Estudos das variáveis de preparação de filmes MnO2 aplicado a supercapacitores

Abstract

The wider use of renewable sources has led to a new generation of high performance electrochemical storage and conversion devices such as electrochemical supercapacitors, fuel cells and portable batteries. Low cost metal oxides such as NiO, CoO2, Ni (OH)2, MnO2 as well as conductive polymers such as polyaniline are studied as electrode materials for electrochemical capacitors in order to overcome the high cost associated with other materials. For this purpose, manganese dioxide is attractive for scientific studies due to its low cost, low toxicity, lower environmental aggressiveness and good theoretical capacitance. MnO2 was electrodeposited using the cyclic voltammetry technique applying an anode potential range from 0 to 1.5 V and as a substrate electropolished titanium plates. In addition to electrodepositing the material, this technique was used to study the electrode obtained in the potential range from 0 to 0.8 V. This technique is extremely important because it provides information about the electrochemical nature that happens in the analyzed species, such as redox processes, capacitance, cycling etc. The electropolishing process of the substrate was analyzed by the atomic force microscopy technique which found the best substrate to receive the oxide film layer. The analysis by scanning electron microscopy made it possible to observe changes in the structure of the materials as there were changes in the concentration and composition of the precursor solutions, and the electrode films that did not contain the supporting electrolyte showed greater uniformity. X-ray diffraction analysis showed the crystalline phase of MnO2, as well as the interplanar distance of the observed peaks. The electrochemical studies were performed by cyclic voltammetry that demonstrated the capacitive profiles of the investigated electrode and by galvanostatic charge-discharge, it was possible to calculate the specific capacitance that reached 375 F.g-1 levels. Electrochemical impedance spectroscopy showed its electrical properties and the considerable resistivity in charge transfer and cyclic stability made it possible to measure the cyclability of the material. However, the results indicate that the study of the variation of the concentration of the precursor solution and the supporting electrolyte improved the specific capacitance results of the MnO2 electrodeposited film, whose values exceed those reported in some literature.