Ultrathin hematite-hercynite films for future unassisted solar water splitting. - In: Advanced Materials Technologies, ISSN 2365-709X, Bd. 8 (2023), 22, 2300655, S. 1-10
Photoelectrochemical (PEC) water splitting requires stable, efficient, and cost-effective photoelectrodes to enable future large-scale solar hydrogen production. Ultrathin hematite-hercynite photoanodes that meet all these criteria in an excellent way is presented here. Hematite-hercynite photoelectrodes are synthesized in a self-forming manner by thermal oxidation of iron-aluminum alloy films and characterized with regard to water splitting applications. Photoanodes fabricated from 17 wt.% Al at 493 ˚C for 8 h and 685 ˚C for 5 min exhibit, for instance, a photocurrent density of 1.24 and 1.53 mA cm−2 at 1.23 V versus RHE, respectively, as well as superior light absorption in the visible range of the solar spectrum. The PEC performance improvement in comparison to pure hematite thin film electrodes is first achieved by adjusting the aluminum concentration with an optimum range of 12-17 wt.% and second by optimizing the annealing conditions. The resulting photocurrent densities are about a factor of three higher than those obtained from electrodes synthesized from pure iron thin films using the same synthesis conditions. Finally, it is shown that ultrathin hematite-hercynite photoelectrodes enable even unassisted solar water splitting in a NaOH (1 m) electrolyte with a maximum solar-to-hydrogen conversion efficiency of 0.78%.
https://doi.org/10.1002/admt.202300655
Gel adsorbed redox mediators tempo as integrated solid-state cathode for ultra-long life quasi-solid-state Na-air battery. - In: Advanced energy materials, ISSN 1614-6840, Bd. 13 (2023), 42, 2302325, S. 1-10
In metal-air batteries, the integrated solid-state cathode is considered a promising design because it can solve the problem of high interfacial resistance of conventional solid-state cathodes. However, solid discharge products cannot be efficiently decomposed in an integrated solid-state cathode, resulting in batteries that are unable to operate for long periods of time. Herein, an integrated solid-state cathode (Gel-Tempo cathode) of sodium-air batteries (SABs) capable of promoting efficient decomposition of discharge product Na2O2 is designed. The Gel-Tempo cathode is synthesized by cationic-π interaction of redox mediator 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) and ionic liquid with carbon nanotubes. The Gel-Tempo cathode serves multiple functions as a redox mediator, flame retardancy, and high stability to air. In quasi-solid-state SABs, the Gel-Tempo cathode reduces overpotential to 1.15 V and improves coulomb efficiency to 84.5% (at a limited discharge capacity of 3000 mAh g−1) compared to gel cathodes. Experiments and density functional theory calculations indicate that Tempo significantly reduces the Gibbs free energy in the decomposition reaction of Na2O2, and high Tempo content is more conducive to enhancing the decomposition kinetics of Na2O2 and hence resulting in an ultra-long cycle life (1746 h). This work is crucial to promote practical applications of SABs, providing guidelines for functionalization design of integrated solid-state cathodes for metal-air batteries.
https://doi.org/10.1002/aenm.202302325
Cholesterin aus Hirn. - In: Nachrichten aus der Chemie, ISSN 1439-9598, Bd. 71 (2023), 1, S. 30-32
Cholesterin hat es bis in den Alltagssprachgebrauch gebracht. Allein deshalb ist es für Praktika im Chemiestudium ein interessanter Vertreter der Steroide. Zudem ist es einfach zu gewinnen.
Cholesterin aus Hirn. - In: Nachrichten aus der Chemie, ISSN 1868-0054, Bd. 71 (2023), 1, S. 30-32
Cholesterin hat es bis in den Alltagssprachgebrauch gebracht. Allein deshalb ist es für Praktika im Chemiestudium ein interessanter Vertreter der Steroide. Zudem ist es einfach zu gewinnen.
https://doi.org/10.1002/nadc.20234132329
Application of nitrogen-doped multi-walled carbon nanotubes decorated with gold nanoparticles in biosensing. - In: Journal of solid state electrochemistry, ISSN 1433-0768, Bd. 27 (2023), 10, S. 2645-2658
Novel films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold nanoparticles (AuNPs) possessing diameter of 14.0 nm. Electron optical microscopy analysis reveals that decoration of N-MWCNTs with AuNPs does not have any influence on their bamboo-shaped configuration. The electrochemical response of fabricated composite films, further denoted as N-MWCNTs/AuNPs, towards oxidation of dopamine (DA) to dopamine-o-quinone (DAQ) in the presence of ascorbic acid (AA) and uric acid (UA) was probed in real pig serum by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The findings demonstrate that N-MWCNTs/AuNPs exhibit slightly greater electrochemical response and sensitivity towards DA/DAQ compared to unmodified N-MWCNTs. It is, consequently, obvious that AuNPs improve significantly the electrochemical response and detection ability of N-MWCNTs. The electrochemical response of N-MWCNTs/AuNPs towards DA/DAQ seems to be significantly greater compared to that of conventional electrodes, such as platinum and glassy carbon. The findings reveal that N-MWCNTs/AuNPs could serve as powerful analytical sensor enabling analysis of DA in real serum samples.
https://doi.org/10.1007/s10008-023-05562-2
Understanding the formation of “false friends” (hidden lack of fusion defects) in laser beam welding by means of high-speed synchrotron X-ray imaging. - In: Welding in the world, ISSN 1878-6669, Bd. 67 (2023), 11, S. 2557-2570
This paper provides a fundamental understanding of “false friend” formation, i.e., hidden defects associated with lack of fusion, using an experimental setup that allowed an insight into the processing zone based on high-speed synchrotron X-ray imaging. The setup enabled the welding of a lap joint of AISI 304 high-alloy steel sheets (X5CrNi18-10/1.4301), with the ability to adjust different gap heights between top and bottom sheet (up to 0.20 mm) and to acquire high-speed X-ray images at 100 kHz simultaneously with the welding process. On this basis, a time-resolved description of the “false friend” formation can be provided by visualizing the interaction between keyhole and melt pool during laser welding and solidification processes within the gap area. The bridgeability of the gap was limited due to the gap height and insufficient melt supply leading to the solidification of the bridge. The distance between the solidified bridge and the keyhole increased with time, while the keyhole and melt pool dynamics initiated the formation of new melt bridges whose stability was defined by melt flow conditions, surface tension, and gap heights. The alternating formation and solidification of melt bridges resulted in entrapped areas of lacking fusion within the weld, i.e., “false friends.” Finally, based on the results of this study, a model concept is presented that concludes the main mechanisms of “false friend” formation.
https://doi.org/10.1007/s40194-023-01581-9
Dipolar NMR relaxation of adsorbates on surfaces of controlled wettability. - In: Magnetic resonance letters, ISSN 2772-5162, Bd. 3 (2023), 3, S. 220-231
In reservoir rocks, the term “ageing” refers to extended exposition to crude oil; a typically water-wet sandstone will then gradually become oil-wet as a consequence of the deposition of insoluble fractions of oil onto the surface grains. Rocks have been aged artificially by subjecting them to a bitumen solution at elevated temperature in order to achieve comparable surface properties for three different types of rock: Bentheimer, Berea Buff and Liège Chalk. Using saturated and aromatic model compounds as proxies for crude oil, the nuclear magnetic resonance (NMR) relaxation dispersion in native and aged rocks was compared and correlated to the properties of paramagnetic impurities in these rock types. Perfluorated liquids were found to follow the same trend as deuterated and naturally occurring oil components, suggesting they can be used as suitable tracers for wettability studies since the 19F nucleus is absent in natural sources. By combining electron paramagnetic resonance (EPR) and dynamic nuclear polarization (DNP) it becomes possible to identify and quantify the origin of the dominating relaxation processes between native and aged rocks, providing an alternative approach to assess wettability in natural rocks.
https://doi.org/10.1016/j.mrl.2023.02.001
Radicals on the silica surface: probes for studying dynamics by means of fast field cycling relaxometry and dynamic nuclear polarization. - In: Magnetic resonance letters, ISSN 2772-5162, Bd. 3 (2023), 3, S. 256-265
Determining the dynamics of adsorbed liquids on nanoporous materials is crucial for a detailed understanding of interactions and processes on the solid-liquid interface in many materials and porous systems. Knowledge of the influence of the presence of paramagnetic species on the surface or within the porous matrices is essential for fundamental studies and industrial processes such as catalysts. Magnetic resonance methods, such as electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and dynamic nuclear polarization (DNP), are powerful tools to address these questions and to quantify dynamics, electron-nuclear interaction features and their relation to the physical-chemical parameters of the system. This paper presents an NMR study of the dynamics of polar and nonpolar adsorbed liquids, represented by water, n-decane, deuterated water and nonane-d20, on the native silica surface as well as silica modified with vanadyl porphyrins. The analysis of the frequency dependence of the nuclear spin-lattice relaxation time is carried out by separating the intra- and intermolecular contributions, which were analyzed using reorientations mediated by translational displacements (RMTD) and force-free-hard-sphere (FFHS) models, respectively.
https://doi.org/10.1016/j.mrl.2023.03.006
Weak interaction between cations and anions in electrolyte enabling fast dual-ion storage for potassium-ion hybrid capacitors. - In: Advanced functional materials, ISSN 1616-3028, Bd. 33 (2023), 52, 2304086, S. 1-10
Identifying an effective electrolyte is a primary challenge for hybrid ion capacitors, due to the intricacy of dual-ion storage. Here, this study demonstrates that the electrochemical behavior of graphite oxide in ether-solvent electrolyte outperforms those in ester-solvent electrolytes for the cathode of potassium-ion hybrid capacitor. The experimental and theoretical assessments verify that the anion and cation are isolated effectively in dimethyl ether, endowing a weaker interaction between cations and anions compared to that of ester-solvent electrolytes, which facilitates the dual-ion diffusion and thus enhances the electrochemical performance. This result provides a rational strategy to realize high-rate cations and anions storage on the carbon cathode. Furthermore, a new low-cost and high-performance capacitor prototype, modified graphite oxide (MGO) cathode versus pristine graphite (PG) in ether-solvent electrolyte (MGOǁDMEǁPG), is proposed. It exhibits a high energy density of 150 Wh kg^−1cathode at a high power density of 21443 W kg^−1cathode (calculation based on total mass: 60 Wh kg^−1 at 8577 W kg^−1).
https://doi.org/10.1002/adfm.202304086
Synthesis and electrochemical properties of sulfur-nitrogen-doped multi-walled carbon nanotubes. - In: Fullerenes, nanotubes & carbon nanostructures, ISSN 1536-4046, Bd. 31 (2023), 11, S. 1082-1095
Multi-walled carbon nanotubes doped with sulfur and nitrogen (S-N-MWCNTs) were grown onto silicon/silicon oxide wafer by means of chemical vapor deposition upon decomposition of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) in presence of catalyst. The S-N-MWCNTs were characterized by scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The findings demonstrate that S-N-MWCNTs exhibit bamboo-shaped nanostructure, quite similar to pure nitrogen-doped carbon nanotubes. The S-N-MWCNTs were investigated with respect to their electrochemical response to ferrocyanide/ferricyanide, [Fe(CN)6]4-/3- in potassium chloride aqueous solutions by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The recorded CVs demonstrate strong dependence of electrochemical response, electron transfer kinetics, and sensitivity of S-N-MWCNTs on concentration of decomposed DMSO precursor. Namely, upon increasing concentration of decayed DMSO up to 2% wt. the current density, the electron transfer kinetics, and the sensitivity of S-N-MWCNTs toward [Fe(CN)6]4-/3- tend to enhance. The extracted EIS results approve that when DMSO reaches the optimum concentration of 2% wt. the barrier for electron transfer decreases significantly leading, consequently, to faster electron transfer kinetics. The S-N-MWCNTs exhibit considerable stability and excellent reproducibility, and thus it can be considered suitable analytical tool for detection of redox systems at micromolar level.
https://doi.org/10.1080/1536383X.2023.2240916