Nitrogen-Doped Hierarchical Porous Carbon Nanowhisker\nEnsembles on Carbon Nanofiber for High-Performance Supercapacitors

Abstract

Controlled\nsynthesis of carbon nanomaterials\nwith particular shape, composition, architecture,\nand doping is very important, yet still a great challenge, for enhancing\nsupercapacitor performance with high energy and power densities and\nlong lifetime. Herein, we demonstrate an interesting process combining\nsurfactantless and templateless wet chemical and post-high-temperature\ncarbonization strategies for obtaining a new class of nitrogen-doped\nhierarchical porous carbon nanowhisker ensembles supported on carbon\nnanofibers (NHCNs) with tunable micropores and a nitrogen-doping level\nfor high-performance supercapacitors. Under the optimal pore size\nand nitrogen doping controlled by carbonization at different temperatures,\nthe NHCNs (NHCNs-750) carbonized at 750 °C shows an optimal specific\ncapacitance of 210.1 F g^–1 at 5 mV s^–1, which is much higher than other one-dimensional carbon nanostructures\n(e.g., pure carbon nanofibers (2.6 F g^–1) and carbon\nnanotubes (10.6 F g^–1) at 5 mVs^–1). NHCNs-750 also showed good rate capability of 78.5% and 75.2%\ncapacitance retention at 100 mV s^–1 and 200 mV s^–1, respectively, and excellent cycling stability of\n96.2% capacitance retention after 3000 cycles. Furthermore, we found\nthat the specific capacitance of NHCNs can be further increased to\n254.3 F g^–1 by a KOH-assisted high-temperature process.\nThe present work opens a new route to design advanced 1D hierarchical\ncarbon nanomaterials with tunable pores and nitrogen doping for enhancing\nenergy storage and conversion applications.