Fabrication of Core-Shell Fe3O4@C@MnO2Microspheres and Their Application in Supercapacitors

Core-shell Fe3O4@C@MnO2microspheres were fabricated using multi-step solution-phase interface deposition. Fe3O4nanoparticles were coated with SiO2via the Stöber method and further covered with resorcinol and formaldehyde (RF) resins. Fe3O4@C nanoparticles with inter-lamellar void were obtained by carbonizing RF under N2, and etching SiO2with NaOH. These nanoparticles served as template and were further coated with MnO2shell to prepare Fe3O4@C@MnO2microspheres. 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 MnO2shell at the outer layer. Fe3O4@C@MnO2microspheres served as supercapacitor electrode materials. The electrochemical performance of the Fe3O4@C@MnO2electrode was investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge. Fe3O4@C@MnO2electrode showed a specific capacitance of 158 F g−1at 0.5 A g−1and outstanding cycle stability with 89.7% capacitance retention after 2000 cycles. By contrast, the specific capacitance of Fe3O4@C electrode was 117 F g−1at 0.5 A g−1exhibited and only 75.2% capacitance retention after 2000 cycles. Thus, Fe3O4@C@MnO2microspheres had great potential in supercapacitor applications in the future.