| 1. |
- Sjödin, Martin, 1974-, et al.
(författare)
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Organic Battery Materials based on Conducting Polymer Backbones with High Capacity Pending Groups
- 2014
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Konferensbidrag (refereegranskat)abstract
- Organic matter based battery materials have attracted large interest due to their inherent ability to provide an environmentally benign alternative to inorganic batteries because such materials can be produced from renewable resources via eco-efficient processes. The development of organic battery materials rely on several key factors that need to be resolved, the most important being dissolution problems, limited electronic conductivity, degradation of active material and slow redox kinetics. Conducting polymers are insoluble in most electrolytes, they are electronically conducting and show fast redox conversion but are, to some extent, unstable and have insufficient charge capacities for battery applications. To understand the instability of conducting polymers we have measured self discharge rates in polypyrrole at different temperatures. From these experiments it is clear that the self-discharge originates from an activated redox reaction with an activation barrier of around 0.4 eV. Although the exact nature of the redox reaction has not been identified we have been able to link the self discharge to, what is commonly referred to as, over-oxidation. Over-oxidation is common to polyacetylene, polyparaphenylene, polypyrrole and polythiophene and this mechanism of self discharge is thus a general feature of conducting polymers. This self-discharge mechanism is suppressed by low polymer doping levels, low potentials and low temperatures. By attaching high capacity redox active groups onto the conducting polymer backbone the charge capacity can be increased while retaining electronic conductivity and insolubility. We have attached quinone groups to each repeat unit of polypyrrole for this purpose. Interestingly, in-situ spectroscopic measurements show that during quinone redox conversion the polymer doping level is in-fact reduced. Since the doping level of the polymer affects the rate of self-discharge the attachment of quinone units to the polypyrrole chain not only increases the charge capacity but also provides a conceptual strategy to control self discharge.
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| 2. |
- Huang, Hao, 1988-, et al.
(författare)
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Synthesis and Characterization of Poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole : investigation on Backbone/Pendant Interactions in a Conducting Redox Polymer
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:16, s. 10427-10435
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Tidskriftsartikel (refereegranskat)abstract
- We herein report the synthesis and electrochemical characterization of poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole, consisting of a polypyrrole backbone derivatized at the beta position by a vinyl-hydroquinone pendant group. The structure of the polymer was characterized by solid state NMR spectroscopy. The interactions between the polypyrrole backbone and the oxidized quinone or reduced hydroquinone pendant groups are probed by several in situ methods. In situ attenuated total reflectance-Fourier transform infrared spectroscopy shows spectroscopic response from both the doping of the polymer backbone and the redox activity of the pendant groups. Using an in situ Electrochemical Quartz Crystal Microbalance we reveal that the polymer doping is unaffected by the pendant group redox chemistry, as opposed to previous reports. Despite the continuous doping the electrochemical conversion from the hydroquinone state to the quinone state results in a significant conductance drop, as observed by in situ conductivity measurements using an InterDigitated Array electrode set-up. Twisting of the conducting polymer backbone as a result of a decreased separation between pendant groups due to π-π stacking in the oxidized state is suggested as the cause of this conductance drop.
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| 3. |
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| 4. |
- Karlsson, Christoffer, 1986-, et al.
(författare)
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Computational Electrochemistry Study of 16 Isoindole-4,7-diones as Candidates for Organic Cathode Materials
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 116:5, s. 3793-3801
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Tidskriftsartikel (refereegranskat)abstract
- Prediction of the redox behavior of electroactive molecules enables screening of a variety of compounds and can serve as a guideline in the search for organic molecules for use as cathode materials in, for example, Li ion batteries. In this study, we present a computational strategy, based on density functional theory, to calculate redox potentials and acid dissociation constants for a series of 16 isoindole-4,7-dione (IID) derivatives. The calculations take all possible electron and proton transfers into account, and the results were found to correlate very well with electrochemical and spectroscopic measurements. The possibility of polymerizing the IID derivatives was also assessed computationally, as polymerization serves as a straightforward route to immobilize the active material. Three of the considered IIDs (5,6-dicyano-2-methyl-isoindole-4,7-dione, 5,6-dihydroxy-2-methyl-isoindole-4,7-dione, and 2-methyl-5-(trifluoromethyl)-isoindole-4,7-dione) are predicted to be particularly interesting for making polymers for organic cathodes because these are calculated to have high redox potentials and high specific capacities and to be readily polymerizable. The presented strategy is general and can be applied in the prediction of the electrochemical behavior of quinones as well as other systems involving proton and electron transfers.
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| 5. |
- Karlsson, Christoffer, 1986-
(författare)
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Conducting Redox Polymers for Electrical Energy Storage : Backbone - Substituent Interactions in Quinone Polypyrrole Model Systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic electrical energy storage (EES) is a growing field of research that is expected to play an important role in the future, as the need for sustainable EES increases. Conducting redox polymers (CRPs), i.e. conducting polymers with incorporated redox active moieties e.g. as pendant groups (PGs), are proposed as a promising class of compounds for this purpose. Redox cycling of the PGs can be utilized for high charge storage capacity, while the conducting polymer backbone provides fast charge transport through the material. Some of the major challenges with small-molecule systems for EES could be solved by using CRPs, e.g. capacity fading due to dissolution of the active compound, and high resistance due to slow charge transport between molecules. The latter issue is often solved by adding large amounts of conducting additives to the active material, drastically lowering the specific capacity. In this project, CRPs are shown to be able to function in battery cells without any additives, making both high capacity and high power possible. Although several CRPs have been reported in the literature, very few detailed studies have been conducted on the electrochemical processes of the two systems (i.e. the conducting polymer backbone and the redox active PGs). An important factor to consider in CRP design is the possibility for interaction between the two redox systems, which could be either beneficial or detrimental to the function as EES material. In this thesis, CRP model systems composed of hydroquinone functionalized polypyrrole have been studied, and they exhibit separate redox reactions for the PGs and the backbone, overlapping in potential. Significant interaction between them was observed, as oxidation of the PGs has severe impact on the backbone: When the oxidized and hydrophobic p-benzoquinone PGs are formed, they pack and force the polymer backbone to twist, localizing the bipolarons, and decreasing the conductivity. This is accompanied by a contraction of the polymer film and expulsion of electrolyte. Overall, the interaction in these polymers is destructive for their EES function, and it could be eliminated by introduction of a long linker unit between the PGs and the backbone.
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| 8. |
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| 9. |
- Karlsson, Christoffer, 1986-, et al.
(författare)
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Impact of Linker in Polypyrrole/Quinone Conducting Redox Polymers
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:15, s. 11309-11316
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Tidskriftsartikel (refereegranskat)abstract
- Organic conducting redox polymers are being investigated as the active component for secondary battery applications, as they have the potential to solve two of the main problems with small molecule-based organic electrodes for electrical energy storage, viz dissolution of the active compound in the electrolyte, and slow charge transport through the material. Herein we report the synthesis of a series of conducting redox polymers based on polypyrrole with hydroquinone pendant groups that are attached to the backbone via different linkers, and we investigate the impact of the linker on the interaction between the backbone and the pendant groups. For the directly linked polymer, oxidation of the pendant groups leads to a decrease of bipolaron absorbance, as well as a decrease in mass of the polymer film, both of which are reversible. The origin of these effects is discussed in light of the influence of the linker unit, electrolyte polarity, and electrolyte salt. For the longest linkers in the series, no interaction was observed, which was deemed the most beneficial situation for energy storage applications, as the energy storage capacity of the pendant groups can be utilized without disturbing the conductivity of the polymer backbone.
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| 10. |
- Karlsson, Christoffer, 1986-, et al.
(författare)
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Investigation of the Redox Chemistry of Isoindole-4,7-diones
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:2, s. 894-901
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Tidskriftsartikel (refereegranskat)abstract
- Quinone derivatives have been proposed as active components in lithium ion battery (LIB) electrode materials. In this work the electrochemistry of a series of substituted isoindole-4,7-diones (IIDs) was investigated. Three new IID derivatives were synthesized and characterized by various electrochemical and spectroscopic techniques. Polymerization was attempted to achieve a conducting polymer with redox active quinone side groups, which would be advantageous in a LIB application. A combination of in situ spectroelectrochemical measurements and density functional theory (DFT) calculations was used to investigate the proton coupled redox reactions of the IIDs. Results from a previous computational study of the IIDs were compared with experimental data here, and the agreement was very good. The energy of the spectroscopic transitions in the UV and in the visible region showed different correlation with redox potential and quinone substituent in the series of IIDs. This behavior was rationalized by examination of the involved molecular orbitals. The results indicated that the properties of the quinone unit, such as the redox potential, could be selectively varied by substitution.
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