ATMP Doped Conductive PANI/CNTs Composite Hydrogel Electrodes toward High Energy Density Flexible Supercapacitors

Although flexible supercapacitors (FSCs) have attracted tremendous attention, synthesis of supercapacitor electrodes that have outstanding electrochemical performance and excellent flexibility remains a continuous dilemma. Herein, conductive polymer composite hydrogels were synthesized via in situ polymerization of aniline (ANI) in a mixture of polyvinyl alcohol (PVA) and carbon nanotubes (CNTs), for which amino trimethylene phosphonic acid (ATMP) was employed as an organic doping acid. The as-prepared polyaniline (PANI)/PVA/ATMP/CNTs (PPAC) composite hydrogel electrodes exhibit a specific capacitance of up to 389.5 F g–1 at 0.5 A g–1, satisfactory long-term cycling stability (83.87% capacitance retained after 10,000 charge/discharge times), and outstanding flexibility (97% capacitance retained over 200 repeated bends), and the incorporation of ATMP enhanced electrochemical performances of PPAC composite hydrogel electrodes. Besides, the synergistic effects offered by high electrical conductivity of CNTs, pseudocapacitance of PANI, and the doping effect of ATMP may further contribute to the excellent electrochemical behavior of hydrogel electrodes. The result of the energy storage mechanism implied that the electrochemical process of the PPAC composite hydrogel electrode involved both diffusion-controlled and surface capacitive processes. The all-hydrogel-state FSC based on the PPAC hydrogel electrode shows a favorable energy density of 12.8 W h kg–1 at 125.0 W kg–1 as well as long-life stability of 77.31% capacitance retention after 10,000 charge/discharge cycles. This work is promising for the preparation of high-performance composite hydrogel electrodes for wearable and flexible energy storage devices.