Óxido de manganês depositado em tecido de carbono como eletrodo para supercapacitores

Abstract

The technological evolution and population growth exponentially increased the global demand for energy, on account of this need, the new systems for energy generation and storage are becoming more and more efficient. Materials based on carbon cloth have been applied for this purpose, more specifically, in electrodes for electrochemical capacitors (ECs), in ECs, the utilized materials are conducting polymers, carbon–based materials and ceramic oxides. Among the oxides, manganese oxide (MnO2) stands out owing to its low cost as well as reduced toxicity, in addition to that, it can be abundantly found in nature. With a view to contribute to the literature, this work described the formation of MnO2 on carbon cloth (substrate) upon electrodeposition using in different times. Scanning electron microscopy (SEM) analyses allowed the observation of the morphological aspects of the deposited material according to electrodeposition time. The X-ray diffraction (XRD) technique, in turn, allowed to detect the γ–MnO2 structural phase and the ascertainment of the formation of ceramic material over the adopted substrate. Electrochemical studies of the materials were performed by cyclic voltammetry (CV), highlighting the redox profiles of the MnO2 electrodes. Moreover, analysis of the galvanostatic charge-discharge curves (GCD) allowed the calculation of a 709 F.g-1 specific capacitance for a 0.5 A.g-1 current density. Regarding electrochemical impedance spectroscopy (EIS), the Nyquist and Bode plots evidenced the ionic and kinetic activities of the material, respectively. The values of the relaxation time constants for the materials obtained were calculated from the EIE data, thus making it possible to observe the charge transfer process, already referring to the values obtained in the complex powers, which corresponds to the intersection of the curves of | Q/S| = |P/S| whose indicates the optimal operating point where materials release stored energy and power more efficiently, these points occurred above 68%, demonstrating the pronounced attractiveness of the material for application in electrodes of energy storage devices (supercapacitors).