ZnCl2-assisted conversion of nitrogen-containing biomass carbon from marigold flower: Toward highly porous activated nitrogen-doped carbon for low ESR and enhanced energy density supercapacitors

Herein, we report the synthesis and characterization of hierarchical porous activated nitrogen-doped carbon from pyrolysis of dried marigold flower precursor as an effect of different impregnation zinc chloride (ZnCl2) (1:1, 1:3 and 1:5) named FZ11, FZ13, and FZ15. BET and FESEM show the enhancement in porosity and surface area with activation with highest specific surface area of 1274.45m2/g for FZ15. XPS confirms the engineering of nitrogen content into functional nitrogen doped sites upon the action of ZnCl2 activation as N-reservoir which results in increase in specific capacitance of fabricated symmetric cell (without any conductive black) increases with activation and shows the highest specific capacitance of 179 F/g, energy density of 23 Wh/kg and power density of 556 W/kg for FZ15 sample. Addition of carbon black helps in lowering ESR to 0.77 Ω and enhancement in energy density and series combination of 3 such cells glow yellow LED for ~3 min.