Few-Layer Graphene Functionalized by Carbon Nanotubes and MnO2 Nanoparticles for High-Performance Supercapacitors

Few-layer graphene (FLG) exfoliated from graphite is an attractive electrode material due to its high conductivity and high chemical stability. But usually limited by their specific surface area (SSA), its capacitance needs to be improved when used in supercapacitors. In this study, FLG has been prepared by combining electrochemical exfoliation and thermal expansion. It has a SSA of 148 m2/g and delivers a capacitance of 55 F/g at a discharge current density of 1 A/g. To increase its capacitance, carbon nanotubes (CNTs) and MnO2 nanoparticles are functionalized onto FLG surface separately. Both modification could achieve a composite electrode with enhanced capacitance. The CNT/FLG and MnO2/FLG electrodes show a specific capacitance of 106 and 336 F/g at the current density of 1 A/g, respectively, while the former exhibits a much better rate performance and cycling stability than the latter. This work demonstrates an optional way to improve the performance of FLG-based supercapacitors.