Tunable synthesis of biomass-based hierarchical porous carbon scaffold@MnO2 nanohybrids for asymmetric supercapacitor

Electrodeposition based on 3D scaffold-templates is a unique and facile method to tune the microstructure of composite electrode materials for energy storage devices. In this work, we developed a green process to fabricate 3D hierarchical porous carbon scaffold-MnO2 (3D-HPCS@MnO2) nanohybrids with colony-like microstructures. Acting as conductive template and pyrolysis accelerant, the 3D-HPCS enables microstructural control of MnO2 electrodeposits and facilitates valence conversion from Mn2+ to Mn4+. Comparing with depositing on nickel foam, the morphology of MnO2 changed from nanospheres to nanowrinkles when depositing on the 3D-HPCS templates. Benefiting from abundant forest-like micro/mesopores, the resultant 3D-HPCS possesses high specific surface area (1627m(2) g(-1)) and rich heteroatom dopants (6.94 wt%), affording a high gravimetric specific capacitance (231.5 F g(-1)) with outstanding cycling performance (95% capacitance retention after 10,000 cycles). The assembled asymmetric supercapacitor based on HPCS//HPCS@MnO2 exhibits an energy density of 60.8 Wh kg(-1) and a maximum power density of 20.7 kW kg(-1). Our investigation has quantitatively proved that mesopores contribute more than micropores in increasing capacitance of HPCS and both surface capacitive and diffusion-controlled processes play roles in capacitive performance of HPCS@MnO2. Moreover, the influence of the morphology and surface functionality on the electrochemical performances of composite electrodes have been analyzed.