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

Controlled synthesis of carbon nanomaterials with particular shape, composition, architecture, and doping is very important, yet still a great challenge, for enhancing supercapacitor performance with high energy and power densities and long lifetime. Herein, we demonstrate an interesting process combining surfactantless and templateless wet chemical and post-high-temperature carbonization strategies for obtaining a new class of nitrogen-doped hierarchical porous carbon nanowhisker ensembles supported on carbon nanofibers (NHCNs) with tunable micropores and a nitrogen-doping level for high-performance supercapacitors. Under the optimal pore size and nitrogen doping controlled by carbonization at different temperatures, the NHCNs (NHCNs-750) carbonized at 750 °C shows an optimal specific capacitance of 210.1 F g^–1 at 5 mV s^–1, which is much higher than other one-dimensional carbon nanostructures (e.g., pure carbon nanofibers (2.6 F g^–1) and carbon nanotubes (10.6 F g^–1) at 5 mVs^–1). NHCNs-750 also showed good rate capability of 78.5% and 75.2% capacitance retention at 100 mV s^–1 and 200 mV s^–1, respectively, and excellent cycling stability of 96.2% capacitance retention after 3000 cycles. Furthermore, we found that the specific capacitance of NHCNs can be further increased to 254.3 F g^–1 by a KOH-assisted high-temperature process. The present work opens a new route to design advanced 1D hierarchical carbon nanomaterials with tunable pores and nitrogen doping for enhancing energy storage and conversion applications