Designing 3D Ternary Hybrid Composites Composed of Graphene, Biochar and Manganese Dioxide as High-Performance Supercapacitor Electrodes

Biochar derived from waste biomass has proven to be an encouraging novel electrode material in supercapacitors. In this work, luffa sponge-derived activated carbon with a special structure is produced through carbonization and KOH activation. The reduced graphene oxide (rGO) and manganese dioxide (MnO2) are in-situ synthesized on luffa-activated carbon (LAC) to improve the supercapacitive behavior. The structure and morphology of LAC, LAC-rGO and LAC-rGO-MnO2 are characterized by the employment of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), BET analysis, Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical performance of electrodes is performed in two and three-electrode systems. In the asymmetrical two-electrode system, the LAC-rGO-MnO2//Co3O4-rGO device shows high specific capacitance (SC), high-rate capability and excellent cycle reversibly in a wide potential window of 0-1.8 V. The maximum specific capacitance (SC) of the asymmetric device is 586 F g-1 at a scan rate of 2 mV s-1. More importantly, the LAC-rGO-MnO2//Co3O4-rGO device exhibits a specific energy of 31.4 W h kg-1 at a specific power of 400 W kg-1. Overall, the synergistic effect between the ternary structures of microporous LAC, rGO sheets and MnO2 nanoparticles leads to the introduction of high-performance hierarchical supercapacitor electrodes.