Abstract
A promising energy storage material, MnO 2 /hierarchically porous carbon (HPC) nanocomposites, with exceptional electrochemical performance and ultrahigh energy density was developed for asymmetric supercapacitor applications. The microstructures of MnO 2 /HPC nanocomposites were characterized by transmission electron microscopy, scanning transmission electron microscopy, and electron dispersive X-ray elemental mapping analysis. The 3-5nm MnO 2 nanocrystals at mass loadings of 7.3-10.8wt % are homogeneously distributed onto the HPCs, and the utilization efficiency of MnO 2 on specific capacitance can be enhanced to 94-96 %. By combining the ultrahigh utilization efficiency of MnO 2 and the conductive and ion-transport advantages of HPCs, MnO 2 /HPC electrodes can achieve higher specific capacitance values (196F g -1 ) than those of pure carbon electrodes (60.8F g -1 ), and maintain their superior rate capability in neutral electrolyte solutions. The asymmetric supercapacitor consisting of a MnO 2 /HPC cathode and a HPC anode shows an excellent performance with energy and power densities of 15.3Wh kg -1 and 19.8kW kg -1 , respectively, at a cell voltage of 2V. Results obtained herein demonstrate the excellence of MnO 2 /HPC nanocomposites as energy storage material and open an avenue to fabricate the next generation supercapacitors with both high power and energy densities. Shaping up for charge: Hierarchically porous carbons combined with nanosized manganese oxides have been utilized as an asymmetric supercapacitor electrode. The unique hierarchical structures accelerate ion diffusion and increase the active surfaces of manganese oxide nanocrystals. The excellent electrochemical properties of the MnO 2 /hierarchical porous carbon composites make this material a possible candidate for high energy and power-density supercapacitors. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.