High Surface Area Carbon Fiber Supercapacitor Electrodes Derived from an In Situ Porogen Containing Terpolymer: Poly(acrylonitrile-co-1-vinylimidazole-co-itaconic Acid)

Despite having an inherently low surface area upon carbonization, polyacrylonitrile (PAN) remains one of the more widely studied precursor polymers for making high-performance carbon fibers (CFs) for supercapacitors because of its electrospinnability and high carbon yield. Copolymerization with vinylimidazole (VIM) or acidic monomers such as itaconic acid (IA) comprises an attractive approach to modify the properties of PAN-based fibers to enhance their electrochemical performance. In this study, a terpolymer, poly(acrylonitrile-co-1-vinylimidazole-co-itaconic acid) (P(AN-co-VIM-co-IA)), was synthesized with different ratios of AN with VIM and/or IA monomers to develop CF precursors for supercapacitor applications. Here, IA serves as an in situ porogen that releases CO2 during the carbonization process to increase the surface area and tailor the pore sizes. VIM moieties disrupt the strong dipole–dipole interactions between nitrile groups in pure PAN, thus facilitating the processability and thermal stabilization of PAN. Benefiting from the above modifications, the resulting CFs of terpolymers exhibited higher specific surface areas and superior electrochemical performances and long-term stability compared to PAN or corresponding copolymers of P(AN-co-VIM) or P(AN-co-IA). The terpolymer with 5 wt % of VIM and 23 wt % of IA shows the highest capacitance of 97.0 F g–1 (10 mV s–1) with an energy density of 49 Wh kg–1 at 10 kW kg–1 upon carbonization, which was enhanced to 136.7 F g–1 (10 mV s–1) and 79 Wh kg–1 at 10 kW kg–1 upon activation with CO2.