Electrospun Carbon Nanofibers Based Materials for Flexible Supercapacitors: A Comprehensive Review

Electrospinning is a versatile, facile, and economical technique for the scalable fabrication of highly conducting freestanding flexible carbon nanofiber (CNFs) and its composite electrodes for supercapacitor (SC) energy storage device construction. It has enough potential to meet the demand of the energy for foldable, wearable, or bendable portable electronics such as hand-held displays, electronic skin, and roll-up individual devices. The virgin CNFs are relatively fragile. Therefore, additives are added to enhance their firmness against bending forces through proper transmittance, and scattering of applied external forces with retention of flexibility. A flexible CNF electrode design includes polymer, metal oxides, and sulfides that enhance the surface area and pseudo-capacitance of electrodes. The electrospun embedding of MOF-derived N-doped porous carbon nanoparticles and transition metal oxides (NiO, CoO x , MnO 2 , V 2 O 5 , Fe 3 O 4 , NiMoO 4 , etc.) used as additives to form uniformly distributed nanoclusters of specific morphologies within CNF fiber matrix because they can spread and scatter the external stresses, reduce the scale of the applied stress per unit area. Hence, it works as a blockade to crack evolution and propagation. Electrospinning developed electrodes established noteworthy electrochemical performance are emphasized. Their performances have been critically analyzed and their energy storage mechanisms, key challenges, and future perspectives for the supercapacitors have been discussed.