Nano "Koosh Balls" of Mesoporous MnO : Improved Supercapacitor Performance through Superior Ion Transport.

Manganese dioxide nanomaterials with "Koosh-ball"-like morphology (MnO -KBs) as well as worm-like nanotubes (MnO -NWs) are obtained by employing Tween 20 as the reducing and structure-directing agent, and KMnO as a MnO precursor. Whereas the MnO -KBs are interconnected through tubular extensions, the MnO -NWs are largely disconnected. Both MnO -KBs and MnO -NWs have large BET surface areas (>200 m  g ), and are thermally robust up to 300 °C. Electrochemical studies reveal that the highest specific capacitance (C ) obtained for MnO -KBs (272 F g ) is significantly higher than that of MnO -NWs (129 F g ). The C values correlate well with the electroactive surface areas of the materials: MnO -KBs have a significantly higher electrolyte-accessible surface area. Electrochemical impedance spectroscopy (EIS) reveals a higher electron-transfer rate at the electrode/electrolyte interface for MnO -KBs than for MnO -NWs. The multiple tubular interconnections between individual MnO -KBs allow improved ion penetration and act as conduits for their propagation, shortening the diffusion distances of the ions from external electrolytes to the interior of the MnO framework. Thus, this work exemplifies the importance of interconnections for enhancing the electrochemical performance of nanomaterials employed for energy storage.