N-doped porous carbon nanofibers with high specific capacitance and energy density for Zn-ion hybrid supercapacitors

N-doped porous carbon nanofibers have shown a wide application prospect for Zn-ion hybrid supercapacitors (ZHSs), but so far, the affordable synthesis remains a daunting challenge. Using the exfoliated silk nanofibrils (SNFs) as carbon and nitrogen sources, NaCl/KCl as carbonization medium and KOH as active agent, herein, a new variety of N-doped porous carbon nanofibers, SPCN-x, is prepared, involved a sequential 'SNFs exfoliation' and 'mixture pyrolysis'. Results confirm that, with the activation of KOH, porosity structure and specific surface area of the nano-fibriform products are clearly enriched, thus forming a hierarchically porous structure. Typically, SPCN-10 shows a N doping content of 5.6 wt%, pore volume of 0.33 cm3 g- 1 and specific surface area of 645 m2 g- 1, and presents a great energy storage property as cathode for ZHSs, such as energy density of 70.4 Wh kg- 1 and specific capacitance of 197.9 F g- 1. Besides, it has excellent durability with a capacitance retention rate of 90.2 % after 10,000 cycles. The electrochemical behavior of SPCN-10 is better than numerous reported ZHS cathodes, which not only highlights our ingenious synthesis, but also ensures a huge potential in large-scale practical application.