Exploration of Oligoaniline Synthesis and Applications in Supercapacitors
Compared to rechargeable batteries, supercapacitors, also known as ultracapacitors or electrochemical capacitors demonstrate higher power and much greater cycle life. As the demand increases for energy storage devices with safe operations, high power ratings and long cycle life, supercapacitors have attracted much attention from both industry and academia. However, most commercial supercapacitors are carbon based, capable of storing only a fraction of the amount of charge that batteries do, limiting their applications to those that need short power bursts, but lower capacities. To enhance the energy density of supercapacitors, pseudocapacitance materials, such as transition metal oxides/hydroxides and conducting polymers, are introduced.
Polyaniline is a promising pseudocapacitance material with high conductivity, tunable morphology and high theoretical specific capacitance. Tetra-aniline (TANI) is the shortest oligomer of PANI that demonstrates high conductivity and redox activities. Furthermore, the short chain length of TANI is believed to improve its resistance to chain breaking during cycling that undermines PANI’s cycle stability. However, compared to PANI, research on the synthesis and supercapacitor applications of nanostructured TANI is relatively scarce. Therefore, the goal of this thesis is to develop methods to prepare TANI with various nanostructures and study the supercapacitor applications of TANI-based supercapacitors.
Chapter 2 presents a facile interfacial chemical synthesis to produce high purity TANI nanowires, while Chapter 3 is a study on the electrochemical deposition of TANI on different substrates using aniline dimer in organic-aqueous electrolyte solutions. Both methods are able to trigger nanostructure formation within TANI, and improve upon the pseudocapacitor performances of the TANI-based electrodes. Chapter 4 reports an original one-pot-one-step hydrothermal synthesis of reduced graphene oxide (rGO) - oligoaniline (OANI) nanocomposites. This process simultaneously reduces graphene oxide and deposits oligoaniline onto the rGO surfaces, inducing synergetic effects between the conducting oligomer and the carbon substrates. Chapter 5 presents an in-depth evaluation on the supercapacitor performances of TANI and its carbon nanocomposites. We composited TANI with 1D (carbon nanotubes), 2D (GO and rGO) and 3D (activated carbon) carbon materials to investigate how morphology and surface functional groups affect the supercapacitor performances of TANI-based electrodes.