Facile synthesis of O and P co-doped hierarchical porous carbon nanosheets from biomass for high-performance supercapacitors

Biomass-derived carbons with porous structures and abundant surface functional groups have been regarded as a competitive electrode material for supercapacitors due to their renewability and easily adjustable porosity. The low-cost and environmentally friendly synthesis method of O and P co-doped hierarchical porous carbon nanosheets from waste coconut shells using potassium bicarbonate (KHCO3) and potassium dihydrogen phosphate (KH2PO4) as both activators and co-doped agents have been investigated for high-performance supercapacitors. Under an appropriate KH2PO4 dosage, the pore structure of PAC-0.9 contains micropores, mesopores and macropores, and its specific surface area is 892.06 m2 g−1. The specific capacitance of PAC-0.9 in three electrode system reached 371.63 F g−1 at a current density of 0.5 A g−1, and remained at 223.25 F g−1 even for a current density of 30 A g−1. The symmetrical supercapacitor assembled with PAC-0.9 as the electrode achieved an energy density of 9.15 Wh kg−1 at a power density of 500 W kg−1. At a current density of 5 A g−1, the specific capacitance of PAC-SSC can still retain 96.23 % after 10,000 charge-discharge cycles.