Yazar "Yagiz, Mikail" seçeneğine göre listele

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    Determination of methanol concentration for DMFC systems by fuel cell-based sensor
    (Wiley-V C H Verlag Gmbh, 2022) Celik, Selahattin; Cuhadar, Nurullah; Yagiz, Mikail
    Direct 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.
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    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, Mikail
    Bipolar 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.
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    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, Gamze
    Open 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%.
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    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, Alparslan
    The 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.
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    Fabrication and optimization of LSM infiltrated cathode electrode for anode supported microtubular solid oxide fuel cells
    (Pergamon-Elsevier Science Ltd, 2023) Timurkutluk, Cigdem; Yildirim, Fuat; Toruntay, Furkan; Onbilgin, Sezer; Yagiz, Mikail; Timurkutluk, Bora
    In this study, anode supported microtubular solid oxide fuel cells (SOFCs) with LSM (lanthanum strontium manganite) catalyst infiltrated LSM-YSZ (yttria stabilized zirconia) cathodes are developed to increase the density of triple/three phase boundaries (TPBs) in the cathode, thereby to improve the cell performance. For this purpose, two different porous YSZ layers are formed on the dense YSZ electrolyte, i.e., one is with co-sintering while the other one is not. Incorporation of LSM into these porous YSZ layers is achieved via dip coating of a sol-gel based infiltration solution. The effects of the fabrication method for porous YSZ, LSM solution dwelling time and the thickness of the porous YSZ layer on the cell performance are experimentally investigated and optimized in the given order. A reference cell having a conventional dip coated cathode prepared by mixing the commercial LSM and YSZ powders is also fabricated for comparison. The results show that among the cases considered, the highest peak power density of 0.828 W/cm(2) can be obtained from the cell, whose single dip coated porous electrolyte layer co-sintered with the dense electrolyte is impregnated with LSM for a dwelling time of 45 min. On the other hand, the peak power density of the reference cell is measured as only 0.558 W/cm(2). These results reveal that similar to 50% increase in the maximum cell performance compared to that of the reference cell can be achieved by LSM infiltration after the optimizations. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Improving the electrochemical performance of solid oxide fuel cells by surface patterning of the electrolyte
    (Elsevier, 2021) Timurkutluk, Cigdem; Altan, Tolga; Yildirim, Fuat; Onbilgin, Sezer; Yagiz, Mikail; Timurkutluk, Bora
    The effect of electrolyte surface patterning on the cell performance is investigated. The patterning process is accomplished by isostatically pressing the electrolyte together with a metal mesh placed on one surface of the electrolyte. In this respect, various electrolyte supports with different surface patterns are fabricated by altering the lamination conditions. Surface analyzes reveal that it is possible to modify the electrolyte surface with consistent patterns by the method suggested and some patterns are also formed on the untreated surface of the electrolyte. Electrolyte supported cells are also built on the patterned electrolyte and tested. Among the cases studied, the highest peak performance of 0.44 Wcm (-2) at 800 degrees C is reached from the cell with an electrolyte support subjected to isostatic pressing with a mesh under 50 MPa pressure and 70 degrees C temperature for 4 min after uniaxially pressing under 20 MPa for 4 min. This electrolyte also shows the lowest average roughness and average depth of the patterns formed. The reference cell with a flat electrolyte, on the other hand, provides 0.32 Wcm(-2) peak power density under the same testing conditions, indicating similar to 38% performance enhancement with the simple method recommended. Impedance measurements are also taken and discussed.
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    Mesh patterned electrolyte supports for high-performance solid oxide fuel cells
    (Wiley, 2022) Timurkutluk, Cigdem; Altan, Tolga; Onbilgin, Sezer; Yildirim, Fuat; Yagiz, Mikail; Timurkutluk, Bora
    In this study, the surface of solid oxide fuel cell electrolyte is decorated with different patterns by mesh pressing to improve the cell performance by increasing the surface area of electrolyte-electrode interfaces. Six various woven and unwoven metal meshes with different mesh gaps are considered in this respect. The patterned electrolyte surfaces are scanned by a profilometer to obtain the surface properties created by each mesh. Electrolyte supported cells are fabricated and tested to investigate the effects of electrolyte surface patterning on the cell performance. A cell with a flat electrolyte support is also manufactured and tested as a reference case. Impedance analyses are performed for a detailed examination beside microstructural observations via a scanning electron microscope. Under the same lamination conditions, woven meshes provide surface patterns with relatively higher average roughness values. Among the cases studied, the cell treated with a woven mesh having 0.57-mm wire diameter and 2-mm mesh gap on a side exhibits the highest maximum performance of 0.626 W cm(-2) at 800 degrees C, whereas that of the reference cell is only 0.320 W cm(-2), indicating that the performance of the reference cell can be almost doubled by the simple method suggested in this study. The impedance results show that the improvement in the cell performances is due to reduced electrode polarizations and ohmic resistance via mesh pressing, resulted from increased surface area of electrode-electrolyte interfaces and partially reduced electrolyte thickness as confirmed by microstructural observations, respectively.
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    Performance comparison of bio-inspired flow field designs for direct methanol fuel cell and proton exchange membrane fuel cell
    (Pergamon-Elsevier Science Ltd, 2024) Yagiz, Mikail; Celik, Selahattin; Topcu, Alparslan
    Bipolar flow channel plate design, which is a key component and performance qualifier of fuel cells, is an extensively investigated area. Recently, bio-inspired flow fields (FFs) have been designed to increase the overall performance as an alternative to traditional FFs. In the present study, performance evaluation of the various bioinspired FFs was carried out in PEM fuel cell and direct methanol fuel cell modes. The effects of the main performance characteristics including the clamping force of the short stack assembly, air flow rate, and operating temperature on the cell power were investigated for both PEMFC and DMFC modes. The highest performance output was ensured with the Morus leaf-inspired FF (MLFF) at PEMFC mode at 55 degrees C with a peak power density of 313 mW/cm2. Besides, the highest performance for DMFC mode was achieved at 35.8 mW/cm2 with the Ficus Carica leaf-inspired FF (FCLFF).