Mechanical Engineering / Makina Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4129

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  • Article
    Citation - WoS: 14
    Citation - Scopus: 15
    Electrochemical Performance of La0.6sr0.4co0.2fe0.8o3-Ce0.9gd0.1o2 Composite Sofc Cathodes Fabricated by Electrocatalyst And/Or Electrocatalyst-Ionic Conductor Infiltration
    (Springer, 2019) Sındıraç, Can; Büyükaksoy, Aligül; Akkurt, Sedat
    Infiltration of electrocatalyst precursor solutions into previously sintered porous ionic conductor scaffolds has been used recently as an alternative method to the conventional co-sintering route to fabricate electrocatalyst-ionic conductor composites for solid oxide fuel cell (SOFC) cathode applications. However, the aqueous nitrate solutions generally used to perform the infiltration process results in electrocatalyst precipitates that are disconnected from each other, yielding poor electrode performance. In this work, polymeric electrocatalyst (La0.6Sr0.4Co0.2Fe0.8O3-LSCF) precursors that produce interconnected thin films upon heat treatment were used to infiltrate porous ionic conductor Ce0.9Gd0.1O2-delta (GDC) scaffolds to overcome these issues. In addition, for the first time in the literature, a mixture of LSCF and GDC polymeric precursors, which would yield LSCF-GDC nanocomposite coatings on the grains of the porous GDC scaffold were used as the infiltration solution. Thus, further enhancement of the electrocatalyst/ionic conductor interfacial area and achievement of improved electrode performance was aimed. As a result of the optimization studies, the lowest measured area specific polarization resistance (ASR(cathode)) values of 0.47 and 0.73 omega.cm(2) were obtained for polymeric LSCF+GDC and LSCF precursor infiltrations respectively at 700 degrees C, in air. In addition, LSCF+GDC infiltration yielded electrodes with much improved long-term stability in comparison to those obtained by LSCF infiltration. [GRAPHICS] .
  • Article
    Citation - WoS: 25
    Citation - Scopus: 26
    Lowering the Sintering Temperature of Solid Oxide Fuel Cell Electrolytes by Infiltration
    (Elsevier Ltd., 2019) Sındıraç, Can; Çakırlar, Seda; Büyükaksoy, Aligül; Akkurt, Sedat
    A dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.
  • Article
    Citation - WoS: 9
    Citation - Scopus: 10
    Formation of La1-Xsrxco1 Cathode Materials From Precursor Salts by Heating in Contact With Cgo Electrolyte
    (Elsevier Ltd., 2016) Sındıraç, Can; Akkurt, Sedat
    The purpose of this study is to determine the solid state reactions leading to the formation of La0.6Sr0.4Co0.8Fe0.2O3 and La0.6Sr0.4Co0.2Fe0.8O3 which are widely used as cathode material in solid oxide fuel cells (SOFC) from precursor salts. Interactions between the cathode and the electrolyte layers are also investigated while the cathode layer formed upon heating in contact with the surface of cerium-gadolinium oxide (CGO) electrolyte substrates. Almost all combinations of precursor salt mixtures were tested to see if all solid state reactions are completed and what phases eventually formed. Most of the transformation was complete after 1050 °C heat treatment to yield different mixed oxides. The cathode layer was usually in porous form but was found to spread well over the substrate. Uneven diffusion of La, Sr, Co or Fe into the substrate influenced the stoichiometry of the resulting cathode layer in varying degrees. Fe was found to diffuse into the substrate.