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© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

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.

Details

Title
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe2O3/Defective α-Fe2O3 Composites in Hybrid Supercapacitors
Author
Bazaluk, Oleg 1   VIAFID ORCID Logo  ; Hrubiak, Andrii 2   VIAFID ORCID Logo  ; Moklyak, Volodymyr 2 ; Moklyak, Maria 3 ; Kieush, Lina 4   VIAFID ORCID Logo  ; Rachiy, Bogdan 3   VIAFID ORCID Logo  ; Gasyuk, Ivan 3 ; Yavorskyi, Yurii 5 ; Koveria, Andrii 6   VIAFID ORCID Logo  ; Lozynskyi, Vasyl 7   VIAFID ORCID Logo  ; Fedorov, Serhii 4 

 Belt and Road Initiative Institute for Chinese-European Studies (BRIICES), Guangdong University of Petrochemical Technology, Maoming 525000, China; [email protected] 
 G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine, 36 Academician Vernadsky Boulevard, 03142 Kyiv, Ukraine; [email protected] 
 The Faculty of Physics and Technology, Vasyl Stefanyk Precarpathian National University, 56 Shevchenko Str., 76018 Ivano-Frankivsk, Ukraine; [email protected] (M.M.); [email protected] (B.R.); [email protected] (I.G.) 
 National Metallurgical Academy of Ukraine, 4 Gagarin Av., 49600 Dnipro, Ukraine; [email protected] (L.K.); [email protected] (S.F.) 
 Department of Physical Materials Science and Heat Treatment, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, 35 Politekhnichna Str., 03056 Kyiv, Ukraine; [email protected] 
 Department of Chemistry, Dnipro University of Technology, 49005 Dnipro, Ukraine; [email protected] 
 Department of Mining Engineering and Education, Dnipro University of Technology, 49005 Dnipro, Ukraine; [email protected] 
First page
6977
Publication year
2021
Publication date
2021
Publisher
MDPI AG
e-ISSN
19961944
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
2602143191
Copyright
© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.