Abstract
Hierarchical MnO(2) nanosheets attached on hollow NiO microspheres have been designed by a facile hydrothermal process. The core-shell structure is achieved by decorating an MnO(2) nanosheet shell on a hollow NiO sphere core. The highly hollow and porous structure exhibits a high surface area, shortened ion diffusion length, outstanding electrochemical properties (558 F g(-1) at a current density of 5 mA cm(-2)), and excellent cycling stability (83% retention after 5000 cycles). To further evaluate the NiO/MnO(2) core-shell composite electrode for real applications, three asymmetric supercapacitors (NiO/MnO(2)//pomelo peel (PPC), NiO/MnO(2)//buckwheat hull (BHC), and NiO/MnO(2)//activated carbon (AC)) are assembled. The results demonstrated that NiO/MnO(2)//BHC delivered a substantial energy density (20.37 W h kg(-1) at a power density of 133.3 W kg(-1)) and high cycling stability (88% retention after 5000 cycles) within a broad operating potential window of 1.6 V.