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Home / Academics / Division of Math & Science / Faculty / Christopher Jones / Dissertation / Chapter 3-Section 3.3

3.3 Electrochemical Response of Conducting Polymers

One unique feature of many conjugated organic polymers like polypyrrole and polythiophene is their ability to reversibly change their electrical properties. In their reduced form, they are insulators. Upon oxidation, they are transformed into an electrically conducting material. As seen in Figure 3.2, poly(3-hexyl thiophene), a soluble conducting polymer which was spray coated on a Au electrode can be electrochemically doped. Spray coating is used for deposition because polymerization of the monomer species requires potentials too high to be used with high-temperature superconductor electrodes. A pre-formed polymer such as poly(3-hexyl thiophene), can be chemically synthesized and subsequently can be spray coated onto the electrode. Unlike the electropolymerization of polypyrrole, the spray-coating technique does not place requirements on the electrical properties of the substrate material for polymer deposition.

The electrochemical response of a thick film (~1-10mm) of poly(3-hexyl thiophene) in a 0.1 M Bu4NBF4 / CH3CN solution on a Au coated glass electrode at a scan rate of 50 mV/sec.

Figure 3.2:The electrochemical response of a thick film (~1-10mm) of poly(3-hexyl thiophene) in a 0.1 M Bu4NBF4 / CH3CN solution on a Au coated glass electrode at a scan rate of 50 mV/sec.

 

Cyclic voltammetry shows the oxidation and reduction of a polypyrrole coated YBa2Cu3O7-x thin film electrode placed in a 0.1 M Et4NBF4 / CH3CN solution at a scan rate of 5 mV/sec.

Figure 3.3:Cyclic voltammetry shows the oxidation and reduction of a polypyrrole coated YBa2Cu3O7-x thin film electrode placed in a 0.1 M Et4NBF4 / CH3CN solution at a scan rate of 5 mV/sec.

Chronoamperometry (CA) showing the doping and undoping of polypyrrole on a YBa2Cu3O7-x electrode in a 0.1 M Et4NBF4 / CH3CN solution.

Figure 3.4: Chronoamperometry showing the doping and undoping of polypyrrole on a YBa2Cu3O7-x electrode in a 0.1 M Et4NBF4 / CH3CN solution.

The availability of this solution processing method expands the diversity in the type of polymer films placed on superconductors.

When the polymer is oxidized, it becomes positively charged and the conjugated backbone is delocalized. To compensate for the charge, a tetrafluoroborate anion is inserted into the polymer matrix. The cyclic voltammetry shows a clear oxidation and reduction of the poly(3-hexyl thiophene) coated gold film in an electrolytic acetonitrile solution of tetraethylammonium tetrafluoroborate. This behavior demonstrates the reversibility and the redox process. It also shows that there is clear electron transfer between the poly(3-hexyl thiophene) and the underlying gold. If the surface of the gold had been coated with an insulating layer, this electron transfer would not have taken place. Similarly, if there had been an insulating barrier coating the surface of YBa2Cu3O7-x in a polypyrrole coated YBa2Cu3O7-x electrode, electron transfer at the interface would be hindered. As seen in Figure 3.3, when proper conditions are used, a reversible electrochemical response from a polypyrrole coated YBa2Cu3O7-x thin film electrode can be obtained. Chronoamperometry can also be used to oxidize and reduce the conducting polymer as seen in Figure 3.4. The data here provides additional evidence for the reversible charge flow between the polymer and the cuprate conductor. While there were reports of conducting polymers deposited on bulk high-temperature superconductors, we were the first to report the electrochemical response of a conducting polymer deposited onto a thin film as well as to explore the polymer’s charging characteristics on the underlying superconductor’s properties (vide infra).49

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Updated on: April 15, 2010 8:26 PM