Fabrication of Core-Shell Fe3O4@C@MnO2 Microspheres and Their Application in Supercapacitors

Core-shell Fe3O4@C@MnO2 microspheres were fabricated using multi-step solution-phase interface deposition. Fe3O4 nanoparticles were coated with SiO2 via the Stober method and further covered with resorcinol and formaldehyde (RF) resins. Fe3O4@C nanoparticles with inter-lamellar void were obtained by carbonizing RF under N-2, and etching SiO2 with NaOH. These nanoparticles served as template and were further coated with MnO2 shell to prepare Fe3O4@C@MnO2 microspheres. The resultant composites showed a typical core-shell structure with distinct magnetite core, 10 nm inter-lamellar void, a 30 nm thick carbon layer in the middle layer, and a 50 nm thick MnO2 shell at the outer layer. Fe3O4@C@MnO2 microspheres served as supercapacitor electrode materials. The electrochemical performance of the Fe3O4@C@MnO2 electrode was investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge. Fe3O4@C@MnO2 electrode showed a specific capacitance of 158 F g(-1) at 0.5 A g(-1) and outstanding cycle stability with 89.7% capacitance retention after 2000 cycles. By contrast, the specific capacitance of Fe3O4@C electrode was 117 F g(-1) at 0.5 A g(-1) exhibited and only 75.2% capacitance retention after 2000 cycles. Thus, Fe3O4@C@MnO2 microspheres had great potential in supercapacitor applications in the future. (C) 2018 The Electrochemical Society.