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@article{faucris.213919247,
abstract = {Photochemical in situ studies in a well-controlled surface science environment can help to understand photochemical reactions in organic thin films in more detail. To perform such studies without external focusing or light guiding systems, we designed a high-intensity UV-photon source, which is compatible with an ultra-high vacuum (UHV) environment. The UV source is based on a high power light-emitting diode (LED), soldered onto a copper heat reservoir to avoid overheating. The LED can be placed in close vicinity in front of a single crystal, providing flux densities of 2 x 10(18) photons s(-1) cm(-2) at a wavelength of 365 nm. Thus, the device provides light intensities one order of magnitude higher as compared to conventional continuous wave arc lamps, at only a small variation of the flux of less than +/- 20% over a sample surface of 10 x 8 mm(2). The UV source is mounted in a UHV infrared reflection absorption spectroscopy system and triggered by using the IR spectrometer. This allows fully automatized in situ IR studies of photochemical reactions at interfaces and thin films. We prove the functionality of the device by studying the photochemical conversion of norbornadiene (NBD) to quadricyclane (QC) mediated by the photosensitizer 4,4'-bis(dimethylamino) benzophenone (Michler's ketone, MK). NBD and MK were grown by physical vapor deposition in the form of thin films on Pt(111) at 120 K. Even at prolonged UV irradiation (>100 s), the temperature of the sample increased by less than 10 K. We report first successful conversion of NBD to QC under UHV conditions and follow the conversion behavior as a function of the photon dose and NBD/MK ratio. Initial quantum yields of up to 23% and selectivity for a QC of 70% are obtained at NBD/MK of 7.4:1, indicating good electronic coupling between NBD and MK even in a frozen multilayer. For both very small and very large NBD loadings, the conversion efficiency decreases, which is attributed to the effect of the metallic substrate and phase separation in thick multilayers, respectively. Published under license by AIP Publishing.},
author = {Schwarz, Matthias and Schuschke, Christian and Nascimento Silva, Thais and Mohr, Susanne and Waidhas, Fabian and Brummel, Olaf and Libuda, Jörg},
doi = {10.1063/1.5079320},
faupublication = {yes},
journal = {Review of Scientific Instruments},
note = {CRIS-Team WoS Importer:2019-03-20},
peerreviewed = {Yes},
title = {{A} simple high-intensity {UV}-photon source for photochemical studies in {UHV}: {Application} to the photoconversion of norbornadiene to quadricyclane},
volume = {90},
year = {2019}
}
@article{faucris.123788984,
author = {Brummel, Olaf and Besold, Daniel and Döpper, Tibor and Wu, Yanlin and Bochmann, Sebastian and Lazzari, Federica and Waidhas, Fabian and Bauer, Udo and Bachmann, Philipp and Papp, Christian and Steinrück, Hans-Peter and Görling, Andreas and Libuda, Jörg and Bachmann, Julien},
doi = {10.1002/cssc.201600765},
faupublication = {yes},
journal = {ChemSusChem},
keywords = {infrared spectroscopy; norbornadiene; quadricyclane; spectroelectrochemistry; voltammetry},
peerreviewed = {unknown},
title = {{Back} {Cover}: {Energy} {Storage} in {Strained} {Organic} {Molecules}: ({Spectro}){Electrochemical} {Characterization} of {Norbornadiene} and {Quadricyclane} ({ChemSusChem} 12/2016)},
volume = {9},
year = {2016}
}
@article{faucris.315110341,
abstract = {In heterogeneous catalysis, ionic liquids (ILs) are used as chemical modifiers to control selectivity. In our work, we aim to apply the same concept to electrocatalytic systems. We studied two competing reactions on low index platinum (111), (100), and (110) single crystal electrodes, namely, the hydrogen evolution reaction (HER) and the acetone reduction reaction. We used the IL [C2C1Im][OTf] dissolved in the supporting electrolyte (0.1 M HClO4) as chemical modifier. In our study, we combined cyclic voltammetry (CV), electrochemical infrared reflection absorption spectroscopy (EC-IRRAS), and differential electrochemical mass spectrometry (DEMS). On all three surfaces, the HER is the predominant reaction at potentials below 0.00 VRHE. While Pt(100) and Pt(111) show no or very low activity toward the reduction of acetone, the Pt(110) surface is active for this reaction in a potential window between 0.08 and 0.00 VRHE. We identified propane to be the main product of acetone reduction. Additionally, we observed the formation of adsorbed COads. In the presence of low concentrations of the IL (0.001 M), acetone reduction is fully suppressed and the activity for HER increases. We assign these effects to the specific adsorption of the IL, which blocks the adsorption sites for sterically more demanding acetone, while the coadsorbate layer remains permeable for the sterically less demanding hydrogen formation. Our results illustrate the potential of ionic liquids to act as molecular filters, which block a specific reaction channel.},
author = {Kastenmeier, Maximilian and Franz, Evanie and Waidhas, Fabian and Yang, Tian and Taccardi, Nicola and Wasserscheid, Peter and Brummel, Olaf and Libuda, Jörg},
doi = {10.1021/acs.jpcc.3c06260},
faupublication = {yes},
journal = {Journal of Physical Chemistry C},
note = {CRIS-Team Scopus Importer:2023-12-15},
peerreviewed = {Yes},
title = {{Competition} of {Acetone} {Reduction} and {Hydrogen} {Evolution} on {Pt} {Single} {Crystal} {Electrodes} in the {Absence} and {Presence} of the {Ionic} {Liquid} [{C2C1Im}][{OTf}]},
year = {2023}
}
@article{faucris.210904730,
abstract = {Liquid organic hydrogen carriers (LOHCs) have great potential as a hydrogen storage medium needed for a future sustainable energy system. Dehydrogenation of LOHCs requires a catalyst, such as supported Pd nanoparticles. Under reaction conditions, hydrogen and carbon may diffuse into the bulk of supported Pd catalyst particles and affect their activity and selectivity. The detailed understanding of this process is critical for the use of LOHCs in future hydrogen storage technologies. In this work, we studied these processes in-situ on a Pd model catalyst using high-energy grazing incidence X-ray diffraction. Pd nanoparticles were evaporated in ultra-high vacuum on a polished alpha-Al2O3(0001) substrate. The particles, with an initial average size of 3.4 nm, were investigated at elevated temperature during their interaction with H-2 and methylcyclohexane (MCH) representing a model LOHC. The interaction with H-2 was studied in-situ at partial pressures up to 1 bar and temperatures between 300 and 500 K. At 300 K, the Pd nanoparticles (NPs) show a transition from alpha-PdH to beta-PdH as a function of the H-2 pressure. The transition occurs gradually, which is attributed to the heterogeneity of the NP system. The hydrogen uptake in beta-PdHx at 300 K and 1 bar is estimated to be X-H 0.37 +/- 0.03 indicating that the miscibility gap is narrowed for the nanoparticular system. With increasing temperature, X-H decreases until no beta-PdH phase is formed anymore at 500 K. At the same temperature, we studied the interaction of the Pd/sapphire model catalyst with MCH, both in the presence and in the absence of H-2. In the absence of H-2, carbon is formed and diffuses into the bulk yielding PdCx with a C concentration of around x 0.05 +/- 0.01. In the presence of H-2 in the gas phase, bulk carbon formation in the Pd/sapphire model catalyst is completely suppressed. These results show that Pd nanoparticles act as an adequate catalyst for the dehydrogenation of MCH.[GRAPHICS].},
author = {Schuster, Ralf and Waidhas, Fabian and Bertram, Manon and Runge, Henning and Geile, Simon and Shayduk, Roman and Abuin, Manuel and Vonk, Vedran and Noei, Heshmat and Lykhach, Yaroslava and Bertram, Florian and Stierle, Andreas and Libuda, Jörg},
doi = {10.1007/s10562-018-2487-0},
faupublication = {yes},
journal = {Catalysis Letters},
keywords = {Liquid organic hydrogen carrier;Dehydrogenation;Carbon;XRD;Nanoparticles},
pages = {2901-2910},
peerreviewed = {Yes},
title = {{Dehydrogenation} of {Liquid} {Organic} {Hydrogen} {Carriers} on {Supported} {Pd} {Model} {Catalysts}: {Carbon} {Incorporation} {Under} {Operation} {Conditions}},
volume = {148},
year = {2018}
}
@article{faucris.203326155,
abstract = {Electrocatalysis is at the heart of our future transition to a renewable energy system. Most energy storage and conversion technologies for renewables rely on electrocatalytic processes and, with increasing availability of cheap electrical energy from renewables, chemical production will witness electrification in the near future(1-3). However, our fundamental understanding of electrocatalysis lags behind the field of classical heterogeneous catalysis that has been the dominating chemical technology for a long time. Here, we describe a new strategy to advance fundamental studies on electrocatalytic materials. We propose to 'electrify' complex oxide-based model catalysts made by surface science methods to explore electrocatalytic reactions in liquid electrolytes. We demonstrate the feasibility of this concept by transferring an atomically defined platinum/cobalt oxide model catalyst into the electrochemical environment while preserving its atomic surface structure. Using this approach, we explore particle size effects and identify hitherto unknown metal-support interactions that stabilize oxidized platinum at the nanoparticle interface. The metal-support interactions open a new synergistic reaction pathway that involves both metallic and oxidized platinum. Our results illustrate the potential of the concept, which makes available a systematic approach to build atomically defined model electrodes for fundamental electrocatalytic studies.},
author = {Faisal, Firas and Stumm, Corinna and Bertram, Manon and Waidhas, Fabian and Lykhach, Yaroslava and Cherevko, Serhiy and Xiang, Feifei and Ammon, Maximilian Michael and Vorokhta, Mykhailo and Smid, Bretislav and Skala, Tomas and Tsud, Nataliya and Neitzel, Armin and Beranova, Klara and Prince, Kevin C. and Geiger, Simon and Kasian, Olga and Wähler, Tobias and Schuster, Ralf and Schneider, M. Alexander and Matolin, Vladimir and Mayrhofer, Karl J. J. and Brummel, Olaf and Libuda, Jörg},
doi = {10.1038/s41563-018-0088-3},
faupublication = {yes},
journal = {Nature Materials},
pages = {592-+},
peerreviewed = {Yes},
title = {{Electrifying} model catalysts for understanding electrocatalytic reactions in liquid electrolytes},
volume = {17},
year = {2018}
}
@article{faucris.242211178,
abstract = {Solar energy conversion using molecular photoswitches holds great potential to store energy from sunlight in the form of chemical energy in a process that can be easily implemented in a direct solar energy storage device. In this context, we investigated the electrochemically triggered energy release of a solar thermal fuel based on the norbornadiene (NBD)/quadricyclane (QC) couple by photoelectrochemical IR reflection absorption spectroscopy (PEC-IRRAS). We studied the photo-induced conversion of the energy-lean 2-cyano-3-(3,4-dimethoxyphenyl)-norbornadiene (NBD ') to the energy-rich 2-cyano-3-(3,4-dimethoxyphenyl)-quadricyclane (QC ') and the electrochemically triggered reconversion using highly oriented pyrolytic graphite (HOPG) as an electrode material. We compared our results with the results obtained previously using Pt(111) electrodes and we characterized the photochemical and electrochemical properties of the storage system. NBD ' can be photochemically converted and electrochemically reconverted with very high selectivity. HOPG largely suppresses the unwanted catalytic reconversion which was observed on Pt(111). We performed repetitive cycling experiments for 1000 cycles to determine the reversibility of the system. Our results show that it is possible to reach reversibility above 99.8% using HOPG as an electrode material.},
author = {Waidhas, Fabian and Jevric, Martyn and Bosch, Michael and Yang, Tian and Franz, Evanie and Liu, Zhi and Bachmann, Julien and Moth-Poulsen, Kasper and Brummel, Olaf and Libuda, Jörg},
doi = {10.1039/d0ta00377h},
faupublication = {yes},
journal = {Journal of Materials Chemistry A},
note = {CRIS-Team WoS Importer:2020-09-04},
pages = {15658-15664},
peerreviewed = {Yes},
title = {{Electrochemically} controlled energy release from a norbornadiene-based solar thermal fuel: increasing the reversibility to 99.8% using {HOPG} as the electrode material},
volume = {8},
year = {2020}
}
@article{faucris.222881942,
abstract = {Solar fuels based on molecular photoswitches hold the potential to combine solar energy conversion, storage, and release in an extremely simple one-photon one-molecule process. In this work we demonstrate electrochemically controlled solar energy storage and release with high reversibility in a tailor-made norbornadiene photoswitch. We investigated the photochemical conversion of the energy-lean 2-cyano-3-(3,4-dimethoxyphenyl)-norbornadiene (NBD’) to its energy-rich counterpart 2-cyano-3-(3,4-dimethoxyphenyl)-quadricyclane (QC’) and the electrochemically triggered reconversion. Characteristic bands of NBD’ and QC’ were identified by density functional theory (DFT) and monitored in-situ during the energy storage and release process by photoelectrochemical infrared reflection absorption spectroscopy (PEC-IRRAS). We identified the stable regions of both isomers at a Pt(111) electrode and tested the stability of the NBD’/QC’ couple over 1000 storage and release cycles. It is shown that reversibilities of more than 99% per cycle can be achieved in this electrochemically triggered energy storage system.},
author = {Waidhas, Fabian and Jevric, Martyn and Fromm, Lukas and Bertram, Manon and Görling, Andreas and Moth-Poulsen, Kasper and Brummel, Olaf and Libuda, Jörg},
doi = {10.1016/j.nanoen.2019.103872},
faupublication = {yes},
journal = {Nano Energy},
keywords = {Electrochemistry; Energy conversion; Molecular photoswitches; Norbornadiene; Quadricyclane},
note = {CRIS-Team Scopus Importer:2019-07-23},
peerreviewed = {Yes},
title = {{Electrochemically} controlled energy storage in a norbornadiene-based solar fuel with 99% reversibility},
volume = {63},
year = {2019}
}
@article{faucris.117544284,
abstract = {We have investigated the electrochemically triggered cycloreversion of quadricyclane (QC) to norbornadiene (NBD), a system that holds the potential to combine both energy storage and conversion in a single molecule. Unambiguous voltammetric traces are obtained for pure NBD and pure QC, the latter a strained polycyclic isomer of the former. The difference in redox potentials is smaller than the energy difference between the neutral molecules. This is owing to a significant energy difference between the corresponding radical cations, as demonstrated by density functional theory (DFT) calculations. The vibrational modes of each pure compound are characterized experimentally in the fingerprint region and identified by DFT methods. Thermal and electrochemical transformations of NBD and QC are monitored insitu by IR spectroelectrochemical methods. The kinetics of the cycloreversion of QC to NBD, which is catalyzed by oxidizing equivalents, can be controlled by an applied electrode potential, which implies the ability to adjust in real time the release of thermal power stored in QC.},
author = {Brummel, Olaf and Besold, Daniel and Döpper, Tibor and Wu, Yanlin and Bochmann, Sebastian and Lazzari, Federica and Waidhas, Fabian and Bauer, Udo and Bachmann, Philipp and Papp, Christian and Steinrück, Hans-Peter and Görling, Andreas and Libuda, Jörg and Bachmann, Julien},
doi = {10.1002/cssc.201600127},
faupublication = {yes},
journal = {Chemsuschem},
keywords = {Infrared spectroscopy; Norbornadiene; Quadricyclane; Spectroelectrochemistry; Voltammetry},
pages = {1424-1432},
peerreviewed = {Yes},
title = {{Energy} {Storage} in {Strained} {Organic} {Molecules}: ({Spectro}){Electrochemical} {Characterization} of {Norbornadiene} and {Quadricyclane}},
volume = {9},
year = {2016}
}
@article{faucris.261044366,
abstract = {Isopropanol (IPA) can be used as a rechargeable electrofuel. In this approach, IPA is oxidized to acetone (ACE) in a direct alcohol fuel cell and the formed ACE is subsequently back-converted to IPA in a heterogeneously catalyzed process. To study the electrochemical reaction mechanisms of the IPA oxidation at the molecular level, appropriate and well-defined model electrocatalysts are necessary. In this work we prepare such model electrocatalysts by surface science methods in ultra-high vacuum (UHV). The catalysts consist of well-defined platinum nanoparticles on carbon supports. As carbon support, we use flat highly ordered pyrolytic graphite (HOPG) and thin (20 nm) magnetron sputtered carbon films on a polycrystalline gold substrate. In a first step, we characterize the model electrocatalysts and investigate their stability in-situ with complementary methods, i.e. by electrochemical scanning tunneling microscopy (EC-STM), electrochemical on-line inductively coupled plasma mass spectrometry (ICP-MS) and CO stripping experiments followed by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS). We determined a stability window ranging from -0.65 VRHE to 1.15 VRHE for both sample types, independent of the presence or absence of IPA in the electrolyte. In the second step, we study the oxidation of IPA on tPt nanoparticles using differential electrochemical mass spectrometry (DEMS) and EC-IRRAS. The onset of IPA oxidation is observed at 0.3 VRHE. ACE is formed with high selectivity, while we identify traces of CO2 as the only side-product formed at higher potentials. However, we do not observe any formation of adsorbed CO. A direct comparison of these results with previous work on Pt(111) suggests that low coordinated Pt sites and size effects play a subordinate role for IPA oxidation on Pt electrocatalysts.},
author = {Stumm, Corinna and Kastenmeier, Maximilian and Waidhas, Fabian and Bertram, Manon and Sandbeck, Daniel and Bochmann, Sebastian and Mayrhofer, Karl and Bachmann, Julien and Cherevko, Serhiy and Brummel, Olaf and Libuda, Jörg},
doi = {10.1016/j.electacta.2021.138716},
faupublication = {yes},
journal = {Electrochimica Acta},
keywords = {2-propanol; Carbon support; In-situ electrochemical methods; Isopropanol oxidation; Isopropyl alcohol; Model catalysis; Platinum nanoparticles},
note = {CRIS-Team Scopus Importer:2021-07-02},
peerreviewed = {Yes},
title = {{Model} electrocatalysts for the oxidation of rechargeable electrofuels - carbon supported {Pt} nanoparticles prepared in {UHV}},
volume = {389},
year = {2021}
}
@article{faucris.228833955,
abstract = {In this work, we investigated the interaction of phenylphosphonic acid (PPA, C6H5PO3H2) with atomically-defined Co3O4(111) thin films, grown on Ir(100), under ultrahigh vacuum (UHV) conditions and in the electrochemical environment. In the first step, we employed infrared reflection absorption spectroscopy (IRAS) and followed the formation of a saturated monolayer (380 K) in UHV. We observed that the binding motif changes from a chelating tridentate in the sub-monolayer regime to a chelating bidentate at full monolayer coverages. In the electrochemical environment, we analyzed the interaction of PPA with the same Co3O4(111) surface by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) (0.3 VRHE-1.3 VRHE). When adsorbed at pH 10 from an ammonia buffered aqueous solution, PPA binds to the surface in form of a fully deprotonated chelating bidentate. With increasing electrode potential, we observed two fully reversible processes. At low buffer concentration, protons are released upon oxidation of surface Co2+ ions and lead to protonation of the anchored phosphonates. At high buffer concentration, most of the protons released are accepted by NH3. Simultaneously, the surface phosphonate changes its adsorption motif from bidentate to tridentate while adopting a more upright geometry.},
author = {Bertram, Manon and Schuschke, Christian and Waidhas, Fabian and Schwarz, Matthias and Hohner, Chantal and Montero, María A. and Brummel, Olaf and Libuda, Jörg},
doi = {10.1039/c9cp03779a},
faupublication = {yes},
journal = {Physical Chemistry Chemical Physics},
note = {CRIS-Team Scopus Importer:2019-11-08},
pages = {23364-23374},
peerreviewed = {Yes},
title = {{Molecular} anchoring to oxide surfaces in ultrahigh vacuum and in aqueous electrolytes: phosphonic acids on atomically-defined cobalt oxide},
volume = {21},
year = {2019}
}
@article{faucris.210922603,
abstract = {PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.},
author = {Khalakhan, Ivan and Waidhas, Fabian and Brummel, Olaf and Vorokhta, Mykhailo and Kus, Peter and Yakovlev, Yurii and Bertram, Manon and Dopita, Milan and Matolinova, Iva and Libuda, Jörg and Matolin, Vladimir},
doi = {10.1021/acs.jpcc.8b06840},
faupublication = {yes},
journal = {Journal of Physical Chemistry C},
pages = {21974-21982},
peerreviewed = {Yes},
title = {{Nanoscale} {Morphological} and {Structural} {Transformations} of {PtCu} {Alloy} {Electrocatalysts} during {Potentiodynamic} {Cycling}},
volume = {122},
year = {2018}
}
@article{faucris.233234519,
abstract = {Employing molecular photoswitches, we can combine solar energy conversion, storage, and release in an extremely simple single molecule system. In order to release the stored energy as electricity, the photoswitch has to interact with a semiconducting electrode surface. In this work, we explore a solar-energy-storing model system, consisting of a molecular photoswitch anchored to an atomically defined oxide surface in a liquid electrolyte and under potential control. Previously, this model system has been proven to be operational under ultrahigh vacuum (UHV) conditions. We used the tailor-made norbornadiene derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) and characterized its photochemical and electrochemical properties in an organic electrolyte. Next, we assembled a monolayer of CNBD on a well-ordered Co3O4(111) surface by physical vapor deposition in UHV. This model interface was then transferred into the liquid electrolyte and investigated by photoelectrochemical infrared reflection absorption spectroscopy experiments. We demonstrate that the anchored monolayer of CNBD can be converted photochemically to its energy-rich counterpart 2-cyano-3-(4-carboxyphenyl)quadricyclane (CQC) under potential control. However, the reconversion potential of anchored CQC overlaps with the oxidation and decomposition potential of CNBD, which limits the electrochemically triggered reconversion.},
author = {Bertram, Manon and Waidhas, Fabian and Jevric, Martyn and Fromm, Lukas and Schuschke, Christian and Kastenmeier, Maximilian and Görling, Andreas and Moth-Poulsen, Kasper and Brummel, Olaf and Libuda, Jörg},
doi = {10.1063/1.5137897},
faupublication = {yes},
journal = {Journal of Chemical Physics},
month = {Jan},
note = {CRIS-Team Scopus Importer:2020-02-04},
peerreviewed = {Yes},
title = {{Norbornadiene} photoswitches anchored to well-defined oxide surfaces: {From} ultrahigh vacuum into the liquid and the electrochemical environment},
volume = {152},
year = {2020}
}
@article{faucris.121122804,
abstract = {The two valence isomers norbornadiene (NBD) and quadricyclane (QC) enable solar energy storage in a single molecule system. We present a new photoelectrochemical infrared reflection absorption spectroscopy (PEC-IRRAS) experiment, which allows monitoring of the complete energy storage and release cycle by in situ vibrational spectroscopy. Both processes were investigated, the photochemical conversion from NBD to QC using the photosensitizer 4,4'-bis(dimethylamino)benzophenone (Michler's ketone, MK) and the electrochemically triggered cycloreversion from QC to NBD. Photochemical conversion was obtained with characteristic conversion times on the order of 500 ms. All experiments were performed under full potential control in a thin layer configuration with a Pt(111) working electrode. The vibrational spectra of NBD, QC, and MK were analyzed in the fingerprint region, permitting quantitative analysis of the spectroscopic data. We determined selectivities for both the photochemical conversion and the electrochemical cycloreversion and identified the critical steps that limit the reversibility of the storage cycle.},
author = {Brummel, Olaf and Waidhas, Fabian and Bauer, Udo and Wu, Yanlin and Bochmann, Sebastian and Steinrück, Hans-Peter and Papp, Christian and Bachmann, Julien and Libuda, Jörg},
doi = {10.1021/acs.jpclett.7b00995},
faupublication = {yes},
journal = {Journal of Physical Chemistry Letters},
pages = {2819-2825},
peerreviewed = {Yes},
title = {{Photochemical} {Energy} {Storage} and {Electrochemically} {Triggered} {Energy} {Release} in the {Norbornadiene}-{Quadricyclane} {System}: {UV} {Photochemistry} and {IR} {Spectroelectrochemistry} in a {Combined} {Experiment}},
volume = {8},
year = {2017}
}
@article{faucris.252112963,
abstract = {A fundamental reaction in industries for producing aldehydes and ketones is the partial oxidation of alcohols. As a model reaction, we investigated the photo-oxidation of 2-propanol on rutile titania, which is a promising chemically nontoxic photocatalyst. Photochemical infrared reflection absorption spectroscopy (PC-IRRAS) was used to study the reaction on powder catalysts in the liquid phase (neat liquid and dissolved in dichloromethane). We compare these results with polarized Fourier transform (FT)-IRRAS and temperature-programmed desorption (TPD) experiments on rutile TiO2(110) single crystals in ultrahigh vacuum (UHV). Our in situ liquid-phase experiments showed that 2-propanol converts into acetone on rutile powders, which is in accordance with previous ex situ studies. Mass transport limitations are the key to avoid total oxidation. However, the yield of acetone is limited. We identified water formed as a byproduct and suspected that water might block the active sites. To elucidate possible reaction mechanisms, further experiments were performed on rutile TiO2(110) single crystals in the presence and absence of oxygen and UV irradiation under UHV conditions. Here, we obtained further insights into the elementary steps of the different 2-propanol reactions. We demonstrated that acetone desorbs from a diolate species, which forms in the presence of oxygen under UV irradiation at temperatures around 200 K. Furthermore, propane was identified for the first time as a new thermally activated deoxygenation product besides the simultaneously formed, formally reported, propene. Propene formation is quenched by UV irradiation. Active site blocking by water is confirmed by TPD and polarized FT-IRRAS measurements.},
author = {Kraeuter, Jessica and Mohrhusen, Lars and Waidhas, Fabian and Brummel, Olaf and Libuda, Jörg and Al-Shamery, Katharina},
doi = {10.1021/acs.jpcc.0c10734},
faupublication = {yes},
journal = {Journal of Physical Chemistry C},
note = {CRIS-Team Scopus Importer:2021-03-19},
peerreviewed = {Yes},
title = {{Photoconversion} of 2-{Propanol} on {Rutile} {Titania}: {A} {Combined} {Liquid}-{Phase} and {Surface} {Science} {Study}},
year = {2021}
}
@article{faucris.210894276,
abstract = {Model studies at complex, yet well-defined electrodes can provide a better understanding of electrocatalytic reactions. New experimental devices are required to prepare such model electrocatalysts with atomic-level control. In this work, we discuss the design of a new setup, which enables the preparation of well-defined electrocatalysts in ultra-high vacuum (UHV) using the full portfolio of surface science techniques. The setup allows for direct transfer of samples from UHV and the immersion into the electrolyte without contact to air. As a special feature, the single crystal sample is transferred without any sample holder, which makes the system easily compatible with most electrochemical in situ methods, specifically with electrochemical infrared reflection absorption spectroscopy, but also with other characterization methods such as single-crystal cyclic voltammetry, differential electrochemical mass spectrometry, or electrochemical scanning tunneling microscopy. We demonstrate the preparation in UHV, the transfer in inert atmosphere, and the immersion into the electrolyte for a complex model catalyst that requires surface science methods for preparation. Specifically, we study Pt nanoparticles supported on well-ordered Co3O4(111) films which are grown on an Ir(100) single crystal. In comparison with reference experiments on Pt(111), the model catalyst shows a remarkably different adsorption and reaction behavior during CO electrooxidation in alkaline environments. Published by AIP Publishing.},
author = {Faisal, Firas and Bertram, Manon and Stumm, Corinna and Waidhas, Fabian and Brummel, Olaf and Libuda, Jörg},
doi = {10.1063/1.5047056},
faupublication = {yes},
journal = {Review of Scientific Instruments},
peerreviewed = {Yes},
title = {{Preparation} of complex model electrocatalysts in ultra-high vacuum and transfer into the electrolyte for electrochemical {IR} spectroscopy and other techniques},
volume = {89},
year = {2018}
}
@article{faucris.240545332,
abstract = {Fuel cells can be operated directly by oxidation of isopropyl alcohol (IPA) to acetone (ACE). If the product ACE is hydrogenated, IPA is formed again. In this way, IPA serves as a rechargeable electrofuel. In this work, we study the oxidation of IPA at Pt electrodes using several complementary experimental methods, including cyclic voltammetry (CV), electrochemical real-time mass spectrometry (EC-RTMS), and electrochemical infrared reflection absorption spectroscopy (EC-IRRAS), in combination with density functional theory (DFT) to assign the vibrational modes of IPA and ACE. Different types of Pt electrodes are investigated, namely single crystalline Pt(111) surfaces, polycrystalline Pt, and nanostructured tubular Pt electrodes. The onset of the IPA oxidation on the Pt electrodes is observed at 0.3 VIE, yielding ACE with high selectivity. At potentials above 0.9 V-RHE, the formation of Pt oxide inhibits the reaction. The only side reaction observed is the formation of small amounts of CO2. We show that adsorbed ACE is formed at the Pt electrodes poisoning the surface. On nanotubular electrodes with high surface area, ACE stays mainly adsorbed on the surface, and only a small fraction desorbs. These observations suggest that poisoning of the Pt electrode by adsorbed ACE limits the oxidation of IPA.},
author = {Waidhas, Fabian and Haschke, Sandra and Khanipourmehrin, Peyman and Fromm, Lukas and Görling, Andreas and Bachmann, Julien and Katsounaros, Ioannis and Mayrhofer, Karl and Brummel, Olaf and Libuda, Jörg},
doi = {10.1021/acscatal.0c00818},
faupublication = {yes},
journal = {ACS Catalysis},
note = {CRIS-Team WoS Importer:2020-07-17},
pages = {6831-6842},
peerreviewed = {Yes},
title = {{Secondary} {Alcohols} as {Rechargeable} {Electrofuels}: {Electrooxidation} of {Isopropyl} {Alcohol} at {Pt} {Electrodes}},
volume = {10},
year = {2020}
}
@article{faucris.250580452,
abstract = {2-Propanol and its dehydrogenated counterpart acetone can be used as a rechargeable electrofuel. The concept involves selective oxidation of 2-propanol to acetone in a fuel cell coupled with reverse catalytic hydrogenation of acetone to 2-propanol in a closed cycle. We studied electrocatalytic oxidation of 2-propanol on complex model Pt/Co3O4(111) electrocatalysts prepared in ultra-high vacuum and characterized by scanning tunneling microscopy. The electrocatalytic behavior of the model electrocatalysts has been investigated in alkaline media (pH 10, phosphate buffer) by means of electrochemical infrared reflection absorption spectroscopy and ex-situ emersion synchrotron radiation photoelectron spectroscopy as a function of Pt particle size and compared with the electrocatalytic behavior of Pt(111) and pristine Co3O4(111) electrodes under similar conditions. We found that the Co3O4(111) film is inactive towards electrochemical oxidation of 2-propanol under the electrochemical conditions (0.3-1.1 V-RHE). The electrochemical oxidation of 2-propanol readily occurs on Pt(111) yielding acetone at an onset potential of 0.4 V-RHE. The reaction pathway does not involve CO but yields strongly adsorbed acetone species leading to a partial poisoning of the surface sites. On model Pt/Co3O4(111) electrocatalysts, we observed distinct metal support interactions and particle size effects associated with the charge transfer at the metal/oxide interface. We found that ultra-small Pt particles (around 1 nm and below) consist of partially oxidized Pt-delta(+) species which show minor activity towards 2-propanol oxidation. In contrast, conventional Pt particles (particle size of a few nm) are mainly metallic and show high activity toward 2-propanol oxidation.},
author = {Yang, Tian and Kastenmeier, Maximilian and Ronovsky, Michal and Fusek, Lukas and Skala, Tomas and Waidhas, Fabian and Bertram, Manon and Tsud, Nataliya and Matvija, Peter and Prince, Kevin C. and Matolin, Vladimir and Liu, Zhi and Johanek, Viktor and Myslivecek, Josef and Lykhach, Yaroslava and Brummel, Olaf and Libuda, Jörg},
doi = {10.1088/1361-6463/abd9ea},
faupublication = {yes},
journal = {Journal of Physics D: Applied Physics},
note = {CRIS-Team WoS Importer:2021-02-26},
peerreviewed = {Yes},
title = {{Selective} electrooxidation of 2-propanol on {Pt} nanoparticles supported on {Co3O4}: an in-situ study on atomically defined model systems},
volume = {54},
year = {2021}
}
@article{faucris.220874233,
abstract = {Molecular photoswitches provide an extremely simple solution for solar energy conversion and storage. To convert stored energy to electricity, however, the photoswitch has to be coupled to a semiconducting electrode. In this work, we report on the assembly of an operational solar-energy-storing organic-oxide hybrid interface, which consists of a tailor-made molecular photoswitch and an atomically-defined semiconducting oxide film. The synthesized norbornadiene derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) was anchored to a well-ordered Co3O4(111) surface by physical vapor deposition in ultrahigh vacuum. Using a photochemical infrared reflection absorption spectroscopy experiment, we demonstrate that the anchored CNBD monolayer remains operational, i.e., can be photo-converted to its energy-rich counterpart 2-cyano-3-(4-carboxyphenyl)quadricyclane (CQC). We show that the activation barrier for energy release remains unaffected by the anchoring reaction and the anchored photoswitch can be charged and discharged with high reversibility. Our atomically-defined solar-energy-storing model interface enables detailed studies of energy conversion processes at organic/oxide hybrid interfaces.},
author = {Schuschke, Christian and Hohner, Chantal and Jevric, Martyn and Petersen, Anne Ugleholdt and Wang, Zhihang and Schwarz, Matthias and Kettner, Miroslav and Waidhas, Fabian and Fromm, Lukas and Sumby, Christopher J. and Görling, Andreas and Brummel, Olaf and Moth-Poulsen, Kasper and Libuda, Jörg},
doi = {10.1038/s41467-019-10263-4},
faupublication = {yes},
journal = {Nature Communications},
note = {CRIS-Team WoS Importer:2019-06-18},
peerreviewed = {Yes},
title = {{Solar} energy storage at an atomically defined organic-oxide hybrid interface},
volume = {10},
year = {2019}
}
@article{faucris.210934071,
abstract = {Pt-doped CeOx thin film electrocatalysts have recently been shown to exhibit high activity and stability at the anode of proton exchange membrane fuel cells (PEM-FC). To identify, the role of the Pt dopant and the origin of the high stability of Pt-CeOx films, we applied electrochemical in situ IR spectroscopy on Pt-CeOx model thin film catalysts during methanol (1 M methanol) oxidation. The model catalysts were prepared by magnetron cosputtering of Pt (9-21 atom %), and CeO2 onto clean, and carbon-coated Au supports, All samples were characterized by scanning electron microscopy (SEM), energy-dispersive, X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) before and after reaction. At pH 1 (0.1 MHClO4) the Pt-CeOx dissolves partially during potential cycling, whereas the films: are largely stable at pH 6 (0.1 M phosphate buffer). Electrochemical IR spectroscopy of the adsorbed CO shows that Metallic Pt is formed on all Pt-CeOx samples during methanol oxidation. In comparison to Pt(111), Pt aggregates on Pt-CeOx show a CO on-top signal, which is red shifted by at least 25 cm(-1) and suppression of the bridging CO signals. Whereas the Pt particles on Pt-CeOx,films with high Pt concentration (>20 atom %) undergo rapid sintering during the potential cycling, small metallic Pt aggregates are stable under the Same conditions on films with lbw Pt concentration (<15 atom % Pt). By means of density functional theory (DFT) calculations we analyzed the spectral shifts of adsorbed CO as a function of nanoparticle size both on free and ceria-supported Pt particles, Comparison with the experiment suggests the formation of "subnano"-particles, i.e., particles with up to 30 atoms (<1 nm particle diameter), which do not expose regular (111) facet sites. At sufficiently low Pt loading) these subnano-Pt particles are efficiently stabilized by the interaction with the ceria support under conditions of the dynamically changing electrode potential.},
author = {Brummel, Olaf and Waidhas, Fabian and Faisal, Firas and Fiala, Roman and Vorokhta, Mykhailo and Khalakhan, Ivan and Dubau, Martin and Figueroba, Alberto and Kovacs, Gabor and Aleksandrov, Hristiyan A. and Vayssilov, Georgi N. and Kozlov, Sergey M. and Neyman, Konstantin M. and Matolin, Vladimir and Libuda, Jörg},
doi = {10.1021/acs.jpcc.6b05962},
faupublication = {yes},
journal = {Journal of Physical Chemistry C},
pages = {19723-19736},
peerreviewed = {Yes},
title = {{Stabilization} of {Small} {Platinum} {Nanoparticles} on {Pt}-{CeO2} {Thin} {Film} {Electrocatalysts} {During} {Methanol} {Oxidation}},
volume = {120},
year = {2016}
}
@article{faucris.210935139,
abstract = {PtNi thin film catalysts provide higher activity and enhanced Pt efficiency in the oxygen reduction reaction (ORR) in comparison to pure Pt catalysts. We explored the structural transformations and degradation mechanisms in such films by cyclic voltammetry (CV), electrochemical atomic force microscopy (EC-AFM), and electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) using CO as a probe. The model catalysts were prepared by magnetron sputtering, and the results were compared to reference experiments on Pt(111). Freshly prepared catalysts show two characteristic IR bands in the on-top CO region. The signal at lower wavenumbers is assigned to isolated CO on Pt sites. Based on density functional theory (DFT) calculations, we suggest that another blue-shifted CO band can be attributed to dicarbonyls on low-coordinated Pt centers, generated by the leaching of surface Ni. This band vanishes upon cycling to 1.1 V versus the reversible hydrogen electrode (V-RHE) and the catalyst shows a weak decrease in grain size in AFM. A dramatic change of the film structure is observed upon potential cycling to 1.2 V-RHE. CV indicates the formation of [110] and [100] steps and AFM points to a strong decrease in particle size. Simultaneously, EC-IRRAS shows the appearance of a new, strongly red-shifted CO band. Based on DFT, we assign these changes to a transient enrichment of Ni in the (sub) surface region. Upon cycling to higher potential, Ni is completely leached from the surface region, and large Pt particles are formed. (C) 2017 Elsevier Ltd. All rights reserved.},
author = {Brummel, Olaf and Waidhas, Fabian and Khalakhan, Ivan and Vorokhta, Mykhailo and Dubau, Martin and Kovacs, Gabor and Aleksandrov, Hristiyan A. and Neyman, Konstantin M. and Matolin, Vladimir and Libuda, Jörg},
doi = {10.1016/j.electacta.2017.08.062},
faupublication = {yes},
journal = {Electrochimica Acta},
keywords = {platinum;nickel;catalyst stability;electrochemical infrared spectroscopy;density functional theory},
pages = {427-441},
peerreviewed = {Yes},
title = {{Structural} transformations and adsorption properties of {PtNi} nanoalloy thin film electrocatalysts prepared by magnetron co-sputtering},
volume = {251},
year = {2017}
}
@article{faucris.268918166,
abstract = {Previous studies on the reaction chemistry of 2-propanol at rutile powders in liquid phase as well as at TiO2(1 1 0) surfaces under UHV conditions, both with low reduction degree, exhibited that partial photo oxidation is observable in the presence of oxygen, however, with low yields. Here, we show that at highly reduced surfaces a partial photo oxidation of 2-propanol is not only possible in the presence of oxygen but also in coadsorption with water or even without coadsorbates below room temperature. Thermally, only the conversion towards propane and propene was observed at temperatures above 550 K. Liquid Phase experiments further showed that the coadsorbate influences the acetone yield of the partial photo oxidation. While in the presence of oxygen an increasing acetone conversion was observed, the acetone yield is reduced in the presence of water in accordance with the hypothesis of an active site blocking by water.},
author = {Kräuter, Jessica and Franz, Evanie and Waidhas, Fabian and Brummel, Olaf and Libuda, Jörg and Al-Shamery, Katharina},
doi = {10.1016/j.jcat.2021.12.025},
faupublication = {yes},
journal = {Journal of Catalysis},
keywords = {Acetone; Isopropanol; Liquid Phase; Model Catalysis; PC-IRRAS; Photo Oxidation; Rutile TiO; UHV; UV Irradiation},
note = {CRIS-Team Scopus Importer:2022-02-04},
pages = {134-144},
peerreviewed = {Yes},
title = {{The} role of defects in the photoconversion of 2-propanol on rutile titania: {Operando} spectroscopy combined with elementary studies},
volume = {406},
year = {2022}
}
@article{faucris.222886347,
abstract = {The high temperature required for hydrogen release from Liquid Organic Hydrogen Carrier (LOHC) systems has been considered in the past as the main drawback of this otherwise highly attractive and fully infrastructure-compatible form of chemical hydrogen storage. According to the state-of-the art, the production of electrical energy from LOHC-bound hydrogen, e.g. from perhydro-dibenzyltoluene (H18-DBT), requires provision of the dehydrogenation enthalpy (e.g. 65 kJ mol-1 (H2) for H18-DBT) at a temperature level of 300 °C followed by purification of the released hydrogen for subsequent fuel cell operation. Here, we demonstrate that a combination of a heterogeneously catalysed transfer hydrogenation from H18-DBT to acetone and fuel cell operation with the resulting 2-propanol as a fuel, allows for an electrification of LOHC-bound hydrogen in high efficiency (>50%) and at surprisingly mild conditions (temperatures below 200 °C). Most importantly, our proposed new sequence does not require an external heat input as the transfer hydrogenation from H18-DBT to acetone is almost thermoneutral. In the PEMFC operation with 2-propanol, the endothermal proton release at the anode is compensated by the exothermic formation of water. Ideally the proposed sequence does not form and consume molecular H2 at any point which adds a very appealing safety feature to this way of producing electricity from LOHC-bound hydrogen, e.g. for applications on mobile platforms.},
author = {Sievi, Gabriel and Geburtig, Denise and Skeledzic, Tanja and Bösmann, Andreas and Preuster, Patrick and Brummel, Olaf and Waidhas, Fabian and Montero, María A. and Khanipourmehrin, Peyman and Katsounaros, Ioannis and Libuda, Jörg and Mayrhofer, Karl and Wasserscheid, Peter},
doi = {10.1039/c9ee01324e},
faupublication = {yes},
journal = {Energy and Environmental Science},
note = {CRIS-Team Scopus Importer:2019-07-23},
pages = {2305-2314},
peerreviewed = {Yes},
title = {{Towards} an efficient liquid organic hydrogen carrier fuel cell concept},
volume = {12},
year = {2019}
}
@article{faucris.284504139,
abstract = {Molecular solar thermal (MOST) systems open application fields for solar energy conversion as they combine conversion, storage, and release in one single molecule. For energy release, catalysts must be controllable, selective, and stable over many operation cycles. Here, we present a MOST/catalyst couple, which combines all these properties. We explore solar energy storage in a tailor-made MOST system (cyano-3-(3,4-dimethoxyphenyl)-norbornadiene/quadricyclane; NBD′/QC′) and the energy release heterogeneously catalyzed at a Au(111) surface. By photoelectrochemical infrared reflection absorption spectroscopy (PEC-IRRAS) and scanning tunneling microscopy, we show that Au triggers the energy release with very high activity. Most remarkably, the release rate of the heterogeneously catalyzed process can be tuned by applying an external potential. Our durability tests show that the MOST/catalyst system is stable over 1000 storage cycles without any decomposition. The surface structure of the catalyst is preserved, and its activity decreases by only 0.1% per storage cycle. },
author = {Franz, Evanie and Stumm, Corinna and Waidhas, Fabian and Bertram, Manon and Jevric, Martyn and Orrego-Hernández, Jessica and Hölzel, Helen and Moth-Poulsen, Kasper and Brummel, Olaf and Libuda, Jörg},
doi = {10.1021/acscatal.2c03043},
faupublication = {yes},
journal = {ACS Catalysis},
keywords = {energy storage; gold; heterogeneous catalysis; norbornadiene; photoswitches; quadricyclane; solar thermal fuels},
note = {CRIS-Team Scopus Importer:2022-11-04},
pages = {13418-13425},
peerreviewed = {Yes},
title = {{Tunable} {Energy} {Release} in a {Reversible} {Molecular} {Solar} {Thermal} {System}},
year = {2022}
}