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Öğe Comparison of electrolyte fabrication techniques on the performance of anode supported solid oxide fuel cells(Pergamon-Elsevier Science Ltd, 2020) Onbilgin, Sezer; Timurkutluk, Bora; Timurkutluk, Cigdem; Celik, SelahattinA comparison of three solid oxide electrolyte fabrication processes, namely dip coating, screen printing and tape casting, for planar anode supported solid oxide fuel cells (SOFCs) is presented in this study. The effect of sintering temperature (1325-1400 degrees C) is also examined. The anode and cathode layers of the anode-supported cells, on the other hand, are fabricated by tape casting and screen printing, respectively. The quality of the electrolytes is evaluated via performance measurements, impedance analyses and micro structural investigations of the cells. It is found that the density of the electrolyte increases with the sintering temperatures for all fabrication methods studied. The results also show that with the process and fabrication parameters considered in this study, both dip coating and screen printing do not yield a desired dense electrolyte structure as proven by open circuit potentials measured and SEM photos. The cells with tape cast electrolytes, on the other hand, provide the highest performances regardless of the electrolyte sintering and cell operating temperatures. The best peak performance of 0.924 W/cm2 is obtained from the cell with tape cast electrolyte sintered at 1400 degrees C. SEM investigations and measured open circuit potentials reveal that almost fully dense electrolyte layer can be obtained with a tape cast electrolyte particularly sintered at temperatures higher than 1350 degrees C. Impedance analyses indicate that the main reason behind the significantly higher performances is due to not only increased electrolyte density but a decrease in the interface resistance of the anode functional and electrolyte layer is also responsible. This can be explained by theload applied during the lamination step in the fabrication of the tape cast electrolyte, providing better powder compaction and adhesion. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Determination of methanol concentration for DMFC systems by fuel cell-based sensor(Wiley-V C H Verlag Gmbh, 2022) Celik, Selahattin; Cuhadar, Nurullah; Yagiz, MikailDirect methanol fuel cells are devices that convert the chemical energy of methanol fuel having high energy density directly into electrical energy by electrochemical reactions. Methanol must be supplied to the fuel cell system as an aqueous solution to complete the reaction. Therefore, controlling and adjusting of methanol ratio in the methanol-water mixture is critical for the continuity of direct methanol fuel cell performance. In this study, two fuel cell-based electrochemical sensors are developed to adjust the amount of methanol in an aqueous solution in a direct methanol fuel cell. The experimental setup is prepared for the developed sensors and the effects of parameters, such as temperature, methanol flow rate, oxidizing effect, and methanol concentration, affecting the sensor performance are observed experimentally. It is observed that the experimental results obtained in the design without air input are more stable than that of the sensor working with air. However, in air-independent design, the measurement value lost its stability after 2M concentration. The change in methanol flow rate did not cause any change in either sensor. High temperature and low methanol concentrations are found to be the main criteria for the best sensor performance.Öğe Development of titanium bipolar plates fabricated by additive manufacturing for PEM fuel cells in electric vehicles(Pergamon-Elsevier Science Ltd, 2022) Celik, Selahattin; Timurkutluk, Bora; Aydin, Ugur; Yagiz, MikailBipolar plates (BPs) are one of the main parts of proton exchange membrane (PEM) fuel cell stacks, which constitute a significant percentage of a PEM fuel cell system in terms of cost, weight, and structural strength. Although frequently used graphite BPs have low density, high conductivity, and high corrosion resistance, machining the desired flow channels on these plates is challenging. On the other hand, BPs made of various materials rather than graphite can be also fabricated by additive manufacturing methods. These methods can be considered as a reasonable alternative to conventional machining for the fabrication of graphite BPs in PEM fuel cells regarding material cost, fabrication of flow channels, and some post-processes in which the large-scale manufacturing of graphite BPs is more complex. This study offers a comparison of formed stainless-steel, additive manufactured titanium and machined composite graphite plates having the same flow-field geometry as a bipolar plate. In addition, titanium BPs are coated with gold and their performances are compared. Among the cells tested, the highest peak power of 639 mWcm-2 is measured from the cell with 450 nm gold coated titanium BP, whereas those of the cell with con-ventional graphite and stainless-steel BP are only around 322 mWcm-2 and 173 mWcm-2, respectively. Moreover, a new titanium bipolar plate design providing high specific power density is also presented. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Effect of binder burnout on the sealing performance of glass ceramics for solid oxide fuel cells(ELSEVIER SCIENCE BV, 2013) Ertugrul, Tugrul Y.; Celik, Selahattin; Mat, Mahmut D.The glass ceramics composite sealants are among few materials suitable for the solid oxide fuel cells (SOFC) due to their high operating temperatures (600 degrees C-850 degrees C). The glass ceramics chemically bond to both the metallic interconnector and the ceramic electrolyte and provide a gas tight connection. A careful and several stages manufacturing procedure is required to obtain a gas tight sealing. In this study, effects of binder burnout process on the sealing performance are investigated employing commercially available glass ceramic powders. The glass ceramic laminates are produced by mixing glass ceramic powders with the organic binders and employing a tape casting method. The laminates are sandwiched between the metallic interconnectors of an SOFC cell. The burnout and subsequent sealing quality are analyzed by measuring leakage rate and final macrostructure of sealing region. The effects of heating rate, dead weight load, solid loading, carrier gas and their flow rates are investigated. It is found that sealing quality is affected from all investigated parameters. While a slower heating rate is required for a better burnout, the mass flow rate of sweep gas must be adequate for removal of the burned gas. The leakage rate is reduced to 0.1 ml min(-1) with 2 degrees C min(-1) + 1 degrees C min(-1) heating rate, 86.25% solid loading, 200 N dead weight load and 500 ml min(-1) sweep gas flow rate. (C) 2013 Elsevier B.V. All rights reserved.Öğe Effect of surface roughness of the metallic interconnects on the bonding strength in solid oxide fuel cells(Pergamon-Elsevier Science Ltd, 2020) Altan, Tolga; Celik, SelahattinIn this study, the joint strengths of glass-ceramic sealant placed between two metallic interconnectors (Crofer (R) 22 APU) are experimentally investigated depending on the surface conditions of the metallic interconnector and electrolyte/electrode materials (YSZ and NiO). The surfaces of the interconnectors are sanded with sandpaper having five different grits (60, 120, 240, 320 and 2000 grits). Thus, roughened surfaces are obtained and the adhesion is examined for each case. Profilometer is used to inspect the surface roughness of the samples. The fracture strengths of 24 samples prepared for each case are determined via tensile tests. Similarly, different electrolyte/electrode materials with modified surfaces are sandwiched between two glass ceramic layers and their mechanical performances are also measured. The results reveal that the joining strength tends to increase with the amount of surface roughness. It is also found that NiO adheres better to glass-ceramic material than YSZ. The microstructures of the adhesion interface of some cases are also investigated by a scanning electron microscopy. The images showed that good adhesion is achieved without any delamination or cracks at the interfaces. Chemical formation between the glass-ceramic sealants, interconnects and SOFC components is further investigated by XRD analyses. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Effects of electrolyte pattern on mechanical and electrochemical properties of solid oxide fuel cells(ELSEVIER SCI LTD, 2012) Timurkutluk, Bora; Celik, Selahattin; Toros, Serkan; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, YukselIn order to enhance the electrochemical performance and reduce the operation temperature of a conventional electrolyte supported solid oxide fuel cell (SOFC), a three layered electrolyte with various geometry is designed and fabricated. Novel three layered electrolytes comprise a dense and thin scandia alumina stabilized zirconia (ScAlSZ) electrolyte layer sandwiched between two hallow ScAlSZ electrolyte layers each having the same thickness as the support but machined into a filter like architecture in the active region with circular, rectangular and triangular cut off patterns. The percent of thin electrolyte layer in the active region is kept constant as 30% for all designs in order to investigate the effect of pattern geometry on the mechanical properties and the performance of the electrolytes. Single cells based on novel electrolytes are manufactured and electrochemical properties are evaluated. A standard electrolyte and electrolyte supported cell are also fabricated as a base case for comparison. Although the electrolyte having triangular patterns has the highest peak power at all operation temperatures considered, it exhibits the lowest flexural strength. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Engineering solid oxide fuel cell electrode microstructure by a micro-modeling tool based on estimation of TPB length(Pergamon-Elsevier Science Ltd, 2021) Timurkutluk, Bora; Altan, Tolga; Toros, Serkan; Genc, Omer; Celik, Selahattin; Korkmaz, Habip GokayIn this study, a typical solid oxide fuel cell (SOFC) electrode microstructure is numerically optimized in terms of the volume fraction of the catalyst, electrolyte and pore phases via a novel tool based on Dream.3D for the synthetic microstructure reconstruction and COM-SOL Multiphysics (R) Modeling for visualizing and computing three/triple phase boundaries (TPBs). First, the properties of the representative volume element are studied by a parameter independence analysis based on the average particle size. The results indicate that the size of the representative volume element should be at least 10 times greater than the largest average particle size in the microstructure, while the number of mesh elements should be selected such that the smallest average particle size in the system is divided into at least 5. The method is then validated with the available studies in the literature and seems to agree well. Therefore, numerical reconstruction of SOFC electrodes by the pro-posed method is found to be a very useful tool in the viewpoints of accuracy, flexibility and cost. Finally, SOFC electrode microstructures having the same particle size distribution of an average particle size of 0.5 mm for each phase but with various phase volume fractions are generated and the resultant TPBs are computed similarly. It is found out that the volume fraction of each phase should be close to each other as much as possible to maximize the active TPB density and among the cases considered, the highest active TPB density of 9.53 mm/mm(3) is achieved for an SOFC electrode including 35 vol% catalyst, 35 vol % electrolyte and 30 vol% porosity. The active TPB density is also found to be around 93% of the total TPB density. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Estimation of microscale redox tolerance for Ni-based solid oxide fuel cell anodes via three-dimensional finite element modeling(Pergamon-Elsevier Science Ltd, 2023) Altan, Tolga; Celik, Selahattin; Toros, Serkan; Korkmaz, Habip Gokay; Timurkutluk, BoraReduction-oxidation (redox) cycles of Ni-based anodes in solid oxide fuel cells (SOFCs) directly affect the cell performance due to breaking anode three/triple phase boundary (TPB) networks at microscale. Furthermore, these microcracks accumulate with the number of redox cycles leading to mechanical damage in the cell as a result of continuous volumetric changes during the inevitable cyclic reduction and oxidation of the nickel oxide and nickel, threatening the service life of SOFC systems. Therefore, the redox process needs to be investigated as a phenomenon at microscale to understand and minimize its effects. In this regard, we suggest a microscale approach for the redox process of Ni-based SOFC anodes in this study. For this purpose, SOFC anode microstructures with different compositions and porosities are synthetically generated by Dream.3D software and me-chanical damages due to the redox cycle are investigated via element deletion through LS-DYNA for the first time in the literature. The anodes are characterized by computing the redox tolerance based on the resultant damage and the anode composition showing the highest redox tolerance is determined among the cases considered.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Experimental improvement of the performance of the open cathode-direct methanol fuel cell stack by magnetic field effect(Pergamon-Elsevier Science Ltd, 2024) Celik, Selahattin; Yagiz, Mikail; Atalmis, GamzeOpen Cathode Direct Methanol Fuel Cell (OC-DMFC) stack performance is achieved at different methanol temperatures (25, 40, 55 and 70 degrees C), methanol concentrations (0.5, 1, 2 and 4 M) and air flow rates (3.5, 4.8 and 6.4 m/s). Each parameter, whose performance was tested separately, was presented by making comparisons within itself. The effect of performance changes on peak power densities under relatively low electromagnetic fields (4.7, 12.4, 28 and 35 mT) was investigated by exposing the 10-cell OC-DMFC stack to a magnetic field with the help of ferritic magnets. Ferritic magnets placed on the OC-DMFC stack anode and cathode surfaces, It is designed to create an electromagnetic field. Thus, the magnetic field affected both surfaces. When the magnetic field was 35 mT, the OC-DMFC reached a power density of 17.5 mW cm(-2). When the DMFC stack is exposed to the magnetic field, its performance is increased by similar to 16%.Öğe Experimental study on the flow field geometry of the PEM fuel cell bipolar plates: The effects of various shaped blocks embedded in serpentine pattern on cell performance(Elsevier Sci Ltd, 2024) Celik, Selahattin; Yagiz, Mikail; Yildirim, Fuat; Topcu, AlparslanThe flow field pattern is crucial in many aspects such as cost-efficiency (in terms of excessive fuel consumption), water management on the cathode side, and achieving a high cell performance. The studies on the reconnaissance of much more effective flow field design have been continuing for years. As a matter of fact, it may be succeeded with some manipulations on the flow area. The current research proposes to investigate the effects of blocks in various shapes and positions on the net power output by changing the shape of the channels in the flow field (FF). For this reason, semicircular and triangular blocks were machined on the serpentine channels and their short-term performances were compared with the conventional serpentine pattern. In addition to the related new FF designs, performance evaluation was made by using nickel foam placed to fill the inner part of the serpentine FF. First, ultimate operating conditions were optimized with the traditional serpentine FF. Then, the performance outputs of the proposed FF designs were compared under the same conditions assigned in the previous section. The single-cell performance tests yielded that the highest power density was ensured with nickel foam (NF)-serpentine FF with 0.267 W/cm2. This increment corresponds to a 38 % enhancement in the power output when compared to the classical serpentine-type FF. Triangular (T) and semicircular (S) obstacles increased the performance significantly. Each manipulation on the traditional serpentine FF affected the power output positively, essentially. The pattern structures of the diagonal semicircle (DS) and diagonal triangular (DT) FFs reduced both water evacuation ability and performance increase rate. NF-serpentine FF contact highly decreased the ohmic resistance level of the cell when compared to the other designs according to the impedance (EIS) measurements. In addition, a correlation was observed between the performance and pressure drop test results. The highest-pressure drop was recorded with NF-serpentine FF (4.225 kPa) whereas the lowest is conventional serpentine FF (0.55 kPa). Traditional serpentine pattern is famous for with high-pressure drop structure. Consecutively, the pressure drop tests proved that the manipulations increased the pressure level of the system directly.Öğe Hydrogen storage capacity of two-dimensional MoS2(Pergamon-Elsevier Science Ltd, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepHydrogen storage holds a crucial place for the future of the world in terms of green energy. Two-dimensional materials, in particular, are important in this regard. The aim of this study is to evaluate the performance of MoS2 which is one of the most popular member of two-dimensional materials family. To do this, bulk and exfoliated MoS2 were used. Firstly, the liquid phase exfoliation method was employed to obtain exfoliated MoS2 layers. Then, the hydrogen storage potential of the bulk and exfoliated MoS2 was addressed under 1, 3, 5, 7, and 9 bar hydrogen pressure. After the absorption process, all the samples were characterized using XRD, Raman Spectrometer, and BET ahead of evaluating their hydrogen storage potential. The XRD pattern showed that the peak positions of bulk and exfoliated MoS2 were not affected critically by hydrogen storage. In the Raman spectra, the A1g and E2g 1 peaks of all hydrogenated materials shifted to low wavelengths. Moreover, the BET measurements revealed that the specific surface area and the pore size of the bulk MoS2 were 12.31 m2/g and <= 67.46 nm respectively. Additionally, the specific surface area and the pore size of the exfoliated MoS2 were 23.16 m2/g and <= 69.28 nm, respectively. The hydrogen storage potential of the bulk and the exfoliated MoS2 was evaluated through an MFC in sccm unit. The bulk and exfoliated MoS2 stored 220 and 450 sccm hydrogen, respectively. Besides, the weight percent hydrogen storage for H-MoS2 and H -exfoliated MoS2 was determined to be 1.2 and 2.4 wt%, respectively. In summary, this study has shown that exfoliated MoS2, one of the twodimensional materials, can play a critical role for hydrogen storage due to their high specific surface area.Öğe Influential parameters and performance of a glass-ceramic sealant for solid oxide fuel cells(ELSEVIER SCI LTD, 2015) Celik, SelahattinGlass-ceramic composites are among the few materials suitable for solid oxide fuel cell (SOFC) sealing application due to their high operating temperatures (600-850 degrees C). Glass-ceramics can chemically bond to both the metallic interconnector and the ceramic electrolyte and provide a gas-tight connection. However, a careful manufacturing procedure, which includes several stages, is required to obtain a gas-tight seal. In this study, the joint strength of the glass-ceramic sealant between two metallic interconnectors is experimentally investigated for different surface properties of the metallic interconnector. According to the experimental results, the optimum sintering temperature and pressure are found to be 870 degrees C and 0.5 kg cm(-2), respectively. In addition, the best bonding strength among the support materials considered is obtained for NiO. Furthermore, the sealing thickness is optimized as 0.6 mm. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Investigating surface area and hydrogen pressure effects on LiH and NaH(Academic Press Inc Elsevier Science, 2024) Altuntepe, Ali; Erkan, Serkan; Olgar, Mehmet Ali; Celik, Selahattin; Zan, RecepNaH and LiH are theoretically capable of storing hydrogen, but several challenges remain to be overcome before they can be widely used for hydrogen storage. In this study, LiH and NaH were ball-milled and the effect of surface area and hydrogen pressure on hydrogen storage capacity was investigated using the solid-state hydrogen storage method. XRD patterns and Raman spectra show significant shifts in main peak positions of LiH and NaH after hydrogen adsorption. BET analysis shows a significant increase in the specific surface area of LiH and NaH from 6.25 m(2)/g to 12.35 m(2)/g and from 1.34 m(2)/g to 2.33 m(2)/g respectively due to ball milling. The FTIR spectra showed more bonds in the 400-1200 cm(-1) fingerprint region after storing hydrogen in LiH and NaH. This suggests structural changes with enhanced bond bending due to hydrogen. At 9 bar pressure, LiH and NaH exhibited excellent hydrogen storage, with ball-milled LiH reaching about 3.55 wt% and 652 sccm, and NaH achieving approximately 1.58 wt% and 291 sccm. These results highlight the significant influence of surface area and hydrogen pressure on hydrogen storage potential. Incorporating the storage potential within the evaluation of PEM fuel cell performance, we suggest that an increased storage capacity directly corresponds to an augmented power density. The analysis of power density over time revealed that the hydrogen adsorbed ball-milled LiH exhibited the highest power density, peaking at 0.075 Wcm(-2) over the long term. In contrast, LiH displayed a lower power density (0.025 Wcm(-2)) while maintaining its long-term performance. The hydrogen adsorbed NaH and hydrogen adsorbed ball-milled NaH displayed power densities 0.050 Wcm(-2) and 0.073 Wcm(-2), respectively, but they showed short-term performance.Öğe Investigation of external compression in scaling up of planar solid oxide fuel cells(Pergamon-Elsevier Science Ltd, 2022) Onbilgin, Sezer; Timurkutluk, Cigdem; Timurkutluk, Bora; Celik, SelahattinThe effect of contact pressure on the performance of electrolyte supported planar solid oxide fuel cells (SOFCs) are experimentally investigated in this study by varying the pressure applied on the push rod. For this purpose, cells with 1 cm(2), 9 cm(2), 16 cm(2), 81 cm(2) and 150 cm(2) active areas are manufactured and tested under different external compression pressures. Maximum power densities of 0.486 W/cm(2), 0.308 W/cm(2) and 0.231 W/cm(2) are obtained from the cells with an active area of 1 cm(2), 9 cm(2) and 16 cm(2), respectively, under the same contact pressure. When the impedance results are considered, it is seen that under the same compression pressure, the cell resistance increases nonlinearly with the cell size. However, when the pressure is adjusted according to the active area, a similar power density of approximately 0.4 W/cm(2) is obtained from these three cells. Moreover, very similar performances are measured from all cells when a portion of cells with 1 cm(2) active is cut and tested under the same contact pressure of 0.2 MPa. The overall results indicate that the external load should be adjusted according to the cell size, but there is no linear relationship between the active area and the applied external pressure. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Investigation of formability of metallic bipolar plates via stamping for light-weight PEM fuel cells(Pergamon-Elsevier Science Ltd, 2020) Karacan, Kivanc; Celik, Selahattin; Toros, Serkan; Alkan, Mahmut; Aydin, UgurBipolar plates (BPs) are one of the main members which constitute a significant percentage of a fuel cell system in terms of cost, weight and structural strength. Although frequently used graphite BPs have low density, high conductivity and corrosion resistance, machining the desired flow channels on the graphite plates is an important issue. On the other hand, metallic BPs can be considered a reasonable alternative material to graphite in the view of the material cost, fabrication of flow channels and some post-processes in which the largescale manufacturing of graphite BPs is more complex compared to cutting and stamping processes for metal ones. This study offers a comparison of the formability of four different metals with four flow channel depths as bipolar plates formed by stamping. 304 Stainless Steel (SS 304), pure Titanium Grade2 (CP-Ti) and Aliminium (Al 6016 and Al 3104) are chosen as the BP materials. A serpentine type flow channel with two different channel widths are formed on to 0.1 mm thick sheets. The channel width is chosen as 1.2 mm and 1.8 mm for the channel depths of 0.36 mm-0.55 mm, and 0.54 mm-0.82 mm, respectively. The stamping processes of the BPs materials are simulated via commercially available eta/ Dynaform v5.9.4. software and formability characteristics are obtained for sixteen various cases. As a result, it is determined that SS 304 is the more appropriate material in the view of the formability for such a complex form. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Investigation of temperature distribution and performance of SOFC short stack with/without machined gas channels(PERGAMON-ELSEVIER SCIENCE LTD, 2016) Canavar, Murat; Mat, Abdullah; Celik, Selahattin; Timurkutluk, Bora; Kaplan, YukselSolid oxide fuel cells (SOFCs) generate clean energy via electrochemical reactions at high operating temperatures. The distribution of the electrochemical reactions in the cell depends on the flow field design of the interconnectors. The non-uniform distribution of the reactions due to the flow field design may cause the development of thermal stresses which may lead to micro or macro cracks in the cell and thus a significant performance loss even a cell failure. In this study, the effects of operating current densities and fuel flow rates on the temperature profile within the cell and the cell performance are experimentally investigated for two different flow-field designs with Crofer 22 APU interconnectors, i.e. Design I and Design II. Design I, which mimics the conventional interconnector structure, has machined gas channels and porous nickel mesh at the anode side for the distribution of hydrogen and the collection of the current generated in the cell while at the anode side of Design II, only wire woven nickel mesh is employed. The experimental results indicate that Design II provides much more uniform temperature distributions under 20-40 A current loads and 1-2 NL/min H-2 flow rates when compared to those of Design I. Furthermore, Design II exhibits a higher peak power density than Design I at an operation temperature of 800 degrees C. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Measurement and estimation of species distribution in a direct methanol fuel cell(PERGAMON-ELSEVIER SCIENCE LTD, 2010) Celik, Selahattin; Mat, Mahmut D.Determination of methanol concentration in a direct methanol fuel cell is crucial for design improvement and performance enhancement Methanol and water concentrations in a direct methanol fuel cell are experimentally and numerically investigated in the experimental program, a single cell direct methanol fuel cell is developed and an experimental setup is devised to measure methanol and water concentrations and performance of the cell depending on operating conditions In theoretical program a mathematical model which includes fluid flow, species distribution, electric field and electrochemistry is adapted and numerically solved The results showed that the performance of a Direct Methanol Fuel Cell (DMFC) is mainly influenced by operating temperature A large drop in methanol concentration methanol is measured at the inlet section of cell The mathematical model is found to satisfactorily capture main physics involved in a DMFC (C) 2009 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reservedÖğe Measurement of the temperature distribution in a large solid oxide fuel cell short stack(PERGAMON-ELSEVIER SCIENCE LTD, 2013) Celik, Selahattin; Timurkutluk, Bora; Mat, Mahmut D.During the operation of solid oxide fuel cells (SOFCs), nonhomogeneous electrochemical reactions in both electrodes and boundary conditions may lead to a temperature gradient in the cell which may result in the development of thermal stresses causing the failure of the cell. Thus, in this study, effects of operating parameters (current density, flow configuration and cell size) on the temperature gradient of planar SOFCs are experimentally investigated. Two short stacks are fabricated using a small (16 cm(2) active area) and a large size (81 cm(2) active area) scandia alumina stabilized zirconia (ScAlSZ) based electrolyte supported cells fabricated via tape casting and screen printing routes and an experimental set up is devised to measure both the performance and the temperature distribution in short stacks. The temperature distribution is found to be uniform in the small short stack; however, a significant temperature gradient is measured in the large short stack. Temperature measurements in the large short stack show that the temperature dose to inlet section is relatively higher than those of other locations for all cases due to the high concentrated fuel resulted in higher electrochemical reactions hence the generated heat. The operation current is found to significantly affect the temperature distribution in the anode gas channel. SEM analyses show the presence of small deformations on the anode surface of the large cell near to the inlet after high current operations. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Mechanical and electrochemical behavior of novel electrolytes based on partially stabilized zirconia for solid oxide fuel cells(ELSEVIER SCI LTD, 2015) Celik, Selahattin; Timurkutluk, Bora; Toros, Serkan; Timurkutluk, CigdemIn this study, 3 mol% yttria stabilized zirconia (3YSZ) is investigated as a SOFC electrolyte alternative to 8 mol% yttria stabilized zirconia (8YSZ). The mechanical and electrochemical properties of both materials are compared. The mechanical tests indicate that the thickness of 3YSZ can be reduced to half without sacrificing the strength compared to 8YSZ. By reducing the thickness of 3YSZ from 150 mu m to 75 mu m, the peak power density is shown to increase by around 80%. The performance is further enhanced by around 22% by designing of novel electrode structure with regular cut-off patterns previously optimized. However, the cell with novel designed 3YSZ electrolyte exhibits 30% lower maximum power density than that of the cell with 150 pm-thick standard 8YSZ electrolyte. Nevertheless, the loss in the performance may be tolerated by decreasing the fabrication cost revealing that 3YSZ electrolyte with cut-off patterns can be employed as SOFC electrolyte alternative to 8YSZ. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Micro level two dimensional stress and thermal analysis anode/electrolyte interface of a solid oxide fuel cell(PERGAMON-ELSEVIER SCIENCE LTD, 2015) Celik, Selahattin; Ibrahimoglu, Beycan; Mat, Mahmut D.; Kaplan, Yuksel; Veziroglu, T. NejatThe delamination and degradation of solid oxide fuel cells (SOFCs) electrode/electrolyte interface is estimated by calculating the stresses generated within the different layers of the cell. The stresses developed in a SOFC are usually assumed to be homogenous through a cross section in the mathematical models at macroscopic scales. However, during the operating of these composite materials the real stresses on the multiphase porous layers might be very different than those at macro-scale. Therefore micro-level modeling is needed for an accurate estimation of the real stresses and the performance of SOFC. This study combines the microstructural characterization of a porous solid oxide fuel cell anode/electrolyte with two dimensional mechanical and electrochemical analyses to investigate the stress and the overpotential. The microstructure is determined by using focused ion beam (FIB) tomography and the resulting microstructures are used to generate a solid mesh of two dimensional triangular elements. COMSOL Multiphysics package is employed to calculate the principal stress and Maxwell Stefan Diffusion. The stress field is calculated from room temperature to operating temperature while the overpotential is calculated at operating temperature. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
