Browsing by Author "Abel, Bernd"
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- ItemControlled electron-beam synthesis of transparent hydrogels for drug delivery applications(Basel : MDPI, 2019) Glass, Sarah; Kühnert, Mathias; Abel, Bernd; Schulze, AgnesIn this study, we highlight hydrogels prepared by electron-beam polymerization. In general, the electron-beam-polymerized hydrogels showed improved mechanical and optical transmittances compared to the conventional UV-cured hydrogels. They were more elastic and had a higher crosslinking density. Additionally, they were transparent over a broader wavelength range. The dependence of the mechanical and optical properties of the hydrogels on the number of single differential and total irradiation doses was analyzed in detail. The hydrogels were prepared for usage as a drug delivery material with methylene blue as a drug model. In the first set of experiments, methylene blue was loaded reversibly after the hydrogel synthesis. Electron-beam-polymerized hydrogels incorporated twice as much methylene blue compared to the UV-polymerized gels. Furthermore, the release of the model drug was found to depend on the crosslinking degree of the hydrogels. In addition, electron-beam polymerization enabled the irreversible binding of the drug molecules if they were mixed with monomers before polymerization.
- ItemConversion of carbon dioxide into storable solar fuels using solar energy(London [u.a.] : Institute of Physics, 2019) Ennaceri, Houda; Abel, BerndNowadays, there are two main energy and environmental concerns, the first is the risk of running out of fossil fuels in the next few decades, and the second is the alarming increase in the carbon dioxide concentrations in the atmosphere, causing global warming and rise of see levels. Therefore, solar-driven technologies represent a substantial solution to fossil fuels dependence, global warming and climate change. Unlike most scientific research, which aim to use solar energy to generate electricity, solar energy can also be harnessed by recycling the carbon dioxide in the atmosphere through high-tech artificial photosynthesis with the objective of producing storable and liquid solar fuels from CO2 and water. There are two types of solar fuels, the first being hydrogen, which can be produced by mean of water splitting processes. The combustion of hydrogen generates water, which is a completely clean option for the environment. The second type of solar fuels consists of carbon-based fuels, such as methane (CH4), carbon monoxide (CO), or alcohols such as methanol (CH3OH) and ethanol (C2H5OH). The production to liquid solar fuels liquid fuels is of great interest, since they can be used in the current industrial infrastructures such as the automobiles' sector, without substantial changes in the vehicles' internal combustion engines. Therefore, guaranteeing a smooth transition from fossil fuel energy to renewable energy without radical economic consequences. Also, and most importantly, when these solar fuels are burned, they will only release the exact amount of CO2 which was initially used, which represents an optimal process for sustainable transport.
- ItemCoordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands(Frankfurt, Main : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2019) Klose, Jennifer; Severin, Tobias; Hahn, Peter; Jeremies, Alexander; Bergmann, Jens; Fuhrmann, Daniel; Griebel, Jan; Abel, Bernd; Kersting, BertholdThe synthesis of mixed-ligand complexes of the type [M2L(μ-L')]+, where L represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, L' is an azobenzene carboxylate co-ligand, and M = Cd(II), Ni(II) or Zn(II), is reported. A series of new complexes were synthesized, namely [M2L(μ-L')]+ (L' = azo-H, M = Cd (1), Ni (2); L' = azo-OH, M = Zn (3), Ni (4); L' = azo-NMe2, M = Zn (5), Cd (6), Ni (7); L' = azo-CO2Me, M = Cd (8), Ni (9)), and characterized by elemental analysis, electro-spray ionization mass spectrometry (ESIMS), IR, UV–vis and NMR spectroscopy (for diamagnetic Zn and Cd complexes) and X-ray single crystal structure analysis. The crystal structures of 3' and 5–8 display an isostructural series of compounds with bridging azobenzene carboxylates in the trans form. The paramagnetic Ni complexes 2, 4 and 7 reveal a weak ferromagnetic exchange interaction with magnetic exchange coupling constant values between 21 and 23 cm−1 (H = −2JS1S2). Irradiation of 1 with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form. © 2019 Klose et al.
- ItemCryo-printed microfluidics enable rapid prototyping for optical-cell analysis(Heidelberg : Springer, 2022) Garmasukis, Rokas; Hackl, Claudia; Dusny, Christian; Elsner, Christian; Charvat, Ales; Schmid, Andreas; Abel, BerndThis paper highlights an innovative, low-cost rapid-prototyping method for generating microfluidic chips with extraordinary short fabrication times of only a few minutes. Microchannels and inlet/outlet ports are created by controlled deposition of aqueous microdroplets on a cooled surface resulting in printed ice microstructures, which are in turn coated with a UV-curable acrylic cover layer. Thawing leaves an inverse imprint as a microchannel structure. For an exemplary case, we applied this technology for creating a microfluidic chip for cell-customized optical-cell analysis. The chip design includes containers for cell cultivation and analysis. Container shape, length, position, and angle relative to the main channel were iteratively optimized to cultivate and analyze different cell types. With the chip, we performed physiological analyses of morphologically distinct prokaryotic Corynebacterium glutamicum DM1919, eukaryotic Hansenula polymorpha RB11 MOX-GFP, and phototrophic Synechocystis sp. PCC 6803 cells via quantitative time-lapse fluorescence microscopy. The technology is not limited to rapid prototyping of complex biocompatible microfluidics. Further exploration may include printing with different materials other than water, printing on other substrates in-situ biofunctionalization, the inclusion of electrodes and many other applications.
- ItemCurvature model for nanoparticle size effects on peptide fibril stability and molecular dynamics simulation data(Amsterdam [u.a.] : Elsevier, 2022) John, Torsten; Martin, Lisandra L.; Risselada, Herre Jelger; Abel, BerndNanostructured surfaces are widespread in nature and are being further developed in materials science. This makes them highly relevant for biomolecules, such as peptides. In this data article, we present a curvature model and molecular dynamics (MD) simulation data on the influence of nanoparticle size on the stability of amyloid peptide fibrils related to our research article entitled “Mechanistic insights into the size-dependent effects of nanoparticles on inhibiting and accelerating amyloid fibril formation” (John et al., 2022) [1]. We provide the code to perform MD simulations in GROMACS 4.5.7 software of arbitrarily chosen biomolecule oligomers adsorbed on a curved surface of chosen nanoparticle size. We also provide the simulation parameters and data for peptide oligomers of Aß40, NNFGAIL, GNNQQNY, and VQIYVK. The data provided allows researchers to further analyze our MD simulations and the curvature model allows for a better understanding of oligomeric structures on surfaces.
- ItemDeposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017) Börner, Martin; Blömer, Laura; Kischel, Marcus; Richter, Peter; Salvan, Georgeta; Zahn, Dietrich R. T.; Siles, Pablo F.; Fuentes, Maria E. N.; Bufon, Carlos C. B.; Grimm, Daniel; Schmidt, Oliver G.; Breite, Daniel; Abel, Bernd; Kersting, BertholdThe chemisorption of magnetically bistable transition metal complexes on planar surfaces has recently attracted increased scientific interest due to its potential application in various fields, including molecular spintronics. In this work, the synthesis of mixed-ligand complexes of the type [NiII2L(L’)](ClO4), where L represents a 24-membered macrocyclic hexaazadithiophenolate ligand and L’ is a ω-mercapto-carboxylato ligand (L’ = HS(CH2)5CO2− (6), HS(CH2)10CO2− (7), or HS(C6H4)2CO2− (8)), and their ability to adsorb on gold surfaces is reported. Besides elemental analysis, IR spectroscopy, electrospray ionization mass spectrometry (ESIMS), UV–vis spectroscopy, and X-ray crystallography (for 6 and 7), the compounds were also studied by temperature-dependent magnetic susceptibility measurements (for 7 and 8) and (broken symmetry) density functional theory (DFT) calculations. An S = 2 ground state is demonstrated by temperature-dependent susceptibility and magnetization measurements, achieved by ferromagnetic coupling between the spins of the Ni(II) ions in 7 (J = +22.3 cm−1) and 8 (J = +20.8 cm−1; H = −2JS1S2). The reactivity of complexes 6–8 is reminiscent of that of pure thiolato ligands, which readily chemisorb on Au surfaces as verified by contact angle, atomic force microscopy (AFM) and spectroscopic ellipsometry measurements. The large [Ni2L] tail groups, however, prevent the packing and self-assembly of the hydrocarbon chains. The smaller film thickness of 7 is attributed to the specific coordination mode of the coligand. Results of preliminary transport measurements utilizing rolled-up devices are also reported.
- ItemDeveloping a Laser Induced Liquid Beam Ion Desorption Spectral Database as Reference for Spaceborne Mass Spectrometers(Malden, Mass. : American Geophysical Union, 2022) Klenner, Fabian; Umair, Muhammad; Walter, Sebastian H. G.; Khawaja, Nozair; Hillier, Jon; Nölle, Lenz; Zou, Zenghui; Napoleoni, Maryse; Sanderink, Arnaud; Zuschneid, Wilhelm; Abel, Bernd; Postberg, FrankSpaceborne impact ionization mass spectrometers, such as the Cosmic Dust Analyzer on board the past Cassini spacecraft or the SUrface Dust Analyzer being built for NASA's upcoming Europa Clipper mission, are of crucial importance for the exploration of icy moons in the Solar System, such as Saturn's moon Enceladus or Jupiter's moon Europa. For the interpretation of data produced by these instruments, analogue experiments on Earth are essential. To date, thousands of laboratory mass spectra have been recorded with an analogue experiment for impact ionization mass spectrometers. Simulation of mass spectra of ice grains in space is achieved by a Laser Induced Liquid Beam Ion Desorption (LILBID) approach. The desorbed cations or anions are analyzed in a time-of-flight mass spectrometer. The amount of unstructured raw data is increasingly challenging to sort, process, interpret and compare with data from space. Thus far this has been achieved manually for individual mass spectra because no database containing the recorded reference spectra was available. Here we describe the development of a comprehensive, extendable database containing cation and anion mass spectra from the laboratory LILBID facility. The database is based on a Relational Database Management System with a web server interface and enables filtering of the laboratory data using a wide range of parameters. The mass spectra can be compared not only with data from past and future space missions but also mass spectral data generated by other, terrestrial, techniques. The validated and approved subset of the database is available for general public (https://lilbid-db.planet.fu-berlin.de).
- ItemDinuclear lanthanide complexes supported by a hybrid salicylaldiminato/calix[4]arene-ligand: Synthesis, structure, and magnetic and luminescence properties of (HNEt3)[Ln2(HL)(L)] (Ln = SmIII, EuIII, GdIII, TbIII)(London : Soc., 2019) Ullmann, Steve; Hahn, Peter; Blömer, Laura; Mehnert, Anne; Laube, Christian; Abel, Bernd; Kersting, BertholdThe synthesis, structures, and properties of a new calix[4]arene ligand with an appended salicylaldimine unit (H4L = 25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and four lanthanide complexes (HNEt3)[Ln2(HL)(L)] (Ln = SmIII (4), EuIII (5), GdIII (6), and TbIII (7)) are reported. X-ray crystallographic analysis (for 4 and 6) reveals an isostructural series of dimeric complexes with a triply-bridged NO3Ln(μ-O)2(OH⋯O)LnO3N core and two seven coordinated lanthanide ions. According to UV-vis spectrometric titrations in MeCN and ESI-MS the dimeric nature is maintained in solution. The apparent stability constants range between logK = 5.8 and 6.3. The appended salicylaldimines sensitize EuIII and TbIII emission (λexc 311 nm) in the solid state or immersed in a polycarbonate glass at 77 K (for 5, 7) and at 295 K (for 7). © The Royal Society of Chemistry 2019.
- ItemEffect of morphology on the photoelectrochemical activity of TiO2 self-organized nanotube arrays(Basel : MDPI, 2020) Ennaceri, Houda; Fischer, Kristina; Hanus, Kevin; Chemseddine, Abdelkrim; Prager, Andrea; Griebel, Jan; Kühnert, Mathias; Schulze, Agnes; Abel, BerndIn the present work, highly ordered titanium dioxide (TiO2) nanotube anodes were grown using a rapid anodization process. The photoelectrochemical performances of these electrodes strongly depend on the anodization conditions. Parameters such as electrolyte composition, anodization potential and anodization time are shown to affect the geometrical parameters of TiO2 nanotubes. The optimal anodization parameters are determined by photocurrent measurements, linear sweep voltammetry and electrochemical impedance spectroscopy. The thickness of the tube wall and its homogeneity is shown to strongly depend on the anodization potential, and the formation mechanism is discussed. This study permits the optimization of the photocurrent density and contributes to further improvement of the photoelectrochemical water-splitting performance of TiO2 nanotube photoelectrodes. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemEfficient synthesis of triarylamine-based dyes for p-type dye-sensitized solar cells(London : Nature Publishing Group, 2016) Wild, Martin; Griebel, Jan; Hajduk, Anna; Friedrich, Dirk; Stark, Annegret; Abel, Bernd; Siefermann, Katrin R.The class of triarylamine-based dyes has proven great potential as efficient light absorbers in inverse (p-type) dye sensitized solar cells (DSSCs). However, detailed investigation and further improvement of p-type DSSCs is strongly hindered by the fact that available synthesis routes of triarylamine-based dyes are inefficient and particularly demanding with regard to time and costs. Here, we report on an efficient synthesis strategy for triarylamine-based dyes for p-type DSSCs. A protocol for the synthesis of the dye-precursor (4-(bis(4-bromophenyl)amino)benzoic acid) is presented along with its X-ray crystal structure. The dye precursor is obtained from the commercially available 4(diphenylamino)benzaldehyde in a yield of 87% and serves as a starting point for the synthesis of various triarylamine-based dyes. Starting from the precursor we further describe a synthesis protocol for the dye 4-{bis[4′-(2,2-dicyanovinyl)-[1,1′-biphenyl]-4-yl]amino}benzoic acid (also known as dye P4) in a yield of 74%. All synthesis steps are characterized by high yields and high purities without the need for laborious purification steps and thus fulfill essential requirements for scale-up.
- ItemEstradiol Removal by Adsorptive Coating of a Microfiltration Membrane(Basel : MDPI, 2021) Niavarani, Zahra; Breite, Daniel; Prager, Andrea; Abel, Bernd; Schulze, AgnesThis work demonstrates the enhancement of the adsorption properties of polyethersulfone (PES) microfiltration membranes for 17β-estradiol (E2) from water. This compound represents a highly potent endocrine-disrupting chemical (EDC). The PES membranes were modified with a hydrophilic coating functionalized by amide groups. The modification was performed by the interfacial reaction between hexamethylenediamine (HMD) or piperazine (PIP) as the amine monomer and trimesoyl chloride (TMC) or adipoyl chloride (ADC) as the acid monomer on the surface of the membrane using electron beam irradiation. The modified membranes and the untreated PES membrane were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water permeance measurements, water contact angle measurements, and adsorption experiments. Furthermore, the effects of simultaneous changes in four modification parameters: amine monomer types (HMD or PIP), acid monomer types (TMC or ADC), irradiation dosage (150 or 200 kGy), and the addition of toluene as a swelling agent, on the E2 adsorption capacity were investigated. The results showed that the adsorption capacities of modified PES membranes toward E2 are >60%, while the unmodified PES membrane had an adsorption capacity up to 30% for E2 under similar experimental conditions, i.e., an enhancement of a factor of 2. Next to the superior adsorption properties, the modified PES membranes maintain high water permeability and no pore blockage was observed. The highlighted results pave the way to develop efficient low-cost, stable, and high-performance adsorber membranes.
- ItemGold-Induced Fibril Growth: The Mechanism of Surface-Facilitated Amyloid Aggregation(Weinheim : Wiley-VCH, 2016) Gladytz, Anika; Abel, Bernd; Risselada, Herre JelgerThe question of how amyloid fibril formation is influenced by surfaces is crucial for a detailed understanding of the process in vivo. We applied a combination of kinetic experiments and molecular dynamics simulations to elucidate how (model) surfaces influence fibril formation of the amyloid-forming sequences of prion protein SUP35 and human islet amyloid polypeptide. The kinetic data suggest that structural reorganization of the initial peptide corona around colloidal gold nanoparticles is the rate-limiting step. The molecular dynamics simulations reveal that partial physisorption to the surface results in the formation of aligned monolayers, which stimulate the formation of parallel, critical oligomers. The general mechanism implies that the competition between the underlying peptide–peptide and peptide–surface interactions must strike a balance to accelerate fibril formation.
- ItemGreen-Emissive Zn2+ Complex Supported by a Macrocyclic Schiff-Base/Calix[4]arene-Ligand: Crystallographic and Spectroscopic Characterization(Weinheim : Wiley-VCH, 2021) Ullmann, Steve; Börner, Martin; Kahnt, Axel; Abel, Bernd; Kersting, BertholdThe macrocyclic calix[4]arene ligand H2L comprises two non-fluorescent 2,6-bis-(iminomethyl)phenolate chromophores, which show a chelation-enhanced fluorescence enhancement upon Zn2+ ion complexation. Macrocyclic [ZnL] complexes aggregate in the absence of external coligands via intermolecular Zn−N bonds to give dimeric [ZnL]2 structures comprising two five-coordinated Zn2+ ions. The absorption and emission wavelengths are bathochromically shifted upon going from the liquid (λmax,abs (CH2Cl2)=404 nm, λmax,em (CH2Cl2)=484 nm) to the solid state (λmax,abs=424 nm (4 wt%, BaSO4 pellet), λmax,em=524 nm (neat solid)). Insights into the electronic nature of the UV-vis transitions were obtained with time-dependent density functional theory (TD-DFT) calculations for a truncated model complex.
- ItemInvestigating the morphology of bulk heterojunctions by laser photoemission electron microscopy(Amsterdam [u.a.] : Elsevier Science, 2022) Niefind, Falk; Shivhare, Rishi; Mannsfeld, Stefan C.B.; Abel, Bernd; Hambsch, MikeThe nanoscale morphology of bulk heterojunctions is highly important for the charge dissociation and transport in organic solar cells and ultimately defines the performance of the cell. The visualization of this nano-morphology in terms of domain size and polymer orientation in a fast and straightforward way is therefore of great interest to evaluate the suitability of a film for efficient solar cells. Here, we demonstrate that the morphology of different blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) can be imaged and analyzed by employing photoemission electron microscopy.
- ItemInvestigation of room temperature multispin-assisted bulk diamond 13C hyperpolarization at low magnetic fields(Bristol : IOP Publ., 2018) Wunderlich, Ralf; Kohlrautz, Jonas; Abel, Bernd; Haase, Jürgen; Meijer, JanIn this work we investigated the time behavior of the polarization of bulk 13C nuclei in diamond above the thermal equilibrium. This nonthermal nuclear hyperpolarization is achieved by cross relaxation between two nitrogen related paramagnetic defect species in diamond in combination with optical pumping. The decay of the hyperpolarization at four different magnetic fields is measured. Furthermore, we use the comparison with conventional nuclear resonance measurements to identify the involved distances of the nuclear spin with respect to the defects and therefore the coupling strengths. Also, a careful look at the linewidth of the signal give valuable information to piece together the puzzle of the hyperpolarization mechanism.
- ItemMagnetic field and angle-dependent photoluminescence of a fiber-coupled nitrogen vacancy rich diamond(Melville, NY : American Inst. of Physics, 2021) Wunderlich, Ralf; Staacke, Robert; Knolle, Wolfgang; Abel, Bernd; Meijer, JanHere, we investigate the magnetic field dependent photoluminescence (PL) of a fiber-coupled diamond single crystal with a high density of nitrogen vacancy (NV) centers. Angle-dependent magnetic field sweep measurements between 0 and 111 mT were performed using an oscillating illumination combined with lock-in techniques. Besides the expected superposed PL of differently oriented NV centers, a zoo of features in the PL are found. These features can be associated with level anti-crossings and cross relaxations. In particular, PL measurements allowed us to detect auto-cross relaxation between coupled NV centers. Moreover, the PL measurements at low magnetic fields show dips suggesting an interaction of NV centers with additional spin defects. The results presented here are not only a study for NV-based fiber-coupled sensors made of diamond, but also show a way to investigate with manageable effort and purely an optical multispin interaction with at least one NV center as a constituent.
- ItemMixed-ligand lanthanide complexes supported by ditopic bis(imino-methyl)-phenol/calix[4]arene macrocycles: synthesis, structures, and luminescence properties of [Ln2(L2)(MeOH)2] (Ln = La, Eu, Tb, Yb)(London : Soc., 2020) Ullmann, Steve; Hahn, Peter; Mini, Parvathy; Tuck, Kellie L.; Kahnt, Axel; Abel, Bernd; Gutierrez Suburu, Matias E.; Strassert, Cristian A.; Kersting, BertholdThe lanthanide binding ability of a macrocyclic ligand H6L2 comprising two bis(iminomethyl)phenol and two calix[4]arene units has been studied. H6L2 is a ditopic ligand which provides dinuclear neutral complexes of composition [Ln2(L2)(MeOH)2] (Ln = La (1), Eu (2), Tb (3), and Yb (4)) in very good yield. X-ray crystal structure analyses for 2 and 3 show that (L2)6- accommodates two seven coordinated lanthanide ions in a distorted monocapped trigonal prismatic/octahedral coordination environment. UV-vis spectroscopic titrations performed with La3+, Eu3+, Tb3+ and Yb3+ ions in mixed MeOH/CH2Cl2 solution (I = 0.01 M NBu4PF6) reveal that a 2 : 1 (metal : ligand) stoichiometry is present in solution, with log K11 and K21 values ranging from 5.25 to 6.64. The ratio α = K11/K21 of the stepwise formation constants for the mononuclear (L2 + M = ML2, log K11) and the dinuclear complexes (ML2 + M = M2L2, log K21) was found to be invariably smaller than unity indicating that the binding of the first Ln3+ ion augments the binding of the second Ln3+ ion. The present complexes are less luminescent than other seven-coordinated Eu and Tb complexes, which can be traced to vibrational relaxation of excited EuIII and TbIII states by the coligated MeOH and H2O molecules and/or low-lying ligand-to-metal charge-transfer (LMCT) states. © 2020 The Royal Society of Chemistry.
- ItemOn-chip mass spectrometric analysis in non-polar solvents by liquid beam infrared matrix-assisted laser dispersion/ionization(Berlin [u.a.] : Springer, 2021) Urban, Raphael D.; Fischer, Tillmann G.; Charvat, Ales; Wink, Konstantin; Krafft, Benjamin; Ohla, Stefan; Zeitler, Kirsten; Abel, Bernd; Belder, DetlevBy the on-chip integration of a droplet generator in front of an emitter tip, droplets of non-polar solvents are generated in a free jet of an aqueous matrix. When an IR laser irradiates this free liquid jet consisting of water as the continuous phase and the non-polar solvent as the dispersed droplet phase, the solutes in the droplets are ionized. This ionization at atmospheric pressure enables the mass spectrometric analysis of non-polar compounds with the aid of a surrounding aqueous matrix that absorbs IR light. This works both for non-polar solvents such as n-heptane and for water non-miscible solvents like chloroform. In a proof of concept study, this approach is applied to monitor a photooxidation of N-phenyl-1,2,3,4-tetrahydroisoquinoline. By using water as an infrared absorbing matrix, analytes, dissolved in non-polar solvents from reactions carried out on a microchip, can be desorbed and ionized for investigation by mass spectrometry.
- ItemRobust nuclear hyperpolarization driven by strongly coupled nitrogen vacancy centers(Melville, NY : American Inst. of Physics, 2021) Wunderlich, Ralf; Staacke, Robert; Knolle, Wolfgang; Abel, Bernd; Haase, Jürgen; Meijer, JanNuclear magnetic resonance techniques are widely used in the natural sciences but they lack sensitivity. Therefore, large sample volumes or long measurement times are necessary. In this work, we investigate the polarization of bulk 13C nuclei in a diamond above the thermal equilibrium at room temperature. Previously studied mechanisms utilize direct coupling to nitrogen vacancy centers or the additional assistance of substitutional nitrogen impurities for this purpose. We exploit strongly coupled nitrogen vacancy centers as polarization sources. We study two approaches to transfer the optically induced polarization of the electron spins of the nitrogen vacancy centers to nearby nuclear spins. First, the electron-nuclear polarization transfer is achieved by energy matching conditions or, second, by magnetic field sweeps inducing Landau–Zener-like transitions. Simulations according to a quantum mechanical system consisting of two coupled nitrogen vacancy centers and a weakly coupled 13C spin show an excellent agreement with the experimental data. Both approaches allow a reduction of the measurement time by roughly three orders of magnitude.
- ItemRole of Reaction Intermediate Diffusion on the Performance of Platinum Electrodes in Solid Acid Fuel Cells(Basel : MDPI, 2021) Lorenz, Oliver; Kühne, Alexander; Rudolph, Martin; Diyatmika, Wahyu; Prager, Andrea; Gerlach, Jürgen W.; Griebel, Jan; Winkler, Sara; Lotnyk, Andriy; Anders, André; Abel, BerndUnderstanding the reaction pathways for the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) is the key to design electrodes for solid acid fuel cells (SAFCs). In general, electrochemical reactions of a fuel cell are considered to occur at the triple-phase boundary where an electrocatalyst, electrolyte and gas phase are in contact. In this concept, diffusion processes of reaction intermediates from the catalyst to the electrolyte remain unconsidered. Here, we unravel the reaction pathways for open-structured Pt electrodes with various electrode thicknesses from 15 to 240 nm. These electrodes are characterized by a triple-phase boundary length and a thickness-depending double-phase boundary area. We reveal that the double-phase boundary is the active catalytic interface for the HOR. For Pt layers ≤ 60 nm, the HOR rate is rate-limited by the processes at the gas/catalyst and/or the catalyst/electrolyte interface while the hydrogen surface diffusion step is fast. For thicker layers (>60 nm), the diffusion of reaction intermediates on the surface of Pt be-comes the limiting process. For the ORR, the predominant reaction pathway is via the triple-phase boundary. The double-phase boundary contributes additionally with a diffusion length of a few nanometers. Based on our results, we propose that the molecular reaction mechanism at the electrode interfaces based upon the triple-phase boundary concept may need to be extended to an effective area near the triple-phase boundary length to include all catalytically relevant diffusion processes of the reaction intermediates. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.