Carbon-based polymeric materials for stretchable supercapacitors
University of New Brunswick
The urgent need for the development of efficient and environmentally-friendly energy storage devices has led to the exploration of new materials with chemically tailored properties. More specifically, the field of super- and ultracapacitors is currently moving forward to incorporate carefully modified carbon allotropes in the modern capacitor design. The main goal for previous research in designing capacitive materials has been to maximize their efficiency, without sacrificing environmental safety. This thesis presents a preparation of highly stretchable and heavy-metal-free electrodes based on polyacrylamide/ poly (N, N’- methylenebis(acrylamide)) hydrogels, which contained nanostructured carbons (e.g., graphene, multi-walled carbon nanotubes; MWCNTs, single-walled carbon nanohorns; SWCNHs) covalently bonded to conjugated polymer (polypyrrole; PPy). Carbon cores provided a large electrochemical double layer capacitance, whereas a conjugated polymer was the source of pseudocapacitance. The approach of joining two capacitance mechanisms within one molecule was completed by utilizing nanostructured carbons as polymerization initiators, while the pyrrole or 2-(1H-pyrrol-1-yl) ethyl methacrylate were used as monomers. Polymers were uniformly distributed around the carbon cores via oxidative radical polymerization, electrochemically aided atom transfer polymerization (e-ATRP), and reversible addition-fragmentation chain transfer polymerization (RAFT). The highest specific gravimetric capacitance of active nanocomposite was 456.86 F g[superscript -1], and was found to be highly dependent on the nature of the operating electrolyte. The detailed mechanistic computations, electrochemical quartz microbalance, and electrochemical studies have revealed that potassium chloride is the most suitable electrolyte for maximizing the electrochemical output of obtained nanocomposites. A series of stretchable (up to 1475 %) electrodes were prepared with emphasis on their conductivity, elasticity, and translucent properties. The task of dispersion of nanocomposites within the solid-state electrolyte, based on pAAm/pMBAA hydrogels containing KCl, was addressed by enhancing the zeta potential of active materials through the incorporation of perfluorated long aliphatic molecules (i.e., Nafion 117®). Electrochemical analysis by alternating the current electrochemical admittance spectroscopy, cyclic voltammetry, and the theoretical modeling of an equivalent circuit based on impedance spectroscopy have revealed a large interfacial specific gravimetric capacitance of the stretchable electrodes (up to 516.86 F g[superscript -1]). Prepared materials are stable up to 7500 charge/discharge cycles in liquid electrolytes and up to 717 cycles in hydrogels. Obtained products are market-grade materials for modern supercapacitors.