MnO₂ nanosheets grown on internal surface of macroporous carbon with enhanced electrochemical performance for supercapacitors

Supercapacitor performance is strongly dependent on the utilization rate of electrode materials. In this paper, MnO₂ nanosheets (MONSs) have been grown on the inner surface of macroporous carbon (MPC) for increasing the utilization rate. The MPC is prepared from luffa sponge fibers. The MPC possesses closely arranged straight channels at the micrometer scale, which makes the MONSs be able to grow on the inner surface. Because of sufficient exposure toward electrolyte, the MONSs exhibit high mass specific capacitance at different loadings such as 1332 F/g (150 μg/cm²) and 354 F/g (5690 μg/cm²). Because of the presence of the large pores allowing the electrolyte solution to access easily, the active materials are capable of working at high loadings, obtaining areal specific capacitance as high as 2.9 F/cm². The assembled supercapacitors show a high specific energy of 194 μWh/cm² at the specific power of 4.5 mW/cm². As the luffa sponge is abundant and pollution-free in production, the MONSs/MPC is of high promise for supercapacitor application. The present method to grow the active materials on an inner surface to increase the utilization rate is also valuable for other applications, e.g., catalysis and Li-ion batteries.