Facial Synthesis of 3D MnO2 Nanofibers Sponge and Its Application in Supercapacitors

Mesoporous Al2O3 template was facially constructed by hydrolysis of aluminum nitrate solution, and 3D MnO2 foam was fabricated by redox reaction of Mn2+ and MnO4- in the nanoholes of Al2O3 template, followed by sacrificial dissolution of the Al2O3 matrix. The as-prepared 3D MnO2 sponge is composed of cross-linked worm-like nanofibers which promise enhanced charge transfer capability. The specific surface area and porosity of the MnO2 sponge is affected by the concentration of Mn2+ ion when the pores of Al2O3 template were immersed, and higher specific surface area, higher pore volume and hence better electrochemical performance were developed at lower Mn2+ concentration. When 0.02mol L-1 of Mn2+ solution was used to immerse the Al2O3 template, a specific capacitance of 215.3F g-1 can be achieved for the resultant 3D MnO2 sponge in 1 mol L-1 Na2SO4 aqueous electrolyte at 2mV s-1 scan rate, and all as-prepared 3D MnO2 sponges provide good long-term charging/discharging stability with approximate 96% retention of capacitance at 5mV s-1 scan rate after 2000 cycles, showing that the facially synthesized 3D MnO2 sponge is a promising electrode material for supercapacitor.