Transition metal doped MnO2 nanosheets grown on internal surface of macroporous carbon for supercapacitors and oxygen reduction reaction electrocatalysts

Abstract

In this work, transition metal (Fe, Co, Ni, and V) ions-doped MnO2 nanosheets (MONSs) have been grown on the internal surface of macroporous carbon (MC) derived from luffa sponge fibers for supercapacitors and electrocatalysts for oxygen reduction reaction (ORR). The MONSs were prepared by redox reaction between the MC and KMnO4 in solution at room temperature. By introducing the corresponding salts into the reaction solutions the transition metal ions were in situ doped into the MONSs during the growth process. The electrochemical performance of the MONSs was considerably enhanced by doping with appropriate elements. The Ni-doped MONSs exhibit the best performance for supercapacitors with a high specific capacitance of 445Fg−1at 1Ag−1, high energy density of 50 Wh kg−1at 0.9kWkg−1, and high capacitance retention of 93% after 1000 cycles. The Co doped MONSs show the best ORR electrocatalytic perfromance with onset potential at 0.01V, high operation stability, and near four electron transfer per oxygen molecule during the ORR process. Besides doping with appropriate metal ions growth on the internal surface of the MC contributes greatly to the excellent electrochemical performance of the MONSs, which increases the utilization efficiency of the active materials due to full exposure towards the electrolytes. We demonstrated that appropriate doping plus growth on internal surface is a good strategy to prepare high performance active materials for electrochemical applications.