Enhanced electrochemical performance of renewable flexible supercapacitors through the synergistic effects of nitrogen-doped carbonaceous fillers and controlled polypyrrole nanostructuring on nanocellulose fibers

Abstract

The growing demand for sustainable, high-performance energy storage solutions has driven advancements in flexible supercapacitors, which offer high power density, fast charging, and adaptability. This study investigates the electrochemical performance of novel, renewable, flexible, lightweight, and cost-effective electrodes synthesized using environmentally friendly one-pot and two-step methods. The electrodes integrate polypyrrole nanotubes (PPy–NT), cellulose nanofibers (CNF), and nitrogen-doped one-dimensional carbonaceous fillers (ACT–NT) or commercial carbon black. ACT–NT obtained by carbonizing and activating of PPy–NT, exhibit a nanotubular structure, high surface area, wettability, and tunable electrical conductivity. To construct a flexible supercapacitor, a simple cellulose hydrogel was synthesized as a dual-function electrolyte reservoir and separator. The PPy–NT/CNF electrode, synthesized via the one-pot method, achieved the highest initial specific capacitance (e.g., 172 F g−1 at 5 mV s−1). This performance was attributed to the uniform growth of PPy–NT on CNF, which improved conductivity and redox activity. However, electrodes with carbonaceous fillers demonstrated better cycling stability by reinforcing the electrode structure and enabling a combination of electric double-layer capacitance and pseudocapacitive charge storage. The two-step synthesis method further enhanced the performance of PPy–NT/ACT–NT/CNF electrode by achieving an optimal balance of conductivity, morphology, wettability, textural and mechanical properties, outperforming their one-pot synthesis counterparts. These findings highlight the importance of material design for flexible, renewable supercapacitors, offering a pathway to more sustainable and efficient energy storage.