Sodium-chloride-assisted synthesis of nitrogen-doped porous carbon shells via one-step combustion waves for supercapacitor electrodes

Heteroatom-doped, multiporous carbon structures are of considerable interest as high-performance electrochemical electrodes. However, their complex and time-consuming synthetic procedures impede a scalable production. Herein, a combustion-driven sodium-chloride-assisted synthesis route of nitrogen-doped, cube-like hierarchical porous carbon shells (N-C-HPCS) is developed for the electrode materials of supercapacitors. Free-standing hybrid films composed of nitrocellulose and NaCl particles serving as the chemical fuel layer and templates are prepared, and self-propagating combustion waves passing through the films within a few seconds fabricate controllable nitrogen-doped porous carbon (N-PC) after the simple removal of the templates by washing. The optimal tuning of thermochemical reactions through the nitrocellulose loadings leads to synthesizing the N-C-HPCS, while other precursors produce sparse or dense N-PC structures. Supercapacitor electrodes using the developed N-C-HPCS exhibit an outstanding specific capacitance (305F/g at 0.5 A/g) and retention at a high current density (∼78 % at 16 A/g), as well as long-term cyclic stability (∼116% after 10,000 cycles). The symmetric two-electrode cell exhibited high power and energy densities (8 kW/kg and 10.1 Wh/kg) and superb cycling stability (107.7 % after 10,000 cycles at 5 A/g). This work will inspire rational synthesis strategies for versatile N-PCs, useful for supercapacitors, batteries, catalysts, filters, and CO₂ adsorption.