Hidróxido misto de níquel e manganês estabilizado na fase alfa: material promissor para dispositivos eletroquímicos de armazenamento de energia
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2019-04-18
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Universidade Federal de Goiás
Resumo
In the search for new energy resources, nickel hydroxide (Ni(OH) 2 ) has been
widely studied as a positive electrode for secondary batteries, however, one of
the limitations of this material is the rapid conversion between its polymorphic
phases, affecting its electrochemical performance and, therefore, commercial
applications. In order to stabilize Ni(OH) 2 on the polymorphic phase alpha, as
well as to improve its electrochemical behavior, Ni 2+ ions were isomorphically
replaced by Mn 2+ ions in different proportions (5, 25 and 50%) in Ni(OH) 2 . The
mixed nickel and manganese hydroxides obtained by the modified Tower
method presented nanometric dimensions (5 - 10 nm) confirmed by the
transmission electron microscopy technique. Through the x-ray photoelectron
spectroscopy technique it was possible to determine that the metal ions of the
mixed hydroxides are in the 2+ oxidation state. All the mixed hydroxides
synthesized showed the diffraction peak (003) at 2θ = 10.6o, thus confirming
the alpha polymorphic phase. The electrochemical behavior of the modified
electrodes was evaluated by cyclic voltammetry and electrochemical
impedance spectroscopy. Even after 1000 voltammetric cycles the electrodes
modified with the mixed hydroxides (Ni-75 and Ni-50) did not present a
significant displacement of the anodic peak potential to more positive
potentials, thus indicating the stabilization of the material in the alpha
polymorphic phase. With the increase in the isomorphic substitution of Ni 2+
ions by Mn 2+ ions, a decrease in Ni 2+ / Ni 3+ charge transfer resistance wasobserved, as well as a significant increase in charge transfer re sistance for the
evolution of O 2 . After 5000 consecutive charge and discharge cycles,
electrodes modified with mixed hydroxides had a specific capacity of 187.5 C
g -1 (Ni-95), 417.5 C g -1 (Ni-75) and 294.5 C g -1 (Ni-50) and a load retention of
90.6% (Ni-95), 86.5% (Ni 75) and 71.4% (Ni-50), these values being higher
than the hydroxide of pure nickel and in summary are quite promising for the
application in energy storage devices.
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GOMES, A. P. Hidróxido misto de níquel e manganês estabilizado na fase alfa: material promissor para dispositivos eletroquímicos de armazenamento de energia. 2019. 106 f. Dissertação (Mestrado em Química) - Universidade Federal de Goiás, Goiânia, 2019.