Bipolar electrochemistry for the synthesis of functionalized carbon-polypyrrole supercapacitor electrodes
University of New Brunswick
Supercapacitors belong to the family of electrical energy storage systems alongside batteries and fuel cells. Their unique feature is having both high power and energy density making them suitable options where fast charging and long-lasting power are desired. Supercapacitance comes in two flavours, electric double layer capacitance (EDLC) and pseudocapacitance (PC). This thesis combines both in a single electrode using carbon EDLC base and polypyrrole PC coating. Various methods to bind the two using bipolar electrochemistry are the major focal points of this thesis. Bipolar electrochemistry is a wireless electrochemical setup that is green, scalable, and easily produces asymmetric/gradient products. The first project functionalizes carbon electrodes through diazonium salt reduction to electrochemically graft a linker group. Polypyrrole then binds to this linker in a copolymer-like fashion. Results showed that aqueous conditions produced a better product than non-aqueous conditions at 200 mF cm−2 compared to 11 mF cm−2. The second project incorporates metal-organic frameworks (MOFs) as the binding agent. This class of materials has some of the largest surface area densities ever measured. Filling this space with polypyrrole transforms the MOF from an electrical insulator to a conductor. Plain powder forms of three different MOFs synthesized using the solvothermal method were used to test the proof of concept. The results showed specific capacitances ranging from 300 to 600 mF cm−2. From this the MOF synthesis was adapted to use bipolar electrochemistry for direct electroplating. Once again carbon featured as the base while Cu MOF was deposited by the anodic dissolution method. The MOF layers were fragile and prone to detachment, but thermal oxidation of pyrrole in air was found to leave the MOFs intact. Loading solutions with higher pyrrole content resulted in greater improvements to the supercapacitance, up to 28 mF cm−2.