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Herein, a kind of hydroxyl and sulfonyl-containing diamine 2,2-bis[4-(3-hydroxy-4-aminophenoxy)phenyl]sulfone (BHAPS) was first synthesized and polymerized with pyromellitic dianhydride (PMDA) to obtain poly(amic acid) (PAA) solution. Then, the PAA nanofibers were fabricated by electrospinning technology, which were further thermally treated at 300 °C for imidization, 450 °C for rearrangement and a certain final temperature for carbonization to obtain carbon nanofibers (CNFs). The PAA concentration, carbonization temperature and thermal rearrangement time were separately optimized, and the HPI-CNF-20-2-800 exhibited better electrochemical properties. Next, the HPI-CNF-20-2-800 was chemically activated with KOH to enhance specific surface area. The preferred A-HPI–CNF–1/3 demonstrated a specific capacitance maximum of 335.0 F g−1 at 0.5 A g−1, with a 73 % capacitance retention at 10 A g−1. Furthermore , the SC device was symmetrically assembled with self-supporting A-HPI–CNF–1/3 membranes, which showed a maximum energy density of 10.42 Wh kg−1 at a power density of 250.0 W kg−1. In addition, the capacitance retention rate of the SC reached 99.94 % even after 50,000 charge/discharge cycles at a current density of 1 A g−1. Thus, this work reports a new precursor to prepare N, O, S co-doped active CNFs with better electrochemical performance, which will provide a reference for the preparation of co-doped self-supporting SC electrodes. • A new kind of diamine monomer containing hydroxyl and sulfonyl was synthesized. • The N, O, S co-doped activated carbon nanofibers were prepared. • The capacitive performance of self-supporting electrode was effectively boosted. [ABSTRACT FROM AUTHOR]