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Le Fantôme de l’Opéra - Studies on Atoms and Electrons Beneath
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-0123-631X
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The carbon dioxide reduction reaction is a promising candidate to tackle ecological challenges of our age. This is due to its capability of reducing carbon dioxide emission generated from the combustion of fossil fuels by converting carbon dioxide into valuable hydrocarbons. Oxide-derived metal nanostructures have been found to exhibit unique catalytic characteristics for facilitating the carbon dioxide reduction reaction. In this thesis work, the stability, influence, and effects of subsurface oxygen atoms are investigated by theoretical computations with various levels of theory and models. It is found that subsurface oxygen atoms are stable and that their presence increases the CO adsorption strength and coverage on oxide-derived Cu surface. This is explained by a reduced σ-repulsion and leads to the breaking of scaling relations. Although it does not directly reduce the CO dimerization barrier, the adsorption of H atoms is inhibited thus steering the selectivity. The presence of subsurface oxygen atoms is also concluded from a joint work with experimental and theoretical efforts of X-ray photoelectron spectroscopy. The precursor region of CO desorption from Ru(0001) is studied with the transition potential method. In contrast, for the simulation of the X-ray spectroscopy results on p4g C/Ni(100), which is a surface reconstruction when carbon atoms adsorb on Ni(100), vibrational effects are also needed for understanding the experimental data.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019. , p. 75
Keywords [en]
Carbon dioxide reduction, Subsurface oxygen, X-ray spectroscopy, Density functional theory, CO desorption
National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-174700ISBN: 978-91-7797-863-3 (print)ISBN: 978-91-7797-864-0 (electronic)OAI: oai:DiVA.org:su-174700DiVA, id: diva2:1359222
Public defence
2019-11-22, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2019-10-30 Created: 2019-10-08 Last updated: 2019-10-21Bibliographically approved
List of papers
1. Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction
Open this publication in new window or tab >>Subsurface Oxygen in Oxide-Derived Copper Electrocatalysts for Carbon Dioxide Reduction
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2017 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, no 1, p. 285-290Article in journal (Refereed) Published
Abstract [en]

Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-140338 (URN)10.1021/acs.jpclett.6b02273 (DOI)000391653200042 ()27983864 (PubMedID)
Available from: 2017-03-07 Created: 2017-03-07 Last updated: 2019-12-04Bibliographically approved
2. Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO2 Reduction
Open this publication in new window or tab >>Stability and Effects of Subsurface Oxygen in Oxide-Derived Cu Catalyst for CO2 Reduction
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 45, p. 25010-25017Article in journal (Refereed) Published
Abstract [en]

Oxide-derived copper (OD-Cu) catalysts are promising candidates for the electrochemical CO2 reduction reaction (CO2RR) due to the enhanced selectivity toward ethylene over methane evolution, which has been linked to the presence of subsurface oxygen (O-sb). In this work, O-sb is investigated with theoretical methods. Although O-sb is unstable in slab models, it becomes stabilized within a manually reduced OD-Cu nanocube model which was calculated by self-consistent charge density functional tight binding (SCC-DFTB). The results obtained with SCC-DFTB for the full nanocube were confirmed with subcluster models extracted from the nanocube, calculated with both density functional theory (DFT) and SCC-DFTB. The. higher stability of O-sb in the nanocube is attributed to the disordered structure and greater flexibility. The adsorption strength of CO on Cu(100) is enhanced by O-sb withdrawing electron density from the Cu atom, resulting in reduction of the sigma-repulsion. Hence, the coverage of CO may be increased, facilitating its dimerization.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-149798 (URN)10.1021/acs.jpcc.7b08269 (DOI)000416202900014 ()
Available from: 2017-12-19 Created: 2017-12-19 Last updated: 2019-12-04Bibliographically approved
3. Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization
Open this publication in new window or tab >>Amorphous, Periodic Model of a Copper Electrocatalyst with Subsurface Oxygen for Enhanced CO Coverage and Dimerization
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 8, p. 4961-4968Article in journal (Refereed) Published
Abstract [en]

Oxide-derived copper electrocatalysts have been found to possess excellent selectivity toward the production of multicarbon products from CO,. The presence of subsurface oxygen in these catalysts has been confirmed experimentally, but the resulting amorphous structure has yet to be captured by theoretical models. In this study, the role of subsurface oxygen atoms is investigated with density functional theory, using a disordered oxide-derived Cu surface model (d-ODCu). The presence of subsurface oxygen atoms increases the maximum adsorption coverage of the important CO intermediate but decreases that of H atoms because of electronic and geometric effects. However, this has no significant influence on the free-energy activation barrier or endothermicity of the CO-dimerization reaction step, allegedly the key to multicarbon product formation.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-167653 (URN)10.1021/acs.jpcc.8b12214 (DOI)000460365200033 ()
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-12-04Bibliographically approved
4. Time-resolved observation of transient precursor state of CO on Ru(0001) using carbon K-edge spectroscopy
Open this publication in new window or tab >>Time-resolved observation of transient precursor state of CO on Ru(0001) using carbon K-edge spectroscopy
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2019 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Article in journal (Refereed) Epub ahead of print
Abstract [en]

The transient dynamics of carbon monoxide (CO) molecules on a Ru(0001) surface following femtosecond optical laser pump excitation has been studied by monitoring changes in the unoccupied electronic structure using an ultrafast X-ray free-electron laser (FEL) probe. The particular symmetry of perpendicularly chemisorbed CO on the surface is exploited to investigate how the molecular orientation changes with time by varying the polarization of the FEL pulses. The time evolution of spectral features corresponding to the desorption precursor state was well distinguished due to the narrow line-width of the C K-edge in the X-ray absorption (XA) spectrum, illustrating that CO molecules in the precursor state rotated freely and resided on the surface for several picoseconds. Most of the CO molecules trapped in the precursor state ultimately cooled back down to the chemisorbed state, while we estimate that ∼14.5 ± 4.9% of the molecules in the precursor state desorbed into the gas phase. It was also observed that chemisorbed CO molecules diffused over the metal surface from on-top sites toward highly coordinated sites. In addition, a new “vibrationally hot precursor” state was identified in the polarization-dependent XA spectra.

National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-174692 (URN)10.1039/C9CP03677F (DOI)
Available from: 2019-10-08 Created: 2019-10-08 Last updated: 2019-10-09

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