Yazar "Mat, Mahmut D." seçeneğine göre listele
Listeleniyor 1 - 20 / 29
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A novel two-part interconnector for solid oxide fuel cells(WILEY-BLACKWELL, 2014) Bakal, Ahmet; Aydin, Fatma; Mat, Mahmut D.; Ibrahimoglu, Beycan; Pamuk, IbrahimA two-part interconnector is developed for solid oxide fuel cell stacks to reduce cost and to improve sealing. The novel interconnector involves a metallic core for current collection and gas distribution and a ceramic support to house the metallic core and to separate two short stacks. The new interconnector reduces usage of expensive metallic alloys and substantially reduce mismatch between stack components due to higher expansion coefficient of metals. The new interconnectors also improve sealing with glass-ceramics eliminating chromium evaporation which is a major reason for sealing failure in fully metallic interconnectors. A proof of concept short stack is manufactured and tested in this study. A comparable performance with a convectional interconnector is obtained with new interconnector, while substantially improving the sealing quality. Copyright (c) 2014 John Wiley & Sons, Ltd.Öğe A review on cell/stack designs for high performance solid oxide fuel cells(PERGAMON-ELSEVIER SCIENCE LTD, 2016) Timurkutluk, Bora; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, YukselBesides the general advantages of fuel cells, including clean and quiet operation, solid oxide fuel cells (SOFCs) as being one of the high-temperature fuel cells also provide a relatively high efficiency due to enhanced reaction kinetics at high operating temperatures, The high operation temperature of SOFC also enables internal reforming of most hydrocarbons and can tolerate small quantities of impurities in the fuel. However, a high operation temperature limits the SOFC application areas to stationary applications because of a long start-up period and also is not desirable from the viewpoint of cost reduction and longterm stability especially for the cell materials. Therefore, the lowering the operation temperature of SOFCs is crucial for the cost reduction and the long term operation without degradation as well as the commercialization of the SOFC systems. The reduced operating temperature also helps to reduce the time and to save the energy required for the system start-up enabling SOFCs to have wider application areas including mobile/portable ones. Apart from the low operating temperature, the high performance along with a small volume is another requirement for SOFC to be used in mobile applications. Both can be achieved by fabricating novel SOFCs generating a high power output at low operating temperatures. Therefore, this paper reviews the current status and related research on the development of these high performance-SOFC cell/stack designs. (C) 2015 Elsevier Ltd. All rights reserved.Öğe A review on micro-level modeling of solid oxide fuel cells(PERGAMON-ELSEVIER SCIENCE LTD, 2016) Timurkutluk, Bora; Mat, Mahmut D.Solid oxide fuel cells (SOFCs) are ceramic based electrochemical devices operating at high temperatures and generates electricity and useful heat energy utilizing various fuels at a high efficiency. The main structure of the cell comprises a dense electrolyte coated with two porous anode and cathode electrodes. The electrolyte is responsible for the transfer of oxide ion while the electrochemical reactions take place in the electrodes. The cell performance is limited by the number of reaction zones known as triple/three phase boundaries (TPBs). Therefore, the electrodes play a crucial role in achieving high power as well as long service life. When the requirements that SOFC electrodes should meet are considered, the most successful electrode materials seem to be composite ones, including ionic and electronic conductive phases with pores for the gas transport. However, this combination is not enough alone since the contiguous contact of these three phases within the electrodes is also necessary to obtain electrochemically active reaction zones. The number of these areas can be a useful metric for predicting the cell performance or provide a relationship between the performance and microstructure. The determination of the electrochemical reaction zones at the micro-scale and the microstructural parameters influencing their density are required to link the microstructure to the performance. Therefore, in this paper, micro-modeling studies of SOFC electrodes through advanced microstructural characterization are reviewed. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Anode-supported solid oxide fuel cells with ion conductor infiltration(WILEY-BLACKWELL, 2011) Timurkutluk, Bora; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, YukselNano ion conductor infiltration to anode andcathode side of solid oxide fuel cell (SOFC) significantly improves the performance of an SOFC. The effects of processing parameters such as molar concentration, sintering temperature and holding time are investigated. The performance of fuel cell is evaluated with a test station and an impedance analyzer. The SEM investigation showed that a nano ion conductor phase forms around the main phase in the anode and the cathode. The results showed that nano infiltration enhances significantly the performance of SOFC. The power density is found to increase around two times with infiltration. It is also found that the particle size and the porosity significantly affect the performance of infiltrated SOFC cell. While smaller infiltrated grains enhance the performance lower porosity adversely affects the performance. Copyrightr (C) 2011 John Wiley & Sons, Ltd.Öğe APPLICATION OF A BUBBLE-INDUCED TURBULENCE MODEL TO SUBCOOLED BOILING IN A VERTICAL PIPE(American Society of Mechanical Engineers (ASME), 1999) Mat, Mahmut D.; Kaplan, Yuksel; Ilegbusi, Olusegun J.Subcooled boiling of water in a vertical pipe is numerically investigated. The mathematical model involves solution of transport equations for vapor and liquid phase separately. Turbulence model considers the turbulence production and dissipation by the motion of the bubbles. The radial and axial void fractions, temperature and velocity profiles in the pipe are calculated. The estimated results are compared to experimental data available in the literature. It is found that while present study satisfactorily agrees with experimental data in the literature, it improves the prediction at lower void fractions. © 1999 American Society of Mechanical Engineers (ASME). All rights reserved.Öğe Application of a coating mixture for solid oxide fuel cell interconnects(PERGAMON-ELSEVIER SCIENCE LTD, 2015) Unal, Fatma Aydin; Mat, Mahmut D.; Demir, Ibrahim; Kaplan, Yuksel; Veziroglu, NejatDue to high operating temperature (800-1000 degrees C) of SOFC's, limited number of alloys can be employed for the purpose of current collection. The electrical conductivity of these alloys usually decreases during the operation of SOFC because of highly corrosive cathode (air side) environment. Cr evaporation from such alloys is also an important problem of performance degradation. A spinel Mn1.5Co1.5O4 and perovskite La0.60Sr0.40FeO3 mixture is coated on Crofer alloy for corrosion and chromium protection in the cathode side of a SOFC. In study firstly, the performance of the fuel cell with the Crofer 22 APU as interconnect material was measured up to 100 h without any coating. Secondly, using a screen printing method, bare Crofer 22 APU was coated with Mn1.5Co1.5O4 and finally Mn1.5Co1.5O4 + La0.60Sr0.40FeO3 ceramic powder slurries were employed as the coating material. Then, the performances of a SOFC short stack with interconnects coated by two methods were compared with uncoated interconnect. Results show that uncoated interconnect experienced a significant performance lost from 4.5 W to 3.8 W. On the other hand the cells with screen printing coated with a mixture Mn1.5Co1.5O4 and La0.60Sr0.40FeO3 exhibited decreases only from 5.78 W to 5.42 W in the short-term performance tests. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Development and testing of a highly efficient proton exchange membrane (PEM) electrolyzer stack(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Selamet, Omer Faruk; Becerikli, Fatih; Mat, Mahmut D.; Kaplan, YukselIntegrated with the renewable energy resources such as wind and solar energy, a Proton Exchange Membrane (PEM) water electrolyzer is one of the important methods for hydrogen production due to its high efficiency, compact structure, releasing no harmful emission and possibility to store the product hydrogen directly to high pressure tanks. In this study, development stages of a highly efficient PEM electrolyzer stack are presented. First, a single cell is developed and its performance is improved from 74% to 87% through design and materials enhancement. Then a 10-cell stack is developed and its operating parameters are optimized for high efficiency. The 10-cell stack produces 5 l/min hydrogen at 1.35 A/cm(2). The single cell is tested for 2000 hours continuously and an acceptable degradation rate of 1.5 mu V/h is measured. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Öğe Development of cathodes for methanol and ethanol fuelled low temperature (300-600 degrees C) solid oxide fuel cells(PERGAMON-ELSEVIER SCIENCE LTD, 2007) Mat, Mahmut D.; Liu, Xiangrong; Zhu, Zhigang; Zhu, BinWe have made extensive efforts to develop various compatible cathode materials for the ceria-carbonate composite (CCC) electrolytes to be used in direct alcohol fuelled solid oxide fuel cells (DLFC). The following cathode materials were mainly investigated: (i) BSCF (BaSrCoFeO) perovskite oxide; (ii) LFN (LaFeO-based oxides, e.g. LaFe0.8Ni0.2O3) perovskite oxides; (iii) bi- or tri-phase metal oxides with or without lithiation. A number of copper- and nickel-based anode composites were also developed for methanol and ethanol with maximum catalytic activity. The tri-metal oxide (CuNiOx-ZnO) cathode produced the maximum power density output of 500 mW/cm(-2) at 580 degrees C for DLFC with methanol operation. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.Öğe Development of high-performance anode supported solid oxide fuel cell(WILEY-BLACKWELL, 2012) Timurkutluk, Bora; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, YukselA high performance five-layered anode supported solid oxide fuel cell (SOFC) is developed by low-cost tape casting, co-sintering, and screen printing techniques. The cell is composed of NiO/scandium stabilized zirconia (ScSZ) anode support, NiO/ScSZ anode functional layer (AFL), ScSZ electrolyte, lanthanum strontium ferrite (LSF)/ScSZ cathode functional layer, and LSF cathode current collecting layer. The effects of fabrication parameters on the cell performance are investigated and optimized, including co-sintering temperature, thickness of the anode support, and AFL. The effects of GDC ion conducting phase impregnated into both electrodes also are investigated. The microstructure of the cell is observed using a scanning electron microscope, and the cell performances at various operation temperatures are evaluated by a fuel cell test station. The final cell produces 1.34 W.cm(-2) maximum power density at an operation temperature of 700 degrees C. The high performance is attributed to optimized cell structure as well as increase in the oxide ion conductivity and three-phase boundaries of both anode and cathode layers by nano ion conductor infiltration. Copyright (c) 2011 John Wiley & Sons, Ltd.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 Nano Ion Conductor Infiltration on the Performance of Anode Supported Solid Oxide Fuel Cells(ELECTROCHEMICAL SOC INC, 2009) Timurkutluk, Cigdem; Timurkutluk, Bora; Mat, Mahmut D.; Kaplan, Yuksel; Ibrahimoglu, Beycan; Pamuk, Ibrahim; Singhal, SC; Yokokawa, HA high performance anode supported solid oxide fuel cell (SOFC) is developed by low-cost tape casting, co-sintering and nano-ion conductor infiltration techniques. A mixture of gadolinium and cerium nitrate solution is infiltrated into both anode and cathode layers and fired at a temperature that gadolinium nitrate and cerium nitrate undergoes a solid state reaction and forms nano ion conductor phase in both electrodes. The effect of molar concentrations and firing temperature of nano ion conductor phase on the cell performance are investigated. The measurements show that nano-sized ion conductor infiltration significantly improves the cell performance. The cell provides 1.718 Wcm(-2) maximum power density at an operation temperature of 750 degrees C. The high performance is attributed to increase in the oxide ion conductivity and three phase boundaries of both anode and cathode layers by nano ion-conductor infiltration.Öğe Effects of anode fabrication parameters on the performance and redox behavior of solid oxide fuel cells(ELSEVIER SCIENCE BV, 2014) Timurkutluk, Bora; Mat, Mahmut D.Anode supported solid oxide fuel cells (SOFCs) having various anode support porosities and electrolyte thicknesses are developed and their effects on the cell performance and redox behavior of the cell are investigated experimentally. An yttria stabilized zirconia based anode supported membrane electrode group (MEG) is developed with the tape casting, co-sintering and screen printing methodologies. For comparison, various anode supported cells with different electrolyte thickness and anode support porosities are also fabricated. An experimental setup is devised for the performance measurement of the cells before and after redox cycling. The mechanical performance of the cell before and after redox cycling is also measured via three point bending tests. Experimental results reveal that the porosity of the anode support and the thickness of the electrolyte should be carefully decided by considering not only the cell performances but also the redox stability. In addition, after single redox cycle the decrease in the mechanical properties of the cell is found to be around 50% while the same cell shows only around 10% electrochemical performance loss. (C) 2014 Elsevier B.V. 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 Effects of operating parameters on the performance of a high-pressure proton exchange membrane electrolyzer(WILEY-BLACKWELL, 2013) Selamet, Omer F.; Acar, M. Caner; Mat, Mahmut D.; Kaplan, YukselIn this study, a 100-cm2 single-cell and a 10-cell stack PEM electrolyzers are designed and manufactured, and the effects of operating parameters such as temperature, pressure, and feed water flow rate on the performance of the PEM electrolyzer are investigated. The hydrogen production capacity of the 10-cell stack is measured to be 7 NL/min hydrogen at 1 A/cm2 current density and atmospheric pressure. Both the single-cell and the 10-cell stack can directly supply both oxygen and hydrogen gases up to 50 bars. The operating temperature is found to be most important parameter affecting on the performance. An 87% efficiency is achieved in single cell at 80 degrees C and 1 A/cm2 current density. Copyright (c) 2012 John Wiley & Sons, Ltd.Öğe Electrochemical behaviour and sulfur tolerance of VxMo(1-x)Oy as solid oxide fuel cell anode(ELSEVIER SCI LTD, 2013) Beyribey, Berceste; Timurkutluk, Bora; Ertugrul, Tugrul Y.; Timurkutluk, Cigdem; Mat, Mahmut D.Vanadium molybdenum oxide system (VxMo(1-x)Oy for x <= 0.13) is synthesized through reducing acidified vanadate and molybdate solution at 60 degrees C by passing hydrogen sulfide gas through the solution. The electrochemical performance of the mixed oxide is tested at various operation temperatures as an anode material for intermediate temperature solid oxide fuel cell (IT-SOFC) under pure and 50 ppm H2S-containing hydrogen fuel. The highest cell performance of 0.18 W cm(-2) peak power is reached at an operation temperature of 750 degrees C for dry H-2. It is found that the addition of 50 ppm H2S to the anode gas causes a 22% decrease in the cell peak power. The loss in the cell performance is attributed to both gas conversion and diffusion. Short-term regeneration tests indicate that 1 h-exposure to sulfur-free gas is insufficient for the reactivation of the cell performance. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Experimental and numerical investigation of effect of particle size on particle distribution in particulate metal matrix composites(ELSEVIER SCIENCE INC, 2006) Mat, Mahmut D.; Aldas, KemalThe effect of particle size on particle distribution during the casting of particulate metal matrix composites (PMMC) is experimentally and numerically investigated. Pb20% Sit alloy and Zr2O3 particles are employed as matrix and reinforcing materials respectively. The casting is performed with an inert gas pressure. The final product is sectioned at several locations and particle fraction is determined using image processing software. Particle fraction is numerically determined by following trajectories of selected particles. It is found that particle fraction decreases along the mold and segregation is reduced with larger particles. The numerical results agree reasonable with experimental data. (c) 2005 Elsevier Inc. 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 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.Öğe Novel electrolytes for solid oxide fuel cells with improved mechanical properties(PERGAMON-ELSEVIER SCIENCE LTD, 2012) Timurkutluk, Bora; Celik, Selahattin; Timurkutluk, Cigdem; Mat, Mahmut D.; Kaplan, YukselThe improvement of the mechanical properties of novel structured electrolytes with triangular cut off geometry in the active region is presented by filleting the tips of triangles. The effect of fillet radius on the bending strength of the yttria stabilized zirconia electrolyte was investigated with a commercial finite element code implementing the calculated Weibull stress through the experimental stress strain curve determined via tensile tests. The model was verified with the experimental three point bending test results for the electrolyte with unfilleted triangular cut off patterns. Ten different fillet radii ranging from 0.05 mm to 0.5 mm were considered in the simulations. The fracture displacement was found to increase with increasing fillet radius as expected. Since the electrolyte with fillet radius of 0.5 mm was found to show the highest flexural strength, single cell based on this electrolyte was fabricated and the cell performance was measured. It was found that the strength of the novel electrolyte with partly reduced thickness can be increased by 26.2% with sacrificing only 10.2% decrease in the performance. Since the final cell still showed 22.2% higher peak performance than the standard electrolyte supported cell, 10.2% decrease in the cell performance compared to the cell having unfilleted triangular cut off patterns is acceptable. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
