Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors
The paper presents a method for obtaining electrochemically active ultrafine composites of iron oxides, superparamagnetic ‘core/shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O<sub>3</sub>, which involved modifying sol-gel citrate synth...
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2021
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oai:doaj.org-article:c97c983747af439eb7034f11a8fdd58c2021-11-25T18:15:23ZStructurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors10.3390/ma142269771996-1944https://doaj.org/article/c97c983747af439eb7034f11a8fdd58c2021-11-01T00:00:00Zhttps://www.mdpi.com/1996-1944/14/22/6977https://doaj.org/toc/1996-1944The paper presents a method for obtaining electrochemically active ultrafine composites of iron oxides, superparamagnetic ‘core/shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O<sub>3</sub>, 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-Fe<sub>2</sub>O<sub>3</sub> → α-Fe<sub>2</sub>O<sub>3</sub>. 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-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O 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-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O<sub>3</sub> have a specific discharge capacity of 124 F/g with a Coulomb efficiency of 93% for current 10 mA.Oleg BazalukAndrii HrubiakVolodymyr MoklyakMaria MoklyakLina KieushBogdan RachiyIvan GasyukYurii YavorskyiAndrii KoveriaVasyl LozynskyiSerhii FedorovMDPI AGarticleultrafine compositeMossbauer spectroscopyphase compositionsuperparamagnetismdefective structurecapacityTechnologyTElectrical engineering. Electronics. Nuclear engineeringTK1-9971Engineering (General). Civil engineering (General)TA1-2040MicroscopyQH201-278.5Descriptive and experimental mechanicsQC120-168.85ENMaterials, Vol 14, Iss 6977, p 6977 (2021) |
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DOAJ |
| collection |
DOAJ |
| language |
EN |
| topic |
ultrafine composite Mossbauer spectroscopy phase composition superparamagnetism defective structure capacity Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85 |
| spellingShingle |
ultrafine composite Mossbauer spectroscopy phase composition superparamagnetism defective structure capacity Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85 Oleg Bazaluk Andrii Hrubiak Volodymyr Moklyak Maria Moklyak Lina Kieush Bogdan Rachiy Ivan Gasyuk Yurii Yavorskyi Andrii Koveria Vasyl Lozynskyi Serhii Fedorov Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| description |
The paper presents a method for obtaining electrochemically active ultrafine composites of iron oxides, superparamagnetic ‘core/shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O<sub>3</sub>, 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-Fe<sub>2</sub>O<sub>3</sub> → α-Fe<sub>2</sub>O<sub>3</sub>. 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-Fe<sub>2</sub>O<sub>3</sub> 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-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O 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-Fe<sub>2</sub>O<sub>3</sub>/defective α-Fe<sub>2</sub>O<sub>3</sub> have a specific discharge capacity of 124 F/g with a Coulomb efficiency of 93% for current 10 mA. |
| format |
article |
| author |
Oleg Bazaluk Andrii Hrubiak Volodymyr Moklyak Maria Moklyak Lina Kieush Bogdan Rachiy Ivan Gasyuk Yurii Yavorskyi Andrii Koveria Vasyl Lozynskyi Serhii Fedorov |
| author_facet |
Oleg Bazaluk Andrii Hrubiak Volodymyr Moklyak Maria Moklyak Lina Kieush Bogdan Rachiy Ivan Gasyuk Yurii Yavorskyi Andrii Koveria Vasyl Lozynskyi Serhii Fedorov |
| author_sort |
Oleg Bazaluk |
| title |
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| title_short |
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| title_full |
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| title_fullStr |
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| title_full_unstemmed |
Structurally Dependent Electrochemical Properties of Ultrafine Superparamagnetic ‘Core/Shell’ γ-Fe<sub>2</sub>O<sub>3</sub>/Defective α-Fe<sub>2</sub>O<sub>3</sub> Composites in Hybrid Supercapacitors |
| title_sort |
structurally dependent electrochemical properties of ultrafine superparamagnetic ‘core/shell’ γ-fe<sub>2</sub>o<sub>3</sub>/defective α-fe<sub>2</sub>o<sub>3</sub> composites in hybrid supercapacitors |
| publisher |
MDPI AG |
| publishDate |
2021 |
| url |
https://doaj.org/article/c97c983747af439eb7034f11a8fdd58c |
| work_keys_str_mv |
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