Core-shell structured Fe3O4@MnO2 nanospheres to achieve high cycling stability as electrode for supercapacitors

A core-shell and spherical structured Fe 3 O 4 @MnO 2 nanostructure is designed and developed via a facile and low-cost two-step method. Core-shell structured Fe 3 O 4 @MnO 2 with uniform morphology can be obtained after layered structured δ-MnO 2 is grown on the surface of Fe 3 O 4 nanospheres. The crystal structures and morphology of as-prepared Fe 3 O 4 @MnO 2 are characterized by scanning electron microscopy, X-ray diffraction, nitrogen isotherm analysis, and transmission electron microscopy. At the current density of 0.1 A g −1 , the specific capacitance of Fe 3 O 4 @MnO 2 is 243.7 F g −1 , and its capacitance retention is almost 100% after 3000 continuous charge/discharge cycles at current density of 1 A g −1 . The excellent cycling stability and low cost make this core-shell structured Fe 3 O 4 @MnO 2 a promising electrode material for practical applications in pseudocapacitors.