▎ 摘　　要

A novel strategy to synthesize hierarchical rod like MnCO3 on the reduced graphene oxide (RGO) sheets by a facile and cost-effective hydrothermal method is demonstrated. The chelating action of citric acid facilitates the formation a complex intermediate of Mn2+ and citrate ions, which finally results a 3D MnCO3/RGO (MRGO) composite with high electrical conductivity (similar to 1056 S m(-1)), good surface area (59 m(2) g(-1)) and high pore volume (0.3 cm(3) g(-1)). The specific capacitance (SC) of the MRGO composite is similar to 1120 F g(-1) at a current density of 2 A g(-1) in three electrode system. An asymmetric device has been designed with MRGO as positive and sono-chemically reduced RGO (SRGO) as negative electrode material. The asymmetric device (MRGO//SRGO) shows the SC of similar to 318 F g(-1) (at 2 A g(-1)) and energy density of similar to 113 W h kg(-1) (at 1600 W kg(-1)). The true energy density (1.7 W h kg(-1)) has been calculated considering the total weight of the device. The MRGO//SRGO device can power a wall clock for similar to 13 min after full charging. The Nyquist plot of the asymmetric cell has been simulated with Z-View software to measure the solution resistance, charge-transfer resistance and Warburg elements. (C) 2015 Elsevier B.V. All rights reserved.