Prof. Dr. Bernhard Rieger
Academic Research Focus
- Ultrafast catalysis for polycarbonates and polyurethanes
- Multinuclear metal complexes enable the photoreduction of carbon dioxide
- Carbon dioxide Utilization (polymers & photocatalysis)
- Silicon Nanocomposites for (Opto)Electronic Applications
- Multinuclear metal complexes enable the photoreduction of carbon dioxide
- Carbon dioxide Utilization (polymers & photocatalysis)
- Silicon Nanocomposites for (Opto)Electronic Applications
Fields of Application
Nanomaterials, Photo-(electro)catalysis, Semiconductor Materials
Publications
12.
Z Li, S Vagin, J Zhang, R Guo, K Sun, X Jiang, T Guan, M Schwartzkopf, B Rieger, C-Q Ma, P Müller-Buschbaum
Suppressed Degradation Process of PBDB-TF-T1:BTP-4F-12-Based Organic Solar Cells with Solid Additive Atums Green Journal Article
In: ACS Applied Materials & Interfaces, vol. 17, no. 6, pp. 9475-9484, 2025, ISSN: 1944-8244.
@article{nokey,
title = {Suppressed Degradation Process of PBDB-TF-T1:BTP-4F-12-Based Organic Solar Cells with Solid Additive Atums Green},
author = {Z Li and S Vagin and J Zhang and R Guo and K Sun and X Jiang and T Guan and M Schwartzkopf and B Rieger and C-Q Ma and P M\"{u}ller-Buschbaum},
url = {https://doi.org/10.1021/acsami.4c21699},
doi = {10.1021/acsami.4c21699},
issn = {1944-8244},
year = {2025},
date = {2025-02-12},
journal = {ACS Applied Materials \& Interfaces},
volume = {17},
number = {6},
pages = {9475-9484},
abstract = {Solid additives have garnered significant attention due to their numerous advantages over liquid additives. This study explores the potential of the green-fluorescent conjugated polymer denoted Atums Green as a solid additive in green-solvent-based PBDB-TF-T1:BTP-4F-12 solar cells. Even tiny amounts of Atums Green doping significantly improve the device performance. For the reference solar cell without any additive, we find that device degradation is not caused by chemical redox reactions but by changes in crystallinity and microstructure evolution during aging in air under illumination. Operando GIWAXS and GISAXS are used to investigate the structure evolution. We discover a four-stage degradation process for the reference cell. In general, the lattice spacing and crystallite coherence length decrease, while the domain sizes increase, which causes the loss of shirt-circuit current JSC and fill factor FF. Furthermore, a decomposition component is detected in GIWAXS and GISAXS, corresponding to the loss of the open-circuit voltage VOC. Atums Green doping effectively suppresses the evolution of crystallinity and domain sizes as well as the continuous decomposition, thereby enhancing the device stability under illumination in air. This finding reveals the kinetic degradation process of organic solar cells, establishes a correlation between the morphological properties and device performance, and further demonstrates the promising potential of Atums Green doping in organic solar cells.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Solid additives have garnered significant attention due to their numerous advantages over liquid additives. This study explores the potential of the green-fluorescent conjugated polymer denoted Atums Green as a solid additive in green-solvent-based PBDB-TF-T1:BTP-4F-12 solar cells. Even tiny amounts of Atums Green doping significantly improve the device performance. For the reference solar cell without any additive, we find that device degradation is not caused by chemical redox reactions but by changes in crystallinity and microstructure evolution during aging in air under illumination. Operando GIWAXS and GISAXS are used to investigate the structure evolution. We discover a four-stage degradation process for the reference cell. In general, the lattice spacing and crystallite coherence length decrease, while the domain sizes increase, which causes the loss of shirt-circuit current JSC and fill factor FF. Furthermore, a decomposition component is detected in GIWAXS and GISAXS, corresponding to the loss of the open-circuit voltage VOC. Atums Green doping effectively suppresses the evolution of crystallinity and domain sizes as well as the continuous decomposition, thereby enhancing the device stability under illumination in air. This finding reveals the kinetic degradation process of organic solar cells, establishes a correlation between the morphological properties and device performance, and further demonstrates the promising potential of Atums Green doping in organic solar cells.
11.
M Christis, A Henning, J D Bartl, A Zeidler, B Rieger, M Stutzmann, I D Sharp
Annealing-Free Ohmic Contacts to n-Type GaN via Hydrogen Plasma-Assisted Atomic Layer Deposition of Sub-Nanometer AlOx Journal Article
In: Advanced Materials Interfaces, vol. n/a, no. n/a, pp. 2300758, 2023, ISSN: 2196-7350.
@article{nokey,
title = {Annealing-Free Ohmic Contacts to n-Type GaN via Hydrogen Plasma-Assisted Atomic Layer Deposition of Sub-Nanometer AlOx},
author = {M Christis and A Henning and J D Bartl and A Zeidler and B Rieger and M Stutzmann and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.202300758},
doi = {https://doi.org/10.1002/admi.202300758},
issn = {2196-7350},
year = {2023},
date = {2023-12-01},
journal = {Advanced Materials Interfaces},
volume = {n/a},
number = {n/a},
pages = {2300758},
abstract = {Abstract A plasma-assisted atomic layer deposition (PE-ALD) process is reported for creating ohmic contacts to n-type GaN that combines native oxide reduction, near-surface doping, and encapsulation of GaN in a single processing step, thereby eliminating the need for both wet chemical etching of the native oxide before metallization and thermal annealing after contact formation. Repeated ALD cycling of trimethyl aluminum (TMA) and high-intensity hydrogen (H2) plasma results in the deposition of a sub-nanometer-thin (≈8 r{A}) AlOx layer via the partial transformation of the GaN surface oxide into AlOx. Hydrogen plasma-induced nitrogen vacancies in the near-surface region of GaN serve as shallow donors, promoting efficient out-of-plane electrical transport. Subsequent metallization with a Ti/Al/Ti/Au stack results in low contact resistance, ohmic behavior, and smooth morphology without requiring annealing. This electrical contracting approach thus meets the thermal budget requirements for Si-based complementary metal\textendashoxide\textendashsemiconductor structures and can facilitate the design and fabrication of advanced GaN-on-Si heterodevices.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract A plasma-assisted atomic layer deposition (PE-ALD) process is reported for creating ohmic contacts to n-type GaN that combines native oxide reduction, near-surface doping, and encapsulation of GaN in a single processing step, thereby eliminating the need for both wet chemical etching of the native oxide before metallization and thermal annealing after contact formation. Repeated ALD cycling of trimethyl aluminum (TMA) and high-intensity hydrogen (H2) plasma results in the deposition of a sub-nanometer-thin (≈8 Å) AlOx layer via the partial transformation of the GaN surface oxide into AlOx. Hydrogen plasma-induced nitrogen vacancies in the near-surface region of GaN serve as shallow donors, promoting efficient out-of-plane electrical transport. Subsequent metallization with a Ti/Al/Ti/Au stack results in low contact resistance, ohmic behavior, and smooth morphology without requiring annealing. This electrical contracting approach thus meets the thermal budget requirements for Si-based complementary metal–oxide–semiconductor structures and can facilitate the design and fabrication of advanced GaN-on-Si heterodevices.
10.
P M Stanley, A Y Su, V Ramm, P Fink, C Kimna, O Lieleg, M Elsner, J A Lercher, B Rieger, J Warnan, R A Fischer
Photocatalytic CO2-to-Syngas Evolution with Molecular Catalyst Metal-Organic Framework Nanozymes Journal Article
In: Advanced Materials, vol. 35, iss. 6, pp. 2207380, 2023, ISSN: 0935-9648.
@article{nokey,
title = {Photocatalytic CO2-to-Syngas Evolution with Molecular Catalyst Metal-Organic Framework Nanozymes},
author = {P M Stanley and A Y Su and V Ramm and P Fink and C Kimna and O Lieleg and M Elsner and J A Lercher and B Rieger and J Warnan and R A Fischer},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202207380},
doi = {https://doi.org/10.1002/adma.202207380},
issn = {0935-9648},
year = {2023},
date = {2023-02-01},
urldate = {2023-02-01},
journal = {Advanced Materials},
volume = {35},
issue = {6},
pages = {2207380},
abstract = {Abstract Syngas, a mixture of CO and H2, is a high-priority intermediate for producing several commodity chemicals, e.g., ammonia, methanol, and synthetic hydrocarbon fuels. Accordingly, parallel sunlight-driven catalytic conversion of CO2 and protons to syngas is a key step toward a sustainable energy cycle. State-of-the-art catalytic systems and materials often fall short as application-oriented concurrent CO and H2 evolution requires challenging reaction conditions which can hamper stability, selectivity, and efficiency. Here a light-harvesting metal-organic framework hosting two molecular catalysts is engineered to yield colloidal, water-stable, versatile nanoreactors for photocatalytic syngas generation with highly controllable product ratios. In-depth fluorescence, X-ray, and microscopic studies paired with kinetic analysis show that the host delivers energy efficiently to active sites, conceptually yielding nanozymes. This unlocked sustained CO2 reduction and H2 evolution with benchmark turnover numbers and record incident photon conversions up to 36%, showcasing a highly active and durable all-in-one material toward application in solar energy-driven syngas generation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Syngas, a mixture of CO and H2, is a high-priority intermediate for producing several commodity chemicals, e.g., ammonia, methanol, and synthetic hydrocarbon fuels. Accordingly, parallel sunlight-driven catalytic conversion of CO2 and protons to syngas is a key step toward a sustainable energy cycle. State-of-the-art catalytic systems and materials often fall short as application-oriented concurrent CO and H2 evolution requires challenging reaction conditions which can hamper stability, selectivity, and efficiency. Here a light-harvesting metal-organic framework hosting two molecular catalysts is engineered to yield colloidal, water-stable, versatile nanoreactors for photocatalytic syngas generation with highly controllable product ratios. In-depth fluorescence, X-ray, and microscopic studies paired with kinetic analysis show that the host delivers energy efficiently to active sites, conceptually yielding nanozymes. This unlocked sustained CO2 reduction and H2 evolution with benchmark turnover numbers and record incident photon conversions up to 36%, showcasing a highly active and durable all-in-one material toward application in solar energy-driven syngas generation.
9.
A Henning, J D Bartl, L Wolz, M Christis, F Rauh, M Bissolo, T Grünleitner, J Eichhorn, P Zeller, M Amati, L Gregoratti, J J Finley, B Rieger, M Stutzmann, I D Sharp
Spatially-Modulated Silicon Interface Energetics Via Hydrogen Plasma-Assisted Atomic Layer Deposition of Ultrathin Alumina Journal Article
In: Advanced Materials Interfaces, vol. 10, iss. 6, pp. 2202166, 2022, ISSN: 2196-7350.
@article{nokey,
title = {Spatially-Modulated Silicon Interface Energetics Via Hydrogen Plasma-Assisted Atomic Layer Deposition of Ultrathin Alumina},
author = {A Henning and J D Bartl and L Wolz and M Christis and F Rauh and M Bissolo and T Gr\"{u}nleitner and J Eichhorn and P Zeller and M Amati and L Gregoratti and J J Finley and B Rieger and M Stutzmann and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.202202166},
doi = {https://doi.org/10.1002/admi.202202166},
issn = {2196-7350},
year = {2022},
date = {2022-12-16},
urldate = {2022-12-16},
journal = {Advanced Materials Interfaces},
volume = {10},
issue = {6},
pages = {2202166},
abstract = {Abstract Atomic layer deposition (ALD) is a key technique for the continued scaling of semiconductor devices, which increasingly relies on scalable processes for interface manipulation of structured surfaces on the atomic level. While ALD allows the synthesis of conformal films with utmost control over the thickness, atomically-defined closed coatings and surface modifications are challenging to achieve because of 3D growth during nucleation. Here, a route is presented toward the sub-nanometer thin and continuous aluminum oxide (AlOx) coatings on silicon substrates for the spatial control of the surface charge density and interface energetics. Trimethylaluminum in combination with remote hydrogen plasma is used instead of a gas-phase oxidant for the transformation of silicon dioxide (SiO2) into alumina. Depending on the number of ALD cycles, the SiO2 can be partially or fully transformed, which is exploited to deposit ultrathin AlOx layers in selected regions defined by lithographic patterning. The resulting patterned surfaces are characterized by lateral AlOx/SiO2 interfaces possessing 0.3 nm step heights and surface potential steps exceeding 0.4 V. In addition, the introduction of fixed negative charges of 9 × 1012 cm−2 enables modulation of the surface band bending, which is relevant to the field-effect passivation of silicon and low-impedance charge transfer across contact interfaces.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Atomic layer deposition (ALD) is a key technique for the continued scaling of semiconductor devices, which increasingly relies on scalable processes for interface manipulation of structured surfaces on the atomic level. While ALD allows the synthesis of conformal films with utmost control over the thickness, atomically-defined closed coatings and surface modifications are challenging to achieve because of 3D growth during nucleation. Here, a route is presented toward the sub-nanometer thin and continuous aluminum oxide (AlOx) coatings on silicon substrates for the spatial control of the surface charge density and interface energetics. Trimethylaluminum in combination with remote hydrogen plasma is used instead of a gas-phase oxidant for the transformation of silicon dioxide (SiO2) into alumina. Depending on the number of ALD cycles, the SiO2 can be partially or fully transformed, which is exploited to deposit ultrathin AlOx layers in selected regions defined by lithographic patterning. The resulting patterned surfaces are characterized by lateral AlOx/SiO2 interfaces possessing 0.3 nm step heights and surface potential steps exceeding 0.4 V. In addition, the introduction of fixed negative charges of 9 × 1012 cm−2 enables modulation of the surface band bending, which is relevant to the field-effect passivation of silicon and low-impedance charge transfer across contact interfaces.
8.
C Thomas, M Wittig, B Rieger
The Puzzling Question about the Origin of the Second Electron in the Molecular Photocatalytic Reduction of CO2 Journal Article
In: ChemCatChem, vol. 14, no. 21, pp. e202200841, 2022, ISSN: 1867-3880.
@article{nokey,
title = {The Puzzling Question about the Origin of the Second Electron in the Molecular Photocatalytic Reduction of CO2},
author = {C Thomas and M Wittig and B Rieger},
url = {https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cctc.202200841},
doi = {https://doi.org/10.1002/cctc.202200841},
issn = {1867-3880},
year = {2022},
date = {2022-09-04},
journal = {ChemCatChem},
volume = {14},
number = {21},
pages = {e202200841},
abstract = {Abstract Herein, a new supramolecular photocatalyst RuRe3 containing three Re(dmb)CO3Cl (dmb=4,4‘-dimethyl-2,2‘-bipyridine) (Re) building blocks connected through an ethylene bridge to one [Ru(dmb)3]2+-unit (Ru) is presented. We investigated the photophysical properties of this novel tetranuclear complex and compared these to compounds with one (RuRe) and two (RuRe2) catalytic units. Under irradiation, all three photocatalysts exhibit high activity and photostability for the reduction of CO2 to CO, with RuRe3 achieving the highest turnover number (11800) reported to date for a Re(I)/Ru(II)-containing homogeneous catalyst. This tetranuclear complex is especially superior at small catalyst concentrations, which is attributed to an efficient second electron transfer via an intramolecular mechanism. Intermolecular electron transfer from small and mobile Re to RuRe motifs are found to also increase the catalytic performance of the system to a similar level (turnover number=12100). These synergistic effects are attributed to an improved catalytic cycle, stabilizing the bi- and tetrametallic complexes by providing the electrons quickly and effectively. Since the second electron provision is not finally clarified for molecular systems until today, our photocatalytic studies present important insights into this crucial step. Further, these investigations should be considered for the design and synthesis of new and efficient supramolecular CO2-reducing photocatalysts.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Herein, a new supramolecular photocatalyst RuRe3 containing three Re(dmb)CO3Cl (dmb=4,4‘-dimethyl-2,2‘-bipyridine) (Re) building blocks connected through an ethylene bridge to one [Ru(dmb)3]2+-unit (Ru) is presented. We investigated the photophysical properties of this novel tetranuclear complex and compared these to compounds with one (RuRe) and two (RuRe2) catalytic units. Under irradiation, all three photocatalysts exhibit high activity and photostability for the reduction of CO2 to CO, with RuRe3 achieving the highest turnover number (11800) reported to date for a Re(I)/Ru(II)-containing homogeneous catalyst. This tetranuclear complex is especially superior at small catalyst concentrations, which is attributed to an efficient second electron transfer via an intramolecular mechanism. Intermolecular electron transfer from small and mobile Re to RuRe motifs are found to also increase the catalytic performance of the system to a similar level (turnover number=12100). These synergistic effects are attributed to an improved catalytic cycle, stabilizing the bi- and tetrametallic complexes by providing the electrons quickly and effectively. Since the second electron provision is not finally clarified for molecular systems until today, our photocatalytic studies present important insights into this crucial step. Further, these investigations should be considered for the design and synthesis of new and efficient supramolecular CO2-reducing photocatalysts.
7.
A S Maier, C Thomas, M Kränzlein, T M Pehl, B Rieger
In: Macromolecules, 2022, ISSN: 0024-9297.
@article{nokey,
title = {Macromolecular Rhenium\textendashRuthenium Complexes for Photocatalytic CO2 Conversion: From Catalytic Lewis Pair Polymerization to Well-Defined Poly(vinyl bipyridine)\textendashMetal Complexes},
author = {A S Maier and C Thomas and M Kr\"{a}nzlein and T M Pehl and B Rieger},
url = {https://doi.org/10.1021/acs.macromol.2c00440},
doi = {10.1021/acs.macromol.2c00440},
issn = {0024-9297},
year = {2022},
date = {2022-06-23},
journal = {Macromolecules},
abstract = {Herein, the first catalytical polymerization of 4-vinyl-4′-methyl-2,2′-bipyridine (VBpy) via Lewis pair-mediated group-transfer polymerization using different combinations of Lewis acidic trialkyl aluminum compounds and Lewis basic phosphines is reported. In this context, a broad screening of different Lewis pairs is conducted, demonstrating the necessity of an adjustment of the steric and electronic properties of the Lewis pair to the demands of the monomer. Further, end-group analysis of short-chain oligomers via electrospray ionization mass spectrometry (ESI-MS) for the experimentally determined optimum combination Al(i-Bu)3/PMe3 ({D} = 1.31\textendash1.36},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Herein, the first catalytical polymerization of 4-vinyl-4′-methyl-2,2′-bipyridine (VBpy) via Lewis pair-mediated group-transfer polymerization using different combinations of Lewis acidic trialkyl aluminum compounds and Lewis basic phosphines is reported. In this context, a broad screening of different Lewis pairs is conducted, demonstrating the necessity of an adjustment of the steric and electronic properties of the Lewis pair to the demands of the monomer. Further, end-group analysis of short-chain oligomers via electrospray ionization mass spectrometry (ESI-MS) for the experimentally determined optimum combination Al(i-Bu)3/PMe3 (Đ = 1.31–1.36
6.
J D Bartl, C Thomas, A Henning, M F Ober, G Savasci, B Yazdanshenas, P S Deimel, E Magnano, F Bondino, P Zeller, L Gregoratti, M Amati, C Paulus, F Allegretti, A Cattani-Scholz, J V Barth, C Ochsenfeld, B Nickel, I D Sharp, M Stutzmann, B Rieger
Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon Journal Article
In: Journal of the American Chemical Society, vol. 143, pp. 19505, 2021, ISSN: 0002-7863.
@article{nokey,
title = {Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon},
author = {J D Bartl and C Thomas and A Henning and M F Ober and G Savasci and B Yazdanshenas and P S Deimel and E Magnano and F Bondino and P Zeller and L Gregoratti and M Amati and C Paulus and F Allegretti and A Cattani-Scholz and J V Barth and C Ochsenfeld and B Nickel and I D Sharp and M Stutzmann and B Rieger},
url = {https://doi.org/10.1021/jacs.1c09061},
doi = {10.1021/jacs.1c09061},
issn = {0002-7863},
year = {2021},
date = {2021-11-12},
urldate = {2021-11-12},
journal = {Journal of the American Chemical Society},
volume = {143},
pages = {19505},
abstract = {Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.
5.
A Henning, J D Bartl, A Zeidler, S Qian, O Bienek, C-M Jiang, C Paulus, B Rieger, M Stutzmann, I D Sharp
Aluminum Oxide at the Monolayer Limit via Oxidant-Free Plasma-Assisted Atomic Layer Deposition on GaN Journal Article
In: Advanced Functional Materials, vol. 31, no. 33, pp. 2101441, 2021, ISSN: 1616-301X.
@article{nokey,
title = {Aluminum Oxide at the Monolayer Limit via Oxidant-Free Plasma-Assisted Atomic Layer Deposition on GaN},
author = {A Henning and J D Bartl and A Zeidler and S Qian and O Bienek and C-M Jiang and C Paulus and B Rieger and M Stutzmann and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202101441},
doi = {https://doi.org/10.1002/adfm.202101441},
issn = {1616-301X},
year = {2021},
date = {2021-06-12},
journal = {Advanced Functional Materials},
volume = {31},
number = {33},
pages = {2101441},
abstract = {Abstract Atomic layer deposition (ALD) is an essential tool in semiconductor device fabrication that allows the growth of ultrathin and conformal films to precisely form heterostructures and tune interface properties. The self-limiting nature of the chemical reactions during ALD provides excellent control over the layer thickness. However, in contrast to idealized growth models, it is challenging to create continuous monolayers by ALD because surface inhomogeneities and precursor steric interactions result in island growth. Thus, the ability to create closed monolayers by ALD would offer new opportunities for controlling interfacial charge and mass transport in semiconductor devices, as well as for tailoring surface chemistry. Here, encapsulation of c-plane gallium nitride (GaN) with ultimately thin (≈3 r{A}) aluminum oxide (AlOx) is reported, which is enabled by the partial conversion of the GaN surface oxide into AlOx using sequential exposure to trimethylaluminum (TMA) and hydrogen plasma. Introduction of monolayer AlOx decreases the work function and enhances reactivity with phosphonic acids under standard conditions, which results in self-assembled monolayers with densities approaching the theoretical limit. Given the high reactivity of TMA with surface oxides, the presented approach likely can be extended to other dielectrics and III\textendashV-based semiconductors, with relevance for applications in optoelectronics, chemical sensing, and (photo)electrocatalysis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Atomic layer deposition (ALD) is an essential tool in semiconductor device fabrication that allows the growth of ultrathin and conformal films to precisely form heterostructures and tune interface properties. The self-limiting nature of the chemical reactions during ALD provides excellent control over the layer thickness. However, in contrast to idealized growth models, it is challenging to create continuous monolayers by ALD because surface inhomogeneities and precursor steric interactions result in island growth. Thus, the ability to create closed monolayers by ALD would offer new opportunities for controlling interfacial charge and mass transport in semiconductor devices, as well as for tailoring surface chemistry. Here, encapsulation of c-plane gallium nitride (GaN) with ultimately thin (≈3 Å) aluminum oxide (AlOx) is reported, which is enabled by the partial conversion of the GaN surface oxide into AlOx using sequential exposure to trimethylaluminum (TMA) and hydrogen plasma. Introduction of monolayer AlOx decreases the work function and enhances reactivity with phosphonic acids under standard conditions, which results in self-assembled monolayers with densities approaching the theoretical limit. Given the high reactivity of TMA with surface oxides, the presented approach likely can be extended to other dielectrics and III–V-based semiconductors, with relevance for applications in optoelectronics, chemical sensing, and (photo)electrocatalysis.
4.
P M Stanley, J Haimerl, C Thomas, A Urstoeger, M Schuster, N B Shustova, A Casini, B Rieger, J Warnan, R A Fischer
Host–Guest Interactions in a Metal–Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction Journal Article
In: Angewandte Chemie International Edition, vol. 60, no. 33, pp. 17854-17860, 2021, ISSN: 1433-7851.
@article{nokey,
title = {Host\textendashGuest Interactions in a Metal\textendashOrganic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction},
author = {P M Stanley and J Haimerl and C Thomas and A Urstoeger and M Schuster and N B Shustova and A Casini and B Rieger and J Warnan and R A Fischer},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202102729},
doi = {https://doi.org/10.1002/anie.202102729},
issn = {1433-7851},
year = {2021},
date = {2021-05-20},
journal = {Angewandte Chemie International Edition},
volume = {60},
number = {33},
pages = {17854-17860},
abstract = {Abstract A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co-immobilization of a CO2 reduction catalyst [ReBr(CO)3(4,4′-dcbpy)] and a photosensitizer [Ru(bpy)2(5,5′-dcbpy)]Cl2 using the isoreticular series of metal\textendashorganic frameworks (MOFs) UiO-66, -67, and -68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location\textemdasheither at the outer MOF particle surface or inside the MOF cavities\textemdashaffecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co-immobilization of a CO2 reduction catalyst [ReBr(CO)3(4,4′-dcbpy)] and a photosensitizer [Ru(bpy)2(5,5′-dcbpy)]Cl2 using the isoreticular series of metal–organic frameworks (MOFs) UiO-66, -67, and -68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location—either at the outer MOF particle surface or inside the MOF cavities—affecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.
3.
P M Stanley, M Parkulab, B Rieger, J Warnan, R A Fischer
Understanding entrapped molecular photosystem and metal–organic framework synergy for improved solar fuel production Journal Article
In: Faraday Discussions, vol. 231, no. 0, pp. 281-297, 2021, ISSN: 1359-6640.
@article{nokey,
title = {Understanding entrapped molecular photosystem and metal\textendashorganic framework synergy for improved solar fuel production},
author = {P M Stanley and M Parkulab and B Rieger and J Warnan and R A Fischer},
url = {http://dx.doi.org/10.1039/D1FD00009H},
doi = {10.1039/D1FD00009H},
issn = {1359-6640},
year = {2021},
date = {2021-04-27},
urldate = {2021-04-27},
journal = {Faraday Discussions},
volume = {231},
number = {0},
pages = {281-297},
abstract = {Artificial photosystems assembled from molecular complexes, such as the photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and the photosensitiser Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine), are a wide-spread approach for solar fuel production. Recently metal\textendashorganic framework (MOF) entrapping of such complexes was demonstrated as a promising concept for catalyst stabilisation and reaction environment optimisation in colloidal-based CO2 reduction. Building on this strategy, here we examined the influence of MIL-101-NH2(Al) MOF particle size, the electron donor source, and the presence of an organic base on the photocatalytic CO2-to-CO reduction performance, and the differences to homogeneous systems. A linear relation between smaller scaffold particle size and higher photocatalytic activity, longer system lifetimes for benign electron donors, and increased turnover numbers (TONs) with certain additive organic bases, were determined. This enabled understanding of key molecular catalysis phenomena and synergies in the nanoreactor-like host\textendashguest assembly, and yielded TONs of ∼4300 over 96 h of photocatalysis under optimised conditions, surpassing homogeneous TON values and lifetimes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Artificial photosystems assembled from molecular complexes, such as the photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and the photosensitiser Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine), are a wide-spread approach for solar fuel production. Recently metal–organic framework (MOF) entrapping of such complexes was demonstrated as a promising concept for catalyst stabilisation and reaction environment optimisation in colloidal-based CO2 reduction. Building on this strategy, here we examined the influence of MIL-101-NH2(Al) MOF particle size, the electron donor source, and the presence of an organic base on the photocatalytic CO2-to-CO reduction performance, and the differences to homogeneous systems. A linear relation between smaller scaffold particle size and higher photocatalytic activity, longer system lifetimes for benign electron donors, and increased turnover numbers (TONs) with certain additive organic bases, were determined. This enabled understanding of key molecular catalysis phenomena and synergies in the nanoreactor-like host–guest assembly, and yielded TONs of ∼4300 over 96 h of photocatalysis under optimised conditions, surpassing homogeneous TON values and lifetimes.
2.
P M Stanley, C Thomas, E Thyrhaug, A Urstoeger, M Schuster, J Hauer, B Rieger, J Warnan, R A Fischer
Entrapped Molecular Photocatalyst and Photosensitizer in Metal–Organic Framework Nanoreactors for Enhanced Solar CO2 Reduction Journal Article
In: ACS Catalysis, vol. 11, no. 2, pp. 871-882, 2021.
@article{,
title = {Entrapped Molecular Photocatalyst and Photosensitizer in Metal\textendashOrganic Framework Nanoreactors for Enhanced Solar CO2 Reduction},
author = {P M Stanley and C Thomas and E Thyrhaug and A Urstoeger and M Schuster and J Hauer and B Rieger and J Warnan and R A Fischer},
url = {https://doi.org/10.1021/acscatal.0c04673},
doi = {10.1021/acscatal.0c04673},
year = {2021},
date = {2021-01-05},
urldate = {2021-01-05},
journal = {ACS Catalysis},
volume = {11},
number = {2},
pages = {871-882},
abstract = {Herein, we report on a molecular catalyst embedding metal\textendashorganic framework (MOF) that enables enhanced photocatalytic CO2 reduction activity. A benchmark photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine) were synergistically entrapped inside the cages of the nontoxic and inexpensive MIL-101-NH2(Al) through noncovalent host\textendashguest interactions. The heterogeneous material improved Re catalyst stabilization under photocatalytic CO2 reduction conditions as selective CO evolution was prolonged from 1.5 to 40 h compared to the MOF-free photosystem upon reactivation with additional photosensitizer. By varying ratios of immobilized catalyst to photosensitizer, we demonstrated and evaluated the effect of reaction environment modulation in defined MOF cages acting as a nanoreactor. This illustrated the optimal efficiency for two photosensitizers and one catalyst per cage and further led to the determination of ad hoc relationships between molecular complex size, MOF pore windows, and number of hostable molecules per cage. Differing from typical homogeneous systems, photosensitizer\textemdashand not catalyst\textemdashdegradation was identified as a major performance-limiting factor, providing a future route to higher turnover numbers via a rational choice of parameters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Herein, we report on a molecular catalyst embedding metal–organic framework (MOF) that enables enhanced photocatalytic CO2 reduction activity. A benchmark photocatalyst fac-ReBr(CO)3(4,4′-dcbpy) (dcbpy = dicarboxy-2,2′-bipyridine) and photosensitizer Ru(bpy)2(5,5′-dcbpy)Cl2 (bpy = 2,2′-bipyridine) were synergistically entrapped inside the cages of the nontoxic and inexpensive MIL-101-NH2(Al) through noncovalent host–guest interactions. The heterogeneous material improved Re catalyst stabilization under photocatalytic CO2 reduction conditions as selective CO evolution was prolonged from 1.5 to 40 h compared to the MOF-free photosystem upon reactivation with additional photosensitizer. By varying ratios of immobilized catalyst to photosensitizer, we demonstrated and evaluated the effect of reaction environment modulation in defined MOF cages acting as a nanoreactor. This illustrated the optimal efficiency for two photosensitizers and one catalyst per cage and further led to the determination of ad hoc relationships between molecular complex size, MOF pore windows, and number of hostable molecules per cage. Differing from typical homogeneous systems, photosensitizer—and not catalyst—degradation was identified as a major performance-limiting factor, providing a future route to higher turnover numbers via a rational choice of parameters.
1.
W Li, S Watzele, H A El-Sayed, Y Liang, G Kieslich, A S Bandarenka, K Rodewald, B Rieger, R A Fischer
Unprecedented High Oxygen Evolution Activity of Electrocatalysts Derived from Surface-Mounted Metal–Organic Frameworks Journal Article
In: Journal of the American Chemical Society, vol. 141, no. 14, pp. 5926-5933, 2019, ISSN: 0002-7863.
@article{,
title = {Unprecedented High Oxygen Evolution Activity of Electrocatalysts Derived from Surface-Mounted Metal\textendashOrganic Frameworks},
author = {W Li and S Watzele and H A El-Sayed and Y Liang and G Kieslich and A S Bandarenka and K Rodewald and B Rieger and R A Fischer},
url = {https://doi.org/10.1021/jacs.9b00549},
doi = {10.1021/jacs.9b00549},
issn = {0002-7863},
year = {2019},
date = {2019-03-19},
journal = {Journal of the American Chemical Society},
volume = {141},
number = {14},
pages = {5926-5933},
abstract = {The oxygen evolution reaction (OER) is a key process for renewable energy storage. However, developing non-noble metal OER electrocatalysts with high activity, long durability and scalability remains a major challenge. Herein, high OER activity and stability in alkaline solution were discovered for mixed nickel/cobalt hydroxide electrocatalysts, which were derived in one-step procedure from oriented surface-mounted metal\textendashorganic framework (SURMOF) thin films that had been directly grown layer-by-layer on macro- and microelectrode substrates. The obtained mass activity of ∼2.5 mA·μg\textendash1 at the defined overpotential of 300 mV is 1 order of magnitude higher than that of the benchmarked IrO2 electrocatalyst and at least 3.5 times higher than the mass activity of any state-of-the-art NiFe-, FeCoW-, or NiCo-based electrocatalysts reported in the literature. The excellent morphology of the SURMOF-derived ultrathin electrocatalyst coating led to a high exposure of the most active Ni- and Co-based sites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The oxygen evolution reaction (OER) is a key process for renewable energy storage. However, developing non-noble metal OER electrocatalysts with high activity, long durability and scalability remains a major challenge. Herein, high OER activity and stability in alkaline solution were discovered for mixed nickel/cobalt hydroxide electrocatalysts, which were derived in one-step procedure from oriented surface-mounted metal–organic framework (SURMOF) thin films that had been directly grown layer-by-layer on macro- and microelectrode substrates. The obtained mass activity of ∼2.5 mA·μg–1 at the defined overpotential of 300 mV is 1 order of magnitude higher than that of the benchmarked IrO2 electrocatalyst and at least 3.5 times higher than the mass activity of any state-of-the-art NiFe-, FeCoW-, or NiCo-based electrocatalysts reported in the literature. The excellent morphology of the SURMOF-derived ultrathin electrocatalyst coating led to a high exposure of the most active Ni- and Co-based sites.