484/25/3/035707] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
In this paper, we report the anisotropic optical and catalytic properties of wurtzite-type hexagonal CoO (h-CoO) nanocrystals, an unusual nanosized indirect semiconductor material. h-CoO nanoplates and nanorods with a divided morphology have been synthesized via facile solution methods. The employment of flash-heating and surfactant tri-n-octylphosphine favors the formation of plate-like morphology, whereas the utilization of cobalt stearate as a precursor is critical for the synthesis of nanorods. Structural analyses indicate that the basal plane of the nanoplates is (001) face and the growth direction of the nanorods is along the c axis. Moreover, the UV–vis absorption spectra, the corresponding energy gap and the catalytic properties are found to vary with the crystal shape and the dimensions of the as-prepared h-CoO nanocrystals. Furthermore, remarkable catalytic activities for H2 generation from the hydrolysis of alkaline NaBH4 solutions have been observed for the as-prepared h-CoO nanocrystals. The calculated Arrhenius activation energies show a decreasing trend with increasing extension degree along the <001> direction, which is in agreement with the variation of the charge-transfer energy gap. Finally the maximum hydrogen generation rate of the h-CoO nanoplates exceeds most of the reported values of transition metal or noble metal containing catalysts performing in the same reaction system, which makes them a low-cost alternative to commonly used noble metal catalysts in H2 generation from the hydrolysis of borohydrides, and might find potential applications in the field of green energy.
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16
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Luo W, Asthagiri A. An ab initio thermodynamics study of cobalt surface phases under ethanol steam reforming conditions. Catal Sci Technol 2014. [DOI: 10.1039/c4cy00582a] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A combination of DFT and ab initio atomistic thermodynamics study illustrated the surface structure evolution of Co0/Co2+ catalysts under ethanol steam reforming conditions.
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Affiliation(s)
- Wenjia Luo
- William G. Lowrie Department of Chemical and Biomolecular Engineering
- The Ohio State University
- Columbus, USA
| | - Aravind Asthagiri
- William G. Lowrie Department of Chemical and Biomolecular Engineering
- The Ohio State University
- Columbus, USA
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17
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Woodruff DP. Quantitative Structural Studies Of Corundum and Rocksalt Oxide Surfaces. Chem Rev 2013; 113:3863-86. [DOI: 10.1021/cr3002998] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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18
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Walsh SR, Rusakova I, Whitmire KH. Rock salt vs. wurtzite phases of Co1−xMnxO: control of crystal lattice and morphology at the nanoscale. CrystEngComm 2013. [DOI: 10.1039/c2ce26440d] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Affiliation(s)
- Claudine Noguera
- Institut des Nanosciences de Paris, UMR 7588, CNRS, and Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
| | - Jacek Goniakowski
- Institut des Nanosciences de Paris, UMR 7588, CNRS, and Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
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20
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Gubo M, Ebensperger C, Meyer W, Hammer L, Heinz K, Mittendorfer F, Redinger J. Tuning the growth orientation of epitaxial films by interface chemistry. PHYSICAL REVIEW LETTERS 2012; 108:066101. [PMID: 22401090 DOI: 10.1103/physrevlett.108.066101] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Indexed: 05/31/2023]
Abstract
The support of epitaxial films frequently determines their crystallographic orientation, which is of crucial importance for their properties. We report a novel way to alter the film orientation without changing the substrate. We show for the growth of CoO on the Ir(100) surface that, while the oxide grows in (111) orientation on the bare substrate, the orientation switches to (100) by introducing a single (or a few) monolayer(s) of Co between the oxide and substrate. This tunability of the orientation of epitaxial films by the appropriate choice of interface chemistry most likely is a general feature.
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Affiliation(s)
- Matthias Gubo
- Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Erlangen, Germany
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21
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Pandey M, Pala RGS. Stabilization and growth of non-native nanocrystals at low and atmospheric pressures. J Chem Phys 2012; 136:044703. [DOI: 10.1063/1.3678181] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
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22
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Nam KM, Choi YC, Jung SC, Kim YI, Jo MR, Park SH, Kang YM, Han YK, Park JT. [100] Directed Cu-doped h-CoO nanorods: elucidation of the growth mechanism and application to lithium-ion batteries. NANOSCALE 2012; 4:473-477. [PMID: 22095097 DOI: 10.1039/c1nr11128k] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Thermal decomposition of Co(acac)(3) and Cu(acac)(2) in benzylamine leads to the formation of [100] directed Cu-doped h-CoO nanorods, which are very stable in an aqueous solution. The formation mechanism of the [100] directed Cu-doped h-CoO nanorods is fully elucidated by using first-principles calculations, demonstrating that Cu-doping not only changes the growth direction but also enhances the stability of the nanorods significantly. Evaluation of the electrochemical performance of Cu-doped h-CoO nanorods shows high initial Coulombic efficiency and ultrahigh capacity with excellent cycling performance, indicating their suitability as an anode material for next generation lithium-ion batteries.
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Affiliation(s)
- Ki Min Nam
- Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Korea
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23
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Gragnaniello L, Barcaro G, Sementa L, Allegretti F, Parteder G, Surnev S, Steurer W, Fortunelli A, Netzer FP. The two-dimensional cobalt oxide (9 × 2) phase on Pd(100). J Chem Phys 2011; 134:184706. [DOI: 10.1063/1.3578187] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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24
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Papaefthimiou V, Dintzer T, Dupuis V, Tamion A, Tournus F, Teschner D, Hävecker M, Knop-Gericke A, Schlögl R, Zafeiratos S. When a Metastable Oxide Stabilizes at the Nanoscale: Wurtzite CoO Formation upon Dealloying of PtCo Nanoparticles. J Phys Chem Lett 2011; 2:900-904. [PMID: 26295626 DOI: 10.1021/jz2003155] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Ambient pressure photoelectron and absorption spectroscopies were applied under 0.2 mbar of O2 and H2 to establish an unequivocal correlation between the surface oxidation state of extended and nanosized PtCo alloys and the gas-phase environment. Fundamental differences in the electronic structure and reactivity of segregated cobalt oxides were associated with surface stabilization of metastable wurtzite-CoO. In addition, the promotion effect of Pt in the reduction of cobalt oxides was pronounced at the nanosized particles but not at the extended foil.
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Affiliation(s)
- Vasiliki Papaefthimiou
- †Laboratoire LMSPC, UMR7515 CNRS-Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
| | - Thierry Dintzer
- †Laboratoire LMSPC, UMR7515 CNRS-Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
| | - Véronique Dupuis
- ‡Laboratoire PMCN UMR 5586, University Lyon 1, CNRS, F-69622 Villeurbanne cedex, France
| | - Alexandre Tamion
- ‡Laboratoire PMCN UMR 5586, University Lyon 1, CNRS, F-69622 Villeurbanne cedex, France
| | - Florent Tournus
- ‡Laboratoire PMCN UMR 5586, University Lyon 1, CNRS, F-69622 Villeurbanne cedex, France
| | - Detre Teschner
- §Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Michael Hävecker
- §Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Axel Knop-Gericke
- §Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Robert Schlögl
- §Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Spiros Zafeiratos
- †Laboratoire LMSPC, UMR7515 CNRS-Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France
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25
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Papaefthimiou V, Dintzer T, Dupuis V, Tamion A, Tournus F, Hillion A, Teschner D, Hävecker M, Knop-Gericke A, Schlögl R, Zafeiratos S. Nontrivial redox behavior of nanosized cobalt: new insights from ambient pressure X-ray photoelectron and absorption spectroscopies. ACS NANO 2011; 5:2182-2190. [PMID: 21309559 DOI: 10.1021/nn103392x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The reduction and oxidation of carbon-supported cobalt nanoparticles (3.50±0.22 nm) and a Co (0001) single crystal was investigated by ambient pressure X-ray photoelectron (APPES) and X-ray absorption (XAS) spectroscopies, applied in situ under 0.2 mbar hydrogen or oxygen atmospheres and at temperatures up to 620 K. It was found that cobalt nanoparticles are readily oxidized to a distinct CoO phase, which is significantly more stable to further oxidation or reduction compared to the thick oxide films formed on the Co(0001) crystal. The nontrivial size-dependence of redox behavior is followed by a difference in the electronic structure as suggested by theoretical simulations of the Co L-edge absorption spectra. In particular, contrary to the stable rocksalt and spinel phases that exist in the bulk oxides, cobalt nanoparticles contain a significant portion of metastable wurtzite-type CoO.
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Affiliation(s)
- Vasiliki Papaefthimiou
- Laboratoire LMSPC UMR7515, CNRS, University of Strasbourg, F-67087, Strasbourg cedex 2, France
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26
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Abstract
Most metals are oxidized under ambient conditions, and metal oxides show interesting and technologically promising properties. This has motivated much recent research on oxide surfaces. The combination of scanning tunneling microscopy with first-principles density functional theory–based computational techniques provides an atomic-scale view of the properties of metal-oxide materials. Surface polarity is a key concept for predicting the stability of oxide surfaces and is discussed using ZnO as an example. This review also highlights the role of surface defects for surface reactivity, and their interplay with defects in the bulk, for the case of TiO2. Ultrathin metal-oxide films, grown either through reactive evaporation on metal single crystals or through oxidation of metal alloys (such as Al2O3/NiAl), have gained popularity as supports for planar model catalysts. The surface oxides that form upon oxidation on Pt-group metals (e.g., Ru, Rh, Pd, and Pt) are considered as model systems for CO oxidation.
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Affiliation(s)
- Ulrike Diebold
- Department of Physics, Tulane University, New Orleans, Louisiana 70118
| | - Shao-Chun Li
- Department of Physics, Tulane University, New Orleans, Louisiana 70118
| | - Michael Schmid
- Institut für Allgemeine Physik, Technische Universität Wien, A-1040 Vienna, Austria
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Gubo M, Ebensperger C, Meyer W, Hammer L, Heinz K. Substoichiometric cobalt oxide monolayer on Ir(100)-(1 × 1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:474211. [PMID: 21832490 DOI: 10.1088/0953-8984/21/47/474211] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A substoichiometric monolayer of cobalt oxide has been prepared by deposition and oxidation of slightly less than one monolayer of cobalt on the unreconstructed surface of Ir(100). The ultrathin film was investigated by scanning tunnelling microscopy (STM) and quantitative low-energy electron diffraction (LEED). The cobalt species of the film reside in or near hollow positions of the substrate with, however, unoccupied sites (vacancies) in a 3 × 3 arrangement. In the so-formed 3 × 3 supercell the oxide's oxygen species are both threefold and fourfold coordinated to cobalt, forming pyramids with a triangular and square cobalt basis, respectively. These pyramids are the building blocks of the oxide. Due to the reduced coordination as compared to the sixfold one in the bulk of rock-salt-type CoO, the Co-O bond lengths are smaller than in the latter. For the threefold coordination they compare very well with the bond length in oxygen terminated CoO(111) films investigated recently. The substoichiometric 3 × 3 oxide monolayer phase transforms to a stoichiometric c(10 × 2)-periodic oxide monolayer under oxygen exposure, in which, however, cobalt and oxygen species are in (111) orientation and so form a CoO(111) layer.
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Affiliation(s)
- M Gubo
- Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstraße 7, D-91058 Erlangen, Germany
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28
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Biedermann K, Gubo M, Hammer L, Heinz K. Phases and phase transitions of hexagonal cobalt oxide films on Ir(100)-(1 × 1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:185003. [PMID: 21825449 DOI: 10.1088/0953-8984/21/18/185003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Cobalt oxides on the unreconstructed Ir(100) surface were prepared by reactive deposition of Co established by simultaneous oxygen flux at about 50 °C and subsequent annealing. The films were investigated by low-energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and thermal desorption spectroscopy (TDS). We show that in spite of the quadratic unit mesh of the substrate, oxide films of (111) orientation develop. As long as oxygen-rich conditions are maintained they are of spinel-type Co(3)O(4)(111). They are non-pseudomorphic and transform to rocksalt-type CoO(111) when oxygen loss is induced by annealing at elevated temperatures. Thin films of CoO(111) are commensurate, and so, in order to realize that, they exhibit a slightly distorted unit cell when below a thickness equivalent to about seven cobalt monolayers. With increasing film thickness the uniaxial strain accompanied by the commensurability is gradually relieved by the insertion of dislocations so that eventually the film assumes ideal hexagonality. All CoO(111)-type surfaces are reconstructed at low sample temperatures equivalent to a [Formula: see text] superstructure. They reversibly transform into a (1 × 1) phase at about 50 °C.
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Affiliation(s)
- K Biedermann
- Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstraße 7, D-91058 Erlangen, Germany
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29
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Meyerheim HL, Tusche C, Ernst A, Ostanin S, Maznichenko IV, Mohseni K, Jedrecy N, Zegenhagen J, Roy J, Mertig I, Kirschner J. Wurtzite-type CoO nanocrystals in ultrathin ZnCoO films. PHYSICAL REVIEW LETTERS 2009; 102:156102. [PMID: 19518654 DOI: 10.1103/physrevlett.102.156102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2008] [Indexed: 05/27/2023]
Abstract
Surface x-ray diffraction experiments reveal that, in cobalt-doped ZnO films two to five monolayers thick, Wurtzite-type CoO nanocrystals are coherently embedded within a hexagonal boron-nitride- (h-BN)-type ZnO matrix, supporting the model of a phase separation. First-principles calculations confirm that, in contrast with ZnO, the formation of h-BN-type CoO is unfavorable in the ultrathin film limit. Our results are important for understanding magnetic properties of transition metal-doped semiconductors in general.
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Affiliation(s)
- H L Meyerheim
- Max-Planck-Institut für Mikrostrukturphysik, D-06120 Halle, Germany
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