MnO2–TiO2/C nanocomposite arrays for high-performance supercapacitor electrodes

• Coaxial TiO2 and C nanotube arrays (TiO2/C NTAs) are fabricated and characterized.
• High pseudocapacitive MnO2 is deposited into conductive TiO2/C NTAs.
• The composite electrodes show considerable specific capacitance and rate performance.

Coaxial TiO2 and carbon nanotube arrays (TiO2/C NTAs) are prepared by hydrothermal treatment of anatase TiO2 nanotube arrays (TiO2 NTAs) in a glucose solution and carbonized under N2 at 700 °C. The TiO2/C NTAs provide an extremely large, solvated, ion accessible surface area as well as a direct pathway for charge transport, thus yielding substantially improved areal capacitance of 26.1 mF/cm2 at a current density of 0.1 mA/cm2 that is 60 times larger than the capacitance of anatase TiO2 NTAs under the same conditions. The TiO2/C NTAs provide a good support for depositing highly pseudocapacitive materials such as MnO2 to form coaxial MnO2, C and TiO2 nanotube arrays (MnO2–TiO2/C NTAs), producing better capacitive properties. The MnO2–TiO2/C electrode shows a high specific capacitance (580 F/g at a current density of 2.6 A/g), an excellent rate capability and a good cycling stability.