Manganous nitrate-assisted potassium hydroxide activation of humic acid to prepare oxygen-rich hierarchical porous carbon as high-performance supercapacitor electrodes

The oxygen-rich hierarchical porous carbon (MOHPC) has been prepared through Mn(NO3)(2)-assisted KOH activation of humic acid with low-dose activating agent. We demonstrate that Mn(NO3)(2) can promote the micropore formation, suppress the mesopore fabrication, and increase oxygen conent, thanks to the low-temperature prefunctionalization effect and synergistic activation effect with KOH at relatively low temperature of 700 degrees C. The MOHPC exhibits large specific surface area (1656 m(2) g(-1)), high oxygen content (21.88 at.%), and optimized hierarchical porous structure possessing rich micropores, appropriate mesopore ratio with narrow mesopore size distribution, and interconnected macropores. Expectedly, MOHPC electrode delivers ultrahigh specific capacitances of 515 F g(-1) and 402 F g(-1) at 0.2 A g(-1), 206 F g(-1) and 233 F g(-1) at 100 A g(-1) in 1 M H2SO4 and 6 M KOH, respectively. Moreover, as symmetric supercapacitor electrode with commercial-level mass loading (similar to 200 mu m, similar to 11.30 mg cm(-2)), MOHPC also displays a high specific capacitance of 304 F g(-1) at 0.057 A g(-1), superior rate capability (246 F g(-1) at 5.7 A g(-1)), and excellent cycling stability in 3 M KOH. The assembled supercapacitor device delivers a considerable energy density of 30 Wh kg(-1) at the power density of 43.6 W kg(-1) in organic electrolyte.