Hierarchical MnO2 Spheres Decorated by Carbon-Coated Cobalt Nanobeads: Low-Cost and High-Performance Electrode Materials for Supercapacitors.

MnO2 is a promising electrode material for supercapacitors, because it exhibits high theoretical specific capacitance (1380 F g(-1)) for electrical charge while also being inexpensive and environmentally benign. However, owing to its low electrical conductivity, the intrinsic pseudocapacity of MnO2 is not fully utilized. In this work, hierarchically structured spheres composed of MnO2 nanoplatelets and carbon coated cobalt nanobeads (MnO2-NPs@Co/C) are chosen as electrode materials for supercapacitor. With a Co/C mass loading of 19 wt %, the electrical conductivity of the hybrid is 122-fold larger than that of pristine MnO2, showing a specific capacitance of the constituent MnO2 as high as 1240 F g(-1), being close to the theoretical value. Such improved specific capacitance of MnO2-NPs@Co/C electrode is largely contributed from the enhanced double-layer charging and Faradaic pseudocapacity of MnO2. Moreover, the fabricated symmetrical supercapacitor also exhibits excellent cycling stability with 89.1% capacitance retention over 10000 cycles, as well as high energy densities in both aqueous and organic electrolyte (24 Wh kg(-1) and 33 W kg(-1), respectively). Compared with frequently used noble metals to enhance the electrochemical performance of MnO2, the utilization of low cost Co/C nanobeads is proven to be more efficient and thus showing great potential for commercial application.