Highly porous graphitic carbon and Ni2P2O7 for a high performance aqueous hybrid supercapacitor

An aqueous Na-ion based hybrid capacitor has been successfully developed by using highly porous graphitic carbon (HPGC) derived from waste writing paper and a new electrode material as a negative and positive electrode, respectively. HPGC was prepared via hydrothermal carbonization and subsequent KOH activation of waste writing paper which showed a highly porous stacked sheet-like morphology with an exceptionally high BET specific surface area (1254 m(2) g(-1)). HPGC exhibited typical electrical double layer capacitor (EDLC) behavior with a high specific capacitance of 384 F g(-1) and good negative working potential (-1.0 V) in an aqueous electrolyte. On the other hand, Ni2P2O7 was synthesized by a simple co-precipitation technique and tested as a cathode material which delivered a maximum specific capacitance of 1893 F g(-1) at 2 A g(-1) current density. The fabricated HPGCMi(2)P(2)O(7) hybrid device displayed excellent cyclic stability up to 2000 cycles and delivered a maximum energy density of 65 W h kg-1 at 800 W kg(-1) power density in a Na-ion based aqueous electrolyte.