Nitrogen- and oxygen-doped carbon with abundant micropores derived from biomass waste for all-solid-state flexible supercapacitors

Fabrication of porous activated carbon derived from biomass waste with high surface area, specific porosity, and excellent electroactivity has attracted much more attention in the energy conversion and storage field. Herein, mango seed waste is utilized as a precursor to synthesize nitrogen (N) and oxygen (O) co-doped porous carbon by high-temperature carbonization coupling with subsequent KOH activation. The more KOH activator was fed in the high-temperature activation process, the larger surface area, higher micropore ratio, and lower N and O doping content of the activated carbon was obtained. The optimized mango seed-derived activated carbon (MSAC) exhibits high surface area (1815 m2 g-1), micropore ratio (94%), doping content of nitrogen (1.71 at.%), and oxygen (10.93 at.%), which delivers an ultrahigh specific capacitance of 402F g-1 at 1 A g-1 and retains 102.4% of initial capacitance after 5000 cycles. The supercapacitor performance of MSAC was also investigated in 6 M KOH, 1 M [BMIM]BF4/AN, and PVA/KOH electrolytes in detail, respectively. A flexible all-solid-state asymmetric supercapacitor (FSAS) fabricated by MSAC anode, CoNiAl layered double hydroxides cathode, and PVA/KOH electrolyte achieves a high energy density of 33.65 Wh kg-1 at a power density of 187.5 W kg-1 and retains 80% of initial capacitance after 10,000 cycles. The low cost, facile synthetic process, and excellent electrochemical performance of MSAC electrode material provide a cheap and accessible strategy to obtain porous carbon material for energy conversion and storage systems.