Construction of TiO ₂ Nanotubes/C/MnO ₂ Composite Films as a Binder-Free Electrode for a High-Performance Supercapacitor

Although titanium dioxide (TiO ₂ ) exhibits excellent promise in electrode materials for supercapacitors, its poor conductivity and low areal specific capacitance hamper further development. In this work, we have designed a clever way to deposit manganese dioxide (MnO ₂ ) in order to improve its electrochemical performance via a facile and typical hydrothermal method. In a hydrothermal process, carbon (C), which deposited via new gas thermal penetration, acts as a reducing agent, while a potassium permanganate (KMnO ₄ ) solution acts as an oxidant. In this way, MnO ₂ , which has a high theoretical capacity, is generated on TiO ₂ nanotube arrays (denoted as TNTs) successfully. Remarkably, a TNTs/C/MnO ₂ film prepared at a hydrothermal temperature of 90 °C and 0.3 g of KMnO ₄ revealed a superior electrochemical property with 55 mF/cm ² areal capacitance at a scan rate of 5 mV/s, 23 times more enhanced than that of a TNTs/C film. Also, the energy density of a TNTs/C/MnO ₂ film reached 46.8 Wh/cm ² when the power density was 0.12 mW/cm ² , and the energy density still remained at 22.4 Wh/cm ² at a high power density of 0.8 mW/cm ² . After 1000 cycle tests, 93.2% capacitance was still retained, indicating excellent reversibility and cycle stability of TNTs/C/MnO ₂ electrode. This work opens up a facile path for efficient growth of electrode materials with high performance for energy storage devices.