Title:
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Electrochemical synthesis of composites of conducting polymers and carbon nanotubes for supercapacitors
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The power units in modem electric vehicles are required to store large amount of
energy and to provide a high power. Supercapacitors being able to export a pulsed high
power can be used in combination with batteries or fuel cell to meet the energy and
power demand of electric vehicles.
Carbon nanotubes with high surface area and conducting polymers with large
pseudocapacitance are both powerful candidates for supercapacitors. This thesis
describes a novel electrochemical route for synthesis of composites of conducting
polymer and nanotubes via co-deposition from solutions containing ionic CNTs and
monomers. The resulting deposits exhibited a unique porous network structure
composed of individual nanotubes coated with a layer of conducting polymers. Carbon
nanotubes served as charge carriers during the polymerisation and also acted as both a
strong backbone and effective dopant within the composite materials. Therefore, the
composites have improved mechanical integrity and an open structure that facilitates
ion and solvent motion during the electrochemical processes. Moreover, the large
immobile CNT anions exert an electrostatic repulsion to the electrons on the polymer
chain. This repulsion makes it easier to remove electrons from the polymer chains. As
a result, the composites showed good conductivity and capacitive properties even at
negative potentials. A systematic study on the charge storage properties of the composites has been carried
out using various electrochemical methods, including CV, AC impedance
spectroscopy, chronocoulometry, chronoamperometry and chronopotentiometry. FTIR
and XPS have been used to study the interaction between CNTs and conducting
polymers.
Prototype supercapacitors were built with the composites as electrode material. Both
symmetric and asymmetric prototypes showed ideal capacitive behaviour, indicating a
good potential for application in supercapacitors using the novel composite materials.
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