Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors
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Date
2021
Journal Title
Journal ISSN
Volume Title
Publisher
MDPI, Switzerland
Abstract
ENG: The paper presents a method for obtaining electrochemically active ultrafine composites of
iron oxides, superparamagnetic ‘core/shell’ γ-Fe2O3/defective
α-Fe2O3, which involved modifying
sol-gel citrate synthesis, hydrothermal treatment of the formed sol, and subsequent annealing of
materials in the air. The synthesized materials’ phase composition, magnetic microstructure, and
structural, morphological characteristics have been determined via X-ray analysis, Mossbauer spectroscopy,
scanning electron microscopy (SEM), and adsorption porometry. The mechanisms of phase
stability were analyzed, and the model was suggested as FeOOH – γ-Fe2O3 –
α-Fe2O3. It was
found that the presence of chelating agents in hydrothermal synthesis encapsulated the nucleus of the
new phase in the reactor and interfered with the direct processes of recrystallization of the structure
with the subsequent formation of the
α-Fe2O3 crystalline phase. Additionally, the conductive properties
of the synthesized materials were determined by impedance spectroscopy. The electrochemical
activity of the synthesized materials was evaluated by the method of cyclic voltammetry using
a three-electrode cell in a 3.5 M aqueous solution of KOH. For the ultrafine superparamagnetic
‘core/shell’ γ-Fe2O3/defective
α-Fe2O composite with defective hematite structure and the presence
of ultra-dispersed maghemite with particles in the superparamagnetic state was fixed increased
electrochemical activity, and specific discharge capacity of the material is 177 F/g with a Coulomb
efficiency of 85%. The prototypes of hybrid supercapacitor with work electrodes based on ultrafine
composites superparamagnetic ‘core/shell’ γ-Fe2O3/defective
α-Fe2O3 have a specific discharge
capacity of 124 F/g with a Coulomb efficiency of 93% for current 10 mA.
Description
O. Bazaluk: ORCID 0000-0002-1623-419X, A. Hrubiak: ORCID 0000-0003-1424-2193, L. Kieush: ORCID 0000-0003-3956-202X, B. Rachiy: ORCID 0000-0001-8895-0737, A. Koveria: ORCID 0000-0001-7840-1873, V. Lozynskyi: ORCID 0000-0002-9657-0635
Keywords
ultrafine composite, Mossbauer spectroscopy, phase composition, superparamagnetism, defective structure, capacity, КЕСЕ (ІПБТ), КМПтаВ (ІПБТ)
Citation
Bazaluk O., Hrubiak A., Moklyak V., Moklyak M., Kieush L., Rachiy B., Gasyuk I., Yavorskyi Yu., Koveria A., Lozynskyi V., Fedorov S. Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors. Materials. 2021. Vol 14, iss. 22. 6977. DOI: 10.3390/ma14226977.