Light-driven synthesis of bio-based polymers and theirsupercapacitance investigation

Abstract

Conjugated conductive polymers, due to their unique chemical, electrical, thermal, and mechanical properties, are widely applied in energy storage devices, sensors, solar panels, and coatings. Among these applications, energy storage devices are the most needed, spanning from electric vehicles to portable speakers. The main drawback of energy storage devices is the inability to achieve high power density and energy density simultaneously. Batteries offer high energy density, while capacitors provide high power density. Supercapacitors bridge the gap between capacitors and batteries. Among the components that constitute a supercapacitor, the electrode holds the most critical importance. Although a wide range of materials (carbon-based materials, metal oxides, metal-organic frameworks (MOFs), MXenes) can be used in supercapacitor electrode synthesis, conjugated conductive polymers represent the most promising class for the electrode component of next-generation supercapacitors. Additionally, synthesizing conjugated conductive polymers in compliance with sustainable and green chemistry principles is crucial due to the serious environmental and health impacts of fossil fuels, historically used as energy sources. Therefore, two essential criteria are the use of renewable materials and mild conditions. Among the methods for synthesizing conjugated conductive polymers, the photopolymerization method surpasses traditional methods due to its lack of toxic solvents, high-temperature requirements, and transition metal catalysts, as well as its shorter reaction time and stereotemporal control. In this thesis, two distinct approaches were investigated to synthesize conjugated conductive polymers in a green solvent medium and under UV-A light using an organic and environmentally safe photoinitiator, phenacyl bromide (PAB). The first approach involves polymerizing the structure of Guaiazulene (1,4-dimethyl-7-isopropyl azulene), a low-cost natural derivative of azulene from plant oils, in the presence of ethyl acetate (EtOAc). The second approach is based on compensating for the brittleness and low adhesion properties of the EDOT (3,4-ethylenedioxythiophene) monomer, a leading entity in the conductive polymer class, by polymerizing it with Dopamine in an ethanol (EtOH) medium. As a result of these approaches, two polymers—poly(guayazulene) (PGz) and polydopamine-doped PEDOT (PDA@PEDOT)—were characterized in terms of spectroscopic (IR, UV-Vis, NMR), thermal (DSC, TGA), microscopic (SEM, TEM, AFM), electrochemical (CV, GCD), and conductivity (electrical and ionic conductivity) properties.The reaction mechanisms of the two materials, whose spectroscopic, thermal, and electrical properties were analyzed, were schematized based on laser-flash photolysis experiments. The two polymers, which were investigated for their supercapacitor electrode properties, exhibited unique supercapacitor electrode characteristics with rapid charge-discharge capabilities and high energy and power densities, in consistent with their morphological organization. In conclusion, this thesis reports the synthesis and complete characterization of two distinct supercapacitor electrode materials, developed using in-situ and environmentally friendly methods as alternatives to commercial supercapacitors.