Self-assembly of mesoporous nanotubes assembled from interwoven ultrathin birnessite-type MnO2 nanosheets for asymmetric supercapacitors

Abstract

Porous nanotubes comprised of MnO 2 nanosheets were fabricated with a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by choice of the membrane pore size and the chemistry. The porous MnO 2 nanotubes were used as a supercapacitor electrode. The specific capacitance in a three-electrode system was 365â€...F g -1 at a current density of 0.25â€...A g -1 with capacitance retention of 90.4% after 3000 cycles. An asymmetric supercapacitor with porous MnO 2 nanotubes as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.5â€...Wh kg -1 and a maximum power density of 146.2â€.. .kW kg -1; these values exceeded those reported for other MnO 2 nanostructures. The supercapacitor performance was correlated with the hierarchical structure of the porous MnO 2 nanotubes.