 Porous graphitic carbon materials (PGCs) with a microtubular structure were synthesized by a simple method simultaneously completing graphitization and activation for the mixture of willow catkins, KCl, and different ferric salts. The introduction of KCl was crucial to develop a porous structure. KCl, replacing corrosive KOH or poisonous ZnCl2, greatly decreased the cost for production of PGCs. The resulting material PGCN, which was produced by willow catkins, KCl, and Fe(NO3)3, not only inherited the natural microtubular morphology of willow catkins but also possessed a high graphitization degree and abundant porosity. As such, PGCN could serve as an ideal substrate for MnO2 deposition to alleviate its accumulation and improve its conductivity. The obtained PGCN/MnO2 composite electrode significantly enhanced high specific capacitance 571.1 F g− 1 at 2 A g− 1 based on the mass of MnO2. Even at a high current density of 50 A g− 1, specific capacitance still reached 382.1 F g− 1. Furthermore, the electrode exhibited outstanding cycling stability with only 14.8% degradation after 3000 cycles. This study proposes a novel graphitization–activation way for synthesis of porous graphitic carbon by utilizing biomass waste to alleviate the dependence on non-renewable sources.