Heteroatom-doped hierarchical porous carbon via molten-salt method for supercapacitors

N, O, P co-doped hierarchical porous carbons (HPCs) have been produced by direct pyrolysis of biomass (soybean meal) and NaH2PO4 via a molten-salt method under air atmosphere without further activation process. Systematic characterizations show that obtained HPCs possess interconnected honeycomb-like macropores, together with numerous meso- and micropores. The Brunner-Emmet-Teller specific surface area for the obtained HPCs can reach up to 483 m2 g−1. Moreover, such a preparation method leads to a successful heteroatom-doping of N, O and P. Intensive electrochemical measurements of HPCs in 1 M H2SO4 electrolyte shows that HPCs possess a high specific capacitance of 360 F g−1 at a current density of 0.2 A g−1, corresponding to an areal specific capacitance of 75 µF cm−2. A supercapacitor assembled with two identical HPC-750 electrodes can achieve a maximum energy density of 10 Wh kg−1. The good supercapacitive performance could be attributed to the interconnected porosity and heteroatoms doping for HPCs.