MnO₂/Porous Carbon Nanotube/MnO₂ Nanocomposites for High-Performance Supercapacitor

In this paper, a superior supercapacitor nanocomposite based on porous carbon nanotubes (PCNTs), MnO₂/PCNT/MnO₂, was synthesized, which displayed superior specific capacitance (C = 341.5 F g^–1, 2 mV s^–1), excellent rate capability (C = 214.3 F g^–1, 63% capacity retention, 100 mV s^–1), and high cyclic stability (98% efficiency after 6000 charge/discharge cycles). The outstanding improvement of its electrochemical performances resulted from the massive nanopores on the walls of PCNTs, which made more MnO₂ nanoparticles filled both in the nanocavity and on the surface of PCNTs as electroactive sites. At the same time, PCNTs improve the electrical conductivity with the pore structure being beneficial to ion exchange, they shorten the ion transport distance, and adjust to the volume expansion and contraction among charge/discharge. In addition, the Mn­(IV)/Mn­(III) redox electric pair in the nanocavity enhances the capacity storage. Therefore, the MnO₂/PCNT/MnO₂ nanocomposite shows higher specific capacitance and excellent cyclic stability.