25 research outputs found
Time Resolved Measurements of pH in Aqueous MagnesiumâAir Batteries during Discharge and Its Impact for Future Applications
In aqueous magnesium air batteries, the influence of the electrochemical behavior on pH of the electrolyte has not been investigated yet, which has a critical effect on the cell performance. We have monitored the evolution of the pH at various discharge current densities inâ
situ in the Mg-air primary cells, which produce sparingly soluble magnesium hydroxide (Mg(OH)). These experiments show the temporal evolution of the pH of the electrolyte in the cell discharge, depending on the current density. The pH first increases rapidly to a maximum of pHâ
11 and then drops down slowly to the equilibrium at pHâ
10.7. At the peak pH oversaturation of Mg(OH) is paramount, leading to the precipitation which balances the Mg(OH) concentration in the electrolyte. This precipitation process coats both cathode and anode which leads to a decrease in cell efficiency and voltage. The results show that the cell design of Mg-air batteries is important for their lifetime and cell performance. The performance of the aqueous magnesium cell is increased several folds when the design is changed to a simple electrolyte flow cell
Capturing NanoâScale Inhomogeneity of the Electrode Electrolyte Interface in SodiumâIon Batteries Through TipâEnhanced Raman Spectroscopy
A prime challenge in the development of new battery chemistries is the fundamental understanding of the generation of the electrodeâelectrolyte interface (EEI) and its evolution upon cycling. Tip-enhanced Raman spectroscopy (TERS) under an inert gas atmosphere is employed to study the chemical components of the anode/cathode electrolyte interface in a sodium-ion battery. After the first cycle, TERS reveals that the EEI mostly consists of organic carbonate/dicarbonate, oligoethylene oxides, α,ÎČ-unsaturated vinyl ketones/acetates, and inorganic species ClO, ClO, and NaCO. Whereas after 5Ă cycling, the EEI composition has evolved to contain long chain monodentate or bridging/bidentate carboxylates and alkoxides. The TERS map reveals the nano-scale heterogeneity present in the EEI layers and elucidates a multilayered nano-mosaic coating structure. The sheer volume of Raman signature present in the TERS signal can completely unravel the mysteries regarding the chemical composition and may shed light to the physicochemical behavior of the EEI
N â B Ladder Polymers Prepared by Postfunctionalization:Tuning of Electron Affinity and Evaluation as Acceptors in All-Polymer Solar Cells
A poly(biphenylene-pyrazinylene) (PPz, E g opt = 3.10 eV) and a head-to-tail regioregular polypyridine (rr-P4Py, E g opt = 3.25 eV) equipped with 1-alkenyl side chains have been prepared and postfunctionalized by hydroboration with different hydroboranes (9H-BBN, (C 6 F 5 ) 2 B-H (BPF-H), Cl 2 B-H) to give the corresponding ladder polymers featuring intramolecular coordinative N â B bonds. Characterization of the optical and electrochemical properties of the postfunctionalized polymers shows that the borylation strongly increases their electron affinity and lowers the optical gaps. Electron affinities between -3.75 eV (PPzBBN, E g opt = 2.16 eV) and -4.35 eV (PPzBPF, E g opt = 2.07 eV) can be reached for hydroborated PPz, while rr-P4Py-derivatives reach LUMO levels of -3.45 eV (P4PyBBN, E g opt = 2.88 eV), -3.85 eV (P4PyBPF, E g opt = 2.95 eV), and -4.15 eV (P4PyBCl 2 , E g opt = 2.95 eV). The potential of this class of compounds as electron acceptors is demonstrated by the investigation of the semiconducting properties of PPzBBN and PPzBPF, which showed ambipolar charge transport with hole and electron mobilities in order of 2 Ă 10 -5 cm 2 V -1 s -1 . The polymers were tested as acceptors in all-polymer solar cells, which yielded functioning devices, with open-circuit voltages that directly reflect the electron affinity of the employed acceptor
MultiâComponent PtFeCoNi CoreâShell Nanoparticles on MWCNTs as Promising Bifunctional Catalyst for Oxygen Reduction and Oxygen Evolution Reactions
The development of commercially viable fuel cells and metal-air batteries requires effective and cheap bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Multi-component PtâFeâCoâNi nanoparticles on multi-walled carbon nanotubes (MWCNTs) were synthesized by wet chemistry route via NaBH reduction of metal salts, followed by sintering at different temperatures. The catalyst demonstrates an excellent ORR activity and a promising OER activity in 0.1â
m KOH, with a bi-functional over-potential, ÎE of 0.83â
V, which is comparable to the values of Pt/C or RuO. Furthermore, it shows outstanding long-term stability in ORR and OER, namely diffusion limited current density at a potential of 0.3â
V decreased just by 5.5â% after 10000 cycles in ORR. The results of the PFCN@NT indicate a significant effect of the substitution of Pt by the transition metal (TM) and the formation of nanoparticles on the catalytic performance, especially in the OER
All-conjugated donor-acceptor block copolymers featuring a pentafulvenyl-polyisocyanide-acceptor
We report a fulvenyl-functionalized polyisocyanide (PIC2) with a high electron mobility of ÎŒe = 10-2 cm2 V-1 s-1. PIC2 has been incorporated into block-copolymers with either regioregular poly(3-dodecylthiophene) (P3DT â P(3DT-b-IC2)) or regioregular polythiazole (PTzTHX â P(TzTHX-b-IC2)). Block copolymer batches with different block-sizes have been isolated and their properties have been studied. Fluorescence quenching in the solid state and transient absorption spectroscopy indicate energy transfer from the donor-to the acceptor block upon photo-excitation. Fabrication of proof-of-principle organic photovoltaic cells with P(3DT-b-IC2) gave cells with an open circuit voltage (VOC) of ca. 0.89 V. The aggregation behavior of P(3DT-b-IC2) from solution was also studied, which revealed self-assembly into discreet microspheres of 1-8 ÎŒm diameter, with a size distribution of 1.72 (±0.37) ÎŒm under optimized aggregation conditions
NiO/poly(4-alkylthiazole) hybrid interface for promoting spatial charge separation in photoelectrochemical water reduction
Molecular Engineering of Metalloporphyrins for HighâPerformance Energy Storage: Central Metal Matters
Porphyrin derivatives represent an emerging class of redox-active materials for sustainable electrochemical energy storage. However, their structureâperformance relationship is poorly understood, which confines their rational design and thus limits access to their full potential. To gain such understanding, we here focus on the role of the metal ion within porphyrin molecules. The AB-type porphyrin 5,15-bis(ethynyl)-10,20-diphenylporphyrin and its first-row transition metal complexes from Co to Zn are used as models to investigate the relationships between structure and electrochemical performance. It turned out that the choice of central metal atom has a profound influence on the practical voltage window and discharge capacity. The results of DFT calculations suggest that the choice of central metal atom triggers the degree of planarity of the porphyrin. Single crystal diffraction studies illustrate the consequences on the intramolecular rearrangement and packing of metalloporphyrins. Besides the direct effect of the metal choice on the undesired solubility, efficient packing and crystallinity are found to dictate the rate capability and the ion diffusion along with the porosity. Such findings open up a vast space of compositions and morphologies to accelerate the practical application of resource-friendly cathode materials to satisfy the rapidly increasing need for efficient electrical energy storage
A ÏâConjugated Porphyrin Complex as Cathode Material Allows Fast and Stable Energy Storage in Calcium Batteries
Rechargeable calcium batteries (RCB) are prospective candidates for sustainable energy storage, as they hold the promise of the high energy density of lithium-ion batteries (LIBs) while simultaneously combining it with highly abundant raw materials. However, for long time, calcium batteries have faced severe issues with regard to cycling stability, until recently developments demonstrated improved battery cycle life when employing CaSn alloy anodes with fluorinated alkoxyborate electrolytes. These findings opened up the possibility to study cathode materials for RCBs not only in a more comparable manner, but also in a practical full cell design. As representative of emerging organic electrode materials (OEMs), we investigated tetrakis(4-pyridyl) porphyrin as both free ligand (HTPyP) and in the form of its copper MOF complex (CuTPyPâMOF) as active cathode species in RCBs. The cells demonstrated high capacities and excellent cycling stability at the same time. Even at elevated current densities of e.âg., 2000â
mA/g the full cells delivered stable capacities of ~90â
mAh/g proving its excellent rate capability. This study explores the electrochemical performance of porphyrin active materials in calcium batteries and represents a significant step forward in the progress toward organic electrodes for multivalent energy storage systems
Experimentelle und theoretische Studien zu Eigenschaften des Dibenzo[c,g]fluorenid-Liganden
Doppelbindungen verminderter Konjugation auftreten, Ă€hnlich der 9,10-Doppelbindung in Phenanthren. Die Eignung von Dbf-1 als η5-Metallocenligand konnte durch die Darstellung einer Reihe von Ăbergangsmetallkomplexen gezeigt werden: Neben dem symmetrischen Ferrocen Dbf2Fe, dessen analoge Fluorenylverbindung nicht bekannt ist, konnten auch die unsymmetrisch substituierten Ferrocene (η5-Dbf)Fe(η5-4Cp) (4Cp: 1,2,3,4- Tetraisopropylcyclopentadienyl) und (η5-Dbf)Fe(η5-Cpâââ) (Cpâââ: 1,2,4-Tri-tert-butylcyclopentadienyl) erhalten werden. Weiterhin wurden Metallocen- und Arenkomplexe mit Gruppe VI-Metallen ((η3-Allyl)(η5-Dbf)M(CO)2, M = Mo, W und (η6-DbfH)Cr(CO)3 isoliert, sowie Metallocene der Metalle Mangan ((η5-Dbf)Mn(CO)3), Cobalt ([(η5-Dbf)Co(η5-Cp*)]PF6, Cp*: 1,2,3,4,5-Pentamethylcyclopentadienyl), Ruthenium ((η5-Dbf)Ru(PPh3)2Cl, [(η5-Dbf)Ru(PPh3)2(NCMe)]SbF6) und Titan (η5-Dbf)(η1-Dbf)Ti(OiPr)2. FĂŒr die lokalisierten Doppelbindungen in 3,4- und 3â,4â-Position wird â wie im Fall des Phenanthren â partielle olefinische ReaktivitĂ€t erwartet. Dies konnte durch die selektive Anwendung olefintypischer Reaktionen an diesen Positionen bestĂ€tigt werden. Reaktion von Dbf-Ferrocenen mit molekularem Wasserstoff in Gegenwart von Pd/C erlaubt selektive Hydrierung der Komplexe an Position 3,4 und 3â,4â und liefert die entsprechenden 3,3â,4,4â-Tetrahydrodibenzo[c,g]fluorenylkomplexe (H4-Dbf)2Fe und (H4-Dbf)Fe(4Cp). Die Umsetzung mit ZnEt2 und ClCH2I erlaubt die selektive Cyclopropanierung der Ferrocens (Dbf)Fe(Cpâââ)
Experimentelle und theoretische Studien zu Eigenschaften des Dibenzo[c,g]fluorenid-Liganden
Doppelbindungen verminderter Konjugation auftreten, Ă€hnlich der 9,10-Doppelbindung in Phenanthren. Die Eignung von Dbf-1 als η5-Metallocenligand konnte durch die Darstellung einer Reihe von Ăbergangsmetallkomplexen gezeigt werden: Neben dem symmetrischen Ferrocen Dbf2Fe, dessen analoge Fluorenylverbindung nicht bekannt ist, konnten auch die unsymmetrisch substituierten Ferrocene (η5-Dbf)Fe(η5-4Cp) (4Cp: 1,2,3,4- Tetraisopropylcyclopentadienyl) und (η5-Dbf)Fe(η5-Cpâââ) (Cpâââ: 1,2,4-Tri-tert-butylcyclopentadienyl) erhalten werden. Weiterhin wurden Metallocen- und Arenkomplexe mit Gruppe VI-Metallen ((η3-Allyl)(η5-Dbf)M(CO)2, M = Mo, W und (η6-DbfH)Cr(CO)3 isoliert, sowie Metallocene der Metalle Mangan ((η5-Dbf)Mn(CO)3), Cobalt ([(η5-Dbf)Co(η5-Cp*)]PF6, Cp*: 1,2,3,4,5-Pentamethylcyclopentadienyl), Ruthenium ((η5-Dbf)Ru(PPh3)2Cl, [(η5-Dbf)Ru(PPh3)2(NCMe)]SbF6) und Titan (η5-Dbf)(η1-Dbf)Ti(OiPr)2. FĂŒr die lokalisierten Doppelbindungen in 3,4- und 3â,4â-Position wird â wie im Fall des Phenanthren â partielle olefinische ReaktivitĂ€t erwartet. Dies konnte durch die selektive Anwendung olefintypischer Reaktionen an diesen Positionen bestĂ€tigt werden. Reaktion von Dbf-Ferrocenen mit molekularem Wasserstoff in Gegenwart von Pd/C erlaubt selektive Hydrierung der Komplexe an Position 3,4 und 3â,4â und liefert die entsprechenden 3,3â,4,4â-Tetrahydrodibenzo[c,g]fluorenylkomplexe (H4-Dbf)2Fe und (H4-Dbf)Fe(4Cp). Die Umsetzung mit ZnEt2 und ClCH2I erlaubt die selektive Cyclopropanierung der Ferrocens (Dbf)Fe(Cpâââ)