Facile synthesis and characterization of MnO₂ nanomaterials as supercapacitor electrode materials

MnO₂ nanomaterials are synthesized via calcinations in air at various temperatures. Amorphous MnO₂ masses appear between 100 and 300 °C and nanorods form above 400 °C. Transmission and scanning electron microscopy are used to observe the geometries of each material, with further structural analyses conducted using X-ray photoelectron spectroscopy, X-ray diffraction, and BET method. The electrochemical properties are investigated through galvanostatic charge/discharge cycling, electrochemical impedance spectra, and cyclic voltammetry within a three-electrode test cell filled with 1 mol L⁻¹ Na₂SO₄ solution. The slightly asymmetric galvanostatic cycling curves suggest that the reversibility of the Faradaic reactions are imperfect, requiring a larger time to charge than discharge. The specific capacitances of each sample are calculated and trends are identified, proving that the samples synthesized at higher temperatures exhibit poorer electrochemical behaviors. The highest calculated specific capacitance is 175 F g⁻¹ by the sample calcinated at 400 °C. However, the lower temperature samples exhibit more favorable geometric properties and higher overall average specific capacitances. For future research, it is suggested that surface modifications such as a carbon coating could be used in conjunction with the MnO₂ nanorods to reach the electrochemical properties required by contemporary industrial applications.