Synergistic Combination of Polydopamine and Polypyrrole in Natural Pectin/PVA-Based Freestanding Electrodes for High-Performance Supercapacitors

In this study, poly(vinyl alcohol) (PVA)/pectin/polypyrrole (PPy) and PVA/pectin/polydopamine (PDA)/PPy hydrogel films were prepared for use as supercapacitor electrodes. The synergistic effect of PDA and PPy on the electrochemical performance of the PVA/pectin/PDA/PPy hydrogel electrode was studied. PVA/pectin composite films (VE10, VE91, VE73, and VE55) with varying pectin proportions were prepared by cross-linking PVA with glutaraldehyde to serve as flexible and stretchable gel substrates for supercapacitor electrodes. PPy was synthesized on the surface of PVA/pectin films via chemical bath deposition. The incorporation of optimized pectin significantly enhanced the PPy content and the capacitance of the PVA/pectin/PPy film (VE73/PPy-90), achieving a measured value of 463.1 mF/cm², which is notably higher than that of films without pectin. To further enhance the surface capacitance of the PVA/pectin/PPy composite, PDA was synthesized in situ on the surface of the PVA/pectin electrode using a chemical bath, followed by PPy polymerization. The synergistic combination of PDA and PPy resulted in a much higher areal and specific capacitance of 1575.7 mF/cm² and 262.6 Fg^1- at a current density of 1 mA/cm² for the PVA/pectin/PDA/PPy (VE73/DA/PPy-90) gel electrode. After charge-discharge cycle testing at a current density of 1 mA/cm², the VE73/PPy-90 and VE73/DA/PPy-90 gel electrodes retained 80% and 70% of their initial capacitance, respectively, indicating reasonable cycle stability. The areal and specific capacitances of the symmetric supercapacitor based on the VE73/DA/PPy-90 electrode, estimated from the galvanostatic charge/discharge plots, were approximately 125.0 mF/cm² and 20.8 F g^-1, respectively, at a current density of 1 mA/cm². The device exhibited moderate electrochemical stability, retaining 68% of its capacitance after 10,000 galvanostatic charge/discharge cycles at a current density of 1 mA/cm².