Surface structure and reactivity of
multi-component oxides at the atomic scale

@article{Jinnouchi2021,

title = {First-principles hydration free energies of oxygenated species at water–platinum interfaces},

author = {Ryosuke Jinnouchi and Ferenc Karsai and Carla Verdi and Georg Kresse},

doi = {10.1063/5.0036097},

year  = {2021},

date = {2021-03-01},

journal = {The Journal of Chemical Physics},

volume = {154},

number = {9},

pages = {094107},

publisher = {AIP Publishing},

abstract = {The hydration free energy of atoms and molecules adsorbed at liquid–solid interfaces strongly influences the stability and reactivity of solid surfaces. However, its evaluation is challenging in both experiments and theories. In this work, a machine learning aided molecular dynamics method is proposed and applied to oxygen atoms and hydroxyl groups adsorbed on Pt(111) and Pt(100) surfaces in water. The proposed method adopts thermodynamic integration with respect to a coupling parameter specifying a path from well-defined non-interacting species to the fully interacting ones. The atomistic interactions are described by a machine-learned inter-atomic potential trained on first-principles data. The free energy calculated by the machine-learned potential is further corrected by using thermodynamic perturbation theory to provide the first-principles free energy. The calculated hydration free energies indicate that only the hydroxyl group adsorbed on the Pt(111) surface attains a hydration stabilization. The observed trend is attributed to differences in the adsorption site and surface morphology.},

keywords = {P03, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Hulva2021,

title = {Unraveling CO adsorption on model single-atom catalysts},

author = {Jan Hulva and Matthias Meier and Roland Bliem and Zdenek Jakub and Florian Kraushofer and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},

doi = {10.1126/science.abe5757},

year  = {2021},

date = {2021-01-22},

urldate = {2021-01-22},

journal = {Science},

volume = {371},

number = {6527},

pages = {375--379},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Understanding how the local environment of a “single-atom” catalyst affects stability and reactivity remains a challenge. We present an in-depth study of copper_{1}, silver_{1}, gold_{1}, nickel_{1}, palladium_{1}, platinum_{1}, rhodium_{1}, and iridium_{1} species on Fe_{3}O_{4}(001), a model support in which all metals occupy the same twofold-coordinated adsorption site upon deposition at room temperature. Surface science techniques revealed that CO adsorption strength at single metal sites differs from the respective metal surfaces and supported clusters. Charge transfer into the support modifies the d-states of the metal atom and the strength of the metal–CO bond. These effects could strengthen the bond (as for Ag_{1}–CO) or weaken it (as for Ni_{1}–CO), but CO-induced structural distortions reduce adsorption energies from those expected on the basis of electronic structure alone. The extent of the relaxations depends on the local geometry and could be predicted by analogy to coordination chemistry.},

keywords = {P02, P04, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Winkler2021,

title = {How the anisotropy of surface oxide formation influences the transient activity of a surface reaction},

author = {Philipp Winkler and Johannes Zeininger and Yuri Suchorski and Michael Stöger-Pollach and Patrick Zeller and Matteo Amati and Luca Gregoratti and Günther Rupprechter},

doi = {10.1038/s41467-020-20377-9},

year  = {2021},

date = {2021-01-04},

urldate = {2021-01-04},

journal = {Nature Communications},

volume = {12},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H_{2} oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Li2021,

title = {Sum frequency generation spectroscopy in heterogeneous model catalysis: a minireview of CO-related processes},

author = {Xia Li and Günther Rupprechter},

doi = {10.1039/d0cy01736a},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Catalysis Science & Technology},

volume = {11},

number = {1},

pages = {12--26},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Sum frequency generation (SFG) vibrational spectroscopy is a unique surface/interface-sensitive method, enabling the identification of chemical species and molecular structures, densities and orientations. SFG has been proven to be a powerful probe to examine adsorbates and reactions at solid–gas interfaces related to heterogeneous catalysis, employing well-defined ultra-high vacuum (UHV) grown model catalysts and UHV-compatible high-pressure reaction cells, enabling bridging both the materials and pressure gaps. SFG was thus among the first methods for ambient pressure surface science, enabling the characterization of “high pressure adsorbates”. In this mini-review, we provide an overview of SFG studies of CO-related processes in heterogeneous model catalysis. This includes pressure- and/or temperature-dependent CO adsorption on single crystals (platinum, palladium, rhodium, iridium, copper, nickel) and oxide/graphene-supported (palladium, platinum) nanoparticles, as well as CO reactions (oxidation/hydrogenation) simultaneously monitored by SFG and mass spectrometry. The adsorption of isotopic CO mixtures on single crystals and nanoparticles provides information on the individual contributions of vibrational coupling and chemical interactions to the adsorbate–adsorbate interactions. Altogether, SFG helps to identify various adsorption sites, adsorbate structures, molecular orientations and CO reactions on prototypical catalyst surfaces of increasing complexity. Specifically, the analysis of molecular orientation (tilt angles) can be carried out by polarization-dependent SFG.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Pramhaas2020,

title = {Interplay between CO Disproportionation and Oxidation: On the Origin of the CO Reaction Onset on Atomic Layer Deposition-Grown Pt/ZrO_{2} Model Catalysts},

author = {Verena Pramhaas and Matteo Roiaz and Noemi Bosio and Manuel Corva and Christoph Rameshan and Erik Vesselli and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1021/acscatal.0c03974},

year  = {2020},

date = {2020-12-17},

urldate = {2020-12-17},

journal = {ACS Catalysis},

volume = {11},

number = {1},

pages = {208--214},

publisher = {American Chemical Society (ACS)},

abstract = {Pt/ZrO_{2} model catalysts were prepared by atomic layer deposition (ALD) and examined at mbar pressure by operando sum frequency generation (SFG) spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) combined with differentially pumped mass spectrometry (MS). ALD enables creating model systems ranging from Pt nanoparticles to bulk-like thin films. Polarization-dependent SFG of CO adsorption reveals both the adsorption configuration and the Pt particle morphology. By combining experimental data with ab initio density functional theory (DFT) calculations, we show that the CO reaction onset is determined by a delicate balance between CO disproportionation (Boudouard reaction) and oxidation. CO disproportionation occurs on low-coordinated Pt sites, but only at high CO coverages and when the remaining C atom is stabilized by a favorable coordination. Thus, under the current conditions, initial CO oxidation is found to be strongly influenced by the removal of carbon deposits formed through disproportionation mechanisms rather than being determined by the CO and oxygen inherent activity. Accordingly, at variance with the general expectation, rough Pt nanoparticles are seemingly less active than smoother Pt films. The applied approach enables bridging both the “materials and pressure gaps”.},

keywords = {P08, P10, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Haunold2020,

title = {An ultrahigh vacuum-compatible reaction cell for model catalysis under atmospheric pressure flow conditions},

author = {Thomas Haunold and Christoph Rameshan and Andrey V Bukhtiyarov and Günther Rupprechter},

doi = {10.1063/5.0026171},

year  = {2020},

date = {2020-12-01},

urldate = {2020-12-01},

journal = {Review of Scientific Instruments},

volume = {91},

number = {12},

pages = {125101},

publisher = {AIP Publishing},

abstract = {Atmospheric pressure reactions on model catalysts are typically performed in so-called high-pressure cells, with product analysis performed by gas chromatography (GC) or mass spectrometry (MS). However, in most cases, these cells have a large volume (liters) so that the reactions on catalysts with only cm^{2} surface area can be carried out only in the (recirculated) batch mode to accumulate sufficient product amounts. Herein, we describe a novel small-volume (milliliters) catalytic reactor that enables kinetic studies under atmospheric pressure flow conditions. The cell is located inside an ultrahigh vacuum chamber that is deliberately limited to basic functions. Model catalyst samples are mounted inside the reactor cell, which is locked to an oven for external heating and closed by using an extendable/retractable gas dosing tube. Reactant and product analyses are performed by both micro-GC and MS. The functionality of the new design is demonstrated by catalytic ethylene (C_{2}H_{4}) hydrogenation on polycrystalline Pt and Pd foils.},

keywords = {P08, P10, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Roekeghem2020,

title = {High-throughput study of the static dielectric constant at high temperatures in oxide and fluoride cubic perovskites},

author = {Ambroise van Roekeghem and Jesús Carrete and Stefano Curtarolo and Natalio Mingo},

doi = {10.1103/physrevmaterials.4.113804},

year  = {2020},

date = {2020-11-13},

journal = {Physical Review Materials},

volume = {4},

number = {11},

pages = {113804},

publisher = {American Physical Society (APS)},

abstract = {Using finite-temperature phonon calculations and the Lyddane-Sachs-Teller relations, we calculate ab initio the static dielectric constants of 78 semiconducting oxides and fluorides with cubic perovskite structures at 1000 K. We first compare our method with experimental measurements, and we find that it succeeds in describing the temperature dependence and the relative ordering of the static dielectric constant ε_{DC} in the series of oxides BaTiO_{3}, SrTiO_{3}, KTaO_{3}. We show that the effects of anharmonicity on the ion-clamped dielectric constant, on Born charges, and on phonon lifetimes, can be neglected in the framework of our high-throughput study. Based on the high-temperature phonon spectra, we find that the dispersion of ε_{DC} is one order of magnitude larger among oxides than fluorides at 1000 K. We display the correlograms of the dielectric constants with simple structural descriptors, and we point out that ε_{DC} is actually well correlated with the infinite-frequency dielectric constant ε_{∞}, even in those materials with phase transitions in which ε_{DC} is strongly temperature dependent.},

keywords = {P09, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Timmermann2020,

title = {IrO_{2} Surface Complexions Identified through Machine Learning and Surface Investigations},

author = {Jakob Timmermann and Florian Kraushofer and Nikolaus Resch and Peigang Li and Yu Wang and Zhiqiang Mao and Michele Riva and Yonghyuk Lee and Carsten Staacke and Michael Schmid and Christoph Scheurer and Gareth S. Parkinson and Ulrike Diebold and Karsten Reuter},

doi = {10.1103/physrevlett.125.206101},

year  = {2020},

date = {2020-11-10},

urldate = {2020-11-10},

journal = {Physical Review Letters},

volume = {125},

number = {20},

pages = {206101},

publisher = {American Physical Society (APS)},

abstract = {A Gaussian approximation potential was trained using density-functional theory data to enable a global geometry optimization of low-index rutile IrO_{2} facets through simulated annealing. Ab initio thermodynamics identifies (101) and (111) (1×1) terminations competitive with (110) in reducing environments. Experiments on single crystals find that (101) facets dominate and exhibit the theoretically predicted (1×1) periodicity and x-ray photoelectron spectroscopy core-level shifts. The obtained structures are analogous to the complexions discussed in the context of ceramic battery materials.},

keywords = {P02, P04, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Wohlfahrt2020,

title = {Ab initio structure and thermodynamics of the RPBE-D3 water/vapor interface by neural-network molecular dynamics},

author = {Oliver Wohlfahrt and Christoph Dellago and Marcello Sega},

doi = {10.1063/5.0021852},

year  = {2020},

date = {2020-10-14},

urldate = {2020-10-14},

journal = {The Journal of Chemical Physics},

volume = {153},

number = {14},

pages = {144710},

publisher = {AIP Publishing},

abstract = {Aided by a neural network representation of the density functional theory potential energy landscape of water in the Revised Perdew–Burke–Ernzerhof approximation corrected for dispersion, we calculate several structural and thermodynamic properties of its liquid/vapor interface. The neural network speed allows us to bridge the size and time scale gaps required to sample the properties of water along its liquid/vapor coexistence line with unprecedented precision.},

keywords = {P12, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Franceschi2020,

title = {Atomically resolved surface phases of La_{0.8}Sr_{0.2}MnO_{3}(110) thin films},

author = {Giada Franceschi and Michael Schmid and Ulrike Diebold and Michele Riva},

doi = {10.1039/d0ta07032g},

year  = {2020},

date = {2020-09-04},

urldate = {2020-09-04},

journal = {Journal of Materials Chemistry A},

volume = {8},

number = {43},

pages = {22947--22961},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {The atomic-scale properties of lanthanum–strontium manganite (La_{1-x}Sr_{x}MnO_{3−δ}, LSMO) surfaces are of high interest because of the roles of the material as a prototypical complex oxide, in the fabrication of spintronic devices and in catalytic applications. This work combines pulsed laser deposition (PLD) with atomically resolved scanning tunneling microscopy (STM) and surface analysis techniques (low-energy electron diffraction – LEED, X-ray photoelectron spectroscopy – XPS, and low-energy He^{+} ion scattering – LEIS) to assess the atomic properties of La_{0.8}Sr_{0.2}MnO_{3}(110) surfaces and their dependence on the surface composition. Epitaxial films with 130 nm thickness were grown on Nb-doped SrTiO_{3}(110) and their near-surface stoichiometry was adjusted by depositing La and Mn in sub-monolayer amounts, quantified with a movable quartz-crystal microbalance. The resulting surfaces were equilibrated at 700 °C under 0.2 mbar O_{2}, i.e., under conditions that bridge the gap between ultra-high vacuum and the operating conditions of high-temperature solid-oxide fuel cells, where LSMO is used as the cathode. The atomic details of various composition-related surface phases have been unveiled. The phases are characterized by distinct structural and electronic properties and vary in their ability to ccommodate deposited cations.},

keywords = {P02, pre-TACO},

pubstate = {published},

tppubtype = {article}

}