Preparation And Eelectrochemical Performance Of Manganese Dioxide

With the rapid development of the global economy, the depletion of fossil fuels, climate change and increasing environmental pollution demand the researchers to find sustainable and renewable resources, and new technologies associated with energy conversion and storage. In recent years, due to the high power density, long lifecycle, and bridging function for the power/energy gap between traditional dielectric capacitors and batteries/fuel cells, supercapacitors have been attracting significant attention. Manganese dioxide (MnO2) has been widely used as the electrode materials of supercapacitors, owing to its high theoretical capacitance (1380F/g), abundance of raw materials, benignity to the environment and wide operating potential window (0.0-1.0V).Based on the simple redox reaction between KMnO4and NaNO2, pure a-,δ-, β-and y-phase MnO2products with different morphorlogies have been fabricated via hydrothermal method, water bath, reflux at95℃, and the calcination of precursors, respectively. The electrochemical test results indicate that the crystal structure of MnO2plays an important role in its electrochemical properties. For different MnO2phases, their specific capacitance values decrease in the order:α-MnO2(200F/g)> δ-MnO2(190F/g)> Υ-MnO2(26F/g)> β-MnO2(17F/g); meanwhile, for any particular MnO2phase, their electrochemical energy storage performances decrease with increasing dwell time and reaction temperature. As the reaction temperature increasing, the specific capacitance values of α-MnO2increase in the order: MnO2(66F/g at160℃)<MnO2(166F/g at120℃)<MnO2(175F/g at100℃)<MnO2(200F/g at15℃). H+, K+and NH4+are in favor of electrochemical properties of of-MnO2products.Rod-and ellipsoid-like s-MnO2products have been synthesized involving the controlled synthesis of manganese oxalates precursors and the controlled thermal decomposition of the salt precursors in air. The morphologies and capacitive values of s-MnO2depend upon the structure of precursors controlled by the pH value of mother solution. The calcination temperatures play an important role in the electrochemical performances of manganese oxides. The specific capacitance values of the products synthesized at different temperatures increase in the order:21F/g (400℃)<147F/g (300℃)<187F/g (250℃).