TAILIEUCHUNG - Electrochemical Polymer Capacitors

‘Metallically’ conducting polymers show good intrinsic conductivity, at least in the charged state. The specific capacitance values, potential ranges, long-term stabilities, and cycle lives of supercapacitors based on polymers are rather moderate, compared to the cycle lives of those based on carbon and metal oxide materials. | Electrochemical Polymer Capacitors P Kurzweil University of Applied Sciences Kaiser-Wilhelm-Ring 23 Amberg Germany 2009 Elsevier . All rights reserved. Conducting Polymers for Supercapacitors Metallically conducting polymers show good intrinsic conductivity at least in the charged state. The specific capacitance values potential ranges long-term stabilities and cycle lives of supercapacitors based on polymers are rather moderate compared to the cycle lives of those based on carbon and metal oxide materials. The materials are relatively cheap compared to metal oxides especially as existing processes for batteries can be employed for supercapacitor fabrication. Pseudocapacitance at Polymer Materials Polyacetylene polyaniline PANI polypyrrole pPy polythiophene and similar aromatic polymers exhibit a large degree of p-orbital conjugation that gives rise to electronic conductivity of 1-100 Scm . In oriented form polyacetylene can reach 105 Scm . The p system can be anodically oxidized or cathodically reduced by withdrawal or injection of electrons respectively. Sometimes the terms p-doping and n-doping are used for oxidation and reduction respectively but they do not describe the actual addition of chemical electron-donor or electron-acceptor impurities in semiconductors which generate a new conduction band or valence band of states and a diminished band gap. The capacitance of a conducting polymer layer in a supercapacitor does not behave like the polymer dielectric in an electrostatic capacitor. Measurable capacitance arises from faradaic rather than electrostatic origins - as distinct from the ideal double-layer capacitance at the phase boundary between a nonpolarizable electrode and an aqueous solution. The so-called pseudocapacitance of conducting polymers is based on battery-type faradaic redox processes associated with Lewis-type acid-base reactions. The electric charge Qrequired for the progression of the charge transfer process is a function of potential j .

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