Softness-rigidness controlled polyaniline nanofiber-structured hydrogels for flexible supercapacitors

Polyaniline (PANI) hydrogels with ultra-high pseudo-capacitance behavior can achieve favorable specific capacitance and boost electrochemical performance for their supercapacitors. However, the high rigidity of PANI molecules results in that the softness-rigidness control of PANI hydrogels for flexible supercapacitors remains challenging. Here, the softness-rigidness controlled PANI nanofiber-structured hydrogels (PANIFH) for flexible supercapacitors are successfully constructed by in-situ polymerization of aniline in the existence of p-phenylenediamine and phytic acid, and followed by hydrothermal process. The resulting PANIFH hydrogels reveal an effortlessly controllable softness-rigidness with outstanding bending, curling capability and compressive strength (29.4–256.7 kPa). The PANIFH supercapacitor electrodes deliver high gravimetric specific capacitance of 516.8 F g⁻¹, exceptional rate capability of 69.7 % from 1 to 20 A g⁻¹ and capacitance retention of 80.3 % after 10000 cycles. The PANIFH-assembled flexible supercapacitors are further demonstrated with exciting areal specific capacitance of 954.9 mF cm⁻², favorable areal energy density of 84.9 μWh cm⁻², and as high as 96.4 % of initial capacitance after 4000 mechanical bending cycles. The promising capability in developing the area of flexible energy storage devices is realized by this study, which proposes a controlled approach for building flexible PANI hydrogel supercapacitors with improved performance.