Hierarchical porous C/MnO2 composite hollow microspheres with enhanced supercapacitor performance
The successful application of supercapacitors in energy conversion and storage hinges on the development of highly efficient and stable electrode materials. Herein, a composite of manganese oxide (MnO2) and N-doped hollow carbon sphere (NHCS) was fabricated by a facile two-step process for supercapacitor electrodes. The MnO2-NHCS composite had a NHCS core and a shell composed of hierarchical birnessite-type MnO2 nanoflakes. NHCS in the composite not only serves as the template for the growth of MnO2 nanoflakes, but also as the electrically conductive channel for electrochemical performance enchancement. The physicochemical and electrochemical properties of the MnO2-NHCS composite were significantly enhanced as compared with those of MnO2 hollow spheres (MnO2 HS). The asymmetric supercapacitors (ASCs) assembled with MnO2-NHCS anode and NHCS cathode exhibited a high energy density of 26.8 Wh kg–1 at a power density of 233 W kg–1, which is superior to that of the ASCs assembled with MnO2 HS anode and NHCS cathode (13.5 Wh kg–1 at 229 W kg–1). The MnO2-NHCS ASCs also show superior cycling stability for 4000 cycles. The enhanced electrochemical performance of MnO2-NHCS makes it a promising electrode material for application in supercapacitors and potentially other energy storage devices.