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January 2024
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9 Reads
Physical Chemistry Chemical Physics
Correction for ‘Optical bands of dodecanuclear compounds H 4 PVMo 11 O 40 · y H 2 O with Keggin structure. Semiclassical vibronic model’ by S. Klokishner et al. , Phys. Chem. Chem. Phys. , 2004, 6 , 2066–2082, https://doi.org/10.1039/B312753B.
December 2023
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68 Reads
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5 Citations
Catalysis Science & Technology
Water splitting is a promising technology in the path towards complete renewable energy within the hydrogen economy but overcoming the sluggishness of the oxygen evolution reaction (OER) is a major challenge. Iridium-based oxides remain the most attractive materials for the OER under acidic conditions since they offer the combination of activity and stability. Gaining knowledge about how these materials have such an ability is of great interest to develop improved electrocatalysts for the OER. Among the different iridium-based oxides the materials with high concentrations of electron deficient oxygen (O I−) have been shown to have higher OER activity, however, they also have high dissolution rates, seemingly due to the presence or formation of Ir III species. In contrast, rutile-type IrO 2 , which does not contain Ir III species, has high dissolution resistance but the OER activity remains comparatively low as only low coverages of O I− species are formed under OER. The apparent link between O I− and Ir III species that comes from these observations has yet to be proven. In this work, using ab initio thermodynamics and in situ X-ray photoelectron and absorption spectroscopy we show that the same electrophilic O I− species that appear on Ir-based oxides under OER can be formed on Ir IV+δ by mild thermal oxidation of rutile-type IrO 2 , without the presence Ir III species.
August 2022
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19 Reads
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3 Citations
Microscopy and Microanalysis
April 2020
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37 Reads
August 2019
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106 Reads
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4 Citations
Microscopy and Microanalysis
Multimodal Operando Electron Microscopy Approach to Study Pt Catalyst During CO Oxidation Reaction - Volume 25 Supplement - M. Plodinec, E. Stotz, L. Sandoval-Diaz, R. Schlögl, T. Lunkenbein
December 2018
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92 Reads
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2 Citations
Topics in Catalysis
The original version of this article unfortunately contained an error. The authors would like to correct the error with this erratum. In Fig. 5 the process C and B were incorrectly labelled. The corrected Fig. 5 with the right labelling is included in this erratum. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
October 2018
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514 Reads
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44 Citations
Surface Science
An electrode for the oxygen evolution reaction based on a conductive bi-layered free standing graphene support functionalized with iridium nanoparticles was fabricated and characterized by means of potentiometric and advanced X-ray spectroscopic techniques. It was found that the electrocatalytic activity of iridium nanoparticles is associated to the formation of Ir 5d electron holes. Strong Ir 5d and O 2p hybridization, however, leads to a concomitant increase O 2p hole character, making oxygen electron deficient and susceptible to nucleophilic attack by water. Consequently, more efficient electrocatalysts can be synthesized by increasing the number of electron-holes shared between the metal d and oxygen 2p.
October 2018
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209 Reads
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27 Citations
Topics in Catalysis
The selective hydrogenation of propyne over a Pd-black model catalyst was investigated under operando conditions at 1 bar making use of advanced X-ray diffraction (bulk sensitive) and photo-electron spectroscopy (surface sensitive) techniques. It was found that the population of subsurface species controls the selective catalytic semi-hydrogenation of propyne to propylene due to the formation of surface and near-surface PdCx that inhibits the participation of more reactive bulk hydrogen in the hydrogenation reaction. However, increasing the partial pressure of hydrogen reduces the population of PdCx with the concomitant formation of a β-PdHx phase up to the surface, which is accompanied by a lattice expansion, allowing the participation of more active bulk hydrogen which is responsible for the unselective total alkyne hydrogenation. Therefore, controlling the surface and subsurface catalyst chemistry is crucial to control the selective alkyne semi-hydrogenation. Electronic supplementary material The online version of this article (10.1007/s11244-018-1071-6) contains supplementary material, which is available to authorized users.
October 2018
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5,269 Reads
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512 Citations
Nature Chemistry
Alloying provides a means by which to tune a metal catalyst's electronic structure and thus tailor its performance; however, mean-field behaviour in metals imposes limits. To access unprecedented catalytic behaviour, materials must exhibit emergent properties that are not simply interpolations of the constituent components' properties. Here we show an emergent electronic structure in single-atom alloys, whereby weak wavefunction mixing between minority and majority elements results in a free-atom-like electronic structure on the minority element. This unusual electronic structure alters the minority element's adsorption properties such that the bonding with adsorbates resembles the bonding in molecular metal complexes. We demonstrate this phenomenon with AgCu alloys, dilute in Cu, where the Cu d states are nearly unperturbed from their free-atom state. In situ electron spectroscopy demonstrates that this unusual electronic structure persists in reaction conditions and exhibits a 0.1 eV smaller activation barrier than bulk Cu in methanol reforming. Theory predicts that several other dilute alloys exhibit this phenomenon, which offers a design approach that may lead to alloys with unprecedented catalytic properties.
January 2018
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10 Reads
... O K-edge XAS studies on highly-OER-active amorphous-IrO x have revealed a low excitation energy resonance (529 eV), attributed to electron-deficient oxygen species, originally denoted as an O Ispecies 5,9 , although such species are characterized by strong covalency, which could make Ir IV+ -O (I+)a more correct description, see Refs. 11,18. We will return to this point later but retain the O Inomenclature to be consistent with previous work and highlight the redox active nature of this oxygen. ...
December 2023
Catalysis Science & Technology
... XPS spectra in the Ir 4f region of Ir/CNT and Ir/CNT@TiO 2 (Fig. 5) display presence of the Ir(0), Ir(III), and Ir(IV) species. 33 In Ir/CNT, Ir species is composed of approximately 14% Ir(0), 22% Ir(III), and 64% Ir(IV) (Fig. S12 †). Ir/CNT@TiO 2 presents corresponding compositions of 15, 36, and 49%. ...
May 2016
... Specifically, after Pd hydride was decomposed at 130°C, the diffraction peak remained at 40.00°, suggesting the preference and stability of Pd metal rather than carbides under this condition. Herein, the formation of PdC x carbide is not favored in the absence of Zn, which can be rationalized by the higher capability of H 2 dissociation on metallic Pd surface that inhibits the formation of surface/subsurface C* species from CO 30 . In contrast, the Zn infiltration during initial carburization of PdO-ZnO (Pd t phase), despite in a very small amount, can further open the channel for the infiltration of interstitial carbon. ...
December 2018
Topics in Catalysis
... XAS principles specify that both the E0 and WL position shifts toward higher excitation energies with iridium oxidation state. The WL intensity, also tied to the total Ir 5d-band hole count, should also monotonically increase with iridium oxidation state [44][45][46] . The WL position and intensity differences result from the fluorescence measurement configuration ( Figure S34) and changing sample nature (schematic in main text Figure 1a). ...
October 2018
Surface Science
... The most well-known examples of such dissolving intermediates are hydrogen, 1,8,9 oxygen, 2,10 and especially carbon. 1,8,[11][12][13] The deposition and subsequent bulk-dissolution of these species can even lead to continuous structural changes of the catalyst under reaction conditions. In fact, there is a growing amount of evidence in the literature that catalyst surfaces should be considered highly dynamic, 7,[14][15][16][17][18][19] and that even the subsurface layers might display dynamic behavior. ...
October 2018
Topics in Catalysis
... [34] The projected density of states (PDOS) shows narrowed Pt-5d band in Pt 2 Ln sites compared to metallic Pt site (Figure 1e), which is caused by the weak wave function overlap between Pt and Ln, which can effectively affect the overall bond strength of the Pt sites to the H* intermediates to modulate the electrocatalytic activity. [35,36] As revealed by d-band centers ( d ) extracted from the Pt-5d PDOS, the incorporation of Ln leads to a significant downshift in the d-band center of Pt due to the ligand effect ( Figure 1f). According to d-band center theory, this d downshift of Pt increases the occupation of antibonding state, thereby weakening the binding strength to H* intermediate ( Figure S6, Supporting Information), facilitating the HER process. ...
October 2018
Nature Chemistry
... To what extent and how deep into the sub-surface 36,37 such transformations progress, depend on the heterogeneous kinetics of the reaction network involved. 38 ). Figure 2 illustrates this for the case of Ni decomposing hydrocarbons. In early stages of reaction, the mosaic grain structure of the metal is well visible with (native) oxide concentrating in grain boundaries and partly covering the grains. ...
Reference:
The functional interface in catalysis
July 2017
Physical Review Letters
... (N)AP-XPS instruments are now commercially available and used both at synchrotrons and in laboratories worldwide to probe the solid/gas, [10][11][12] the liquid/gas, and the solid/liquid interface. [13][14][15][16][17] Consequently, electrochemistry and XPS can be combined in one experiment. Although numerous laboratory NAP-XPS instruments are currently in use, electrochemical in-situ experiments in an aqueous electrolyte solution have to date, to the best of our knowledge, only been conducted at synchrotron facilities (e.g., at ALS [13] and BESSY II [18] ). ...
March 2017
Journal of Electron Spectroscopy and Related Phenomena
... The dynamics of CVD graphene growth and the structure of graphene are highly controlled by the morphology and texture of the catalysts (166). It was observed that the graphene growth rate on the catalyst surface varies throughout the growth process, resulting in an inhomogeneous formation of graphene across different parts of the catalyst and compromising the quality of the graphene (167). Thus, further development of low-cost polycrystalline catalysts and a comprehensive understanding of the influence of the surface orientations and grain boundaries of the catalysts are required for the production of graphene films with a controlled domain structure. ...
October 2016
... Using this approach, the electronic structure and orientation dependence of water molecules near a electrically polarized gold electrode was investigated, prepared by physical vapor deposition (PVD), 20 nm thick, onto the SiN x membrane. 69 The PVD Au thin film on the inside part of the membrane is the working electrode in presence of a 10 mM aqueous solution of NaCl. The EY-XAS spectra collected as a function of applied potential are shown in Fig. 11A. ...
December 2016
