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    Assessment on the stable and high capacity Na-Se batteries with carbonate electrolytes
    (Wiley, 2022) Erdöl, Zeynep; Ata, Ali; Çakan, Rezan Demir
    Factors affecting proper functioning of Na-Se system are investigated focusing on the polyselenide formation in ether- and carbonate-based electrolytes. To do so, Se cathode is prepared by ball milling with commercial carbon and selenium powders. It is revealed that the soluble polyselenide species form in ether while no signature in carbonates proven by the in-situ cyclic voltammetry and ex-situ ultraviolet-visible spectroscopy measurements as well as monitoring self-discharge behaviours. Different Se discharge mechanism is also highlighted by staircase potentio electrochemical impedance spectroscopy (SPEIS) that is an impedance measurement applied to each potential step. Volume expansion is targeted using different types of binders in which carboxyl methylcellulose-styrene butadiene rubber (CMC-SBR) delivers the highest reversible capacity and the best rate performance resulting from its high adhesion strength. To further improve the performances, fluoroethylene carbonate (FEC) is used as a film forming additive that preserves Na metal integrity proven by the Na-Na symmetric cells and voltage relaxation upon cycling. As a whole, binders and electrolyte compositions are found to be the two crucial factors to obtain stable and high-capacity Na-Se cells. This study underlines that much effort needs to be put on the strategies to overcome volume expansion than that of Se confinement into porous cathode.
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    Öğe
    Morphological, microstructural and photocatalytic characterization of undoped and Ni, Co doped Fe2O3 particles synthesized by sonochemical method
    (Scientific & Technical Research Council Turkey-TUBITAK, 2022) Kaya, Elif Emil; Evren, Burak; Erdöl, Zeynep; Ekinci, Duygu; İpekoğlu, Mehmet; Özenler, Sibel
    In this study, an abundant and eco-friendly photocatalytic material, Fe2O3 particles were synthesized by sonochemical method. Morphological and microstructural investigations of synthesized undoped and Ni, Co-doped Fe2O3 particles were performed. The effect of particle morphology and microstructure on its photocatalytic performance was further investigated. Comparative studies for evaluating particle crystallite sizes were conducted by Williamson-Hall (W-H) method and modified Debye-Scherrer (MDS). Crystallite sizes and lattice strains of Fe2O3 induced by process parameters were calculated by W-H method based on uniform deformation model (UDM). The crystallite sizes of the synthesized powders were calculated in the range of 200 nm and 76 nm by Williamson-Hall analysis. In addition to structural investigation, dislocation density of the synthesized particles was calculated by Williamson-Smallman relation. Afterwards, photocatalytic performance of Fe2O3 particles was investigated in detail. The photodegradation of methylene blue solutions in the presence of light in 20 min with samples 3,4, and 5 in 20 min were 0.937, 0.896, and 0.855, respectively. Moreover, the photodegradation of methylene blue solution with sample 5 for 15, 30, and 45 min were 0.9, 0.828, and 0.757, respectively. A photocatalytic activity of 24.25% has been observed under optimum conditions for the time interval of 45 min.