Synthesis and electrochemical characterization of amorphous MnO2 for electrochemical capacitor

Amorphous MnO2 was synthesized by an improved reduction reaction. The synthesized product was characterized physically by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and transmission electron microscope (TEM). Electrochemical characterization was performed using cyclic voltammetry and chronopotentiometry in a 0.5 mol/L Na2SO4 aqueous solution electrolyte. The prepared materials remained amorphous until 300 °C and then transformed to crystalline α-MnO2 at 400 °C. A specific capacitance of approximately 242 F/g was obtained by annealing at 200 °C. Annealing temperatures higher than 200 °C resulted in a decline of the specific capacitance. The specific capacitance of MnO2 annealed at 200 °C remained constant up to 400 cycles.