Synthesis O/S/N doped hierarchical porous carbons from kelp via two-step carbonization for high rate performance supercapacitor

Generally, porous carbons prepared by the KOH activation method possess a high specific surface area, however, narrow pore size distribution and tortuous porous structure affect the rate capability and cycling stability of porous carbon based supercapacitors. In this study, O/S/N doped hierarchical porous carbons (HPCs) were fabricated from kelp by two-step carbonization without adding any chemical reagents. The porosities of HPCs are dependent on carbonization temperature and steps, and the formation mechanism of HPCs was also proposed. The optimal sample (O/S/N-HPC800) carbonized at 800 °C for two steps displays prominent capacitances of 276 and 200 F g−1 at 1 and 100 A g−1 in 6 M KOH electrolyte. When assembled in a two-electrode system, O/S/N-HPC800 offers a maximum capacitance of 166 F g−1 at 0.5 A g−1, and exhibits a maximum energy density of 5.76 Wh kg−1 at a power density of 124.92 W kg−1. Specifically, it can still keep a 97% retention of the initial specific capacitance at 3 A g−1 after 10,000 charge–discharge cycles. This work not only provides a feasible and environmentally friendly route for the preparation of biomass-derived HPCs, but also has guidance for the design of other high-performance supercapacitor electrode materials.