N-doped 3D porous carbon-graphene/polyaniline hybrid and N-doped porous carbon coated gC3N4 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 H2SO4, 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 H2SO4 and 0.5 M Na2SO4 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 Na2SO4. 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. (C) 2019 Elsevier Ltd. All rights reserved.