Modification of carbon electrode materials with anthraquinone and dihydroxybenzene functionalities for supercapacitors

Algharaibeh, Zaher Abdelgader (2013) Modification of carbon electrode materials with anthraquinone and dihydroxybenzene functionalities for supercapacitors. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The main purpose of this thesis was to study the modification of carbon materials with anthraquinone (AQ) and dihydroxybenzene (DHB) functionalities, via diazonium chemistry and electrochemical oxidative polymerization of their amines, and to examine their usefulness as new electrode materials for supercapacitor applications. -- High surface area carbon materials have been widely used as electrode materials for supercapacitors. They store charges primarily through an electrostatic double layer charging mechanism which limits their energy density. The need for cost effective supercapacitors with high power and energy densities is crucial for many potential new applications. -- Modified electrodes were investigated by one or more of the following techniques: cyclic voltammetry, galvanic cycling, electrochemical impedance spectroscopy, scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy and elemental analysis. -- The performances of the supercapacitors were evaluated by cyclic voltarnmetry and constant current discharging chronopotentiometry. Ragone plots were used to determine energy and power densities. -- Various diazonium coupling approaches were successfully implemented to attach anthraquinone, 3,4-dihydroxybenzene and 3,4-dimethoxybenzene to different types of carbon electrode materials including carbon fabric (Spectrocarb 2225), Vulcan XC72, Black Pearls 2000 and glassy carbon. -- AQ modified carbon fabric was used as a negative electrode with Ru oxide as a positive electrode in a 1 M H₂SO₄ (aq) asymmetric supercapacitor. Better energy and power densities were achieved from this device using 64% less Ru compared to an expensive symmetric Ru oxide device of the same mass as a result of the extended cell voltage and the higher specific capacitance that the AQ modification provides. Replacing the Ru oxide electrode with DHB modified carbon fabric electrode resulted in doubling the energy densities compared to the symmetric unmodified carbon fabric device. -- An electrochemical oxidative polymerization approach was successfully used to prepare the following conducting polymers; poly(l-aminoanthraquinone ), poly( anilineco-1-aminoanthraquinone), poly( dimethoxyaniline) on carbon electrodes. -- Interestingly, poly(l-aminoanthraquinone) films prepared from 6 M H₂SO₄ (aq) solution showed unusual electrochemical behaviour. These films were extensively studied by cyclic voltarnmetry and impedance spectroscopy and it was found that the AQ electrochemical activity was strongly affected by the conductivity of the polyaniline-like backbone. Accordingly, a charge trapping phenomenon was recognized.

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