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Thermoelectric Devices with Electronic and Ionic Conducting Polymers
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The energy consumption in the world is continuously growing and the sources of energy are largely dominated by fossil fuels. However, the resources of oil, gas and coal are diminishing in capacity. Moreover the CO2 emissions arising from their combustion is a great concern because it induces climate changes that threaten our habitat. There is a dire need to look for alternative sources of energies and to minimize losses of energy in our surroundings. Heat engines and turbines typically running with fossil energy have efficiencies of about 35%, i.e. 65% of the energy is lost in the form of heat. Low temperature heat (<200 C) is almost always wasted in power plants, industries, automobiles and household appliances. This is a huge resource that can be directly converted to electricity through the concept of thermoelectricity. Major challenges for heat to electricity conversion include finding the abundant materials with efficient thermoelectric (TE) conversion that can be mass produced at low cost.

This thesis presents an investigation of the TE properties of electronic and ionic conducting polymers, as well as their implementation in thermoelectric devices. This is a journey from thin solid films on a substrate to wet and liquid media and towards bulk structures utilizing the same core concept of thermoelectricity. The TE device concepts introduced here are suitable for various heat sources i.e. continuous, intermittent and instantaneous. The thesis has three major parts as follows:

Conducting polymers (CPs) have been studied mainly as thin films. They have been synthesized in different ways and their properties have been compared to propose the most efficient amongst them for thermoelectricity. Simple methods of exposure to certain gases or liquids have been used to tune their TE properties and demonstrated its applications in thermoelectric generator (TEGs).

Ionic materials have also been studied as potential candidates for thermoelectricity. Polyelectrolytes constitute a special class of electrolytes with dissimilar sizes of ions; a polymeric ion and a small counter ion. The movement of the small sodium (Na+) cation under heat gradient was explored in wet films and in solution. Because the ions could not cross the electrolyte-electrode junction, we propose the idea of ionic thermoelectric supercapacitor (ITESC), suitable for intermittent heat source.

Nanofibrillated cellulose (NFC) has been used along with conducting polymers to realize the three dimensional conducting bulks as a TEG leg. NFC bulks were coated with conducting polymers as a first approach and later the mixture of (NFC & CP) was freeze-dried. The later approach resulted in mechanically flexible structures that were used as dual sensors for pressure and temperature based on the TE properties of the CP which can be utilized for electronic skin applications.

The thesis shows new ways of utilizing waste heat using polymeric materials and points to a sensory application area, broadening the horizons of thermoelectricity.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. , 50 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1709
Keyword [en]
Thermoelectricity, conducting polymers, thermoelectric devices
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:liu:diva-121982ISBN: 978-91-7685-931-5 (print)OAI: oai:DiVA.org:liu-121982DiVA: diva2:860845
Public defence
2015-11-12, Resuren (Pronova), Campus Norrköping, Norrköping, 10:00 (English)
Opponent
Supervisors
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved
List of papers
1. Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)
Open this publication in new window or tab >>Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)
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2011 (English)In: NATURE MATERIALS, ISSN 1476-1122, Vol. 10, no 6, 429-433 p.Article in journal (Refereed) Published
Abstract [en]

Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 degrees C, the best commercially available inorganic semiconductors are bismuth telluride (Bi2Te3)-based alloys, which possess a figure of merit ZT close to one(1). Most of the recently discovered thermoelectric materials with ZT andgt; 2 exhibit one common property, namely their low lattice thermal conductivities(2,3). Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (lambda = D 0.37W m(-1) K-1) yields a ZT = 0.25 at room temperature that approaches the values required for efficient devices.

Place, publisher, year, edition, pages
Nature Publishing Group, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68783 (URN)10.1038/nmat3012 (DOI)000290855100016 ()
Available from: 2011-06-08 Created: 2011-06-07 Last updated: 2015-10-14
2. Semi-metallic polymers
Open this publication in new window or tab >>Semi-metallic polymers
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2014 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 13, no 2, 190-194 p.Article in journal (Refereed) Published
Abstract [en]

Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications. We measure the thermoelectric properties of various poly( 3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.

Place, publisher, year, edition, pages
Nature Publishing Group, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-104644 (URN)10.1038/nmat3824 (DOI)000330182700027 ()
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2015-10-14
3. Acido-basic control of the thermoelectric properties of poly(3,4-ethylenedioxythiophene)tosylate (PEDOT-Tos) thin films
Open this publication in new window or tab >>Acido-basic control of the thermoelectric properties of poly(3,4-ethylenedioxythiophene)tosylate (PEDOT-Tos) thin films
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2015 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, Vol. 3, 10616-10623 p.Article in journal (Refereed) Published
Abstract [en]

PEDOT-Tos is one of the conducting polymers that displays the most promising thermoelectric properties. Until now, it has been utterly difficult to control all the synthesis parameters and the morphology governing the thermoelectric properties. To improve our understanding of this material, we study the variation in the thermoelectric properties by a simple acido-basic treatment. The emphasis of this study is to elucidate the chemical changes induced by acid (HCl) or base (NaOH) treatment in PEDOT-Tos thin films using various spectroscopic and structural techniques. We could identify changes in the nanoscale morphology due to anion exchange between tosylate and Cl- or OH-. But, we identified that changing the pH leads to a tuning of the oxidation level of the polymer, which can explain the changes in thermoelectric properties. Hence, a simple acid-base treatment allows finding the optimum for the power factor in PEDOT-Tos thin films.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2015
National Category
Polymer Chemistry Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:liu:diva-121977 (URN)10.1039/C5TC01952D (DOI)000363251600035 ()
Note

Funding agencies: European Research Council (ERC) [307596]

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-11-16Bibliographically approved
4. Ionic Thermoelectric Supercapacitor
Open this publication in new window or tab >>Ionic Thermoelectric Supercapacitor
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2015 (English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-121978 (URN)
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved
5. Ionic Thermoelectric effect in Polyelectrolytes
Open this publication in new window or tab >>Ionic Thermoelectric effect in Polyelectrolytes
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2015 (English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-121980 (URN)
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved
6. Nanofibrillated cellulose aerogels functionalized with conducting polymers for thermoelectric and dual-sensing applications
Open this publication in new window or tab >>Nanofibrillated cellulose aerogels functionalized with conducting polymers for thermoelectric and dual-sensing applications
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Large amount of heat is wasted in industries, power generation plants and ordinary household appliances. This waste heat, can be a useful input to a thermoelectric generator (TEG) that can convert it to electricity. Conducting polymers (CPs) have been proved as best suited thermoelectric (TE) materials for lower temperatures, being not toxic, abundant in nature and solution processible. So far, CPs have been characterized as thin films, but it needs the third dimension to realize vertical TEGs which is possible by coating it on low thermal conductivity 3D skeletons. In this work, porous bulk cellulose structures have been used as a supporting material and were coated with CPs in various ways. The blend of cellulose and polymer were also freeze-dried, resulting in conducting and soft composites. Those flexible aerogels were utilized as a dual parameter sensor to sense pressure and temperature, based on the concept of thermoelectricity. It opens another application area of sensing, utilizing the thermoelectric phenomenon beyond the prevailing power generation concept. The sensitivity of such materials can be enhanced to make them useful as electronic skin in healthcare and robotics.

National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-121981 (URN)
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved

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