Aqueous Supercapacitors Based on Polymer-Biomass Composites

Abstract

The development of sustainable aqueous supercapacitors requires the integration of high-performance conductive materials and abundant, environmentally friendly resources. This thesis investigates the electrochemical performance of composite electrodes comprising of conjugated polymers and lignosulfonate, a low-cost biomass derivative theoretically capable of providing additive pseudocapacitance through quinone-based reversible redox reactions. A comprehensive comparative analysis was conducted between established p-type polymers (PEDOT:F and PEDOT:PSS) and a novel, ultra-highly conductive n-type polymer, poly(benzodifurandione) (PBFDO). The active materials were deposited onto plasma-treated carbon paper substrates via a controlled sequential drop-casting method and evaluated in symmetrical two electrode Swagelok cells utilizing an aqueous perchloric acid electrolyte. Baseline electrochemical characterization via Cyclic Voltammetry (CV), Galvanos tatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) revealed that pristine PBFDO vastly outperformed both PEDOT derivatives. Eval uated at a low comparative current density of 0.25 A/g, PBFDO exhibited superior specific capacitance, exceptional structural resilience, and minimal Equivalent Series Resistance (ESR). Contrary to the central hypothesis, the incorporation of unmodified lignosulfonate severely degraded the performance of all tested polymers. Rather than acting as a synergistic redox contributor, the water-soluble and electrically insulating ligno sulfonate acted as an electrochemically inactive dead weight. While the p-type PEDOT composites suffered catastrophic electrochemical failure at a 1:1 polymer to-lignin mass ratio, the self-doped n-type PBFDO matrix demonstrated remarkable structural resilience. Although the specific capacitance of PBFDO systematically declined as the lignin concentration increased across 3:1, 1:1, and 1:3 mass ratios, it maintained its fundamental charge-storage mechanisms without the massive internal resistance spikes observed in the p-type cells. Ultimately, while highlighting the lim itations of physically blending raw lignosulfonate in aqueous electrolytes, this study unequivocally establishes the novel n-type PBFDO network as a premier, highly robust conjugated polymer for next-generation energy storage applications