Crosslinked carbon nanofiber films with hierarchical pores as flexible electrodes for high performance supercapacitors

Flexible, cross-linked carbon nanofibers (CNFs) film with hierarchical micro-meso-macro-porous structure is prepared by carbonization of the elestrospun polyacrylonitrile (PAN)/NaN₃ composite nanofiber mats. The gas liberation of NaN₃ during the carbonization is responsible for the tuning of both specific surface area and the pore size distribution. In addition, the exothermal decomposition of NaN₃ at the heating stage of carbonization leads to the melting of the PAN/NaN₃ composite fibers, resulting in a cross-linked CNF structure. The CNF film with 5 wt% NaN₃ carbonized at 900 °C (CNF-5-900) shows a high specific capacitance of 222.92 F g^{− 1}, nearly twice as high as that of the CNF film without NaN₃ (CNF-0-900). It also shows an excellent capacitance retention ratio of 81.97% of its initial capacitance from 0.5 A/g to 50 A/g, much superior to the value of 51.02 % for CNF-0-900. Moreover, it has an excellent cycling stability with cycling retention ratio achieves 94.5% after 10,000 charge-discharge cycles. Coupled with its excellent mechanical stability (only 1.6% conductivity loss after bending of CNF-5-900 film at curvature radii (r) = 2.5 × 10^{− 3} m for 10,000 cycles) and facile fabrication process, the flexible, cross-linked CNF films with hierarchical micro-meso-macro-porous structure is a potential electrode materials and/or backbone to support other active materials for various application, including the flexible energy storage and electrocatalytic.