Bazaluk Oleg, Hrubiak Andrii, Moklyak Volodymyr, Moklyak Maria, Kieush Lina, Rachiy Bogdan, Gasyuk Ivan, Yavorskyi Yurii, Koveria Andrii, Lozynskyi Vasyl, Fedorov Serhii
Belt and Road Initiative Institute for Chinese-European Studies (BRIICES), Guangdong University of Petrochemical Technology, Maoming 525000, China.
G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine, 36 Academician Vernadsky Boulevard, 03142 Kyiv, Ukraine.
Materials (Basel). 2021 Nov 18;14(22):6977. doi: 10.3390/ma14226977.
The paper presents a method for obtaining electrochemically active ultrafine composites of iron oxides, superparamagnetic 'core/shell' γ-FeO/defective α-FeO, 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-FeO → α-FeO. 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-FeO 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-FeO/defective α-FeO 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-FeO/defective α-FeO have a specific discharge capacity of 124 F/g with a Coulomb efficiency of 93% for current 10 mA.
本文提出了一种制备氧化铁电化学活性超细复合材料的方法，即超顺磁性“核/壳”γ-FeO/缺陷α-FeO，该方法包括改性溶胶-凝胶柠檬酸盐合成、对形成的溶胶进行水热处理以及随后在空气中对材料进行退火。通过X射线分析、穆斯堡尔光谱、扫描电子显微镜（SEM）和吸附孔隙率测定法确定了合成材料的相组成、磁微观结构以及结构和形态特征。分析了相稳定性机制，并提出了FeOOH→γ-FeO→α-FeO的模型。发现水热合成中螯合剂的存在将新相的核包裹在反应器中，并干扰了结构直接重结晶并随后形成α-FeO晶相的过程。此外，通过阻抗谱测定了合成材料的导电性能。使用三电极电池在3.5M KOH水溶液中通过循环伏安法评估了合成材料的电化学活性。对于具有缺陷赤铁矿结构且存在超顺磁态颗粒的超分散磁赤铁矿的超细超顺磁性“核/壳”γ-FeO/缺陷α-FeO复合材料，其电化学活性增强，材料的比放电容量为177F/g，库仑效率为85%。基于超细复合材料超顺磁性“核/壳”γ-FeO/缺陷α-FeO制成工作电极的混合超级电容器原型，在电流为10mA时，比放电容量为124F/g，库仑效率为93%。
