Effect of various ammonium salts as activating additive on the capacitance performance of hierarchical porous carbon derived from camellia husk

Activator is crucial for the preparation of biomass-derived hierarchical porous carbons (BHPCs) because the activator mainly determines their pore structures and active sites. Herein, we propose to use camellia husk as a precursor to prepare BHPCs by a hydrothermal carbonization and ammonium salts including (NH4)3PO4, NH4Cl, (NH4)2SO4, NH4HCO3, etc. assisted KOH activation. The prepared BHPCs showed a hierarchical porous structures containing micro-, meso- and macropores as well as a large specific surface area of 1874.6 m2 g−1. Among additional ammonium salts, the (NH4)3PO4 and NH4Cl showed positive effects, NH4HCO3 exhibited almost no effect, but (NH4)2SO4 released negative effect on the capacitance performance of as-prepared BHPCs. The (NH4)3PO4 assisted KOH activated BHPC (BHPC-AP) delivered a higher specific capacitance of 253.7 F g−1 at 1 A g−1 than other BHPCs in 6 M KOH. At the current density of 50 A g−1, the specific capacitance of BHPC-AP remained 225.6 F g−1 with a high capacitance retention of 88.9%. The symmetric supercapacitors assembled by BHPC-AP (BHPC-AP SSC) released a high energy density of 12.11 Wh kg−1 with power density of 250 W kg−1. Furthermore, the BHPC-AP SSC exhibited a high cycling stability with 94.4% capacitance retention after 20,000 cycles at 5 A g−1. The results indicate that the (NH4)3PO4 assisted KOH activation may be an effective approach to prepare porous carbons as electrode materials for high-performance supercapacitors.