Hierarchically porous carbon nanosheets derived from Moringa oleifera stems as electrode material for high-performance electric double-layer capacitors

A facile one-step pyrolysis route for the synthesis of hierarchically porous carbon nanosheets (PCNSs) derived from Moringa oleifera stems (MOSs) is reported, in which no post-activation-process in needed. The as-prepared PCNSs possesses unique porous nanosheet morphology with high specific surface area of ca. 2250 m 2  g −1 , large pore volume of ca. 2.3 cm 3  g −1 , appropriate porosity as well as heteroatom doping (N and O), endowing outstanding electrochemical properties as electrode material for high-performance supercapacitors . The PCNS-based electrodes are investigated in various aqueous electrolytes including 1.0 M Na 2 SO 4 , 1.0 M H 2 SO 4 , and 6.0 M KOH. The PCNSs exhibit a maximum specific capacitance of ca. 283 F g −1 (0.5 A g −1 ), excellent rate capability (ca. 72% of capacitance retention even at an ultrahigh current density of 50 A g −1 ), and a tremendous long-term cycling stability in the three-electrode system. Moreover, the as-assembled PCNS-based symmetric supercapacitor shows a high energy density of ca. 25.8 Wh kg −1 (in 1.0 M Na 2 SO 4 electrolyte) and remarkable long-term cycling stability (almost no capacitance fade in aqueous electrolytes), indicating the promising of the as-prepared PCNSs for electrochemical energy storage and conversion .