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Asymmetric supercapacitors based on carbon nanofibre and polypyrrole/nanocellulose composite electrodes
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
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2015 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 21, 16405-16413 p.Article in journal (Refereed) Published
Abstract [en]

Asymmetric, all-organic supercapacitors (containing an aqueous electrolyte), exhibiting a capacitance of 25 F g-1 (or 2.3 F cm-2) at a current density of 20 mA cm-2 and a maximum cell voltage of 1.6 V, are presented. The devices contain a composite consisting of polypyrrole covered Cladophora cellulose fibres (PPy-cellulose) as the positive electrode while a carbon nanofibre material, obtained by heat treatment of the same PPy-cellulose composite under nitrogen gas flow, serves as the negative electrode. Scanning and transmission electron microscopy combined with X-ray photoelectron spectroscopy data show that the heat treatment gives rise to a porous carbon nanofibre material, topologically almost identical to the original PPy-cellulose composite. The specific gravimetric capacitances of the carbon and the PPy-cellulose electrodes were found to be 59 and 146 F g-1, respectively, while the asymmetric supercapacitors exhibited a gravimetric energy density of 33 J g-1. The latter value is about two times higher than the energy densities obtainable for a symmetric PPy-cellulose device as a result of the larger cell voltage range accessible. The capacitance obtained for the asymmetric devices at a current density of 156 mA cm-2 was 11 F g-1 and cycling stability results further indicate that the capacity loss was about 23% during 1000 cycles employing a current density of 20 mA cm-2. The present results represent a significant step forward towards the realization of all-organic material based supercapacitors with aqueous electrolytes and commercially viable capacitances and energy densities.

Place, publisher, year, edition, pages
2015. Vol. 5, no 21, 16405-16413 p.
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials; Computerized Image Processing
Identifiers
URN: urn:nbn:se:uu:diva-243564DOI: 10.1039/C4RA15894FISI: 000349524700075OAI: oai:DiVA.org:uu-243564DiVA: diva2:787575
Available from: 2015-01-26 Created: 2015-02-10 Last updated: 2017-12-04Bibliographically approved
In thesis
1. On the electrochemical performance of energy storage devices composed of cellulose and conducting polymers
Open this publication in new window or tab >>On the electrochemical performance of energy storage devices composed of cellulose and conducting polymers
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Applications that require electrical energy storage are becoming increasingly diverse. This development is caused by a number of factors, such as an increasing global energy demand, the advent of electric vehicles, the utilization of intermittent renewable energy sources, and advances in disposable and organic electronics. These applications will set different demands on their electrical energy storage and, thus, there will be no single technology used for all applications. For some applications the choice of energy storage materials will be extremely important. Conventional batteries and supercapacitors rely on the use of nonrenewable inorganic materials mined from depleting ores, hence, requiring large amounts of energy for their processing. Such materials also add a significant cost to the final product, making them less attractive for large scale applications. Conducting polymers, on the other hand, constitute a class of materials that can be used for organic matter based energy storage devices.

The aim of this thesis was to investigate the use of a composite consisting of the conducting polymer polypyrrole (PPy) and cellulose derived from Cladophora sp. algae for electrical energy storage. The polymer was coated onto the cellulose fibers by chemical polymerization resulting in a flexible material with high surface area. By using this composite as electrodes, electrochemical cells consisting of disposable and non-toxic materials can be assembled and used as energy storage devices. The resistances of these prototype cells were found to be dominated by the resistance of the current collectors and to scale with the thickness of the separator, and can hence be reduced by cell design. By addition of nanostructured PPy, the weight ratio of PPy in the composite could be increased, and the cell voltages could be enhanced by using a carbonized negative electrode. Composites of cellulose and poly(3,4-ethylenedioxythiophene) could also be synthesized and used as electrode materials. The porosities of the electrodes were controlled by mechanical compression of the composite or by coating of surface modified cellulose fibers with additional PPy. Finally, the self-discharge was studied extensively. It was found that oxygen was responsible for the oxidation of the negative electrode, while the rate of self-discharge of the positive electrode increases with increasing potential. Through measurements of the charge prior to and after self-discharge, as well as with an electrochemical quartz crystal microbalance, it was found that the self-discharge of the positive electrode was linked to an exchange of the counter ions by hydroxide ions. It is also demonstrated that the self-discharge rate of a symmetric PPy based device can be decreased dramatically by proper balancing of the electrode capacities and by reducing the oxygen concentration. The results of this work are expected to contribute towards future industrial implementation of electric energy storage devices based on organic materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1403
Keyword
polypyrrole, supercapacitors, self-discharge
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-300917 (URN)978-91-554-9651-7 (ISBN)
External cooperation:
Public defence
2016-09-30, Å80121, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Available from: 2016-09-09 Created: 2016-08-16 Last updated: 2016-09-13

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Tammela, PetterWang, ZhaohuiFrykstrand, SaraZhang, PengSintorn, Ida-MariaNyholm, LeifStrömme, Maria

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