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Rismanchian, AzadehElectrochemical and Photocatalytic Oxidation of Hydrocarbons
Doctor of Philosophy, University of Akron, 2014, Polymer Science
This study demonstrates the development of a stable anode for electrochemical oxidation of hydrocarbons in solid oxide fuel cell (SOFC) and a highly active TiO2 based catalyst for photocatalytic reactions. The Ni/YSZ anode of SOFC was modified by Cu electroless plating. The catalytic activity toward H2 and CH4 oxidation were compared by the Faraday resistance (RF) obtained from the impedance spectroscopy. The RF ratio of Cu-Ni/YSZ in CH4 to H2 was greater than that of Ni/YSZ, indicating low catalytic activity of Cu-Ni/YSZ toward CH4 oxidation. The addition of Cu decreased the catalytic activity, but increased stability to 138 h in dry CH4. Characterization of the carbon type with Raman spectroscopy and temperature programmed oxidation showed that Cu formed disordered carbon rather than graphitic carbon which is the precursor to coking. Addition of CO2 to CH4 was studied as another approach to prevent coking. Electrochemical performance and mass spectrometry of the reactor effluent showed that the CH4-CO2 SOFC generated electricity from CO and H2, products of dry reforming reaction, with CO as the major contributor to current generation. CH4-CO2 decreased the activation polarization but showed a limiting current due to the fuel depletion at the interlayer-electrolyte interface. Anode interlayer was modified by reducing the particle size to 2 µm. The fine microstructure increased the three phase boundary length and reduced the activation polarization. The pore loss in the fine microstructure resulted in diffusion limitation and a limiting current in CH4 which was eliminated by adding 4 wt% of pore former at interlayer. Further addition of pore former lowered the performance by creating discontinuity at electrolyte-interlayer interface. The photocatalytic oxidation of ethanol on TiO2 and TiO2 modified with Ag and Au nanoparticles was studied by in-situ IR spectroscopy. Au and Ag increased the surface hydroxyl groups, which further served as active species to oxidize ethanol. Higher rate of electron transfer to Au than to Ag, evidenced by IR spectroscopy, resulted in higher rate of oxidation in Au-TiO2. This resulted in formation of formate (HCOO) on Au-TiO2 and acetate (CH3COO) on Ag-TiO2 as the major intermediate during the initial period of the photocatalytic oxidation.

Committee:

Steven Chuang, Dr (Advisor); Darrell Reneker, Dr (Committee Member); Yu Zhu, Dr (Committee Member); Xiong Gong, Dr (Committee Member); Homero Castaneda-Lopez, Dr (Committee Member)

Subjects:

Chemical Engineering; Energy

Keywords:

SOFC; Cu electroless plating; Raman spectroscopy; carbon type in CH4-SOFC; impedance spectroscopy;Faraday resistance; limiting current in CH4-CO2; interlayer microstructure; Photocatalytic oxidation on TiO2; in-situ IR spectroscopy; Au and Ag co-catalyst

Chakravarthula, Venkata AdithyaTransient Analysis of a Solid Oxide Fuel Cell/ Gas Turbine Hybrid System for Distributed Electric Propulsion
Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering
Gas turbine technology for aerospace applications are approaching limits in efficiency gains as increases in efficiency today occurs in very small increments. One limitation in conventional gas turbine technology is the combustion process, which destroys most of the exergy in the cycle. To address this limitation in a traditional Brayton power cycle, a hybrid system which is integrated with Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. Power generation systems with improved performance from low fuel utilizations and low maintenance costs are possible. The combination of a SOFC fuel cell with a gas turbine has shown higher efficiencies than conventional gas turbine systems due to the reduction of exergy destruction in the heat addition process. A one-dimensional dynamic model of a Solid Oxide Fuel Cell (SOFC) integrated with a gas turbine model to develop an efficient electrical power generation system for aviation applications is investigated. The SOFC - Combustor concept model was developed based on first principles with detailed modeling of the internal steam reformer, electrochemical and thermodynamics analysis is included. Initially, a detailed investigation of internal steam reformer kinetics is presented. The overall purpose of this thesis is to analyze the performance of the hybrid SOFC-GT system for both on-design and off-design operation in an aerospace application. Transient analysis is performed to understand the uncertainties in the SOFC temperatures and hybrid system; control and stability with sudden transient iii changes of the system (rapid throttle changes, environment changes like climb). Finally, SOFC model integrated with a compressor and turbine model and investigation on the overall performance of the innovative hybrid thermodynamic cycle is presented. The SOFC hybrid system has a lower power density at sea level compared to a turbo-generator, but in a typical commercial flight the SOFC hybrid system outperforms the turbo-generator in both endurance and power-to-weight ratio at cruising altitude.

Committee:

Rory Roberts, Ph.D. (Advisor); Mitch Wolff, Ph.D. (Committee Member); Scott Thomas, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

SOFC; Hybrid Systems; SOFC-GT; Internal Steam reformer

Kaufman, Brian A.The Effect of Operational Voltage on a Solid Oxide Fuel Cell Operating on Coal Syngas Containing Trace Amounts of Phosphine
Master of Science (MS), Ohio University, 2011, Mechanical Engineering (Engineering and Technology)
Electrolyte-supported Solid Oxide Fuel Cells have been proven capable of generating usable electricity when supplied with various fuels, including a synthetic fuel (syngas) generated from gasified coal. Coal, however, contains contaminants, namely phosphine (PH3), that remain in the syngas despite cleanup technologies, which can lead to lowered electrical performance caused by the formation of secondary compounds. This study investigates a strategy of varying the operational voltage to potentially mitigate the formation of secondary compounds, including nickel phosphide (NixPy), thus prolonging the life of the cell. Two operational voltage conditions were investigated, 0.7 volts and 0.6 volts, with four cells per voltage tested. The degradation of the cell was determined using electrical data generated as well as with material analysis. Post-mortem cells were analyzed for the presence of secondary formations with techniques including XRD, SEM/EDX, and XPS. The results indicate that the operational voltage has little effect on the formation of nickel phosphides and the prevailing nickel phosphide specie was Ni2P in both operational voltage conditions.

Committee:

David Bayless (Advisor); Gregory Kremer (Committee Member); Carole Womeldorf (Committee Member); Gang Chen (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Solid Oxide Fuel Cell; operational voltage; phosphine; SOFC

Mirzababaei, JelvehnazSolid Oxide Fuel Cells with Methane and Fe/Ti Oxide Fuels
Doctor of Philosophy, University of Akron, 2014, Chemical Engineering
Direct methane SOFCs, operated by supplying methane to Ni/YSZ anodes, suffer from degradation via accumulation of carbon deposits on the Ni surface. We proposed the anode modification by La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) perovskite catalyst to improve long-term stability of direct CH4-SOFCs. Coating a 40 µm thin film of LSCF on the Ni/YSZ anode surface decreased the amount of carbon deposits and slowed down the degradation rate. The improvement in the anode durability could be related to the oxidation activity of LSCF which facilitated oxidation of CH4 and carbon deposits. Analysis of the crystalline structure of LSCF revealed that LSCF was stable in the reducing anode environment under H2 and CH4 flow at 750 °C and retained its perovskite structure throughout the 475 h long-term stability test. Toward development of stable direct CH4-SOFCs we studied internal dry reforming of methane in SOFC stack. Dry reforming of CH4 with CO2 on the Ni/YSZ anode of SOFC produced H2 and CO which further underwent electrochemical oxidation for power generation. The CH4/CO2-SOFC exhibited long-term stability greater than 290 h. The stable performance of the SOFC stack was attributed to less carbon deposition on the anode as evidenced by the result of Raman spectroscopy and calculated amount of CO2 produced from oxidation of deposited carbon. For the first time, Fe-Ti-O (titania-supported iron oxide) chemical looping particle was used as a solid fuel for direct contact with the Ni/YSZ anode surface. Electrochemical oxidation of reduced Fe-Ti-O at 750 °C produced a maximum power density of 97 mW/cm2, corresponding to 84% of that in H2 fuel. The Fe-Ti-O pellets were able to generate stable electricity under repeated electrochemical oxidation and hydrogen reduction cycles. This study demonstrated that coupling a SOFC with an external reducer using Fe-Ti-O oxygen carrier is a good candidate for electricity generation. We developed two main approaches for improvement of long-term stability of direct methane SOFCs including anode modification and adjusting fuel composition for coke-free operation. We also proposed a novel concept of coupling the SOFC stack with chemical looping process and directly utilize Fe-Ti-O chemical looping particles as solid fuel for power generation in SOFC.

Committee:

Steven Chuang, Dr. (Advisor); Bi-min Newby, Dr. (Committee Member); Gang Cheng, Dr. (Committee Member); William Landis, Dr. (Committee Member); Robert Weiss, Dr. (Committee Member)

Subjects:

Chemical Engineering; Energy

Keywords:

fuel cell; SOFC; natural gas; methane; coke; anode; catalyst; perovskite; LSCF; degradation; stability; dry reforming; redox; voltage; current; impedance; IR spectroscopy; chemical looping

Lakshminarayanan, NanditaInvestigation and development of electro catalysts for Solid Oxide Fuel Cells
Doctor of Philosophy, The Ohio State University, 2010, Chemical and Biomolecular Engineering

Solid Oxide Fuels Cells (SOFCs) have tremendous potential as efficient and clean energy conversion devices. They are the most desirable fuel cells for stationary power generation and as auxiliary power sources in transport applications. The fuel flexibility and higher efficiency of the SOFC make it a favorable choice over conventional combustion systems. However, there are some major roadblocks to the effective commercialization of SOFC technology. High operating temperatures are required due to low activity of the cathode catalysts, thus dictating the use of more expensive materials for the SOFC components as well as balance of plant. Moreover, the state-of-the-art Nickel –Yttria Stabilized Zirconia (Ni-YSZ) cermet anode catalysts are extremely susceptible to poisoning by sulfur in the fuel, as well as coking on operation with carbonaceous fuels. Ni also tends to sinter at elevated temperatures. Since these fuel cells are envisioned to be used with Coal and Natural Gas as fuels, stable and active anode catalysts are required.

There is a need for significant work in developing and testing new catalyst formulations for both electrodes. The cathode reaction is the reduction of gas phase oxygen to form oxide ions that are then transported through the electrolyte to the anode. At the cathode, the drive is to develop perovskite oxide materials which are capable of conducting and activating oxygen at lower temperatures and are more active than the state of the art Lanthanum Manganite based catalysts. The current research focused on developing new formulations based on doping of Lanthanum Ferrites and exploring their properties and their activity and performance as SOFC cathodes. The effect of varying the dopant levels on the physiochemical properties as well oxygen mobility and oxygen content in the samples is explored. The effect of substitution of the La ions with Sr on the A-site is studied in detail and the oxygen activation and transport properties are explored as a function of Sr content. Methane oxidation is used as a model reaction to study oxygen activation energies over the materials. X-ray Photoelectron Spectroscopy and Mössbauer Spectroscopy are used to study the surface and bulk properties. Additional doping with aliovalent metals such as Zn, Cu and Ni on the B-site is studied and the surface and bulk properties are examined using X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), X-Ray Absorption Fine Structure (XAFS) techniques and using methanol as a probe molecule. Further in-sight into oxygen activation properties is obtained by CO2 Temperature-Programmed Oxidation (TPO) and methane oxidation reactions. On the anode side, the emphasis is in exploring the nature and mechanism of deactivation of the state of the art Nickel-Yttria stabilized Zirconia (Ni-YSZ) catalysts. The effect of water in sulfur poisoning on the catalyst is examined through steady-state reaction testing as well as bulk and surface characterization using XAFS studies and temperature programmed desorption (TPD) experiments. Based on these results, new formulations are explored and tested for their activity for the various anode reactions as well as the tolerance to sulfur poisoning and coking. The new catalyst development is carried out in a two pronged approach. Transition metal based bi-metallic catalysts are explored. Simultaneously, perovskite oxide materials are also tested for their catalytic activity and performance as SOFC anodes. Coking and sulfur tolerance studies are performed and characterization is performed using XPS and TPD studies.

Committee:

Umit Ozkan, Dr. (Advisor); Jeffrey Chalmers, Dr. (Committee Member); Andre Palmer, Dr. (Committee Member)

Subjects:

Chemical Engineering; Energy; Engineering

Keywords:

SOFC; Catalysts; Electrpcatalysts; Fuel Cells

Chien, Chang-YinMethane and Solid Carbon Based Solid Oxide Fuel Cells
Doctor of Philosophy, University of Akron, 2011, Chemical Engineering

Mechanics and performance of solid oxide fuel cells (SOFCs) have been investigated with methane and solid carbon as fuels. The work with methane fuels investigated methane reactions on Ni/YSZ and deactivation of Ni/YSZ. The Cu-Ni/YSZ anode was developed to resist the coking and sustain the durability of Ni/YSZ anodes. The results of Ni/YSZ deactivation showed that the coking caused by methane was fast (i.e., less than 5 min) and irreversible. A combined in situ infrared (IR) and mass spectroscopy (MS) complemented the deactivation studies in open circuit and suggested that CH4 reactions on Ni/YSZ followed (i) dissociation of C-H bond, (ii) initial oxidation of adsorbed carbon to CO2 and CO followed by depletion of lattice oxygen, and (iii) accumulation of carbon on the anode surface. The Cu-Ni/YSZ anode was made by electroless plating copper on Ni/YSZ anodes. Addition of copper slowed down the C-H dissociation and carbon accumulation from CH4 by formation of Cu-Ni alloy, which was tolerant to coking and sulfur. The X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed the successful copper deposition on Ni/YSZ anodes. The maximum power density of 125 mW cm-2 was achieved using the Cu-Ni/YSZ anode in CH4 (100 ml min-1) at 750 °C. A preparation protocol of copper plating on the anode of SOFCs was established for the applications of coking resistant methane- and carbon-based SOFCs.

The work with solid carbon fuels tested the feasibility of direct use of solid carbon on SOFCs for power generation and investigated the chemical reactions involved. Two types of solid carbon: biomass-derived coconut coke and bituminous Ohio #5 coke, were used on carbon-based SOFCs (C-SOFCs). The results showed that biomass-based coconut coke exhibited a higher oxidation and gasification reactivity than bituminous Ohio # 5 coke due to higher content of functional groups and alkali metals. The power generation from coconut coke produced a power density of 140 mW cm-2 continuously over 15 h and an electrical efficiency of 51.82 % based on CO2 production at 800 °C. Transient techniques consisting of pulse injection and step switch showed that both Boudouard reaction (C+CO2→2CO) and CO electrochemical oxidation contributed to power generation of carbon fuel cells. The carrier gas flow rates also affected these gaseous reactions on C-SOFCs by changing the residence time of gas species and their concentration. The results showed that low carrier gas flow rates increased residence time of CO, thereby increasing its contribution to current generation. The contribution of CO oxidation to current generation was estimated to 66 % at the carrier gas flow rate of 50 ml min-1. The pulse transient studies confirmed the effect of flow rates on cell performance and also revealed that CO and CO2 can displace adsorbed hydrogen on carbon fuels. The results demonstrated the successful utilization of solid carbon on Ni/YSZ anode supported SOFCs for power generation and provided the insight of reaction mechanisms for development of carbon-based fuel cells.

Committee:

Steven S. C. Chuang, Dr. (Advisor); George Chase, Dr. (Committee Member); Edward Evans, Dr. (Committee Member); David Perry, Dr. (Committee Member); Yang Yun, Dr. (Committee Member)

Subjects:

Chemical Engineering

Keywords:

SOFC; carbon fuel cells,methane; Ni/YSZ; anode deactivation; Boudouard reaction; electroless plating

Cooper, Celeste EatonDegradation in Performance of Lanthanum Strontium Manganite Based Solid Oxide Fuel Cell Cathodes Under Accelerated Testing
Master of Sciences, Case Western Reserve University, 2017, Materials Science and Engineering
The performance of solid oxide fuel cells (SOFCs) with three different lanthanum strontium manganite (LSM) based cathode compositions were evaluated. All cells were yttria-stabilized zirconia (Zr0.92Y0.08O2-d, 8YSZ) electrolyte-supported button cells, consisting of a nickel oxide – yttria-stabilized zirconia (NiO-8YSZ) anode and a cathode of 8YSZ and LSM. The three LSM compositions differed in the amount of excess Mn: Composition A was (La0.85Sr0.15)0.90MnO3±d (10% excess Mn); Composition B was (La0.80Sr0.20)0.95MnO3±d (5% excess Mn); and Composition C was (La0.80Sr0.20)0.98MnO3±d (2% excess Mn). The cells were tested under conventional and accelerated conditions, where the accelerated conditions were meant to simulate the results of months of long-term testing in just 500 hours (approximately three weeks) of testing by using high operating temperature and current density. Accelerated tests showed lower degradation rates, lower continuous area specific resistance (ASR), and higher power output than conventional tests for all cathode compositions. Continuous measurements of the cells' output voltage versus time, together with periodic electrochemical impedance spectroscopy (EIS) measurements, were used to evaluate the performance of the cells in terms of ASR degradation rates (% ASR rise per kh) and power outputs. The EIS measurements also permitted a partial deconvolution of the cathode ASR from the anode ASR. Cathodes with 10% excess Mn tested under accelerated conditions had the lowest degradation rates, but the highest continuous ASR and lowest power outputs. Cathodes with 2% excess Mn tested under accelerated conditions had the lowest continuous ASR and highest power outputs; thus it was concluded that cells with the lowest amount of excess Mn cathodes performed the best.

Committee:

Mark De Guire (Advisor); Arthur Heuer (Committee Member); Roger French (Committee Member)

Subjects:

Energy; Materials Science

Keywords:

SOFC; solid oxide fuel cell; cathode; accelerated testing; lanthanum strontium manganite; LSM; performance degradation; area specific resistance; ASR; electrochemical impedance spectroscopy; EIS

Parikh, Harshil RMicrostructure Changes In Solid Oxide Fuel Cell Anodes After Operation, Observed Using Three-Dimensional Reconstruction And Microchemical Analysis
Doctor of Philosophy, Case Western Reserve University, 2015, Materials Science and Engineering
Solid oxide fuel cells (SOFCs) have great importance as a more efficient source of electrical power than conventional systems. Nonetheless, there is limited understanding of the processes by which their performance decreases with time, especially during long-term operation (>2 kh). This study sought explanations for performance loss in the microstructural changes that take place in the anodes during operation of periods from 2 to 16 kh. Recently developed three-dimensional (3D) analysis techniques enable the study of aspects of the anode microstructure, such as tortuosity and triple-phase boundary density, that cannot be fully depicted in two-dimensional analyses. The complex multi-phase microstructure of SOFC anodes adds other challenges for applying this technique to study lifetime degradation of SOFCs. The project is divided into four sections: 1) sample preparation and experimentation, including adaptations of standard techniques to the porous microstructures of SOFC anodes; 2) 3D reconstruction and results, including development of original computer codes for the determination of active and inactive triple phase boundary density; 3) microstructural characterization of anodes tested for up to 16 kh at 800 °C, 860°C or 925 °C, including qualitative analysis of chemical composition of the anodes using energy dispersive x-ray spectroscopy (EDS); 4) development of kinetic models of microstructural change in SOFCs during operation, based on the quantitative analysis and calculated microstructure parameters for the tested SOFC anodes, to enable predictions of long-term performance of SOFCs. Application of 3D reconstruction to SOFC anodes provided insight to the anode microstructure. The microstructural parameters such as volume fractions, particle diameter, active/inactive triple phase boundary, tortuosity; were calculated for the as-reduced cell and cells after operations. Ni and pore phase re-distribution to the anode interfaces were observed during cell operation. The classic relaxation kinetic model was developed to study the long-term Ni growth and reduction in triple phase boundary.

Committee:

Mark De Guire (Committee Chair); Arthur Heuer (Advisor); James McGuffin-Cawley (Committee Member); M. Cenk Cavusoglu (Committee Member)

Subjects:

Materials Science

Keywords:

Solid Oxide Fuel Cell, SOFC, Anode, 3D Reconstruction, long-term performance prediction, triple phase boundary, performance modeling, tortuosity

Gardner, PaulAerosol Jet Printing of LSCF-CGO Cathode for Solid Oxide Fuel Cells
Master of Science (MS), Wright State University, 2011, Chemistry
Solid oxide fuel cell (SOFC) technology has attracted great attention due to advantages such as low emissions and high efficiency. In this work, solid oxide fuel cells were fabricated by incorporating functional layers deposited by a novel aerosol jet® printing method. The buffer and cathode layers were printed from gadolinium doped ceria (Ce0.9Gd0.1)O1.95 (CGO) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) inks, respectively. The CGO layer was deposited on the sintered electrolyte and then LSCF was subsequently deposited onto the CGO layer. The polarization curves showed a 19% improvement in current density using LSCF as the cathode instead of LSM. Cathode grain size was shown to change by 85% over the sintering temperatures examined. Lastly, the effect that ethyl cellulose additive had on the resulting cathode was determined. It was discovered that the porosity of the microstructure was not correlated to the additive's molecular weight. The actual causes of the cathode porosity may be the order of polymer branching or the ethoxy content of the ethyl cellulose.

Committee:

Eric Fossum, PhD (Advisor); David Grossie, PhD (Committee Chair); Rachel Aga, PhD (Committee Chair)

Subjects:

Chemistry

Keywords:

solid oxide fuel cell; SOFC; LSCF; cathode; LSM; fuel cell; aerosol jet; aerosol jet deposition; aerosol jet deposition technique; Optomec; AJDT;

Cooper, Matthew E.Energy Production from Coal Syngas Containing H2S via Solid Oxide Fuel Cells Utilizing Lanthanum Strontium Vanadate Anodes
Doctor of Philosophy (PhD), Ohio University, 2008, Chemical Engineering (Engineering and Technology)

Lanthanum strontium vanadate (LSV), a perovskite ceramic electrocatalyst suitable for use as a solid oxide fuel cell (SOFC) anode, has shown significant activity toward the selective oxidation of H2S from a fuel stream. With this in mind, the feasibility of a two-stage SOFC reaction process using LSV-based SOFCs as an alternative to H2S sorbents was investigated. A procedure for producing a bilayer LSV anode via an inexpensive screen-printing method was optimized and planar SOFCs utilizing these bilayer LSV anodes were tested under H2, syngas and syngas with H2S environments. Considering LSV/yttria stabilized zirconia (YSZ) bilayer anodes, it was found that the optimum anode thickness of 65 μm at 800°C yields a maximum power density of 5.85 mW/cm2, while at 900°C the optimized anode thickness of 80 μm realizes a maximum power density of 17.96 mW/cm2. Substitution of gadolinium-doped ceria (GDC) for YSZ in the bilayer LSV anode was shown to improve catalytic performance; peak power densities for optimized LSV/GDC-based SOFCs at 800 and 900°C were 16.60 and 34.86 mW/cm2, respectively.

It was demonstrated that all tested LSV-based SOFCs showed little to no performance degradation due to catalytic poisoning when utilizing syngas containing H2S as fuel, corroborating previous results. It was also shown that LSV had poor activity toward CO oxidation either directly or as a water-gas shift catalyst over the tested temperature range. A feasibility study of the aforementioned two-stage SOFC reaction process showed that SO2 found in the exhaust from the LSV-based SOFC caused performance degradation to a Ni-based SOFC, though not to the extent caused by an equal amount of H2S; this finding suggests that SOFCs utilizing LSV/YSZ anodes may indeed offer promise as a method for warm-gas remediation of H2S contained in hydrocarbon fuel streams.

Committee:

David J. Bayless, PhD (Advisor); Michael Prudich, PhD (Committee Member); Howard Dewald, PhD (Committee Member); Daniel Gulino, PhD (Committee Member); Jeffrey Rack, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

lanthanum strontium vanadate (LSV); solid oxide fuel cell (SOFC); coal syngas; H2S; SO2; electrochemical AC impedance spectroscopy (EIS); mathematical modeling

Kaseman, Brian J.An Investigation of Secondary Formations of High Temperature Solid Oxide Fuel Cells
Master of Science (MS), Ohio University, 2012, Mechanical Engineering (Engineering and Technology)

Solid Oxide Fuel Cells (SOFCs) are aimed to operate using coal syngas but the gas may have a negative impact on the component materials. The gas contains impurities such as phosphorus could react with an anode component gadolinia doped ceria (GDC). Nextcells with a Ni-GDC interlayer were operated at 0.7V in coal syngas containing 10 and 20ppm PH3 at 800 and 900°C for 42 hours. The power density reduced by 92% at 800°C when exposed to both PH3 concentrations. Degradation was determined to be caused by ohmic, activation, and concentration polarizations. X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) show the formation of CePO4. It is determined that phosphorus species are detrimental to the Ni-GDC interlayer in accelerated testing.

Additionally, the main components of coal syngas (hydrogen, nitrogen, carbon monoxide, carbon dioxide, and steam) may form secondary phases with the silver (Ag) current collector. SOFCs with anode Ag current collectors were operated in coal syngas at 850°C for 100 hours. XRD did not detect any secondary formations of Ag. Coal syngas is not believed to have an affect on the Ag current collector. The migration of Ag through the scandia stabilized zirconia (ScSZ) electrolyte by electro- and thermomigration was also investigated. SOFCs were operated at 0.7V in H2 at 900°C for 200 hours to activate these migration mechanisms. Secondary Electron Microscope (SEM) showed Ag at the interface but elemental mapping did not detect Ag in the ScSZ electrolyte. It was found that Ag will not short circuit the SOFC in short term testing.

Committee:

David Bayless, PhD (Advisor); Carole Womeldorf, PhD (Committee Member); Ben Stuart, PhD (Committee Member); David Ingram, PhD (Committee Member)

Subjects:

Engineering

Keywords:

SOFC; Syngas; Phosphine; GDC; Ag; Migration

Sinnamon, Ryan R.Analysis of a Fuel Cell Combustor in a Solid Oxide Fuel Cell Hybrid Gas Turbine Power System for Aerospace Application
Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering
Over the last few years, fuel cell technology has significantly advanced and has become a mode of clean power generation for many engineering applications. Currently the dominant application for fuel cell technology is with stationary power generation. Very little has been published for applications on mobile platforms, such as unmanned aerial vehicles. With unmanned aerial vehicles being used more frequently for national defense and reconnaissance, there is a need for a more efficiency, longer endurance power system that can support the increased electrical loads onboard. It has already been proven by others that fuel cell gas turbine hybrid systems can achieve higher system efficiencies at maximum power. The integration of a solid oxide fuel cell combustor with a gas turbine engine has the potential to significantly increase system efficiency at off-design conditions and have a higher energy density compared to traditional heat based systems. This results in abilities to support larger onboard electrical loads and longer mission durations. The majority of unmanned air vehicle mission time is spent during loiter, at part load operation. Increasing part load efficiency significantly increases mission duration and decreases operational costs. These hybrid systems can potentially have lower power degradation at higher altitudes compared to traditional heat based propulsion systems. The purpose of this research was to analyze the performance of a solid oxide fuel cell combustor hybrid gas turbine power system at design and off-design operating conditions at various altitudes. A system level MATLAB/Simulink model has been created to analyze the performance of such a system. The hybrid propulsion system was modeled as an anode-supported solid oxide fuel cell integrated with a commercially-available gas turbine engine used for remote control aircraft. The design point operation of the system was for maximum power at sea-level. A steady-state part load performance analysis was conducted for various loads ranging from 10 = L = 100 percent design load at varying altitudes ranging from 0 = Y = 20,000 feet. This analysis was conducted for four different fuel types: humidified hydrogen, propane, methane, and JP-8 jet fuel. The analysis showed that maximum system efficiency was achieved at loads of 40 = L = 60 percent design load at each altitude and fuel type. The system utilizing methane fuel, internally-steam reformed within the fuel cell, proved to have the highest system efficiency of 46.8 percent (LHV) at a part load of L = 60 percent and an altitude of Y = 20,000 feet.

Committee:

Rory Roberts, Ph.D. (Advisor); Scott Thomas, Ph.D. (Committee Member); Hong Huang, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

SOFC; Fuel Cell; Aerospace; UAV; Hybrid Power System; Unmanned Aircraft;

Perera, Chaminda KithsiriThe Effects of Mercury on the Performance of Ni/YSZ Anode in a Planar Solid Oxide Fuel Cell
Doctor of Philosophy (PhD), Ohio University, 2010, Mechanical Engineering (Engineering and Technology)
This study was made to determine effects of mercury as a contaminant in coal syngas on the performance of a Ni/YSZ anode of a planar solid oxide fuel cell (SOFC). Anode supported SOFCs were operated with Hg-contaminated fuel gas at two different temperatures and at two different gas compositions. Significant modifications to the testing system were made to reduce the effects of stagnation layers. A reliable method of mercury delivery to the cell was designed, calibrated, and implemented prior to testing. A novel technique of area specific resistance (ASR) calculation using electrochemical impedance spectroscopy (EIS) was used, coupled with standard electrochemical techniques. The novel EIS technique for ASR analysis provided a reliable and repeatable method for determining cell degradation. Post-experimental materials analyses using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to determine the effects of mercury on SOFC performance. Electrochemical analyses coupled with material analyses demonstrated that mercury at concentrations as high as 1000 ppb had no discernable effect on normal cell performance. A novel method is proposed for computing cell degradation rate based on cell ASR that is much less current dependent than the present voltage-based method. Recommendations for future work include methods to improve SOFC test systems to obtain more reliable data by removing uncertainties in operational conditions.

Committee:

David Bayless, PhD (Advisor); Ben Stuart, PhD (Committee Member); Greg Kremer, PhD (Committee Member); Gerardine Botte, PhD (Committee Member); Jacqueline Glasgow, PhD (Committee Member); Howard Dewald, PhD (Committee Member)

Subjects:

Chemical Engineering; Energy; Engineering; Mechanical Engineering

Keywords:

SOFC; Coal Syngas; Contaminant; EIS; ASR; Energy

VENKATA, PADMA PRIYAComputational Modeling of Heat and Mass Transfer in Planar SOFC: Effects of Volatile Species/Oxidant Mass Flow Rate and Electrochemical Reaction Rate
MS, University of Cincinnati, 2008, Engineering : Mechanical Engineering
A three dimensional computational model of an intermediate temperature planar, tri-layered solid oxide fuel cell is considered for a steady incompressible fully developed laminar flow in the interconnect ducts of rectangular cross section. A constant supply of volatile species (80% H2 + 20% H2O vapor) and oxidant (20% O2 + 80% N2) is maintained at the electrolyte surface on the anode and cathode side respectively. The governing equations of mass, momentum and energy coupled with the electrochemical species equations are solved computationally. Darcy-Forchheimer model is used to account for the porosity effects of the electrodes where the flow is in thermal equilibrium with the solid matrix. The anode-side triple phase boundary is resolved as a finite region to accurately capture the physics of electrochemical reaction which results in current generation and volumetric heat dissipation. Parametric effects of the interconnect contact design and channel aspect ratio on the variation of thermal-hydrodynamic and electrical performances of the cell are presented. The effect of the flow rate and duct aspect ratio on the area-specific resistance and its subsequent effects on current density, temperature and mass/species distributions, flow friction factor and convective heat transfer coefficient are presented. Interconnect channels of cross-section aspect ratio ~0.5-2.0 and interconnect channel half width of 500 µm are compared for overall electrical and convective cooling performance of the planar anode-supported SOFC.

Committee:

Raj M Manglik, PhD (Advisor); Milind A Jog, PhD (Committee Member); Anastasios P Angelopoulos, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

SOFC; Solid oxide fuel cells; ASR; interconnect; CFD; heat and mass transfer; electrochemistry

Mirzababaei, JelvehnazLSCF Synthesis and Syngas Reactivity over LSCF-modified Ni/YSZ Anode
Master of Science in Engineering, University of Akron, 2011, Chemical Engineering
Simulated coal syngas reactivity over Ni/YSZ and LSCF (La0.6Sr0.4Co0.2Fe0.8)-modified Ni/YSZ anode of SOFC (solid oxide fuel cell) was investigated in this study. The contribution of H2 and CO oxidation to total current density generation was determined from the electrochemical measurement and gas effluent analysis of the SOFC reactor. H2 oxidation was the dominant oxidation reaction over the Ni/YSZ anode reactions. Adding the LSCF on the Ni/YSZ anode increased the rate of CO oxidation, resulting in almost equal rate of H2 and CO oxidation. High oxidation rate of coke over LSCF-Ni/YSZ resulted in low carbon deposition on the anode surface. High oxidation rate of carbon was attributed to the high ionic conductivity of the LSCF which provided large amount of oxygen ions for fast oxidation of coke. LSCF was synthesized through the pechini method by replacing the standard calcination process with rapid combustion. Microstructure analysis, crystallography and resistivity measurement of the synthesized LSCF demonstrated similar properties to those of standard calcined LSCF. This result indicates that rapid combustion is a promising method for substitution of standard calcination process.

Committee:

Steven Chuang, Dr. (Advisor); Bi-min Zhang Newby, Dr. (Committee Member); Gang Cheng, Dr. (Committee Member)

Subjects:

Chemical Engineering

Keywords:

SOFC; LSCF; syngas; anode

Rismanchian, AzadehCopper Nickel Anode for Methane SOFC
Master of Science, University of Akron, 2011, Chemical Engineering

Ni/YSZ anode is a well-studies catalyst in solid oxide fuel cell which works best in hydrogen. Hydrogen does not naturally exist and is produced by steam reforming of hydrocarbon fuels. High operating temperature of solid oxide fuel cells has made them popular for direct oxidation of hydrocarbons. A direct hydrocarbon SOFC will remove the energy losses and complexities of the external reformers but introduces problems such as coking and sulfur poisoning which both lead to anode deactivation.

Anode modification is required to develop a direct hydrocarbon SOFC. Cu electroless plating has been studied as an approach to improve the durability of Ni/YSZ anode both in pure and sulfurous CH4. The first objective of this study was to investigate the effect of Cu concentration on the durability of the Cu electroless plated anode operated in CH4. Two cells with different Cu concentrations were studies under long-term exposure to CH4 for this purpose. The second objective was to investigate the effect of the Cu electroless plated anode on increasing the sulfur tolerance of the Ni/YSZ, while exposed to sulfurous fuel. A Ni/YSZ anode and a Cu electroless plated anode were exposed to mixture of CH4 and SO2 and their performance were compared.

The long-term durability was measured by polarization curves and electrochemical impedance spectroscopy (EIS). The experiments were complemented by post characterization of cells with scanning electron microscopy (SEM), dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF), and X-ray diffraction (XRD). Results of this study showed that Cu electroless plating was successful in increasing the durability of Ni/YSZ anode in CH4 and sulfurous fuels. High Cu concentration on the surface and well diffusion of Cu into Ni/YSZ matrix was required to prevent coking.

Committee:

Steven Chuang (Advisor)

Subjects:

Chemical Engineering

Keywords:

SOFC;electroless plating;coking;sulfur poisoning

Zalar, Frank MModel and theoretical simulation of solid oxide fuel cells
Doctor of Philosophy, The Ohio State University, 2007, Materials Science and Engineering

Solid oxide fuel cells have been investigated frequently with models predicated on linear electrical circuit elements, ignoring finer details of electrochemical transport. To gain better understanding of the operation of solid oxide fuel cells based on their underlying physics, the most simple system of fundamental equations, consistent with solid oxide fuel cell thermodynamics, has been constructed. The system includes the continuity equation for mass/charge transport, the Poisson equation relating electrostatic potential and charge density, and interface flux expressions reflecting activated state processes. The driving force of all transport processes is the electrochemical potential gradient of mobile species. This potential includes entropic interaction and electrostatic energies. Gas phase mass transport was not considered in this work.

The equation system governed calculations simulating various electrical and electro-chemical measurement experiments, specifically: equilibrium open-circuit cell voltage measurement, cell voltage measurement with increasing dc current density, and electrochemical impedance spectroscopy. The 1-D solid oxide fuel cell system investigated is composed of two dense mixed-conducting electrodes and a dense purely ion-conducting electrolyte. Relaxing the system from initial non-equilibrium, the calculated equilibrium cell voltage agreed O(10 −9%) with the theoretical Nernst voltage. Also, non-thermodynamic and non-material parameters did not affect this agreement, validating the thermodynamics of the equation system.

The effects of kinetic and geometric variables on the behavior of the investigated system were clearly observed in both dc current density and electrochemical impedance simulations. As the perturbation amplitude was increased, the onset of nonlinear impedance response was seen.

Committee:

Henk Verweij (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Solid Oxide Fuel Cell; SOFC; Model; Simulation

Davis, Andrew ScottTemperature Induced Deflection of Yttria Stabilized Zirconia Membranes
Master of Science, The Ohio State University, 2012, Mechanical Engineering
Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices capable of producing electrical power with high efficiency and low emissions. SOFCs are characterized by ceramic electrolyte membranes which transport oxide ions in the range of temperatures between 600°C and 1000°C. In order to facilitate efficient, low-range temperature operation the electrolyte is typically made very thin, on the order of 40 µm. SOFCs also employ porous electrodes on either side of the electrolyte which are then placed in contact with current collectors and seals. In the fuel cell environment, with high temperatures, substantial thermal gradients, mechanical loading between layers, as well as the desire to be able to thermally cycle the cell, one of the layers or components must provide mechanical support. It is typical for either the anode or electrolyte to provide the necessary mechanical support. This thesis focuses on an electrolyte that is used for electrolyte-supported SOFC configuration. To address the need for mechanically robust electrolytes, NexTech Materials has developed the FlexCellTM electrolyte. This electrolyte design incorporates 40 µm thick conducting regions in a honeycomb pattern, and surrounding 200 µm thick stability regions. Various experiments on and determinations about this material and design must be made to ensure sufficient mechanical stability during fuel cell operation. Thermal stresses from high temperatures, temporal and spatial temperature gradients, and differential thermal expansion of contacting materials, are critical issues within SOFCs. The critical property related to these issues, coefficient of thermal expansion (CTE), was measured in this work. An apparatus to measure the CTE of the FlexCellTM electrolyte material was designed and implemented. The average CTE of 3 mol% Y2O3-ZrO2 (yttria stabilized zirconia or 3YSZ) was found to increase from 9 µm•m-1•°C-1 between room temperature (RT) and 180°C to nearly 11.5 µm•m-1•°C-1 from RT to about 650°C. A torch heating experiment was performed to study thermal gradients. For 200 µm thick YSZ electrolyte samples it was found that that heating experiment induced a directional dependence into unexpectedly large out-of-plane deflections. Digital image processing was used to capture deflection magnitudes which were compared against two finite element models. The two finite element models differed in how the through-thickness CTE variation was implemented. The first model contained a pseudo-continuous CTE gradient, whereas the second model contained an abrupt surface layer change in CTE. Both models were able to replicate the experimental results, thus pointing to CTE variation as the driving mechanism causing unexpected deflections in the experiments. Literature review and results from X-ray diffraction led to the conclusion that the tetragonal to monoclinic phase change in YSZ is the most likely reason for CTE change. It is proposed that the combination of heating and the initial tensile strain field are the root cause of this transformation.

Committee:

Dr. Mark E. Walter (Advisor); Dr. Brian D. Harper (Committee Member)

Subjects:

Materials Science; Mechanical Engineering

Keywords:

SOFC; Solid Oxide Fuel Cell; CTE; Coefficient of thermal expansion; YSZ; phase

McCoppin, Jared RayFabrication and Analysis of Compositionally Graded Functional Layers for Solid Oxide Fuel Cells
Master of Science in Engineering (MSEgr), Wright State University, 2010, Materials Science and Engineering
Solid Oxide Fuel Cell (SOFC) structures must be optimized for high performance, increased life, and low cost. Fabrication methods are an area of research interest in bringing down the total cost of SOFCs, and can also impact cell life and performance. Graded functional layers have been shown to enhance cell performance, but current fabrication methods require multiple fabrication steps. This thesis describes a novel fabrication method capable of compositional gradation of functional layers for SOFCs. Using colloidal spray deposition technology, a controlled co-deposition strategy was utilized to fabricate SOFC's with compositionally graded cathode and anode functional layers (CGCFL/CGAFL). In this research, compositionally graded CGCFL/CGAFL SOFCs were tested and analyzed using current-voltage measurements and energy impedance spectroscopy methods. Scanning electron microscopy and elemental mapping were utilized for structural characterization. The fabrication technique presented in this thesis allows for the rapid and precise, single-step deposition of a compositionally graded SOFC interlayer, and should facilitate the optimization of SOFC stack designs.

Committee:

Daniel Young, PhD (Advisor); Daniel Young, PhD (Committee Chair); Hong Huang, PhD (Committee Member); Sharmila Mukhopadhyay, PhD (Committee Member); Thomas Reitz, PhD (Committee Member)

Subjects:

Alternative Energy

Keywords:

SOFC; Soild Oxide Fuel Cell; Graded Functional Layer

Fisher, James CA Novel Fuel Cell Anode Catalyst, Perovskite LSCF: Compared in a Fuel Cell Anode and Tubular Reactor
Master of Science, University of Akron, 2006, Chemical Engineering
The development of solid oxide fuel cells (SOFCs) has attracted research interest the recently due to an increasing concern on the depletion of available crude oil reserves and environmental issues such as global warming and emission of pollution. SOFCs have received special attention because of their higher energy efficiency, rapid electrode kinetics without using expensive electro-catalysts such as platinum, relative resistance to impurities in the fuel and the ability to use hydrocarbons as fuel. Research efforts have resulted in the development of traditional SOFC materials such as zirconia electrolytes stabilized with various metals, lanthanum doped strontium (LSM) cathodes and Ni-YSZ cermet anodes. Nickel has disadvantages when applied as an anode catalyst and operated with hydrocarbon fuels. The most significant problems are deactivation through coking, long term sintering and sulfur poisoning. The perovskite lanthanum strontium cobalt iron oxide (LSCF) was used as a fuel cell anode; LSCF is a common cathode material. LSCF has been shown by previous research to be resistant to coking, resistant to sulfur poisoning and structurally stable at high temperatures. Perovskites are electronically conductive, like nickel, and are also conductive of oxygen ions. This is allows an extension on the three phase boundary, where the fuel, electron and ions meet and the reaction occurs. Due to the complexity of fabricating and producing a functioning SOFC, traditionally minimal research was done on the catalyst in the fuel cell. A large amount of catalysis research has been done a various catalyst in a tubular reactor that emulates a fuel cell anode, but there is no research to test the validity of this data and its usefulness in relation to a SOFC. A comparison of LSCF as the fuel cell anode and in a tubular reactor was done to further understand the advantages and disadvantages of tubular reactors that emulate SOFC conditions. This study involves developing a functional SOFC that yields respectable results using LSCF as the anode. The results of this study demonstrate the possibility of using the same material on both the cathode and anode reducing complexity of the SOFC and potentially reducing manufacturing costs. This can eliminate the need for cleaning sulfur from fuel and other contaminates from the fuel as shown by utilizing industrial propane as fuel. The tubular reactor study has shown that some results in the SOFC maybe simulated in simple and quick testing system; reducing the time to test a catalyst from 1 month in a tradition SOFC to 1 day in a tubular reactor. Future studies should include testing other perovskite catalyst on the anode or adding promoters to the LSCF. Coking was observed in the SOFC, studies on how to prevent this and the damage done by coking should be considered. More catalysts need to be tested in the tubular reactor and related to its performance in a SOFC anode to make a substantial conclusion that a catalyst’s behavior in a SOFC can be accurately emulated. Future studies should also focus on the effects of electron and/or ion charge that occurs in the SOFC, how it effects the electro-catalytic properties of the catalyst and if it can be emulated in the tubular reactor should be evaluated.

Committee:

Steven Chuang (Advisor)

Subjects:

Engineering, Chemical

Keywords:

LSCF; SOFC; double cathode; perovskite anode; LSCF anode

Choi, HyunkyuPerovskite-type oxide material as electro-catalysts for solid oxide fuel cells
Doctor of Philosophy, The Ohio State University, 2012, Chemical and Biomolecular Engineering
Solid oxide fuel cells (SOFCs) are one of the most promising energy conversion devices for the next generation. This is mainly a result of the low emission of environmental hazardous species associated with SOFC’s, high fuel conversion efficiency, and fuel flexibility. However, current ‘state-of-the art’ catalysts used in SOFCs are suffering from several drawbacks that encumber a commercial application of SOFCs in the direct conversion of hydrocarbons. In this application, high operating temperatures are required due to low oxygen reduction reaction (ORR) activity at the cathode, which limits the use of less expensive materials. In addition, ‘state of the art’ anode catalysts are very susceptible to sulfur poisoning and carbon depositions when it is operated with carbonaceous fuels. Since SOFCs aim to use the relatively abundant fuel sources, such as coal-derived syngas and natural gas, high activity and stable catalysts are required. Therefore, the need in developing and testing new catalysts formulations for both cathode and anode catalysts are crucial. The current research aims to find solutions for these problems through development of novel electro-catalysts based on perovskite materials. The objective is to develop perovskite materials which are capable of enhancing ORR activity as well as possessing a high tolerance to sulfur poisoning and carbon laydown. New formulations of cerium-doped perovskite material were synthesized with varying concentrations of cerium. The bulk structure, oxygen mobility, and electro-catalytic performance of the catalysts were examined using in-situ X-ray diffraction (XRD), oxygen temperature-programmed desorption (O2-TPD), X-ray absorption fine structure (XAFS), CO2 temperature programmed oxidation (TPO) and button cell/impedance measurements. Cerium-doped perovskites exhibit a cubic structure at room temperature and no apparent structural changes were observed with increasing temperature. An additional CeO2 phase was observed when cerium concentration exceeded 15% in the A-site of perovskite. Thermal compatibility of the catalyst gets closer to that of galdolinia-doped ceria (GDC) electrolyte by addition of cerium. Oxidation states of both Fe and Co were shown to be very close to their valence state with different cerium dopant levels at room temperature, indicating that the charge imbalance is compensated by the creation of oxygen vacancies. The oxygen vacancy was generated mainly from the reduction of Co where the Fe contribution was minimal. It was observed that the oxygen vacancy generation was inversely proportional to the dopant level of Ce. However, the electrocatalytic activity showed that the intermediate concentration of Ce doping has the best unit cell performance, which suggests that the secondary ceria phase at higher cerium dopant levels has a detrimental effect on the performance. The trend of the unit cell performance followed the CO2-TPO experiment results and found to be a good probe for button cell performance. On the anode side, the structural stability of the new formulations was examined under anodic conditions. As the temperature was raised the catalyst with lower cerium loadings changed from its initial cubic structure to a lower symmetry structure while the higher loading cerium samples remained in the original cubic structure. The catalytic activity of cerium-doped catalysts for the methane oxidation showed fairly matched to that of state of the art anode Ni-YSZ catalyst. The sulfur tolerance was significantly enhanced with cerium-doped perovskites showing no deactivation up to 10 hrs of operation while Ni-YSZ catalysts deactivated almost immediately upon introduction of H2S. Surface analysis using XPS on poisoned samples showed that the sulfur exists as strontium sulfate where no significant changes for the transition metals, which are critical for oxidation catalytic activity, were observed. The button cell performance of intermediate cerium-loading catalyst matched to that of Ni-YSZ, while the highest cerium-loading samples showed lower performance due to the presence of secondary phase (CeO2). Lowest cerium-loading showed instability issues during the performance test. Therefore, the catalyst with intermediate cerium-loading catalyst is suitable for the anode catalyst.

Committee:

Umit Ozkan, PhD (Advisor); Jeffrey Chalmers, PhD (Committee Member); Andre Palmer, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

SOFC; perovskite; anode; cathode

Fisher, James C.The Reduction of CO2 Emissions Via CO2 Capture and Solid Oxide Fuel Cells
Doctor of Philosophy, University of Akron, 2009, Chemical Engineering

The increase in CO2 emissions over past decades are the result of a growing dependence on fossil fuels. Examination of CO2 emission sources revealed that more than 33% of global CO2 emissions result from coal-fired power plants, which represent the largest stationary source of CO2. Two proposed approaches for reduction of CO2 emissions: (i) a short term (i.e. 7-10 years) capture of CO2 from coal-fired power plants and (ii) a long term (i.e. 10-15 years) approach is the replacement of coal-fired power plants by coal-based fuel cells. These approaches purify CO2 for sequestration. Carbon capture from existing power plants could be accomplished by passing the flue gas through a sorbent. The sorbent captures the CO2 from the flue gas then regenerated producing purified CO2. Direct coal fuel cells directly convert coal to electricity through the electrochemical oxidation of carbon. The mixing of air and coal does not occur in the fuel cell, leading to highly concentrated CO2 effluent for sequestration.

CO2 capture was investigated by transient flow, bed temperature measurement, and temperature programmed CO2 desorption coupled with IR effluent measurement of seventeen sorbents, which had SiO2, carbon, or beta zeolite as a support. The heat released during the exothermic adsorption of CO2 onto amine resulted in a bed temperature rise. The heat generated could be dissipated with a smaller particle size and greater thermal conductivity. The heat released was used to verify the capture capacity using a thermal camera and high throughput adsorber that screened thirteen sorbents simultaneously. The carbon initially investigated produced an ammonia odor and had a low capture capacity. The ammonia odor was the result of acid-base interaction between the support and amine groups. The use of a neutral carbon increased the capture capacity to 2.8 mmol CO2/g-sorbent. Beta zeolite, which captures 1.8 mmol CO2/g-sorbent, was found to contain acid sites that lowered the capture capacity. Molecular probing with benzene indicated a reduction of acidic sites with basic NH3 treatment and the reduction of surface –OH groups with basic NH4OH treatment. Beat zeolite treatment with NH3 and NH4OH resulted in a capture capacity of 2.0 and 2.2 mmol CO2/g-sorbent, respectively. Further DRIFTS IR investigation showed the amine interacted with the –OH groups of beta zeolite. Adsorption of CO2 formed carbonates, which may utilized the O atom from the interaction of the amine and support. The carbonate formation profile was parallel to H-bonding indicating adsorbed CO2 had a dual-interaction where a carbonate and H-bond was formed. This dual interaction may have inhibited gas and adsorbed phase CO2 exchange observed on metal surfaces.

LSCF was investigated as an anode material for a direct CH4 solid oxide fuel cell (SOFC) through unsteady state response coupled with mass spectrometer analysis. Comparison of a Ni anode and LSCF/Ni anode was done to determine if LSCF promoted the electrochemical oxidation of carbon. The introduction of 50% CH4 into the LSCF/Ni anode SOFC produced a greater amount of CO than the Ni anode, indicating the LSCF increased the initial intrinsic rate of carbon oxidation. The H2 and CO profile produced by the LSCF/Ni anode lacked a parallel structure indicating different reaction pathways. Current-voltage measurement over LSCF/Ni during 50% CH4 led to a higher formation of CO than that of the Ni anode, confirming a high intrinsic rate of formation. Removal of CH4 from the Ni anode resulted in a rapid drop in current; removal of CH4 from the LSCF/Ni anode resulted in a slow decrease in current and the formation of CO and CO2. The formation of CO2 on the LSCF/Ni anode suggests the presences H2 and CH4 inhibit the electrochemical oxidation of carbon to CO2. The formation of CO2 over the LSCF/Ni anode indicates LSCF ability to completely electrochemically oxidize carbon, which was not observed on the Ni anode. Structural degradation led to failure the Ni anode cell after 0.5 hours of pure CH4 operation and after 2 hours on the LSCF/Ni anode. These results suggest LSCF promotes the electrochemical oxidation of carbon resulting in a lower intrinsic rate of formation of coke in the Ni/LSCF SOFC.

Committee:

Steven S.C. Chuang, PhD (Advisor)

Subjects:

Chemical Engineering; Energy; Environmental Engineering

Keywords:

TEPA; solid sorbent; LSCF; SOFC; solid oxide fuel cell; CO2 capture; carbon capture

Siengchum, TrittiElectrochemical Oxidation of Methane on Ni-Doped Perovskite Anode Solid Oxide Fuel Cell
Master of Science, University of Akron, 2009, Chemical Engineering

The operating temperature of a solid oxide fuel cell (SOFC) is generally between 600 and 1000 °C. With the high operating temperature, SOFC has an advantage of fuel flexibility by being tolerant to CO. Another advantage is that the process of steam reforming hydrocarbons, which is preferable for most applications, can be sustained at the SOFC operating temperature. However, steam reforming has several disadvantages, such as diluting fuel and adding to system cost. On the other hand, the direct electrochemical oxidation of CH4 on SOFC has been investigated as a potential of commercialization due to inexpensive cost of natural gas and coal. The most commonly used anode material is a mixture of Ni and yttria-stabilized zirconia (YSZ), which exhibits excellent catalytic properties for fuel oxidation and current collection. As Ni is a good catalyst for hydrocarbon cracking, this anode cannot be utilized in direct hydrocarbon fuel because of carbon deposition or coking. In order to overcome the disadvantages, Ni-doped perovskites have been studied as potential anodes for SOFC.

In this study, the development of Ni-doped perovskites was addressed by two approaches. The first objective of this study is to develop a method to synthesis La0.8Sr0.2CoO3 (LSC) or La0.8Sr0.2Co0.4Fe0.6O3 (LSCF) perovskite in a SOFC anode operating environment. This objective aims to shorten the time and reduce energy consumption of the perovskite preparation process. The objective will be achieved through an infiltration of the solution containing LSC or LSCF nitrate precursors onto Ni/YSZ anode.

The second objective is to modify a Ni/YSZ anode with LSCF perovskite to prevent coking in a direct CH4 SOFC. LSCF is a good O2- and electronic conducting material, which has been widely used for hydrocarbon oxidation reaction catalyst. Those properties are strongly desired in a direct CH4 SOFC. This objective will be achieved through screen printing of LSCF onto the surface of Ni/YSZ anode. The resulted SOFC will then be tested in a direct CH4 experiment which an electrochemical performance will be monitored.

Results of this study showed that the infiltration of LSC or LSCF nitrate precursor solutions on the anode did not increase electrochemical performance of the SOFC. The characterization results from X-ray diffraction indicated that LSC or LSCF perovskite were not obtained from the electrochemical oxidation at 800°C. The degradation of SOFC was studied for the second objective. Mechanical failure of the SOFC with modified anode by LSCF/YSZ was not observed after 120 minutes of pure CH4 exposure at 800°C whereas the baseline Ni/YSZ fuel cell deactivated after 20 minutes. This result indicated significant improvement on the structural stability.

Committee:

Steven Chuang (Advisor)

Subjects:

Chemical Engineering; Energy

Keywords:

SOFC; methane; fuel cell; LSCF; LSC; perovskite; anode support

Bozeman, Joe FrankSULFUR-TOLERANT CATALYST FOR THE SOLID OXIDE FUEL CELL
Master of Science in Engineering (MSEgr), Wright State University, 2010, Renewable and Clean Energy
JP-8 fuel is easily accessible, transportable, and has hydrogen content essential to solid oxide fuel cell (SOFC) operation. However, this syngas has sulfur content which results in a poisonous hydrogen sulfide that degrades electrochemical activity and causes complete SOFC failure in some cases. The goal is to synthesize and verify a cost-effective, catalyst supported on cerium oxide that either stabilizes ionic conductivity in the presence of hydrogen sulfide and/or is highly sulfur-resistant. After thorough computational analysis, it was concluded that the platinum-copper skin catalyst was the most cost-effective, sulfur-resistant catalyst. Experimental synthesis of copper, platinum, and platinum-copper skin catalysts supported on cerium oxide was verified. Further experimentation must be performed to establish the platinum-copper skin catalyst supported on cerium oxide operational affects on the SOFC system in a sulfur environment.

Committee:

Hong Huang, Ph.D. (Advisor); Ruby Mawasha, Ph.D. (Committee Member); Allen Jackson, Ph.D. (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Materials Science

Keywords:

SOFC; fuel cell; sulfur resistant; sulfur tolerance; catalyst; gaussian

Allen, Jeremy L.The Effect of Baffle Arrangements on Flow Uniformity in a Manifold for a Unique Solid Oxide Fuel Cell Stack Design
Master of Science (MS), Ohio University, 2011, Mechanical Engineering (Engineering and Technology)
Flow uniformity through channels of a complex fuel cell stack is studied for several baffle arrangements using ANSYS Fluent, a computational fluid dynamics (CFD) package. Flow mal-distribution occurs from pressure differentials throughout the flow structure and causes a drop in stack performance. Three baffle arrangements were introduced into the flow structure and compared to a control case with no baffle in an attempt to improve the flow regime. A flow uniformity coefficient Γ was introduced to compare results from case to case. It was found that all three arrangements significantly increased flow uniformity, with the slotted baffle arrangement providing the most uniform flow. By increasing flow uniformity, the efficiency of the stack is also increased.

Committee:

David Bayless (Advisor); Gregory Kremer (Committee Member); John Cotton (Committee Member); Greg Van Patten (Committee Member)

Subjects:

Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

SOFC; fuel cell; Simulation; CFD; ANSYS Fluent; manifold; baffle; uniform flow

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