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10.3390/ma14226977
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Article

Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors

by
Oleg Bazaluk
1,
Andrii Hrubiak
2,*,
Volodymyr Moklyak
2,
Maria Moklyak
3,
Lina Kieush
4,
Bogdan Rachiy
3,
Ivan Gasyuk
3,
Yurii Yavorskyi
5,
Andrii Koveria
6,
Vasyl Lozynskyi
7 and
Serhii Fedorov
4
1
Belt and Road Initiative Institute for Chinese-European Studies (BRIICES), Guangdong University of Petrochemical Technology, Maoming 525000, China
2
G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine, 36 Academician Vernadsky Boulevard, 03142 Kyiv, Ukraine
3
The Faculty of Physics and Technology, Vasyl Stefanyk Precarpathian National University, 56 Shevchenko Str., 76018 Ivano-Frankivsk, Ukraine
4
National Metallurgical Academy of Ukraine, 4 Gagarin Av., 49600 Dnipro, Ukraine
5
Department of Physical Materials Science and Heat Treatment, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, 35 Politekhnichna Str., 03056 Kyiv, Ukraine
6
Department of Chemistry, Dnipro University of Technology, 49005 Dnipro, Ukraine
7
Department of Mining Engineering and Education, Dnipro University of Technology, 49005 Dnipro, Ukraine
*
Author to whom correspondence should be addressed.
Materials 2021, 14(22), 6977; https://doi.org/10.3390/ma14226977
Submission received: 1 November 2021 / Revised: 9 November 2021 / Accepted: 15 November 2021 / Published: 18 November 2021
(This article belongs to the Special Issue Advances in Energy Storage and Conversion Composites)
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Abstract

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.
Keywords: ultrafine composite; Mossbauer spectroscopy; phase composition; superparamagnetism; defective structure; capacity ultrafine composite; Mossbauer spectroscopy; phase composition; superparamagnetism; defective structure; capacity

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MDPI and ACS Style

Bazaluk, O.; Hrubiak, A.; Moklyak, V.; Moklyak, M.; Kieush, L.; Rachiy, B.; Gasyuk, I.; Yavorskyi, Y.; Koveria, A.; Lozynskyi, V.; et al. Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors. Materials 2021, 14, 6977. https://doi.org/10.3390/ma14226977

AMA Style

Bazaluk O, Hrubiak A, Moklyak V, Moklyak M, Kieush L, Rachiy B, Gasyuk I, Yavorskyi Y, Koveria A, Lozynskyi V, et al. Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors. Materials. 2021; 14(22):6977. https://doi.org/10.3390/ma14226977

Chicago/Turabian Style

Bazaluk, Oleg, Andrii Hrubiak, Volodymyr Moklyak, Maria Moklyak, Lina Kieush, Bogdan Rachiy, Ivan Gasyuk, Yurii Yavorskyi, Andrii Koveria, Vasyl Lozynskyi, and et al. 2021. "Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors" Materials 14, no. 22: 6977. https://doi.org/10.3390/ma14226977

APA Style

Bazaluk, O., Hrubiak, A., Moklyak, V., Moklyak, M., Kieush, L., Rachiy, B., Gasyuk, I., Yavorskyi, Y., Koveria, A., Lozynskyi, V., & Fedorov, S. (2021). Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors. Materials, 14(22), 6977. https://doi.org/10.3390/ma14226977

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