Hydrothermal Synthesis of AI-Doped α-MnO2 Nanotubes and Their Electrochemical Performance for Supercapacitors

alpha-MnO2 and AI-doped alpha-MnO2 were synthesized via a hydrothermal method. The morphologies, structures, and electrochemical performances of as-synthesized un-doped and doped alpha-MnO2 were studied. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM)show that these un-doped and doped alpha-MnO2 are nanotube shaped. The band gaps of alpha-MnO2 are investigated by ultraviolet-visible absorption spectroscopy, which indicates that the band gap of alpha-MnO2 decreases upon Al doping. The electrochemical performances of un-doped and doped alpha-MnO2 as electrode materials for supercapacitors were measured by cyclic voltannmetry (CV) and galvanostatical charge/discharge tests. The specific capacitances of un-doped and Al-doped alpha-MnO2 respectively reach 204.8 and 228.8 F . g(-1) under a current density of 50 mA.g(-1). It was discovered that the electrochemical impedance of AI-doped alpha-MnO2 was decreased by AI doping analyzed using electrochemical impedance spectra (EIS), which provides a beneficial increase to its electrochemical specific capacitance. Enhanced specific capacitance and preferable cycling stability (up to 1000 cycles) for Al-doped alpha-MnO2 mean that these systems are favorable prospects for application in supercapacitors.