Preparação de heteroarquiteturas contendo óxido de grafeno, polímeros condutores e dióxido de manganês: aplicação em supercapacitores de alta performance

Abstract

One of the main problems generated by the current growing in energy demand lies in the low storage efficiency of energy generated by clean and renewable sources, making the use of fossil fuels, increasingly scarce and highly polluting, remain as the main energy source. The development of high performance, low-cost supercapacitors is identified as a key factor in solving the problems of storage and conversion of clean energy into intermittent electrical energy, capable of being widely used. Thus, this work refers to the development of supercapacitor electrodes formed by different pseudocapacitive materials whose different construction methodologies allowed a wide view of the factors capable of influencing the capacitive behavior. On a first stage, after structural characterizations, high thickness electrodes were prepared, formed by hybrid binary composites resulting from the proportional combination between GO and α-MnO2 and GO and polyaniline (emeraldine salt). Its electrochemical characterizations revealed a specific capacitance value of 279.8 F g-1 for the 25% GO and 75% α-MnO2 composite, with a capacitive efficiency of 99.7% and 91% of retention after 1000 charge and discharge cycles. The GO/PAni composite with the same proportions presented specific capacitance value of 511.1 F g-1, capacitive efficiency of 91.2%and 83% retention after 1000 cycles. On a second stage, electrodes formed by the electrodeposition of MnO2 thin films over pyrolytic graphite rods expanded surface, showed a profile of improvement in capacitive behavior with increasing electrodeposited mass, reaching274.25 F g-1 for a mass of only 0.41mg of MnO2 on the electrode; an improvement of about 600% in relation to the high mass electrodes previously evaluated. Finally, using electrochemical analyzes and classical molecular dynamics simulations, the influence on the capacitive response of α-MnO2 electrodes (drop coating on glassy carbon) caused by the substitution of the alkali metal cation in neutral aqueous electrolytes, was evaluated. Among allthe analyzed ions, K+ presented the best intercalation density in the 2x2 tunnel structure of αMnO2, such behavior resulting from its greater ion mobility, molar conductivity and lower solvation sphere, providing the electrode highest specific capacitance value.