N-doped 3D porous carbon-graphene/polyaniline hybrid and N-doped porous carbon coated gC <inf>3</inf> N <inf>4</inf> nanosheets for excellent energy density asymmetric supercapacitors

Nitrogen doped hierarchically porous 3D porous carbon-graphene/polyaniline (3D PC-g/PANi) hybrid nanocomposites are prepared by a simple in-situ polymerization process. 3D PC is synthesized using bio-waste Bombax malabaricum seeds as the carbon precursor and the interconnected 3D PC-g are prepared by a simple refluxing and activation process with a large specific surface area of 2418 m 2 g −1 . The specific capacitance (Cp) of 3D PC-g and 3D PC-g/PANi electrodes are 610 and 1198 F g −1 in 1 M H 2 SO 4 , respectively at a very high current density of 2 A g −1 . Also, a symmetric supercapacitor (SSC) exhibits a high energy density (Ed) of 61 Wh kg −1 and 117 Wh kg −1 in 1 M H 2 SO 4 and 0.5 M Na 2 SO 4 electrolytes, respectively. It still persist a high power density (Pd) of 15 kW kg −1 and 20 kW kg −1 with an Ed of 49.1 Wh kg −1 and 84.4 Wh kg −1 at a very high current density of 30 A g −1 . Further, an asymmetric supercapacitor (ASC) based on 3D PC-g/PANi as positive and hierarchical porous N-doped porous carbon covered gC 3 N 4 nanosheets (N-P(gCN)-700) as a negative electrode is successfully fabricated, which exhibit a high Ed of 97.5 Wh kg −1 in 0.5 M Na 2 SO 4 . The presented results are higher than most of earlier reported PANi based composite carbon electrode materials. Further, the assembled SSC and ASC devices exhibit 94% and 91% capacitance retention even after 10,000 cycles. Furthermore two ASC connected in series can power up red LED for 30 min after charging for 60 s.