Aqueous Supercapacitors Based on Polymer-Biomass Composites

Sammanfattning

The development of sustainable aqueous supercapacitors requires the integrationof high-performance conductive materials and abundant, environmentally friendlyresources. This thesis investigates the electrochemical performance of compositeelectrodes comprising of conjugated polymers and lignosulfonate, a low-cost biomassderivative theoretically capable of providing additive pseudocapacitance throughquinone-based reversible redox reactions. A comprehensive comparative analysis wasconducted between established p-type polymers (PEDOT:F and PEDOT:PSS) and anovel, ultra-highly conductive n-type polymer, poly(benzodifurandione) (PBFDO).The active materials were deposited onto plasma-treated carbon paper substratesvia a controlled sequential drop-casting method and evaluated in symmetrical twoelectrode Swagelok cells utilizing an aqueous perchloric acid electrolyte.Baseline electrochemical characterization via Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS)revealed that pristine PBFDO vastly outperformed both PEDOT derivatives. Evaluated at a low comparative current density of 0.25 A/g, PBFDO exhibited superiorspecific capacitance, exceptional structural resilience, and minimal Equivalent SeriesResistance (ESR).Contrary to the central hypothesis, the incorporation of unmodified lignosulfonateseverely degraded the performance of all tested polymers. Rather than acting asa synergistic redox contributor, the water-soluble and electrically insulating lignosulfonate acted as an electrochemically inactive dead weight. While the p-typePEDOT composites suffered catastrophic electrochemical failure at a 1:1 polymerto-lignin mass ratio, the self-doped n-type PBFDO matrix demonstrated remarkablestructural resilience. Although the specific capacitance of PBFDO systematicallydeclined as the lignin concentration increased across 3:1, 1:1, and 1:3 mass ratios, itmaintained its fundamental charge-storage mechanisms without the massive internalresistance spikes observed in the p-type cells. Ultimately, while highlighting the limitations of physically blending raw lignosulfonate in aqueous electrolytes, this studyunequivocally establishes the novel n-type PBFDO network as a premier, highlyrobust conjugated polymer for next-generation energy storage applications