Hydrothermal synthesis of al-doped α-MnO2 nanotubes and their electrochemical performance for supercapacitors

Abstract

α-MnO2 and Al-doped α-MnO2 were synthesized via a hydrothermal method. The morphologies, structures, and electrochemical performances of as-synthesized un-doped and doped α-MnO2 were studied. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) show that these un-doped and doped α-MnO2 are nanotube shaped. The band gaps of α-MnO2 are investigated by ultraviolet-visible absorption spectroscopy, which indicates that the band gap of α-MnO2 decreases upon Al doping. The electrochemical performances of un-doped and doped α-MnO 2 as electrode materials for supercapacitors were measured by cyclic voltammetry (CV) and galvanostatical charge/discharge tests. The specific capacitances of un-doped and Al-doped α-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 Al-doped α-MnO2 was decreased by Al 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 α-MnO2 mean that these systems are favorable prospects for application in supercapacitors.