1,721,635 research outputs found
DSR: enhanced modelling and refinement of disordered structures with SHELXL
No full textOne of the remaining challenges in single-crystal structure refinement is the
proper description of disorder in crystal structures. This paper describes a
computer program that performs semi-automatic modelling of disordered
moieties in SHELXL [Sheldrick (2015). Acta Cryst. C71, 3–8.]. The new
program contains a database that includes molecular fragments and their
corresponding stereochemical restraints, and a placement procedure to place
these fragments on the desired position in the unit cell. The program is also
suitable for speeding up model building of well ordered crystal structures
Salts of electrophilic cations and Lewis acid-base adducts with weakly coordinating anions : synthesis, characterization and quantum chemical calculations
Full text linkDuring the last decades, weakly coordinating anions (WCAs) have become a field of great interest both in basic and applied chemistry, as – if compared to "normal" classical anions like Cl- or SO42- – they have a lot of unique and unusual properties, such as high solubility in low dielectric media (like CH2Cl2 or toluene), "pseudo gas phase conditions" in condensed phases and the stabilization of strong electrophilic cations as well as of weakly bound and low charged complexes. Within the present thesis, several contributions to the chemistry of WCAs were made: Based on quantum chemical calculations, the stability of the most widely used WCAs have been investigated, using parameters such as the fluoride ion affinity (FIA), partial charges or frontier orbital energies. One class of the WCAs, the poly- and perfluorinated alkoxyaluminates of the type [Al(ORF)4]- and [(RFO)3Al-F-Al(ORF)3]-, has been used to investigate weakly bound Ag(P4S3) Lewis acid-base adducts and electrophilic cations: When the silver salts of fluorinated alkoxyaluminates are reacted with P4S3, different structure types are found for the adducts, depending on the anion used. The dynamics of these complexes has been explored by different spectroscopic methods (IR, Raman, MAS-NMR, NMR in solution) and X-ray diffraction. The first structurally characterized trihalocarbenium ions CI3+ as salts of different aluminates have been prepared and fully characterized using various spectroscopic techniques, e.g. NMR and vibrational spectroscopy, as well as single-crystal diffraction. The Lewis acidities of the halocarbenium ions have been investigated both on experimental and theoretical grounds and they have been compared to those of the isoelectronic haloboranes. The NO2+ salt of the [Al(OC(CF3)3)4]- anion has been synthesized by a metathesis reaction. It has been reacted with P4 in order to obtain naked phosphorus cations Px+. Another project was the synthesis and characterization of the tetraalkylammonium salts of the [Al(ORF)4]- anions, a promising class of substances for the use in electrochemical applications in non-polar solvents. All subjects treated experimentally within this thesis have been accompanied by quantum chemical calculations
On the correlation of gas-phase ion-chemistry and related processes in solution – heterodinuclear transition-metal complexes as model systems
No full textIn this work, a series of heterodinuclear, formal M+IPt0 complexes (M = Au, Ag, Cu) was synthesized and characterized in order to establish a correlation between processes observed in mass-spectrometric gas-phase experiments and related processes in solution. The characterization of the model complex [(Ph3P)AuPt(PPh3)3](BArF4) revealed a high fluxionality of the ligand sphere, which manifests itself in fast intramolecular and slow intermolecular PPh3-ligand exchange-processes. While the platinum atom in [(Ph3P)AuPt(PPh3)3](BArF4) is coordinated in a square-planar fashion, a trigonal-pyramidal geometry is found in the first olefin-stabilized Au+IPt0 complex [(Ph3P)AuPt(nbe)3](BArF4). An explanation for the preferred geometry is provided by inspection of the molecular orbitals of the precursor complexes [Pt(PPh3)3] and [Pt(nbe)3]. In the series [(Ph3P)AuPt(PPh3)n(nbe)3–n](BArF4), both the Au–Pt-dissociation energy and the elementary charge shift from the respective Pt0 Lewis-bases to the Lewis-acid [(Ph3P)Au]+ decrease with an increasing number of norbornene ligands. [(Ph3P)AuPt(nbe)3](BArF4) was further probed as a precursor for other AuPt complexes.When [(Ph3P)AuPt(PPh3)3](BArF4) is heated in solution, the formation of benzene is observed. This process is preceded by reversible phenyl-group exchange between the PPh3 ligands as elucidated by deuterium-labeling studies. Both the elimination of benzene and the preceding phenyl-group exchange are also observed in mass-spectrometric fragmentation experiments. Apparently, the primary reactivity is identical both in gas phase and in solution. Based on the sum of observations, the heterometallic nature is expected to be key for the observed reactivity in both realms. In order to examine the influence of the coinage metal on the observed processes upon CID and heating of [(Ph3P)AuPt(PPh3)3](BArF4), the homologous complexes [(Ph3P)MPt(PPh3)3](BArF4) (M = Ag or Cu) were investigated as well. For both complexes, a lower PPh3-dissociation energy is observed in the course of CID and NMR experiments as well as DFT studies. For [(Ph3P)AgPt(PPh3)3](BArF4), kinetic experiments revealed a faster intermolecular PPh3-ligand exchange, when compared with [(Ph3P)AuPt(PPh3)3](BArF4). Moreover, Pt–P-bond cleavage appears to be the rate-determining step in these processes. To investigate the relative Pt–P-bond dissociation-energies for the cationic complexes [Au, Pt, L4]+ (L = PPh3, PTol3, PPhF3, PPhOMe3) and [Ag, Pt, (PPh3)4]+, breakdown graphs were acquired in gas-phase experiments. The obtained collision energies correlate well with calculated dissociation energies. For the Pt–P-bond cleavage-processes, rate constants were determined at different collision energies. These rate constants together with calculated values of ΔH and ΔS were used to estimate the effective ion temperatures in the employed ion-trap massspectrometer
Electrochemical activation of strained donor-acceptor substituted carbocycles and selective hydrogenation of benzylic olefins by electroreduction
No full textDonor–acceptor (D–A, D = aryl, A = malonate) cyclopropanes are readily available, masked 1,3-zwitterionic C3-synthons which are valuable building blocks for synthetic organic chemistry. Utilizing Lewis acid catalysis, the activated C–C single bond between the donor- and the acceptor-substituted carbon is easily cleaved allowing a variety of transformations from the formally generated zwitterionic form. Searching for new activation pathways an electrochemical approach that removes the need for Lewis acids was followed. Electrochemical activation of D–A cyclopropanes or cyclobutanes via anodic oxidation strategies paved the way for the synthesis of oxidized products by formal O2 insertion. Experimental and quantum-chemical mechanistic investigations were carried out on the reaction pathway, revealing the formation of a radical cation intermediate after C(sp3)-C(sp3) cleavage. Further research on this activation concept led to the development of a Friedel-Crafts-type arylation of D–A cyclopropanes and cyclobutanes.Hydrogenation conveniently allows the construction of C(sp3)-centers from readily available olefins or alkynes while also providing orthogonality in protecting group strategies. However, the control of siteselectivity when more than one group that is affected by hydrogenation is present, is hard to achieve. This project started with a serendipitous discovery and was developed into a robust protocol that overcame limitations of previously reported electroreductive methods for benzylic olefin hydrogenation. Known methods required aryl-EWG substitution on the alkene and used self-made electrochemical systems which hindered reproducibility. This procedure utilizes H2O or D2O for the selective hydrogenation and deuterationof benzylic olefins when other C(sp2)/C(sp)-centers or protecting groups are present. In addition to a broad substrate scope (> 50 examples), experiments to support a mechanistic proposal were performed
Studies on upscaled bifunctional catalysts and their mutual interactions in direct CO2 hydrogenation to DME
No full textIn the present work, the direct synthesis of dimethyl ether (DME) from CO2 and H2 was investigated as a central focus for CO2 valorisation. The two-part reaction requires a bifunctional catalyst, which consists of a CO2 hydrogenation catalyst for MeOH formation and a dehydration catalyst for DME formation.A CuO/ZnO/ZrO2 (CZZ) system was used as the hydrogenation catalyst. The synthesis of CZZ was successfully scaled up by a factor of 7 in this work, enabling a synthesis of 35 g CZZ per day. Several BRØNSTED-acidic zeolites (H-ZSM5_93, H-ZSM5_440, H-FER_20, H-MOR_32, H-BEA_25, H-SAPO_11) were screened as dehydration catalysts in various mixtures. In addition, literature-known tungstosilicic acid-coated Al2O3 and ZrO2 (HPA@Al and HPA@Zr) were used as dehydration catalysts.In a project funded by the Federal Ministry of Education and Research (BioDME project), a transportable synthesis station was designed and put into operation. The best systems from the screening (H-ZSM5_93, H-FER_20 and HPA@Al) were further analysed in this reactor. The systems showed high CO2 conversions (approx. 24 %) and DME selectivities (approx. 60 %).Depending on the mixture method, some dehydration catalysts (H-FER_20, H-MOR_32) showed strong variations in their DME productivity while others showed no dependencies. Therefore, surface tests were performed to investigate the changes of the dehydration catalysts when mixed with CZZ. The investigations revealed a weakening of the strong-acid sites. However, no direct correlation with the DME activity could be identified.Due to the high material costs of CZZ, an in-house developed, fluorinated CuO/ZnO/MgO (CZMg-F) was investigated in direct DME synthesis. The results showed partially higher DME selectivities for CZMg-F. In general, the successful upscaling of the CZZ synthesis provided enough raw material for the operation of a new synthesis station. This made it possible to investigate bifunctional catalyst systems with high CO2 conversions. Furthermore, different methods were investigated to better understand the interaction between hydrogenation catalyst and dehydration catalyst.In addition, CZMg-F was successfully established as a MeOH-forming component in the direct DME synthesis
Through-mask electrochemical machining for conductor track manufacturing – fundamental insights and practical implications
No full textThis work presents a comprehensive analysis of Through-mask Electrochemical Machining (TMECM) metal patterning processes, with a particular focus on copper in sodium nitrate electrolyte. The previously limited understanding of the fundamental processes at the microscopic and nanoscopic scale is significantly enhanced. Initial steps have been taken towards developing industrially feasible processes for application in the Printed Circuit Board (PCB) industry.The first part of the thesis, which addresses the mechanistic aspects of TMECM processes, contains three main findings. The first major achievement is the demonstration of in-situ evidence for the so far only postulated copper nitrate surface film by Raman spectroscopy. The direct connection between mass transport limitation and the formation of the surface film is proven. Based on this, the influence of the surface film on the reaction mechanisms is investigated in a second step. By recording polarization curves, the three process regimes (below, at, and above the limiting current density) are elucidated in terms of their electrochemical behavior. The surface film properties, such as viscosity, conductivity, and thickness, determine the extent of mass transport limitation and the onset voltage for etching with overlimiting current densities. In particular, a model based on an alternative complexation and transportation mechanism at overlimiting current densities is proposed, explaining so far not understood features in the polarization curves. It is based on "solvo-nitration" and requires the presence of the surface film matrix at the metal surface. Substantial indications were found that this model can also be used to describe other metal-electrolyte combinations.In a third step, the gained knowledge is applied to explain the anisotropy of TMECM processes. A clear correlation between the applied process regime and the resulting anisotropy is found. The spatial distribution of the mechanism change significantly influences the anisotropy. Etch factors as high as 25 (meaning 25 times faster etching in depth than in width) were achieved for an etch depth of 60 µm at intermediate current densities (approx. 5 x limiting current density). The second part of this thesis focuses on the practical development of TMECM and its application to real samples. A process chamber that provides homogeneous impinging electrolyte flow and a small interelectrode gap of 1 mm is developed. Mask designs with increasing complexity have been applied over the course of this thesis, particularly the etch homogeneity has been addressed in detail. Significant improvements from more than 30 % deviation to approx. 5 % deviation were achieved on real PCB designs by choosing appropriate processing conditions (limiting current density and homogeneous flow conditions). The presented results, particularly the in-depth investigations on the surface film and its influence on the dissolution mechanism, allow for the prediction of processing results at given boundary conditions or the tailoring of processing conditions to achieve desired results.Die vorliegende Arbeit befasst sich mit der umfassenden Untersuchung elektrochemischer Metallstrukturierungsprozesse (TMECM) mit besonderem Schwerpunkt auf Kupfer in Natriumnitrat-Elektrolyt. Das bisher begrenzte Verständnis der grundlegenden Prozesse auf mikroskopischer und nanoskopischer Ebene wird deutlich verbessert. Zusätzlich wurden erste Schritte zur Entwicklung industriell durchführbarer Prozesse für die Anwendung in der Leiterplattenindustrie durchgeführt.Der erste Teil der Arbeit, der sich mit den mechanistischen Aspekten von TMECM-Prozessen befasst, beinhaltet drei wesentliche Erkenntnisse. Die erste wichtige Errungenschaft ist der Nachweis des bisher nur postulierten Kupfernitrat-Oberflächenfilms mittels in-situ Raman-Spektroskopie. Der direkte Zusammenhang zwischen der Massentransportlimitierung und der Bildung des Oberflächenfilms konnte bestätigt werden. Darauf aufbauend wird in einem zweiten Schritt der Einfluss des Oberflächenfilms auf die Reaktionsmechanismen untersucht. Dazu wurden Polarisationskurven aufgenommen, um die drei Prozessregimes (unterhalb, bei und oberhalb der Grenzstromdichte) bezüglich ihres elektrochemischen Verhaltens zu analysieren. Die Eigenschaften des Oberflächenfilms, wie Viskosität, Leitfähigkeit und Dicke, bestimmen das Ausmaß der Massentransportlimitierung und die Anstiegsspannung für das Ätzen oberhalb der Grenzstromdichte. Insbesondere wird ein Modell vorgeschlagen, das auf einem alternativen Komplexierungs- und Transportmechanismus oberhalb der Grenzstromdichte beruht und bisher unverstandene Charakteristika der Polarisationskurven erklärt. Das Modell basiert auf „Solvo-Nitration“ und setzt das Vorhandensein einer Oberflächenfilmmatrix an der Metalloberfläche voraus. Erste Experimente deuten darauf hin, dass dieses Modell auch zur Beschreibung anderer Metall-Elektrolyt-Kombinationen verwendet werden kann.In einem dritten Schritt werden die gewonnenen Erkenntnisse angewandt, um die Anisotropie von TMECM-Prozessen zu erklären. Es lässt sich eine deutliche Korrelation zwischen dem angewandten Prozessregime und der resultierenden Anisotropie feststellen. Die räumliche Ausdehnung des Mechanismuswechsels übt einen signifikanten Einfluss auf die Anisotropie aus. Es konnten Ätzfaktoren von bis zu 25 (d.h. 25-mal schnelleres Ätzen in die Tiefe als in die Breite) bei einer Ätztiefe von 60 µm bei mittleren Stromdichten (ca. 5 x Grenzstromdichte) erreicht werden. Im zweiten Teil dieser Arbeit wurde die praktische Entwicklung der TMECM-Prozesse und deren Anwendung auf reale Proben vorangetrieben. Es wurde eine Prozesskammer entwickelt, die einen homogenen frontalen Elektrolytfluss und kleine Elektrodenabstände von 1 mm ermöglicht. Im Rahmen dieser Arbeit wurden Maskendesigns mit zunehmender Komplexität verwendet, wobei insbesondere die Ätzhomogenität eingehend untersucht wurde. Signifikante Verbesserungen von mehr als 30 % auf ca. 5 % Abweichung wurden mit realen Leiterplatten-Designs durch die Wahl geeigneter Prozessbedingungen (Grenzstromdichte und homogene Strömungsbedingungen) erzielt. Die präsentierten Ergebnisse, insbesondere die detaillierten Untersuchungen zum Oberflächenfilm und dessen Einfluss auf den Auflösungsmechanismus, erlauben die Vorhersage von Prozessergebnissen bei gegebenen Randbedingungen oder die Anpassung der Prozessbedingungen, um die gewünschten Resultate zu erzielen
Investigation of novel transition metal carbonyl cations and dinitrogen complexes
No full textThe aim of this work was the synthesis and full characterization of novel transition metal cations with weakly bound ligands. In particular, the fluoride bridged perfluorinated alkoxyaluminate anion [F Al ORF 3 2] and the weakly coordinating solvent 1,2,3,4 tetrafluorobenzene were essential for the stabilization of these reactive cations in the condensed phase. The first homoleptic transition metal carbonyl complex Ni CO 4 was synthesized over 130 years ago. Early on, metal carbonyls fascinated due to their molecular structure and unusual physical properties. Here, especially the cationic metal carbonyls exhibit a higher reactivity and weaker M CO bond compared to their neutral or anionic analog. For this reason, nickel carbonyl cations [Ni CO 4 5] were hitherto not known in the condensed phase, although these cations were already detected in the gas phase by advanced mass spectrometry. In this work, however, the first nickel carbonyl cation [Ni CO 4] was obtained as a salt of a weakly coordinating anion via an oxidative synthetic route. The same method was used to generate the [Au CO 2] cation in an organic solvent. Previously, the synthesis of this cation was limited to superacidic media. Subsequently, the use of these compounds [Ni CO 4][F Al ORF 3 2] and [Au CO 2][F Al ORF 3 2] for the synthesis of other novel transition metal cations was investigated. The reaction with benzene or 1,2 difluorobenzene o dfb yielded the corresponding half sandwiches complexes [Ni C6H6 CO 2] , [Ni o dfb CO 2] , and [Au C6H6 CO ] . Additionally, by irreversible removal of CO from the equilibrium, the sandwich complexes [Ni C6H6 2] and [Ni o dfb 2] were obtained. The conversion of [Au CO 2] with the inorganic cages P4 and P4S3 gave access to the corresponding AuI complexes [Au P4 2] and [Au P4S3 2] . These results clearly demonstrate the value of carbonyl cations as starting materials in organometallic chemistry. Their advantage is particularly evident by the access to the very weakly bound NiI complex [Ni o dfb 2] . Compared to the isoelectronic carbonyl complexes, hitherto, no homoleptic dinitrogen complex was reported in the condensed phase. Attempts to prepare such a complex as a salt of a perfluorinated alkoxyaluminate were not successful. Instead, coordination of the anion was observed and the compound [Cu N2 Al ORF 4 ] was obtained. This electron poor complex exhibits an unusually weak metal dinitrogen bond, which is evident by vibrational spectroscopy. A detailed investigation of this bond using the charge displacement analysis showed a significantly weakened amp; 960; back bonding compared to a wide series of electron rich dinitrogen complexes known from the literatur
Synthese und Untersuchung von redoxaktiven Polymeren für die Anwendung als Elektrodenmaterialien in organischen Batterien
No full textDiese Arbeit gliedert sich in zwei Forschungsthemen, beginnend mit der Synthese und Untersuchung von Redox-Polymeren als Elektrodenmaterialien für organische Batterien. Zu diesem Zweck wurden drei redoxaktive Gruppen untersucht: Phenothiazin (PT) wurde als p- Typ-Material verwendet, während Dibenzocyclooctatetraen (DBCOT) und Thioxanthon (TX) wegen ihrer Elektronenspeicherfähigkeiten als n-Typ-Materialien verwendet wurden. Phenothiazin ist bekannt für seine Fähigkeit, zwei Elektronen abzugeben, was es als Batteriematerial geeignet macht, jedoch blieb die zweite Oxidation mit den bis heute synthetisierten Derivaten in diesen Systemen instabil. Um die Stabilität der kationischen Form zu verbessern, wurden verschiedene arylsubstituierte Phenothiazine synthetisiert und elektrochemisch untersucht. Das vielversprechendste wurde in eine Polymerstruktur eingeführt, für die Messung in Batteriesystemen, jedoch führte die hohe Löslichkeit des Polymers zu unzureichenden Leistungen und erforderte eine Optimierung. Ein vernetztes Derivat konnte die volle Kapazität der ersten Oxidation erreichen, die zweite blieb jedoch irreversibel. Durch die Erweiterung der Flexibilität der Seitengruppen mit einem Phenylspacer wurde die Leistung verbessert, verglichen zum linearen Analogon-Polymer, aber die zweite Oxidation blieb selbst bei einem quervernetzten Derivat irreversibel. COT zeigt aufgrund seines tiefliegenden Redoxpotentials und seiner Fähigkeit, zwei Elektronen zu speichern, vielversprechende Eigenschaften als Anodenmaterial für organische Batterien, jedoch führte die Instabilität des geladenen Zustands zu einer Umlagerung und Irreversibilität der Redoxreaktion. Um diese Reaktion zu verhindern, wurde die Struktur mit Phenyleinheiten modifiziert, was zu DBCOT führte, dass in zwei Polymerstrukturen mit unterschiedlichen Hauptketten eingebaut und schließlich elektrochemisch untersucht wurde. Die Messung in Lösung zeigte Redoxaktivitäten, die aber mit dem Material unter Batteriebedingungen nicht reproduziert werden konnten. Trotz Strukturoptimierung durch unlösliche Polymere und Änderung der Elektrodenzusammensetzung konnte die volle Redoxaktivität von DBCOT nicht erreicht werden. Aufgrund seiner verwandten chemischen Struktur mit den heute verwendeten organischen Batteriematerialien könnte Thioxanthon TX vielversprechend für die Ladungspeicherung sein. Die elektrochemische Aktivität in Lösung konnte nachgewiesen werden und konnte unter Verwendung chemischer Modifikation, zusätzliche Redoxprozesse beobachten was die mögliche Anwendung als Batteriematerial bekräftigte. Beide Strukturen TX und TXO konnten nach Optimierung der Reaktionsbedingungen für die Untersuchung in Batteriesystemen in polymere Strukturen eingebaut werden, jedoch verschwand die Redoxaktivität nach wenigen Zyklen, und auch nach Variation der Messbedingungen konnte kein reversibles Verhalten beobachtet werden. Schließlich wurde die Passivierung von Silizium als potentieller Heteroübergang für Solarzellen unter Verwendung organischer Moleküle untersucht. Zu diesem Zweck wurde die Oberfläche geätzt, gefolgt von der Funktionalisierung langer Alkylketten auf die Oberfläche mittels der Hydrosilylierungsreaktion. Als Indikator für die Qualität der Oberfläche diente die Lebensdauer der nach dem Beleuchten des Wafers entstandenen Ladungsträgers. Um diese Lebensdauer zu verbessern, wurden die Reaktionsbedingungen variiert und eine Nachmodifizierung der Monoschicht durchgeführt. Da permanente Dipole bekanntermaßen die Selektivität der Ladungsträger während ihres Transports zur jeweiligen Kontaktelektrode in Solarzellen verbessern, wurde am Ende der Alkylketten die Aminosäure Histidin angebracht
Development and analysis of new liquid electrolytes from abundant metals for battery application
No full textDie vorliegende Arbeit beschäftigt sich in drei Abschnitten mit der Synthese und Charakterisierung von Batterieelektrolyten basierend auf den häufig vorkommenden Elementen Mg, Al, Mn, Fe und Zn.Für die all-Mn-Redox-Flow-Batterie (RFB) wurden neue Elektrolytsysteme unter Verwendung von [MnCl4]2− Salzen untersucht. Dabei wurde eine Löslichkeit von Elektrolytsalzen in org. Lösungsmitteln gesucht, um eine möglichst hohe Kapazität zu ermöglichen. Bei ausreichender Löslichkeit von ca. 50 Gew.% wurden die Elektrolyte in cyclovoltammetrischen (CV) Experimenten, sowie Batteriezellexperimenten bezüglich der Zyklierbarkeit des Batteriesystems untersucht. Durch die CV-Experimente wurde ersichtlich, dass die Mn-Abscheidung häufig nahe der Lösungsmittelzersetzung stattfindet. Eine Mn-Auflösung wurde meist nicht beobachtet. In Zellexperimenten konnte festgestellt werden, dass die untersuchten Elektrolyte eine hohe Überspannung für die Mn-Abscheidung und -Auflösung aufweisen und die mechanische Stabilität des abgeschiedenen Mangans nicht ausreichend ist. Beides könnte in Zukunft durch geeignete Additive verbessert werden. Zudem konnte bei zwei der analysierten Lösungsmitteln Probleme mit der Stabilität bei den untersuchten Bedingungen festgestellt werden. Daher wurden, alternativ zu den org. Lösungsmitteln, in Kooperation mit der ABBOTT Arbeitsgruppe „Deep Eutectic Solvents“ (DES) aus CaCl2∙6 H2O und Ethylenglykol für die Verwendung in der all-Mn-Batterie untersucht. Da der Elektrolyt unter Verwendung von MnCl2 keine Möglichkeit der Zyklierung aufwies, wurden Fe und Zn Salze untersucht. CV Experimente zeigten die mögliche elektrochemische Zyklierung von FeCl2, FeCl3, sowie ZnCl2 und ZnI2. Besonders auffällig war hierbei die sehr hohe Löslichkeit von ZnCl2 in den untersuchten DES und die saubere Zn-Abscheidung und Auflösung. Die Unverträglichkeit des Lösungsmittels mit den untersuchten Anionentauschermembranen bei Zellexperimenten wurde durch Einlegen der verwendeten Membran in deion. Wasser gelöst. Die Elektrolyte ermöglichten die Zyklierung von symmetrischen Zellen bei akzeptablen Überspannungen. Sie zeigten jedoch geringe COULOMBeffizienzen (CE) in Vollzell-Studien.Für Mg-Batterien wurde die Verwendung von [Al(OC(CF3)4]− ausführlich untersucht. Dabei wurde eine saubere Syntheseroute gewählt und die Reinheit des Elektrolytsalzes nachgewiesen. Das Salz zeigte in 1,2-Dimethoxyethan bei verschiedensten Bedingungen keine Möglichkeit der Mg-Abscheidung. Quanten-chemische Rechnungen zeigten, dass das Anion unter Bildung von MgF2 an der negativen Elektrode zersetzt werden kann, was durch XPS-Messungen bestätigt wurde. Die Synthese von alternativen Elektrolytsalzen unter Verwendung von [hfipO3SO]− oder [P(C2O4)3]− erwies sich als nicht erfolgreich. Unsere quantenchemischen Rechnungen konnten jedoch [Al(Ohfip)4]− aufgrund seiner exzellenten Stabilität als das am besten geeignete Anion für Mg-Batterien ausmachen.Ionische Flüssigkeiten (IL) basierend auf [EMIM]Cl oder [BMP]Cl und AlCl3 im Verhältnis 1:1,5 wurden mit fluorierten Benzolen (xFB) (x = 0 – 6) (20 Gew.%) versetzt und auf die Verwendung in Al-Batterien (AIB) elektrochemisch untersucht. Ein inertes Co-Solvens sollte die Viskosität verringern und eventuell lokal anfallende Salze lösen. Während [EMIM]-Chloroaluminat-ILs zu jeder Zeit flüssig sind, fällt [BMP]AlCl4 beim zyklieren lokal als Feststoff aus, wenn kein Co-Solvens verwendet wird. Die Elektrolyte wurden zykliert und die Überspannungen sowie die CE beobachtet. Obwohl die Überspannungen unter der Verwendung von 2FB erhöht waren, trug die Anwesenheit des Additivs zur stark verbesserten Stabilität der CE in Zellexperimenten bei. Weitere Zyklierexperimente zeigten verringerte Überspannungen bei der Verwendung weiterer Fluorbenzole in [EMIM]Cl/AlCl3. Die Stabilität der Elektrolyten wurde per NMR überprüft und zeigte mögliche Reaktionen mit dem Dichtmaterial bei niedrig fluorierten Aromaten (x Erste CV-Experimente in Kooperation mit der ESSER Gruppe zeigten, dass das Polymer PVMPT, anders als in Lithium-Ionen-Batterien, in Al-ILs zwei Redoxstufen aufweist. Dies erlaubt die volle Kapazität des Materials zu nutzen. In einem ersten Zellexperiment konnte die AIB zykliert werden. Es konnte jedoch auch gezeigt werden, dass es zu Problemen durch „Infinite Charge“ Prozesse kommt, die möglicherweise auf der Löslichkeit des Polymers in der IL basieren. Das Zyklierexperiment zeigt jedoch die enormen Möglichkeiten für zukünftige AIBs mit positiven Polymerelektroden auf.This thesis discusses the synthesis and characterization of battery electrolytes based on the abundant elements Mg, Al, Mn, Fe and Zn in three sections.For the all-Mn-redox-flow-batteries (RFB) new electrolytes using [MnCl4]2− salts as active materials were investigated. Whereby it was aimed for high solubility and conductivity in the organic solvents to yield a high capacity for battery application. If a sufficient solubility of ca. 50 wt.% was determined, further studies by cyclic voltammetry (CV) and battery cell experiments were conducted. During these CV experiments it became obvious that the deposition of Mn often occurs near the solvent decomposition limits. The dissolution of Mn from the electrode was rarely observed. In cell experiments, a high overpotential for Mn deposition and dissolution, as well as an insufficient mechanical stability of deposited Mn was observed. Both these issues could be addressed in the future by utilization of a suitable additive. Additionally, two of the investigated solvents showed stability issues under cycling conditions. As an alternative to organic solvents, deep eutectic solvents (DES) from CaCl2∙6 H2O and ethylene glycol (CEG) were investigated for application in the all-Mn-RFB in cooperation with the ABBOTT group. Since a CEG electrolyte using MnCl2 displayed no possibility for electrochemical application, alternative electrolytes using Fe and Zn halides were investigated. CV experiments exhibited the possibility of electrochemical cycling of CEG electrolytes containing FeCl2, FeCl3, ZnCl2 or ZnI2. Here, the high solubility of ZnCl2 along with the clean Zn deposition and dissolution were noteworthy. In symmetric cells all electrolytes displayed applicable overpotentials, while full-cell battery experiments showed issues during cycling due to the membranes used in the experiments. This was circumvented by soaking the membranes in deionized water prior to the cycling experiment. The assembled full-cells then showed low COULOMBIC efficiencies (CEs) during cycling.The use of [Al(OC(CF3)4]− in Mg batteries was extensively investigated. For this, a clean synthesis route was chosen, avoiding common contaminants, to verify the high purity of the active material. During CV experiments in 1,2-dimethoxyethane, no electrochemical activity was observed under all tested conditions. Quantum chemical calculation suggested the decomposition of the anion at the polarized negative electrode under the formation of insulating MgF2. The formation of MgF2 was verified by XPS measurement and compared with Mg deposition from [Al(Ohfip)4]− electrolytes. As alternative electrolytes salts, the synthesis of Mg-salts from [hfipO3SO]− or [P(C2O4)3]− was attempted. According to our calculations, [Al(Ohfip)4]− was found to be the most suitable anion for Mg-batteries, due to its excellent stability.For aluminum ion batteries (AIBs), LEWIS acidic ionic liquids based on [EMIM]Cl or [BMP]Cl in combination with AlCl3 in a 1:1.5 ratio were produced. The addition of fluorinated benzenes (xFBs) (x = 0 – 6) (20 wt.%) to these electrolytes and the effect on cycling behavior and overpotentials was investigated. While [EMIM]-chloroaluminates are liquid at all times, [BMP][AlCl4] is suspected to solidify locally during cycling at the negative electrode, impeding with the cell chemistry. The addition of an inert co-solvent could reduce viscosity, while solvating locally produced solids. Hence, overpotentials and CEs of the cycled cells were monitored at different electrodes. Despite increased overpotentials, the use of 2FB noticeably stabilized the CEs, when [BMP]+ was used. Further cycling experiments in symmetric Al/Al cells, showed decreased overpotentials utilizing other fluorinated benzenes in [EMIM]Cl/AlCl3-ILs. The stability of the co-solvent was investigated by means of NMR-spectroscopy and displayed possible side reactions of the sealing material with xFBs with x Preliminary experiments in cooperation with the ESSER group showed that PVMPT displays two redox steps unlike in lithium ion batteries. This allows to access the polymers full capacity in AIBs. In a first cell experiment, an AIB with Al/PVMPT was able to be cycled. Here, it was shown that infinite charge occurs, similar to Li/S batteries, which might be traced to a solubility of the polymer in the IL. However, this cell experiment demonstrates the great possibilities of organic polymer positive electrodes for AIBs
Synthesis of the weakly coordinating anion [Al(OC10F15)4]− and continuous anhydrous synthesis of oxymethylene dimethyl ethers with gaseous molecular formaldehyde
No full textOne goal of this thesis was the synthesis of the novel weakly coordinating anion [Al(OC10F15)4]− ([pfAd]−). The [pfAd]− anion exhibits a higher stability towards fluoride-ion abstraction compared to the frequently used [Al{OC(CF3)3}4]− according to performed quantum-chemical calculations. The synthetic access towards the [pfAd]− anion was achieved by reaction of LiAlH4 with C10F15OH in 1,2- diflurorobenezene, providing the versatile Li[Al(OC10F15)4]. However, Li[pfAd] was not obtained free of alcohol impurities. Albeit salt metathesis reactions enabled the synthesis of pure Ag[pfAd], [Ph3C][pfAd], and [H(OEt2)2][pfAd], that were characterized by NMR-, IR-, and Raman-spectroscopy, as well as single-crystal X-ray diffraction analysis. Synthesis of Tl[pfAd] in an aqueous reaction media, as well as [P9][pfAd] by reaction of [NO][pfAd] with P4 represent the stability and first applications of this novel WCA. This thesis further deals with novel synthesis pathways towards oxymethylene dimethyl ethers (OMEn; CH3(-OCH2)n-OCH3). For this purpose, the reaction of molecular formaldehyde (FA) with both dimethoxymethane (OME1) and dimethyl ether (DME) was investigated. A wide catalyst screening in a batch reactor was initially performed. The salts Mx+[NTf2]x with M = Cu+, Co2+ and Mg2+ and [NTf2]− = [N(SO2CF3)2]− were identified as very active catalysts in the reaction of FA with OME1. Supported ionic liquid phase (SILP) catalysts were prepared based on these metal salts and demonstrated the successful synthesis of OMEn in a continuous process. SILP catalysts with the ionic liquid (IL) EMIM[BF4] (EMIM = 1-Ethyl-3-methylimidazolium) showed a fast and strong deactivation. In contrast, those prepared with the IL EMIM[NTf2] showed an excellent catalytic performance and stable results in the continuous process, even if stored under ambient conditions for almost two months. The ideal reaction conditions in regard of OME1 conversion and OMEn>1 selectivity were identified by variations in the reaction temperature and the weight hourly space velocity (WHSV). The very active SILP catalysts were also utilized in the reaction of FA with DME. However, only traces of OME1 were observable during these reactions. Further SILP catalysts using less polar ILs, as well as different SiO2 carrier materials, were prepared. Analysis of the product-gas stream revealed only trace amounts of OME1. Thus, conclusions about the success of the reaction should be made with the utmost caution. Instead, the unprecedented reaction of FA with DME was successfully catalyzed by heterogeneous zeolites. Brønsted-acidic zeolites with a 3D pore structure, including H-BEA-25 and H-ZSM-5, proved to be catalytically active. The possibility of shifting the product selectivity in favor of OMEn and suppressing FA disproportionation to methyl formate was demonstrated by feed-gas FA:DME ratio variations
- …
