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Oxygen-induced doping on reduced PEDOT
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-3899-4891
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-8478-4663
Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
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2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 9, p. 4404-4412Article in journal (Refereed) Published
Abstract [en]

The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) has shown promise as air electrode in renewable energy technologies like metal-air batteries and fuel cells. PEDOT is based on atomic elements of high abundance and is synthesized at low temperature from solution. The mechanism of oxygen reduction reaction (ORR) over chemically polymerized PEDOT: Cl still remains controversial with eventual role of transition metal impurities. However, regardless of the mechanistic route, we here demonstrate yet another key active role of PEDOT in the ORR mechanism. Our study demonstrates the decoupling of conductivity (intrinsic property) from electrocatalysis (as an extrinsic phenomenon) yielding the evidence of doping of the polymer by oxygen during ORR. Hence, the PEDOT electrode is electrochemically reduced (undoped) in the voltage range of ORR regime, but O-2 keeps it conducting; ensuring PEDOT to act as an electrode for the ORR. The interaction of oxygen with the polymer electrode is investigated with a battery of spectroscopic techniques.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY , 2017. Vol. 5, no 9, p. 4404-4412
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-136229DOI: 10.1039/c6ta10521aISI: 000395926100019OAI: oai:DiVA.org:liu-136229DiVA, id: diva2:1086226
Note

Funding Agencies|European Research Council (ERC) [307596]; Knut and Alice Wallenberg foundation; Wenner-Gren Foundations; Swedish Research Council; Swedish Foundation for Strategic Research [0-3D]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Available from: 2017-03-31 Created: 2017-03-31 Last updated: 2018-05-07
In thesis
1. Application of Vibrational Spectroscopy in Organic Electronics
Open this publication in new window or tab >>Application of Vibrational Spectroscopy in Organic Electronics
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rapid technological developments enforce us to live in an increasingly electronic world, and the revolutionary usage of conjugated polymers in electronics in the late 1970s accelerated these developments, based on the unique characteristics of conjugated polymers, such as low cost, easy processing, mechanical flexibility, large-area application and compatibility with a variety of substrates. Organic electronic devices are commercially available in the form of, for example, solar cells, transistors, and organic light-emitting diode (OLED) displays. Scientists work on electroactive polymers to enhance their chemical, electrical and mechanical properties, to improve parameters such as charge carrier mobility and doping capacity, in order to reach acceptable efficiency and stability to fabricate organic electronic devices. A comprehensive understanding of the changes in chemical structure, in response to external factors such as applied potential and temperature gradients, which can disturb the chemical equilibrium of the constituent materials, and of the conduction mechanisms of the operating devices, can help to enhance the performance of organic electronics devices. Vibrational spectroscopy is a powerful analytical method for in-situ monitoring of such chemical or electrochemical reactions and associated structural changes of conjugated polymers in a working device.

In this thesis, Fourier-transform infrared (FTIR) spectroscopy has been used to study the structural changes in electroactive organic materials, in response to chemical or electrochemical reactions, and to study electrical and thermal conduction mechanisms in different organic electronic devices. FTIR microscopy was used to approach a realistic conduction mechanism by time-resolved chemical imaging of active materials in planar light-emitting electrochemical cells (LECs), investigated as an alternative to organic light emitting diodes (OLEDs). These chemical images are used for in-situ mapping of anion density profiles, polymer doping, and dynamic junction formation in the active layer under an applied bias. Results confirm the electrochemical doping model and help the systematic improvement of function and manufacture of LECs. Mixed ion-electron polymeric conductor materials such as PEDOT-PSS are used as active materials in organic thermoelectric generators (OTEGs), where charge carrier transport through the active layer promotes internal electrochemical reactions under a temperature gradient. FTIR microscopy and FTIR-attenuated total reflection (FTIR-ATR) were used to study thermoelectric and electrical properties of the conducting polymers. Recently, electrochemical supercapacitors have emerged as an alternative to conventional batteries, and polymeric materials are used to design polymer electrodes for renewable energy storage. To understand the charge transfer and structural changes of the polymer during the redox reaction, we have used FTIR-ATR as a tool for the in-situ spectroelectrochemical study of redox states in polypyrrole/lignin composites; we clarified the structural changes in the materials during charging and discharging of the composite. In further work, FTIR-ATR was also used for in-situ spectroelectrochemical studies of PEDOT:Cl, to monitor the effects of dissolved oxygen on PEDOT:Cl films, which are used as electrodes in renewable energy technologies. Further, time-resolved oxygen reduction reactions of PEDOT:Cl have been studied via polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) to reveal chemical changes in electrochemically doped PEDOT upon exposure to oxygen.

Taken together, these studies provide an advancement in the use of infrared spectroscopy as a tool to understand electroactive materials under wet conditions, and have provided detailed chemical and electrochemical information of materials and devices under operation, that is not easily accessible with other methods.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 61
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1884
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-142216 (URN)9789176854440 (ISBN)
Public defence
2017-11-17, Planck, F-House, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2017-10-23Bibliographically approved
2. Conducting Polymer Electrodes for Oxygen Reduction Reaction
Open this publication in new window or tab >>Conducting Polymer Electrodes for Oxygen Reduction Reaction
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Both the pollution level of the environment and the increasing energy demands have stimulated intense research on the development of low-cost environmentally-friendly energy conversion and storage systems with high efficiency, such as metal-air batteries and fuel cells.

One of the most essential parts of both fuel cells and metal–air batteries is the air-electrode which is responsible for the reduction of O2. The air-electrode can use O2 from air facilitating the layout of the device; however, the process taking place on it is significantly complex. Currently, platinum (Pt) is the benchmark for air-electrodes in such technologies, although it is expensive and exhibits other important disadvantages which diminish the fuel cell performance. Therefore, extensive research has been devoted to reduce the amount of Pt used in air-electrodes and to develop a noble metal-free version of these electrodes.

The area of printed electronics could facilitate the development of low-cost electrodes produced in high volume for such applications. Conducting polymers are attractive materials for this technology because they may combine several desired properties, like electronic conduction, ionic conduction and catalysis of electrochemical reactions.

Among other conducting polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) emerged as an alternative cathode catalyst material to Pt, due to its ability to effectively catalyze the oxygen reduction reaction (ORR), while it also exhibits high electrical and ionic conductivity.

The focus of this thesis is to study the electrocatalytic activity and mechanism of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) when employed as an airelectrode in energy storage devices, such as fuel cells and metal-air batteries. Although PEDOT is extensively studied during the last decade as an air-electrode for fuel cell and metal-air batteries, vital pieces of the catalytic mechanism that PEDOT follows remain unknown, namely: (i) the sites of PEDOT on which O2 interacts and (ii) the intermediate species which are formed during the ORR. The content of this thesis tackles these topics, both from experimental and theoretical point of view. Moreover, it investigates the use of PEDOT as an active electrocatalyst in a polymer exchange membrane (PEM) fuel cell, by embedding the polymer in a cellulose matrix, aiming to fabricate a gas diffusion electrode for the ORR side of the device. Finally, the goal of the thesis surpasses the limit of the p-doped PEDOT and undertakes the evaluation of a n-type conjugated polymer of high electron affinity as a cathode in reduction processes.  

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 103
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1915
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:liu:diva-147720 (URN)9789176853450 (ISBN)
Public defence
2018-06-01, K3, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-07Bibliographically approved

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