The effect of heat treatment on the capacitance performance of nanocrystalline mesoporous MnCO3
摘要
Nanocrystalline mesoporous manganese carbonate (N-MnCO3) is synthesized by a soft template method using cetyltrimethylammonium bromide (CTAB) as the template. The as-synthesized N-MnCO3 is systematically characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermal analysis, field emission electron scanning microscopy, transmission electron microscopy, and surface area analysis. N-MnCO3 exhibits a specific capacitance of 214 F g−1 at 0.5 A g−1, with a good rate performance and excellent cycle life in 0.1 M MgClO4. An insignificant change in the specific capacitance is observed on increasing the loading level from 1 to 8 mg cm−2, indicating it’s utility at various loading levels. This superior capacitance performance of N-MnCO3 is attributed to the mesoporous network that favors uniform ion distribution and responsible for the improvement in rate performance by facilitating faster transport of electrolyte ions at higher specific current rates. While N-MnCO3 retains its crystal structure on heating up to 400 °C, a thermal degradation to MnO and subsequent partial oxidation to MnO2 is observed on increasing the temperature to 500 °C. Owing to the loss of adsorbed water, only a minor variation in the specific capacitance value of N-MnCO3 is observed on heat treatment up to 400 °C and it decreases sharply on increasing the temperature to 500 °C, which is attributed to the phase transformation to MnO and subsequent partial oxidation to MnO2.