Electropolymerization of polyaniline as high-performance binder free electrodes for flexible supercapacitor

Polyaniline (PANI), as one of the most promising electrode materials for flexible supercapacitors, faces the problems of limited capacitive behavior and poor cycling stability. Herein, we demonstrated that dopants have a great effect on the electrochemical performance of PANI. Selecting a suitable dopant can be used as an effective way for enhancing the electrochemical performance of PANI electrodes. All PANI electrodes were synthesized by electropolymerization method using hydrochloric acid (HCl), perchloric acid (HClO4), sulfuric acid (H2SO4), p-toluenesulfonic acid (p-TSA), phosphoric acid (H3PO4) and phytic acid (PA) as dopants, respectively. The influence of dopants on morphology, doping level, redox sites accessibility and electrochemical performance of PANI electrodes were studied systematically. The results show that, PANI/HClO4 has the best capacitive behavior with a maximum specific capacity of 1341 C g−1 at 5 mV s−1 along with a 57% capacity retention after 2000 cycles. Moreover, PANI/p-TSA shows the best cycling stability with 70% of capacity retention after 2000 cycles accompanied with a relatively high specific capacity (722 C g−1 at 5 mV s−1). Furthermore, PANI/HClO4 and PANI/p-TSA were used as electrodes for the fabrication of flexible all-solid-state symmetric supercapacitors. Results indicate that PANI/HClO4 device has higher energy density (12.57 Wh kg−1 at 283 W kg−1) than that of PANI/p-TSA (8.86 Wh kg−1 at 199 W kg−1). In contrast, PANI/p-TSA device with a capacity retention over 80% after 3000 cycles has better stability than PANI/HClO4 device which maintains 73% capacity after 3000 cycles. This fundamental study provides a much easier route in achieving high performance flexible PANI-based electrodes and opens new opportunities for facilitating PANI-based electrodes as promising candidates for wearable electronics.