MnO2 Nanostructures Deposited on Graphene-Like Porous Carbon Nanosheets for High-Rate Performance and High-Energy Density Asymmetric Supercapacitors

Graphene-like porous carbon nanosheets (GPCNs) have been proved to have great potential in high-rate performance supercapacitors. However, the relatively low specific capacitance and low working voltage of GPCN-based supercapacitors hinder their practical application in high-energy density devices. Herein, we demonstrate the direct deposition of MnO 2 nanostructures onto the salvia splendens-derived GPCNs (GPCN-SS) surface through a hydrothermal method. The as-fabricated MnO 2 /GPCN-SS composite possesses a relatively high specific surface area (483 m 2 g –1 ) and an appropriate mesopore size (2–5 nm). Thanks to the synergistic effect of GPCN-SS and MnO 2 nanostructures, the MnO 2 /GPCN-SS composite electrode exhibits high specific capacitance of 438 F g –1 at 0.5 A g –1 (almost twice as high as the pristine GPCN-SS) and high rate capability (67.8% capacity retention at 50 A g –1 ) in the Na 2 SO 4 electrolyte. More importantly, an asymmetric supercapacitor assembled with MnO 2 /GPCN-SS composite cathode and GPCN-SS anode in neutral electrolyte displays excellent rate capability (77.8% capacity retention from 0.5 to 50 A g –1 ) and high energy density (50.2 Wh kg –1 at 516 W kg –1 ). Considering the abundance and sustainability of biomass-derived GPCNs along with the low-cost of MnO 2, the MnO 2 /GPCN-SS composite can serve as a promising new class of electrode materials for high-rate and high-energy density supercapacitors.