Design and synthesis of MnO₂/Mn/MnO₂ sandwich-structured nanotube arrays with high supercapacitive performance for electrochemical energy storage.

We demonstrate the design and fabrication of novel nanoarchitectures of MnO(2)/Mn/MnO(2) sandwich-like nanotube arrays for supercapacitors. The crystalline metal Mn layers in the MnO(2)/Mn/MnO(2) sandwich-like nanotubes uniquely serve as highly conductive cores to support the redox active two-double MnO(2) shells with a highly electrolytic accessible surface area and provide reliable electrical connections to MnO(2) shells. The maximum specific capacitances of 937 F/g at a scan rate of 5 mV/s by cyclic voltammetry (CV) and 955 F/g at a current density of 1.5 A/g by chronopotentiometry were achieved for the MnO(2)/Mn/MnO(2) sandwich-like nanotube arrays in solution of 1.0 M Na(2)SO(4). The hybrid MnO(2)/Mn/MnO(2) sandwich-like nanotube arrays exhibited an excellent rate capability with a high specific energy of 45 Wh/kg and specific power of 23 kW/kg and excellent long-term cycling stability (less 5% loss of the maximum specific capacitance after 3000 cycles). The high specific capacitance and charge-discharge rates offered by such MnO(2)/Mn/MnO(2) sandwich-like nanotube arrays make them promising candidates for supercapacitor electrodes, combining high-energy densities with high levels of power delivery.