Desenvolvimento de materiais nanoestruturados baseados em hidróxidos mistos de cobalto / manganês para aplicação em dispositivos eletroquímicos de armazenamento de energia
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2021-06-29
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Universidade Federal de Goiás
Resumo
In recent years, the development of new electrode materials for energy storage devices has been intensified, owing to increasing energy consumption levels, as well as depletion of nonrenewable energy resources. Thus, low-cost electrode materials, easy to obtain, and with excellent electrochemical performance are desirable. In this sense, the cobalt hydroxide has drawn attention due to its structure, morphology, and electrochemical features and then becoming a promising electrode material for energy storage devices. Thus, in this work, cobalt hydroxide and mixed cobalt/manganese hydroxide (in the proportions of Co:Mn 75:25 and 50:50), named respectively as Co-100, CoMn-75:25, and CoMn-50:50, were synthesized using the modified Tower method. Through the X-ray diffraction technique, it was possible to determine that the materials are in the alpha phase since the (003) diffraction peak was found in low angle regions 2θ. In addition, the morphology of the materials was evaluated using transmission electron microscopy, where the images showed that nanoparticles presented spherical shape and an average size of ~5 nm. The CoMn-75:25 and CoMn-50:50 were classified as double hydroxide salt since the metal ions presented the same valence state (+2), determined by X-ray Photoelectron Spectroscopy. The materials were deposited on FTO electrodes using the spin-coating technique and the electrochemical behavior of the modified electrodes was evaluated cyclic voltammetry, galvanostatic charge/discharge curves and electrochemical impedance spectroscopy. Through electrochemical studies, it was possible to determine that the energy storage mechanism is of the extrinsic intercalation pseudocapacitance type, due to the nanostructured of the materials. It was observed that the Epa, related to the Co+2/Co+3 redox process, was shifted to more negative potentials and there was an increase in ipa intensity for CoMn-75:25 and CoMn-50:50, as a consequence of the isomorphic substitution of Co2+ by Mn2+ ions in the crystal lattice of Co-100. Besides, the CoMn-75:25 showed a specific capacitance two and a half fold higher (677.0 F g-1) than Co-100 (268.7 F g-1). Also, the CoMn-75:25 presented a capacitance retention of 70.64% even after 5000 galvanostatic charge/discharge cycles. Finally, the electrochemical impedance spectroscopy studies (Nyquist diagram and Bode phase) confirmed that the electrode materials present a pseudocapacitive signature.
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Materiais eletroativos , Dispositivos de armazenamento de energia , Hidróxidos mistos de cobalto e manganês , Materiais nanoestruturados , Pseudocapacitância de intercalação extrínseca , Energy storage devices , Mixed cobalto and manganese hydroxides , Nanostructured materials , Extrinsic intercalation pseudocapacitance , Electroactive materials
Citação
SILVA, C. G. Desenvolvimento de materiais nanoestruturados baseados em hidróxidos mistos de cobalto / manganês para aplicação em dispositivos eletroquímicos de armazenamento de energia. 2021. 118 f. Dissertação (Mestrado em Engenharia Química) - Universidade Federal de Goiás, Goiânia, 2021.