Synthesis and Energy Storage Performance of Novel Redox-Active Polymers

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Title: Synthesis and Energy Storage Performance of Novel Redox-Active Polymers
Authors: Mahmood, Arsalan Mado Mahmood
Thesis advisor: Prof. Dr. Andreas Hennig
Thesis referee: Prof. Dr. Uwe Beginn
Abstract: The lithium-ion battery is the most preferred choice for energy storage, for example, in electric vehicle batteries and electronic devices. These commonly utilized transition metal-based cathodes and graphite anodes. However, replacing the active materials with organic, redox-active materials is of great interest since these organic batteries are excelling in charging speed and cycling stability. Therefore, in the present thesis, the synthesis and characterization of potential organic electroactive materials, mainly polymers, are investigated. Concerning the structure of the polymers, linear polymers, three-dimensional / crosslinked polymers, as well as dendrimers, were chosen. The electroactive subunits include viologen, imide, triphenylamine, porphyrin, and ferrocene, either as homopolymer or copolymer, as well as active materials like graphene oxide (GO) or electrolytes. The characterization of the structures was performed by means of NMR, FTIR spectroscopy, and elemental analysis. The electrochemical properties of products were investigated by the cyclic voltammetry (CV) technique. Electrodes were prepared by drop-casting a solution of the polymers onto a current collector, and the (dis)charge performance was investigated. To enhance the conductivity of the layers, composites of the polymers with GO were prepared. Since the performance depends on the electrolyte composition, different types of solvents and salts were used and compared. The capacities in a thin film of pure polymers and dendrimers were much smaller than in the composite film with rGO. These performances are based on the molecular self-assembly of polymers and dendrimers on individual GO sheets yielding colloidal polymer/dendrimer@GO and efficient GO/rGO transformation electrocatalyzed by polymers and dendrimers. However, the stability and capacity of some polymers and dendrimers such as P2, P5, P6 and G2 were not optimal in this type of composite film. Moreover, the peak potential in the positive charge range assigned to the nitrogen centre of triphenylamine and porphyrin was found to decrease after the first scan, which is probably due to a dissolution of the film. Therefore different methods were used to composite polymer or dendrimer with GO such as reducing GO before mixing. As noticed that the redox behaviour of amine and ferrocene are reversible, but the stability of radical cation species is not stable in organic solvent after oxidation. Besides the preparation of electrodes by drop-casting, the layer-by-layer process was used by alternate dipping between cationic polymer solution and anionic GO or Poly(sodium p-styerenesulfonate) (PSS) solution. PSS acts as a counter ion for the polymer, which changes the moving species in the electrolyte from anion to cation. As noted that a large cation (TBA+) shows lower capacity compared to small cations (Li+, K+). Apart from the CV, quartz crystal microbalance (QCM) was used to monitor layer growth.
Subject Keywords: Organic battery; Graphene oxide composites
Issue Date: 21-Mar-2022
License name: Attribution 3.0 Germany
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Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB06 - E-Dissertationen

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