Synergistic urea-assisted activation and nitrogen doping of biomass-derived porous carbon from coconut shell for high-performance supercapacitors

Abstract

Biomass-derived carbon offers a renewable and low-cost route for fabricating advanced carbon-based supercapacitors. In this study, a cost-effective biomass precursor, coconut shell, was used to successfully prepare nitrogen-doped porous carbon materials through a synergistic modification strategy combining molten salt-assisted alkali activation with nitrogen doping. The as-obtained nitrogen-enriched porous carbons, denoted as NPCA-X (X represents the urea-to-carbon ratio), exhibited nitrogen contents increasing from 1.37% (NPCA-1) to 7.92% (NPCA-4), with the optimal sample NPCA-3 possessing a nitrogen content of 6.58%. The enhanced nitrogen doping effectively improved the electrochemical activity, thereby increasing the specific capacitance. In a two-electrode system using 6 M KOH electrolyte, the optimized NPCA-3 electrode delivered a specific capacitance of 238 F·g −1 at a scan rate of 5 mV·s −1 and retained 190 F·g −1 even at 200 mV·s −1 . Moreover, it maintained 98.3% of its initial capacitance after 5000 cycles at a current density of 1 A·g −1 . These results demonstrate the potential of coconut-shell-derived nitrogen-doped porous carbon as a supercapacitor electrode with a specific capacitance of 238 F·g −1 , favorable rate capability, and good cycling stability over 5000 cycles.