Strategic N/P self-doped biomass-derived hierarchical porous carbon for regulating the supercapacitive performances

Biomass-derived porous carbons have received an extensive importance as effective electrode materials owing to their abundance and low cost. The unique porous architectures and large specific surface areas of biomass are beneficial for manipulating the charge storage performance of assembled supercapacitor devices. Here, we demonstrate nitrogen and phosphorus self-doped hierarchical porous carbon (N/P-HPC) derived from yeast (Y) and phytic acid (PA) precursors via freeze-drying-assisted esterification reaction and pyrolysis treatment. The supercapacitive performance and charge storage capability of N/P-HPC were regulated by optimizing the Y/PA composition and controlling the carbonization temperature. Accordingly, the resultant N/P-HPC-Y:PA(2:1)-800 (fabricated with an optimized Y:PA ratio of 2:1 and carbonized at 800 °C) reveals a high specific surface area of 978 m2 g−1 and a large pore volume of 0.592 cm3 g−1. As an electrode material, N/P-HPC-Y:PA(2:1)-800 delivers a high specific capacitance of 432 F g−1 at a current density of 1 A g−1 and can sufficiently retain about 250 F g−1 at 20 A g−1 under a three-electrode cell configuration in 1.0 M H2SO4 electrolyte. Moreover, the as assembled symmetric supercapacitor device operated with the N/P-HPC-Y:PA(2:1)-800 as both positive and negative electrode material exhibits an energy density of 13.6 Wh kg−1 at a power density of 500 W kg−1. Even at a larger current density of 20 A g−1, the device maintains an energy density of 10.4 Wh kg−1 and a maximum power density of 10 kW kg−1. The constructed device displays a large capacitance retention of 93.3% after 10 000 charge/discharge times at a higher current density of 10 A g−1, manifesting the enhanced cycling stability.