Abstract
With MnSO4, NaOH and K2S2O8 as the raw materials, the amorphous and δ-type manganese dioxide (MnO2) is separately prepared by using different chemical precipitation-oxidation methods. The results of charge–discharge and electrochemical impedance spectroscopy (EIS) tests show that (i) the specific capacitance of the amorphous MnO2 reaches to 301.2 F g−1 at a current density of 200 mA g−1 and its capacitance retention rate after 2000 cycles is 97%, which is obviously higher than 250.8 F g−1 and 71% of the δ-type one, respectively; (ii) good electrochemical capacitance properties of the amorphous MnO2 should be contributed to easy insertion/extraction of ions within the material; (iii) when 5 wt% Bi2O3 is coated on the amorphous MnO2, its specific capacitance increases to 352.8 F g−1 and the capacitance retention rate is 90% after 2000 cycles.
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