Activated few-layered graphene (a-FLG) materials with porous structures are prepared using a KOH-assisted microwave irradiation technique from natural graphite. The employment of KOH as a chemical etchant efficiently activates the surface pore structure of graphene during the exfoliation of graphite exposed to microwave irradiation. The resultant a-FLG materials exhibit favorable and tailorable large surface areas and porous structures for the deposition of electrochemically active MnO2. When measuring electrochemical characteristics, MnO2/a-FLG exhibits a high specific capacitance (265 F/g), high rate capability, and excellent long-term stability. Moreover, asymmetric supercapacitor devices fabricated using a-FLG as a negative electrode and MnO2/a-FLG as a positive electrode show high energy (40.8 Wh/kg) and power (16.3 kW/kg) densities with high capacitance retention (96% over 10000 cycles). (C) 2018 Elsevier B.V. All rights reserved.