Entwicklung und Anwendung Kobalt-katalysierter Reaktionen ungesättigter Kohlenwasserstoffe und deren Umsetzung in elektrochemischen Reaktionen

Die Kobalt-katalysierte gekreuzte [4+2]-Benzanellierung von C4-substituierten 1,3-Eninen 29/41 mit disubstituierten Buta-1,3-diinen 38konnte,unter Verwendung des HILT-Katalysators, bestehend aus dem PräkatalysatorCoBr2(dppp), dem Reduktionsmittel Zinkpulver, der LEWIS-Säure Zinkiodid und dem ösungsmittel Dichlormethan, realisiert werden. Zunächst wurden die Umsetzungen von C4-substituierten 1,3-Eninen 29a-h/41mit den symmetrischen Buta-1,3-diinen 38a-d untersucht. Als Produkte wurden die 1,2,3-trisubstituierten Benzolderivate106a-l erhalten. Dabei verlief die Reaktion unter vollständiger Kontrolle der Regioselektivität und es wurde ausschließlich das Produkt mit der Alkin-Funktion in der C2-Position als einziges Regioisomer erhalten. Die Reaktionen tolerierten eine Vielzahl an funktionellen Gruppen und die Produkte 106a-l konnten in akzeptablen bis guten Ausbeuten erhalten werden. Des Weiteren wurde die gekreuzte [4+2]-Benzanellierung zwischen dem Phenyl-substituierten 1,3-Enin 41 und verschiedenen unsymmetrisch substituierten Buta-1,3-diinen 38j-p unter Verwendung des Kobalt-Katalysatorsystem untersucht. In den Reaktionen konnten die beiden regioisomeren 1,2,3-trisubstituierten Benzolderivate 117 und 118 in akzeptablen bis guten Ausbeuten und guten bis sehr guten Regioselektivitäten erhalten werden. Als Hauptprodukte wurden die 1,2,3-trisubstituierten Benzolderivate 117, mit dem sterisch weniger anspruchsvollen Substituenten (R=Alkyl, Aryl) am anellierten Ring und dem sterisch anspruchsvollerem Substituenten am Alkin (TMS), bevorzugt gebildet. Der direkte Vergleich dieser Ergebnisse mit denen der literaturbekannten, komplementären Palladium-katalysierten gekreuzten [4+2]-Benzanelierung nach YAMAMOTO und GEVORGYAN zeigte, dass unter Palladium-Katalyse genau die gegensätzlichen 1,2,3-trisubstituierten Benzolderivate 118 als Hauptisomere, mit dem sterisch anspruchsvolleren Rest (TMS) am anellierten Ring und dem sterisch weniger anspruchsvollen Rest (R=Alkyl, Aryl) am Alkin, bevorzugt erhalten wurden. Durch die Verwendung des Kobalt-Katalysatorsystems war es demzufolge erstmals möglich die 1,2,3- trisubstituierten Benzolderivate 117 als Hauptprodukte in der gekreuzten [4+2]-Benzanellierung zu erhalten und somit die Substratbreite der Reaktion um ein weiteres, durch andere Methoden nur schwer zugängliches Benzolderivat, zu erweitern

"Stürzt Facebook autoritäre Regime?" - Eine Analyse der Revolution in Ägypten

Weitreichende und vielversprechende Veränderungen trieben die Menschen 2010/11 auf die Straßen von Tunesien, Ägypten und Libyen. Dabei begleiteten soziale Netzwerke die Proteste in der realen Welt. Nach dem Fall von autoritären Regimen entwickelte sich eine lebhafte Debatte über die Macht jener Netzwerke im "Arabischen Frühling". Es stellt sich die Frage, inwieweit die neuen Angebot des Internets die politische Partizipation der ägyptischen Bevölkerung befördern konnten und ob gar von einer Facebook- oder Twitter-Revolution gesprochen werden kann

The Effects of Gas Saturation of Electrolytes on the Performance and Durability of Lithium‐Ion Batteries

Traces of species in batteries are known to impact battery performance. The effects of gas species, although often reported in the electrolyte and evolving during operation, have not been systematically studied to date and are therefore barely understood. This study reveals and compares the effects of different gases on the charge-discharge characteristics, cycling stability and impedances of lithium-ion batteries. All investigated gases have been previously reported in lithium-ion batteries and are thus worth investigating: Ar, CO$_{2}$, CO, C$_{2}$H$_{4}$, C$_{2}$H$_{2}$, H$_{2}$, CH$_{4}$ and O$_{2}$. Gas-electrolyte composition has a significant influence on formation, coulombic and energy efficiencies, C-rate capability, and aging. Particularly, CO$_{2}$ and O$_{2}$ showed a higher C-rate capability and a decrease in irreversible capacity loss during the first cycle compared to Ar. Similar discharge capacities and aging behaviors are observed for CO, C$_{2}$H$_{4}$ and CH$_{4}$. Acetylene showed a large decrease in performance and cycle stability. Furthermore, electrochemical impedance spectroscopy revealed that the gases mainly contribute to changes in charge transfer processes, whereas the effects on resistance and solid electrolyte interphase performance were minor. Compared to all other gas–electrolyte mixtures, the use of CO$_{2}$ saturated electrolyte showed a remarkable increase in all performance parameters including lifetime

DER ANAESTHESIST UND SEINE FÜNF SINNE

Nach der Akademischen Abschiedsvorlesung an der Medizinischen Fakultät der Otto-von-Guericke-Universität Magdeburg am 19. Oktober 200

Microkinetic Barriers of the Oxygen Evolution on the Oxides of Iridium, Ruthenium and their Binary Mixtures

The performance of electrocatalytic water splitting in polymer electrolyte membrane electrolysis is substantially determined by the microkinetic processes of the oxygen evolution reaction (OER). Even highly active catalysts such as the nanoparticulated transition metal oxides IrO$_{2}$, RuO$_{2}$ and their mixtures, Ir$_{x}$Ru$_{1-x}$O$_{2}$, exhibit overpotentials up to several hundreds of millivolts. The surface of the oxide mixtures Ir$_{x}$Ru$_{1-x}$O$_{2}$ is found to consist of actives sites of both Ir and Ru on which the OER mechanism is processed independently and at different overpotentials. By applying microkinetic modelling and parameterization via cyclic voltammograms we show that there is a correlation between performance and the relative Ir content, that can be explained by two different deprotonation steps. These are in particular the formation of the adsorbate species *OOH on rutile RuO$_{2}$ and *OO on IrO$_{2}$. The respective free reaction energies are quantified to 1.44 eV and 1.58 eV, which are the highest values of the process and thus determining the overpotential. The additional finding of adsorbed oxygen *O covering >40 % of the active sites during the OER suggests that subsequent water adsorption is the major performance limiting step. Finally, a synergetic effect between both active sites on the binary transition metal oxides is identified: the respective other metal lowers the potential determining reaction energy on the Ru or Ir active site. This insight into the surface processes on Ir and Ru binary oxides forms the basis for deeper understanding of the active sites for further OER catalyst development

Identifying the oxygen evolution mechanism by microkinetic modelling of cyclic voltammograms

Electrocatalytic water splitting is currently one of the most promising reactions to produce “green” hydrogen in a decarbonized energy system. Its bottleneck reaction, the oxygen evolution reaction (OER), is catalysed by hydrous iridium, a stable and active catalyst material. Improving the OER requires a better and especially quantitative understanding of the reaction mechanism as well as its kinetics. In this work, we present an experimentally validated microkinetic model that allows to quantify the mechanistic pathways, emerging surface species prior and during the OER, the reaction rates for the single steps and essential thermodynamic properties. Therefore, two mechanisms based on density functional theory and experimental findings are evaluated on which only simulation results of the theory-based one are found to be in full accordance with cyclic voltammograms even at different potential rates and, thus, able to describe the catalytic system. The simulation implies that oxygen is evolving mostly via a fast single site pathway (∗OO → ∗ + O2 ) with an effective reaction rate, which is several orders of magnitude faster compared to the slow dual site (2∗ O → 2∗ + O2) pathway rate. Intermediate states of roughly 7% Ir(III), 25% Ir(IV) and 63% Ir(V) are present at typical OER potentials of 1.6 V vs RHE. We are able to explain counterintuitive experimental findings of a reduced iridium species during highly oxidizing potentials by the kinetic limitation of water adsorption. Although water adsorption is in general thermodynamically favourable, it is kinetically proceeding slower than the electrochemical steps at high potential. In the lower potential range from 0.05 to 1.5 V vs RHE the stepwise oxidation of the iridium is accompanied with van der Waals like ad- and desorption processes, which leads in comparison to Langmuir-type adsorption to a broadened peak shape in the cyclic voltammograms. Overall, our analysis shows that the dynamic microkinetic modelling approach is a powerful tool to analyse catalytic microkinetics in depth and to bridge the gap between thermodynamic calculations and experiments

Synthesis, Characterization and Electrochemical Performance of a Redox-Responsive Polybenzopyrrole@Nickel Oxide Nanocomposite for Robust and Efficient Faraday Energy Storage

A polybenzopyrrole@nickel oxide (Pbp@NiO) nanocomposite was synthesized by an oxidative chemical one-pot method and tested as an active material for hybrid electrodes in an electrochemical supercapattery device. The as-prepared composite material exhibits a desirable 3D cross-linked nanostructured morphology and a synergistic effect between the polymer and metal oxide, which improved both physical properties and electrochemical performance. The unprocessed material was characterized by X-ray diffraction, FTIR and UV–Vis spectroscopy, scanning electron microscopy/energy disperse X-ray analysis, and thermogravimetry. The nanocomposite material was deposited without a binder on gold current collectors and investigated for electrochemical behavior and performance in a symmetrical two- and three-electrode cell setup. A high specific capacity of up to 105 C g$^{-1}$ was obtained for the Pbp@NiO-based electrodes with a gravimetric energy density of 17.5 Wh kg$^{-1}$, a power density of 1,925 W kg$^{-1}$, and excellent stability over 10,000 cycles

Physical, Chemical, and Electrochemical Properties of Redox-Responsive Polybenzopyrrole as Electrode Material for Faradaic Energy Storage

Polybenzopyrrole (Pbp) is an emerging candidate for electrochemical energy conversion and storage. There is a need to develop synthesis strategies for this class of polymers that can help improve its overall properties and make it as suitable for energy storage applications as other well-studied polymers in this substance class, such as polyaniline and polypyrrole. In this study, by synthesizing Pbp in surfactant-supported acidic medium, we were able to show that the physicochemical and electrochemical properties of Pbp-based electrodes are strongly influenced by the respective polymerization conditions. Through appropriate optimization of various reaction parameters, a significant enhancement of the thermal stability (up to 549.9 °C) and the electrochemical properties could be achieved. A maximum specific capacitance of 166.0 ± 2.0 F g−1 with an excellent cycle stability of 87% after 5000 cycles at a current density of 1 A g−1 was achieved. In addition, a particularly high-power density of 2.75 kW kg−1 was obtained for this polybenzopyrrole, having a gravimetric energy density of 17 Wh kg−1. The results show that polybenzopyrroles are suitable candidates to compete with other conducting polymers as electrode materials for next-generation Faradaic supercapacitors. In addition, the results of the current study can also be easily applied to other systems and used for adaptations or new syntheses of advanced hybrid/composite Pbp-based electrode materials

Investigation of Alumina-Doped Prunus domestica Gum Grafted Polyaniline Epoxy Resin for Corrosion Protection Coatings for Mild Steel and Stainless Steel

Eco-friendly inhibitors have attracted considerable interest due to the increasing environmental issues caused by the extensive use of hazardous corrosion inhibitors. In this paper, environmentally friendly PDG-g-PANI/Al$_2$O$_3$ composites were prepared by a low-cost inverse emulsion polymerization for corrosion inhibition of mild steel (MS) and stainless steel (SS). The PDG-g-PANI/Al$_2$O$_3$ composites were characterized by different techniques such as X-ray diffraction (XRD), UV/Vis, and FTIR spectroscopy. XRD measurements show that the PDG-g-PANI/Al$_2$O$_3$ composite is mostly amorphous and scanning electron micrographs (SEM) reveal a uniform distribution of Al$_2$O$_3$ on the surface of the PDG-g-PANI matrix. The composite was applied as a corrosion inhibitor on mild steel (MS) and stainless steel (SS), and its efficiency was investigated by potentiodynamic polarization measurement in a 3.5% NaCl and 1 M H$_2$SO$_4$ solution. Corrosion kinetic parameters obtained from Tafel evaluation show that the PDG-g-PANI/Al$_2$O$_3$ composites protect the surface of MS and SS with inhibition efficiencies of 92.3% and 51.9% in 3.5% NaCl solution, which is notably higher than those obtained with untreated epoxy resin (89.3% and 99.5%). In particular, the mixture of epoxy/PDG-g-PANI/Al$_2$O$_3$ shows the best performance with an inhibition efficiency up to 99.9% on MS and SS. An equivalent good inhibition efficiency was obtained for the composite for 1M H$_2$SO$_4$. Analysis of activation energy, formation enthalpy, and entropy values suggest that the epoxy/PDG-g-PANI/Al$_2$O$_3$ coating is thermodynamically favorable for corrosion protection of MS and exhibits long-lasting stability

Polyindole Embedded Nickel/Zinc Oxide Nanocomposites for High-Performance Energy Storage Applications

Conducting polymers integrated with metal oxides create opportunities for hybrid capacitive electrodes. In this work, we report a one-pot oxidative polymerization for the synthesis of integrated conductive polyindole/nickel oxide (PIn/NiO), polyindole/zinc oxide (PIn/ZnO), and polyindole/nickel oxide/zinc oxide (PNZ). The polymers were analyzed thoroughly for their composition and physical as well as chemical properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), and thermogravimetric analysis (TGA). The PIn and its composites were processed into electrodes, and their use in symmetrical supercapacitors in two- and three-electrode setups was evaluated by cyclic voltammetry (CV), galvanostatic discharge (GCD), and electrochemical impedance spectroscopy (EIS). The best electrochemical charge storage capability was found for the ternary PNZ composite. The high performance directly correlates with its uniformly shaped nanofibrous structure and high crystallinity. For instance, the symmetrical supercapacitor fabricated with PNZ hybrid electrodes shows a high specific capacitance of 310.9 F g$^{−1}$ at 0.5 A g$^{−1}$ with an energy density of 42.1 Wh kg$^{−1}$, a power density of 13.2 kW kg$^{−1}$, and a good cycling stability of 78.5% after 5000 cycles. This report presents new electrode materials for advanced supercapacitor technology based on these results