Organic redox additive incorporated PANI hydrogel electrodes for flexible high-energy-density supercapacitors

For high-performance flexible supercapacitors (FSCs), electrodes with high capacitance and flexibility play a significant role in determining the electrochemical behavior for their applications. Herein, conductive polymer hydrogel (CPH) electrodes have been successfully synthesized via in situ polymerization of aniline (ANI) in an aqueous solution of polyvinyl alcohol (PVA), phytic acid (PA), and hydroquinone (HQ), in which PA acted as a crosslinking agent and HQ served as an effective organic redox additive. The incorporation of HQ is expected to enhance the capacitance of conductive PHP hydrogel electrodes. The effective redox additive HQ incorporated PANI/HQ/PVA (PHP) hydrogel electrode exhibited a favorable specific capacitance of 642 F g-1 at 0.5 A g-1, which was much higher than the pristine one without introducing any redox additive (421 F g-1 at 0.5 A g-1) due to the extra redox reaction. Additionally, the PHP hydrogel electrode also showed excellent flexibility (93.3% capacitance retention after 500 cycles of bending) and superior cycling stability (81.5% after 10 000 cycles). For practical application, the all-hydrogel-state FSCs assembled with redox additive HQ incorporated PHP hydrogel electrodes and PVA/H2SO4 electrolyte delivered a high energy density of 12 W h kg-1 at a power density of 125 W kg-1, which was remarkably larger than that of PP-based FSCs (7.85 W h kg-1). The supercapacitor demonstrated prolonged cycling stability with a capacitance retention of 77.6% up to 10 000 charge/discharge cycles. This work provides a novel design for conductive polymer hydrogel electrodes with prospective applications in next-generation flexible energy storage devices. Organic redox additive hydroquinone (HQ) is incorporated into PANI hydrogel electrodes for flexible high-energy-density supercapacitors.