bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Highly Robust, Volume-Manufacturable Metal-Supported SOFCs for Operation Below 600°
Authors: Leah Robert T. , Bone Adam , Selcuk Ahmet , Corcoran Derek , Lankin Mike , Dehaney-Steven Zachary , Selby Mark , Whalen Phil
Published: April 2011

Ceres Power has been developing fuel cell stacks and mCHP systems based on its unique metal-supported SOFC design incorporating a Gadolinia-doped ceria (CGO) electrolyte operating in the 450-600°C temperature range. The present generation of cells being manufactured are designed to meet the commercial requirements for a wall mounted, natural gas fuelled mCHP product, producing an average of 140mWcm-2 at 0.75V/cell at 570°C and 60% fuel utilization, operating on steam-reformed natural gas. Open-circuit voltages are around 1.10V operating on hydrogen/nitrogen; close to theoretical values indicating the effective suppression of internal short-circuits. The unique metal supported design facilitates simple and robust hermetic sealing of the cell to the interconnect by welding, and layer-to layer sealing and isolation is achieved using a commercial gasket material, thus largely eliminating degradation due to thermal stress induced seal leakage found in conventional planar SOFC designs.
Development of Long-Term Stable and High-Performing Metal-Supported SOFCs
Authors: Klemenso̸ Trine , Nielsen Jimmi , Blennow Peter , Persson Asa , Stegk Tobias , Hjalmarsson Per , Christensen Bjarke , So̸nderby Steffen , Hjelm Johan , Ramousse Severine
Published: April 2011

Metal-supported SOFCs are believed to have high potential for commercialization due to lower material costs and higher robustness in fabrication and operation. However, the development of the cell is challenged by the metal properties during fabrication, and the necessary lower operating temperatures, while retaining both the energy output and the stability. The metal-supported SOFC design developed at Riso̸ DTU has been optimized to an ASR value of 0.62 Ωcm2 at 650 °C, and a steady degradation rate of 1.0% kh-1 demonstrated for 3000 h on a 16 cm2 active cell level. Additional improvement in the performance has been demonstrated possible with cobalt-based cathode materials in combination with a magnetron sputtered CGO cathode barrier layer. Initial ASR values down to 0.27 Ωcm2 at 650 °C and power densities up to 1.14 Wcm-2 was observed with this design on a 0.5 cm2 active cell level.
NexTech's FlexCell Technology for Planar SOFC Stacks
Authors: Day Michael , Swartz Scott L. , Arkenberg Gene
Published: April 2011

NexTech Materials is developing solid oxide fuel cell stacks based on its patent-pending FlexCell™ design. The FlexCell is an electrolyte-supported planar cell with unique characteristics that enable high electrochemical performance and long term durability. Demonstrated attributes of NexTech's FlexCell include scalability to large areas and tolerance to high levels of sulfur impurities in fuel. NexTech is building and testing stacks with power outputs in the 1-10 kW range, and has demonstrated that these stacks deliver targeted power outputs at high voltage and high fuel utilization.
2R-Cell: A Universal Cell for an Easy and Safe SOFC Operation
Authors: Ihringer Raphaël
Published: April 2011

Thank to their high power density in a wide range of temperature, anode supported thin film electrolytes are nowadays the mostly used cells in the SOFC area. Unfortunately, the latter suffer from an important problem: they are totally destroyed when re-oxidation occurs in the anode chamber. This happens, for instance when fuel supply inappropriately stops. Cell peripheral re-oxidation is another well known figure where failures are initiated. In all cases, when re-oxidation starts, the stack quickly undergoes a fatal destruction and the SOFC system definitely falls down. Fiaxell Sàrl, a new company active in the SOFC area has developed and is now offering a novel anode supported thin electrolyte, made with standard NiO-ZrO2 material, the 2R-Cell that provides robustness and reliability upon multi thermo and redox-cycles. Such cells have now demonstrated for thousands of cumulated hours that they withstand full redox-cycles without any failure in the anode substrate neither in the thin electrolyte as described with pictures. This paper presents the electrochemical behaviour of such cells, tested over 1700 hours and 16 full redox cycles in a short stack at Hexis AG (CH). No performance degradation could be measured from the last redox-cycle till the end of the test, 800 hours later. 2R-Cell of 6 (cm) in diameter and with cathode of 3.7 (cm) have been tested in POX simulation in the open flanges test set-up with Crofer interconnect. Without any sealing, a power density of 225 (mW/cm2) could be achieved with an electrical efficiency of 39.8 (%).
Development of an All Ceramic SOFC
Authors: Wærnhus Ivar , Vik Arild , Ilea Crina Silva , Faaland Sonia
Published: April 2011

High temperature SOFC with operation temperature from 800 - 1000oC is suitable for high efficiency fuel cell systems based on heat integration with other technologies, such as SOFC-GT, gasification or hydrogen production. This requires alternatives to the commonly used metallic interconnects. Prototech is currently developing an all ceramic SOFC suitable for operation in this temperature region in larger systems with heat integration.
Improved Redox and Thermal Cycling Resistant Tubular Ceramic Fuel Cells
Authors: Hanifi Amir R. , Torabi Alireza , Zazulak Mark , Etsell Thomas H. , Yamarte Luis , Sarkar Partha , Tucker Michael
Published: April 2011

A new generation of tubular SOFCs with an approach to solve the thermal and redox cycling issues of these fuel cells is introduced and the method of fabrication is explained. The cell consists of a porous support coated with a thin electrolyte. Following porous support infiltration of Ni-SDC to create the anode, 100 thermal and 10 redox cycling tests were carried out. The cell shows extremely high failure resistance to the thermal and redox cycling as confirmed by unaltered OCV values. SEM analysis shows a crack free anode microstructure and electrolyte.
Tubular Metal Support Solid Oxide Fuel Cell Manufacturing and Characterization
Authors: Rodriguez-Martinez Lide M. , Rivas Mikel , Otaegi Laida , Gomez Nuria , Alvarez Mario Alberto , Sarasketa-Zabala Elixabet , Manzanedo Jaio , Burgos Nerea , Castro Francisco , Laresgoiti Ander , Villarreal Igor
Published: April 2011

Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. The most significant results to date include successful thermal cycling of the cell and anodic connection during 450 cycles and 2000 hours, oxidation testing of the metal support for more than 2500 hours and a comparison of influence of porosity during 100 hours oxidation of metal porous substrates under high water vapour atmospheres.
Ultra-Low Mass Planar SOFC Design
Authors: Badding Michael , Bouton William , Brown Jacqueline , Kester Lanrik , Pollard Scott , Tanner Cameron W. , Tepesch Patrick
Published: April 2011

This work describes Corning Incorporated's early stage efforts to develop an ultra-low mass SOFC design based on a "frit-frame." In this approach, patterned glass or glass-ceramic frit layers perform sealing, manifolding and framing functions without the aid of conventional supporting framing components. In this construction, thermal expansion matching is simplified and thermal mass mismatches are minimized. Consequently planar frit-frame structures can be thermally cycled at comparatively fast rates for SOFC. We show that 12 cm x 15 cm multi-cell packets survive multiple thermal cycles with heating to operating temperature in ten-minutes.
Thin Film Low Temperature Solid Oxide Fuel Cell (LTSOFC) by Reactive Spray Deposition Technology (RSDT)
Authors: Maric Radenka , Furusaki K , Nishijima Dai , Neagu Roberto
Published: April 2011

The present work describes the effect on the performance of a SOFC when a Gd0.2Ce0.8O1.9 (GDC) layer has been introduced as diffusion barrier layer between the yttria stabilized zirconia (YSZ) electrolyte and the La0.6Sr0.4Co1-xFexO3-δ (LSCF) cathode of an anode supported cell with a Ni-YSZ anode. The dense, thin and fully crystalline GDC films were directly applied by RSDT, without any post-deposition heating or sintering steps. The quality of the film and performance of the cell prepared by Reactive Spray Deposition Technology (RSDT) was compared to a GDC blocking layer deposited by screen printing (SP) and then sintered at 1000 oC. By applying RSDT to deposit the GDC- barrier layer onto the YSZ electrolyte a lower ohmic resistance has been obtained for the RSDT deposited cell vs. the SP cell. The lower resistance can be attributed to the well crystallized, thin and dense GDC layer deposited at 900 oC.
Accelerated Degradation by Impurities for Evaluating Life Time of SOFCs
Authors: Horita Teruhisa , Kishimoto Haruo , Yamaji Katsuhiko , Brito Manuel E. , Shimonosono Taro , Cho Do-Hyong , Izuki Manabu , Wang FangFang , Yokokawa Harumi
Published: April 2011

The accelerated degradation by impurities was investigated at cathodes with flowing CrO3 and SO2 gases. Relatively high pressures (p~10-8-10-4 atm) of CrO3 and SO2 were applied to the cathodes and the degradation behaviors were investigated as a function of operation time. The degradation mechanism was examined by considering chemical reactivity and electrochemical reaction at the active cathode/electrolyte interfaces. In the case of CrO3 poisoning, the relationship between the deposited Cr2O3 amounts and degradation rates of cathode performance was different with cathode materials and polarization. In the case of SO2 poisoning, the chemical reactivity of cathodes changed the performance by forming the Sr-Sulfate on the surface. The accelerated degradation enabled us to estimate the life time of cathode within a short period of time.
Evaluation of Stress Conditions in Operated Anode Supported Type Cells Based on In-Situ Raman Scattering Spectroscopy
Authors: Nagai Masafumi , Iguchi Fumitada , Onodera Syo , Sata Noriko , Kawada Tatsuya , Yugami Hiroo
Published: April 2011

We develop the evaluation method of stress conditions in operated SOFC based on in-situ raman scattering spectroscopy. This method uses F2g vibration mode of CeO2 in interlayer of anode supported type SOFC as a probe, and we can calculate stress in an interlayer, i.e. stress in an electrolyte from the shift of a raman peak. We apply this method to typical anode supported type cells and evaluate stress conditions during operation. Using this method, stress conditions in the electrolyte before operation is evaluated to be compressive, consistent with XRD and literature. During operation, stress conditions were changed by the reduction of NiO to Ni. The compressive stress was decreased. In addition, the standard deviation of stress becomes larger than before reduction, and nonreversible. Those results indicate that compressive residual stress introduced into the electrolyte during fabrication process is relaxed, and suggest that an electrolyte become mechanically unstable during operation.
Fractal Current Distribution Structures for Thin Electrolyte Supported Fuel Cells
Authors: Tanner Cameron W. , Work Kim L.
Published: April 2011

The performance of electrochemical devices like fuel cells is strongly affected by the transport of electrons between interconnects and active regions of an electrode. We examine the use of an auxiliary, precious metal current distributor placed over the cathode of a solid oxide fuel cell to supplement the transport process. Cell resistance was minimized by computer modeling as a function of the shape of the structure under the constraint that its total volume is fixed. The optimal shapes are shown to be fractals that resemble structures found in nature. A thin fractal current distribution structure made from platinum was demonstrated to facilitate the transport process in oxygen pump cells constructed from porous lanthanum strontium manganite (LSM) - yttria-stabilized zirconia (YSZ) composite electrodes on a 15 µm thick tape of 3 mol percent YSZ.
Development of Planar Solid Oxide Fuel Cell in Niroo Research Institute, Iran
Authors: Mohebbi Hamed , Raoufi Arman , Ghobadzadeh Amir H. , Aslannejad Hamed , Mahmoodi Reza , Azarian Iman , Shiva Molud
Published: April 2011

SOFC single cell was fabricated by using two simple and most frequently methods: tape casting and screen printing. Anodic and anodic active layer was made by tape casting method and screen printing method was used to fabricate electrolyte and cathode layer. Properties and performance of the cell were examined and compared with commercial cells. Results showed that fabricated cell has good properties and its performance is comparable with commercial one.
Fabrication and Development of Perovskite Anode Supported Planar SOFCs
Authors: Tesfai Alem T. , Savaniu Cristian , Irvine John T.
Published: April 2011

Anode supported A-site deficient Lax-Sr1-1.5x TiO3 has been developed. In this study, 5 x 5 cm planar SOFC, which consisted anode current collector (140 μm of NiO tape), anode supported planar fuel cell (A-site deficient Lax-Sr1-1.5x TiO3 1200 μm), electrolyte (YSZ, 15 μm), and cathode (La0.6Sr0.4CoO3, 30 μm) has been developed and tested. The contacting studies were carried out using pressure detection film. Compressibility of different thickness alumina felt gaskets was investigated at different torque compression force. Appropriate gasket thickness were selected to achieve sufficient sealing and contact pressure. To validate the test facility, commercially available H.C.Starck ASC3 standard 5cm x 5cm anode supported planar fuel cells, a total output power of 2.1W (0.125Wcm−2) was achieved at 850 °C, with 0.97V of open circuit voltage and ohmic resistance (Rohm) of 0.8 Ω cm2 and the polarization resistance (Rp) of 1.16 Ω cm2. Initial data produced with A-site deficient Lax-Sr1-1.5x TiO3 in the same test configuration has shown total resistance of 3.12 Ω cm2.
SOFC Material and Stack Characterization Tests for Micro-CHP Application
Authors: McPhail Stephen , Padella Franco , Cinti Giovanni , Discepoli Gabriele
Published: April 2011

In the present work preliminary characterization tests, finalized to application as a residential micro-CHP system, are reported. Through systematic, parallel testing under predetermined conditions, laboratories at ENEA and the University of Perugia aim at establishing the real lifetime expectancy and performance characteristic of 1 kW-class SOFC stacks fed with natural gas from the grid, downstream of a specifically developed desulphurizer for the abatement of odorants. Through the assessment of material response and delivered power also at single cell level, it will be possible to establish and improve the behaviour in time of a SOFC system operated under realistic conditions. There is continuous feedback with both the system optimization engineers as with powder development chemists, in order to bring the concept swiftly and efficiently to market maturity, as well as prepare the basis for second generation systems with improved stack performance and durability.
Current-Voltage Relationship Considering Electrode Degradation Using Sm-Doped Ceria Electrolytes in SOFCs
Authors: Miyashita Tomofumi
Published: April 2011

Numerous efforts have been made to solve the basic transport equation that describes a solid-oxide fuel cell (SOFC) with mixed ionic and electronic conductors (MIECs). Classically, the open circuit voltage (OCV) is calculated with Wagner's equation. The current (I) - voltage (V) relationship is calculated using the model of Choudhury and Patterson. The Riess model is the most famous for accounting for polarization voltage losses using Sm-doped ceria electrolyte (SDC). Furthermore, the model of Wachsman is used without the constant field approximation. However, every electrode degrades with time. Thus, an I-V calculation considering electrode degradation using SDC electrolytes is described in this report. This model is successful in treating electrode degradation with time. However, the OCV should change with time using this model, though it remains unchanged experimentally.
Challenges Of Thin Layers For SOFC Devices: From Low-Cost Chemical Bath Deposition (CBD) to Atomic Layer Deposition (ALD)
Authors: Medina-Lott Bianca , Tassé Marine , Brahim C. , Ringuedé Armelle , Niinistö Lauri , Cassir Michel
Published: April 2011

Nowadays, it is clear that thin layers play a fundamental role in the development of a new generation of SOFC (solid oxide fuel cell) and more specifically when operating at lower temperatures ≤ 700°C. According to the role and specification of the thin layers, different deposition techniques can be adopted. A relatively sophisticated technique, Atomic Layer Deposition (ALD) and a cheaper one, Chemical Bath Deposition (CBD), are presented and compared in the specific case of thin layers of yttria-doped ceria (YDC) which can play the role of electrolyte, interfacial layer or catalyst in SOFC devices. High-quality ALD-processed YDC thin layers, with interesting properties, are obtained. The feasibility of YDC thin layers is evidenced by CBD, but further optimization is required for obtaining deposits more adherent and without cracks.
Performance of Anode Microstructure Controlled Ni-ScSZ/LSGM/LSCF-Ag SOFCs by Low Temperature Fabrication Process
Authors: Endo Yoichi , Sasaki Kazuya , Suzuki Akihiro , Terai Takayuki
Published: April 2011

An anode microstructure controlled solid oxide fuel cell was successfully fabricated by low temperature process and the maximum power density of the cell was 33mW/cm2 at 600 degree C. The LSGM electrolyte thin film was available by post-annealing at 1000 degree C after deposition using radio frequency magnetron sputtering. Thus, the sintering temperature of the anode support could be reduced. The porosity and the diameter of Ni and ScSZ particles were 55% and 0.23 μm and 0.14 μm when the anode support was fabricated by sintering at 1100 degree C and adding 10 wt. % of the pore former. The wider area of three phase boundary is obtained by the low temperature process.
Evaluation of Fuel Cell Performance and Degradation
Authors: Williams Mark , Gemmen Randall , Richards G.
Published: April 2011

The concepts of area specific resistance (ASR) and degradation are developed for different fuel cell operating modes. The concepts of exergetic efficiency and entropy production were applied to ASR and degradation. It is shown that exergetic efficiency is a time-dependent function useful describing the thermal efficiency of a fuel cell and the change in thermal efficiency of a degrading fuel cell. Entropy production was evaluated for the cases of constant voltage operation and constant current operation of the fuel cell for a fuel cell undergoing ohmic degradation. It was discovered that the Gaussian hypergeometric function describes the cumulative entropy and electrical work produced by fuel cells operating at constant voltage. The Gaussian hypergeometric function is found in many applications in modern physics. This paper builds from and is an extension of several papers recently published by the authors in the Journal of The Electrochemical Society (ECS), ECS Transactions, Journal of Power Sources, and the Journal of Fuel Cell Science and Technology.
La0.4Sr0.6Co0.8Fe0.2O3-δ / Ce0.9Gd0.1O2-δ Interface: Characterization by High Resolution SEM and TEM
Authors: Soldati Analia L. , Baqué Laura , Troiani Horacio , Cotaro Carlos , Schreiber Anja , Caneiro Alberto , Serquis Adriana
Published: April 2011

In this work we successfully applied a FIB/lift-out technique to prepare site-specific thin samples containing the cathode/electrolyte interface between two La0.4Sr0.6Co0.8Fe0.2O3-δ (LSCF) / Ce0.9Gd0.1O2-δ (CGO) half cells. Despite different cathode thickness (15 μm and a 5 μm), both samples presented similar composition and nanostructure. However, an exhaustive microscopic analysis by SEM and TEM at high resolution modes, revealed that: the 15 μm sample presented a perfectly attached interface, while the other showed pores at the interfacial boundary, decreasing the real LSCF/CGO contact. In this way we could explain part of the difference in area specific resistance between measured between them.
Analytical Investigation of Cell Performance of Intermediate-Temperature Disk Type Seal-Less SOFC Fueled by Methane
Authors: Tanaka Tadashi , Inui Yoshitaka , Chitose Norihisa
Published: April 2011

In this study, the authors improve the existing simulation code of intermediate-temperature disk type seal-less SOFC for pure hydrogen to make the simulation of methane fuel case possible. At first, the validity of the newly developed code for methane as fuel is confirmed through the comparison of the numerically obtained i-V curves with those obtained by corresponding experiments. Then, numerical simulations are carried out by means of the newly developed code in the cases of various pre-reformer temperatures and S/C ratios. Employing the numerically obtained results, the effect of the pre-reformer temperature and S/C rate on the cell performance is investigated.
The Performance of a Single-Chamber Solid Oxide Fuel Cell Operated under Thin Oxygen Condition within Methane Fuel
Authors: Liu Yutong , Lü Zhe , Tian Yanting
Published: April 2011

An anode-supported single-chamber solid oxide fuel cell (SC-SOFC) with dense yttria-stabilized zirconia film as the electrolyte was fabricated by the slurry spin coating technique. The single cell was operated at a temperature range between 500°C and 700°C in a mixture gas of methane and oxygen with a quit lower oxygen concentration than usual. A stable methane-oxygen mixture (total flow rate: 150 ml/min) was used and the O2 percentage was varied from 5% to 25%. A maximum OCV can be achieved near the oxygen percentage of 10%. At 600°C, the maximum power density was 6.43 mW/ cm2. The performance indicates that SC-SOFC under such low oxygen concentration still have potential for portable applications.
Towards Understanding the Dual Membrane Fuel Cell (IDEAL-Cell) Using a Metallic Central Membrane
Authors: Ilhan Zeynep , Ansar Asif , Wagner Norbert , Presto Sabrina , Viviani Massimo , Babucci Antonio , Vladikova Daria , Stoynov Zdravko , Thorel Alain
Published: April 2011

This work presents results of a measurement setup which was constructed for understanding the performance contributions of the individual compartments and reactions taking place in the patented concept of IDEAL-Cell (described in detail in[1]). By inserting a third measurement point at the central membrane of an ideal cell it was possible to measure the cell in three different modes corresponding to hydrogen, oxygen compartment and the full cell. Recorded maximum power densities of (~4, ~7, 11, 16) mW/cm² at (600, 650, 700, 750) °C in H2-O2 atmosphere respectively were observed which were similar to the values of proof of concept ideal cell samples tested so far. Moreover in our setup it was possible to record higher maximum power densities for the hydrogen (proton conducting) compartment which was (~14, 22, 33*, ~38*) mW/cm² at (600, 650, 700, 750) °C.
Internal Methane Reforming High Temperature Proton Conductor (HTPC) Fuel Cells
Authors: Luisetto Igor , Di Bartolomeo Elisabetta , D'Epifanio Alessandra , Basoli Francesco , Licoccia Silvia
Published: April 2011

High temperature proton conductor (HTPC) based fuel cells directly fed with methane mixtures were investigated. Doped barium zirconate was chosen as electrolyte because of its good chemical stability in CO2 and H2O containing atmosphere. The sintering temperature of doped barium zirconate was decreased down to 1350 °C by doping with 1wt. % ZnO. A co-pressing method was used for fabricating anode supported single cell. Flat and reproducible bottom cell of NiO BZYZn / BZYZn / LSCF were produced. OCV measurements, I-V curves, and impedance spectra were recorded in the 600-700 °C temperature range The addition of carbon dioxide to methane improved SOFC stability by suppressing coking in Ni anodes.
Performance of Solid Oxide Fuel Cells with In-Doped BaZrO3 Electrolyte Films on Different Anode Substrates
Authors: Bi Lei , Fabbri Emiliana , Traversa Enrico
Published: April 2011

In-doped BaZrO3 showed improved sinteractivity compared with Y-doped BaZrO3 at the cost of reducing its total conductivity. With BZI-NiO as the anode, the fuel cell with BZI film electrolyte was fabricated and tested. Although the cell performance improved compared with the cell with thicker electrolyte, the BZI low conductivity limited the cell performance. With BZY-NiO as the anode, ionic diffusion of Y from anode to electrolyte happened and Y3+ ions substituted the In3+ in the electrolyte layer, which produced the final electrolyte film made of BZY instead of BZI. The ionic diffusion method took advantage of In-doped sample high sinteractivity avoiding the negative effect of In on the electrolyte films, resulting in very promising fuel cell performance.
Chemically Stable Electrolytes and Advanced Electrode Architectures for Efficient Proton Ceramic Fuel Cells
Authors: Taillades Gilles , Battochi Pierre , Taillades Melanie , Jones Deborah , Roziére Jacques
Published: April 2011

BaCe0.9Y0.1O2.95, BaCe0.8Zr0.1Y0.1O2.95 and BaCe0.6Y0.3Nb0.1O2.9 proton conducting electrolytes were successfully elaborated by flash combustion. It was shown by XRD that Zr and Nb-substituted samples have a better stability in CO2 atmosphere than BaCe0.9Y0.1O2.95. The conductivities of BaCe0.8Zr0.1Y0.1O2.95 and BaCe0.6Y0.3Nb0.1O2.9 reach 5 mS cm-1 at 600 °C, slightly lower than BaCe0.9Y0.1O2.95 (10 mS cm-1). Fuel cells with BaCe0.9Y0.1O2.95, BaCe0.8Zr0.1Y0.1O2.95 and BaCe0.6Y0.3Nb0.1O2 as electrolyte, Ni-cermet as anode and Ba0.5Sr0.5Co0.8Fe0.2O3 as cathode were successfully prepared and tested in humidified hydrogen from 550 to 700 °C. The peak power densities were 161, 20 and 29 mW cm-2 at 600 °C respectively
Modeling SOFC Cathodes Based on 3-D Representations of Electrode Microstructure
Authors: Kreller Cortney , Drake Melanie , Adler Stuart B. , Chen Hsun-Yi , Yu Hui-Chia , Thornton Katsuyo , Wilson James R. , Barnett Scott A.
Published: April 2011

In order to better understand the role of microstructure in mediating these rates, our group has been developing detailed microkinetic models (based on finite-element analysis), which employ various 3D representations of the electrode microstructure. These models have been used to explore where and under what circumstances the fine details of the microstructure matter to performance, and where macrohomogeneous approximations can be made without loss of accuracy.
First Principles Modeling of Oxygen Mobility in Perovskite SOFC Cathode and Oxygen Permeation Membrane Materials
Authors: Kotomin Eugene , Merkle Rotraut , Mastrikov Yuri , Kuklja Maija M. , Maier Joachim
Published: April 2011

Based on first principles DFT calculations, we analyze activation energies of oxygen vacancy migration in several complex ABO3-type perovskite candidate materials for SOFC cathodes and permeation membranes ((La(Co,Fe)O3-δ (LCF) and (Ba,Sr)(Co,Fe)O3-δ (BSCF))The atomic relaxation, charge redistribution and energies of the transition states of oxygen migration are compared to understand the microscopic origin of the exceptionally high oxygen mobility in BSCF. It is shown that the B-O distance is considerably shortened in the transition state for BSCF due to covalency of this chemical bond, which could be a reason for the significant reduction of the oxygen migration energy in this material
Computational Study on Impurities Poisoning and Degradation of an SOFC Anode Based on Density Functional Theory
Authors: Ogura Teppei , Nakao Kazuhide , Ishimoto Takayoshi , Koyama Michihisa
Published: April 2011

Solid oxide fuel cells (SOFCs) have been expected to be most efficient and versatile system for chemical to electrical energy conversion. One of advantages of SOFC is the possibility of direct utilization of various types of hydrocarbon fuels. It is however well known that fuel impurities in practical SOFC fuels such as sulfur compounds could cause SOFC poisoning or degradation. Therefore, understanding the effect of impurities in an atomic scale is essential to develop impurity-tolerant SOFCs with long-term durability. Here, we have studied the poisoning and degradation mechanisms of nickel anode by typical impurities, i.e. hydrogen sulfide, hydrogen chloride, etc., using density functional theory method.
Multi-Scale Modeling of Solid Oxide Fuel Cells: From Patterned Anodes to a Power Plant System
Authors: Bessler Wolfgang G.
Published: April 2011

Methods of mathematical modeling and numerical simulation of solid oxide fuel cells (SOFCs) are increasingly being used as tool to understand and optimize both, fundamental electrochemical properties and technological applications. The goal of modeling activities is to identify critical components and processes responsible for cell and system performance, lifetime and cost. We present a multi-scale and multi-physics modeling and simulation methodology that covers (i) elementary kinetics on the surfaces, (ii) properties of porous electrodes, (iii) mass, charge and heat transport of cells and stack repeat elements, and (iv) system integration with balance-of-plant components. The coupling over the various scales is realized via tailored simulation programs and software interfaces. Various examples are given. The activities demonstrate the viability of a multi-scale and multi-physics modeling approach for both, understanding fundamental processes and supporting application design of SOFCs.
Simulation of Two-Dimensional Electrochemical Impedance Spectra of Solid Oxide Fuel Cells Using Transient Physical Models
Authors: Shi Yixiang , Wang Hongjian , Cai Ningsheng
Published: April 2011

A two-dimensional (2D) EIS simulation approach was developed by solving a SOFC unit cell model with imposed sinusoidal voltage perturbations at different frequencies. The transient SOFC unit cell model described the intricate interdependency among the ionic/electronic conduction, multi-component species transport, electrochemical reaction processes and electrode microstructure as well as the coupling processes of mass, energy, momentum transport within flow channels. The model calculates the local transient response and impedance spectra as a function of channel position. The effects of the reaction depletion, product accumulation as well as the temperature variation along the flow channels on the EIS spectra was numerically simulated with a counter-flow mode. The results show that the convection-diffusion process along the flow channel has significant effects on the low frequency circle of the impedance spectra. The temperature oscillations accumulate along the flow channels, and then affect the current response which probably lead to an electro-heat impedance effects.
A Three Dimensional Electrical Model of SOFC Stack
Authors: Le-Ny Mathieu , Chadebec Olivier , Cauffet Gilles , Dedulle Jean-Marc , Bultel Yann
Published: April 2011

An electrical interaction model was developed to simulate the electrical stack behaviour. The model consists about solving the charge transport equation in three dimensions. In order to avoid interfacial issues with the non ohmic voltage drop that occurs in the PENs, a special source term is added in the transport equation. A numerical investigation of cell voltages variation is performed by considering the impact of material properties. Numerical results show the effects on stack voltage change due to a single cell with anomalous.
Analytical Models for SOFC Electrodes with Variable Cross-Section Microstructures
Authors: Nelson George , Peracchio Aldo , Cassenti Brice , Chiu Wilson K.
Published: April 2011

An extended surface modeling concept is applied to charge transport within the solid oxide fuel cell (SOFC) electrode microstructure using an analytical modeling approach analogous to thermal fin analysis. The approach presented has the ability to account for variable cross-section solid geometry. One-dimensional models are presented for microstructural geometries with variable cross-sections simulated by periodic structures composed of conical base units. Predictions of electrode performance based on these one-dimensional models are compared to measured electrode performance in the literature. This comparison demonstrates the merit of applying the models developed to the design of electrode microstructure. A set of dimensionless parameters and performance metrics are presented for the assessment of electrode microstructure. There parameters and metrics are further applied to the definition of microstructure-related transport regimes relevant to electrode design.
Thermodynamic Influence Analysis of Available Fuels and Reforming Methods on SOFC System Efficiency
Authors: Heddrich Marc Philipp , Jahn Matthias , Michaelis Alexander , Reichelt Erik
Published: April 2011

In this paper the results of a thermodynamically exact calculation method for determining SOFC (solid oxide fuel cell) system efficiencies depending on reforming method and fuel are presented. Several fuels (diesel, gasoline, liquefied petroleum gas, ethanol, methane and biogas) are studied. The aim is to identify combinations of fuels and reforming methods with the potential for high efficiencies. The influence of the S/C (steam/carbon) ratio and reformer air ratio λRef on achievable efficiency is examined, explaining the superiority of steam reforming. Only with biogas partial oxidation can achieve comparable values to steam reforming due to its specific composition containing CO2 making biogas an ideal fuel for SOFCs. Also a close look is taken at the demand of heat flux to or from the reforming step in order to reveal potential necessities of a complex heat management.
An Innovative Electrochemical Model for Three-Dimensional Modeling of a SOFC Stack Used in Electrolysis Mode
Authors: Grondin Dominque , Deseure Jonathan , Brisse Annabelle , Zahid Mohsine , Grondin-Perez Brigitte , Chabriat Jean-Pierre , Ozil Patrick
Published: April 2011

A one-dimensional model has been developed to model the mass and charge transfer occurring in the water reduction on nickel-cermet. An artificial neural network (ANN) was identified and validated from this model. The ANN, in equation form, was used in a three-dimensional model of a serial repeat unit of a Solid Oxide Electrolysis Cell stack. The electrochemical processes can be modeled with acceptable accuracy with the one-dimensional model based on a two-step mechanism for the water reduction. The presented results show that the ANN could be employed to model electrochemical reactions and be implemented in a macro-scale model.
Comparison between FIB-SEM Experimental 3-D Reconstructions of SOFC Electrodes and Random Particle-Based Numerical Models
Authors: Choi Hae-Won , Gawel Duncan , Berson Arganthaël , Pharoah Jon , Karan Kunal
Published: April 2011

There has been a rapidly growing interest in three-dimensional micro-structural reconstruction of solid oxide fuel cell (SOFC) electrodes so as to derive more accurate descriptors of the pertinent geometric and effective transport properties. Experimental based reconstruction technique is based on processing of a sequence of images obtained by dual-beam focused ion beam-scanning electron microscopy. Numerical reconstruction of electrodes is based on random distribution of particles with specified nominal phase volume fractions (porosity and electron-conducting particle volume fraction). In this study, we compare both approaches and investigate ways of improving model geometries so that they match better with experimental measurements.
Experimental And Theoretical Approach Of Surface Reactivity Of CeO2 For SOFC Application
Authors: Désaunay Thomas , Medina-Lott Bianca , Ringuedé Armelle , Cassir Michel , Adamo Carlo , Labat Frédéric
Published: April 2011

A first experimental and modeling approach is presented on cerium oxide (CeO2) as a potential catalyst for methane oxidation at the SOFC anode. Cerium oxide thin films were coated on Ni/YSZ substrates by atomic layer deposition (ALD). These films are crystalline but show no preferential orientation. Structural and electronic properties of bulk ceria, (111) and (110) surfaces were calculated by density functional theory (DFT) with the PBE0 functional. The (111) surface is found to be the most stable consistently with previous theoretical studies and experimental observations.
Self-Consistent-Field Electrochemistry
Authors: Gatewood Daniel , Turner C. Heath , Dunlap Brett I.
Published: April 2011

Two self-consistent-field Kinetic Monte Carlo (KMC) models are developed to simulate the operating cathode and anode of 9 mol % Yttria Stabilized Zirconia (YSZ) solid oxide fuel cells (SOFCs) using a database of elementary reaction rates obtained from experimental and first-principles rates. The rates are used in the unit cells of two asymmetrical YSZ lattices for the cathode and anode. KMC then gives the current-voltage (I-V) characteristics of this sequential set of elementary chemical reactions. The resistance of a single electrolyte lattice layer added to either simulation cell is extracted by Taylor-series interpolation of the I-V curves for simulation cells of different thickness. Its conductivity is obtained from this resistance using the cross-sectional area of the simulation cells. These conductivities are compared to experiment and a statistically independent model of this set of chemical reactions.
Current Distribution Analysis of a Microtubular Solid Oxide Fuel Cell with Surface Temperature Measurements
Authors: Nakajima Hironori , Kitahara Tatsumi
Published: April 2011

Current distribution of a practical solid oxide fuel cell (SOFC) has been analyzed from a thermal analysis combined with surface temperature measurements. Electrochemical impedance spectroscopy with two-electrode set-up is employed on an anode-supported microtubular SOFC. This cell is an intermediate temperature SOFC composed of an Ni/(ZrO2)0.9(Y2O3)0.1 cermet anode, an La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte, and an (La0.6Sr0.4)(Co0.2Fe0.8)O3 cathode. The impedance spectra give the resistances at the anode and cathode, and the cell Ohmic resistance. By numerically integrating these resistances, overpotentials are evaluated. The overpotentials and the single electrode (electrochemical) Peltier heats, at the anode and cathode provide individual heat production rates. Since the energy balance equations incorporating these heat production rates determined by current yield the surface temperatures of the cell, local current densities are obtained so that this calculated and measured temperatures by thermocouples at several positions in the anode and cathode surfaces coincide.
Pulsed Laser Deposition of Superlattices Based on Ceria and Zirconia
Authors: Pergolesi Daniele , Tebano Antonello , Fabbri Emiliana , Balestrino Giuseppe , Licoccia Silvia , Traversa Enrico
Published: April 2011

Rapidly growing attention is being recently directed towards the investigation of the ionic conducting properties of oxide film hetero-structures. Experimental evidence has been reported showing that interfacial phenomena at hetero-phase interfaces give rise to faster ion conduction pathways than the bulk or homo-phase interfaces. Nonetheless, a deeper understanding of the interface transport properties is still needed to exploit these effects. In this work we have investigated the growth mechanism of different superlattices fabricated by pulsed laser deposition (PLD) coupling doped and undoped cerium and zirconium oxides. Single crystalline MgO wafers were selected as deposition substrates. The superlattice structures were obtained by means of a thin buffer layer of SrTiO3 (STO). The growth mechanism was investigated by reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD) analyses.
Gadolinia-Doped Ceria Cathode Interlayer for Low Temperature Solid Oxide Fuel Cell
Authors: Kim Young Beom , Gür Turgut M. , Prinz Fritz B.
Published: April 2011

This paper reports the fabrication and investigation of gadolinia-doped ceria (GDC) cathode interlayer on solid oxide fuel cell performance. About 60nm of GDC layer was deposited on the cathode side of 100µm-thick polycrystalline 8mol% yttria-stabilized zirconia (YSZ) substrates, upon which porous platinum electrodes were employed to fabricate the fuel cell element. Current-voltage (I-V) behavior was compared with a YSZ-only control cell. Cathode interface impedances were obtained from electrochemical impedance spectroscopy in the temperature range of 400-450oC. Due to reduced cathode interface resistance of the interlayered cell structure, fuel cell performance was enhanced when compared to that of YSZ-only control cell.
Influence of Small Amounts of NiO on the Electrical Conductivity of 8YSZ
Authors: Batista Rafael , Muccillo Eliana N.
Published: April 2011

The effect of small amounts of nickel oxide on the microstructure and the electrical conductivity of zirconia-8 mol% yttria was systematically investigated by scanning electron microscopy and impedance spectroscopy techniques. Nickel carbonate was added to commercial yttria-stabilized zirconia powder, and the mixture was used to prepare green compacts. Sintering experiments were carried out at several sintering temperatures. The electrical conductivity of sintered specimens are similar for nickel oxide additions up to 1 mol% and sintering times up to 5 h. For larger sintering times, reduction of the grain boundary electrical conductivity, along with microstructure defects were observed in specimens containing the additive. Energy-dispersive spectroscopy analysis in several micro-regions of sintered specimens revealed a heterogeneous distribution of nickel. The nickel segregation phenomenon occurring with long sintering times is responsible for an additional blocking effect on the electrical conductivity of the solid electrolyte.
Defect Formation in SOFC Electrolyte Films during Fabrication
Authors: Wang Xin , Yota Takahiro , Atkinson Alan
Published: April 2011

A defect-free electrolyte film is an essential component for a solid oxide fuel cell. Fabrication often requires the electrolyte film to be sintered under the constraint of a non-sintering (effectively rigid) substrate and large defects can be formed as a result of this constrained sintering. A full understanding of the formation of such large defects is still lacking. In this work, particle packing uniformity in screen-printed electrolytes was investigated using photoluminescence spectroscopy mapping on the green film in which α-Al2O3 particles had been introduced by impregnation. This revealed the existence of low density domains of size 30-50 µm in the green film. The mechanical properties of the green films were investigated by nano-indentation, which showed the polymeric binder used in screen-printing can significantly increase the creep of green film. Defects were also generated by indentation and their evolution during sintering was examined and is discussed in detail.
Characterization of Zirconia-India Ceramics Sintered by Spark Plasma
Authors: De Florio Daniel Z. , Coral Fonseca Fabio
Published: April 2011

We present the synthesis and characterization of ZrO2:x mol %In2O3 ceramics with x = 8, 10 and 12. Sintering has been achieved with spark plasma sintering which allows for higher densification (~ 97% of theoretical density). The powders were characterized by thermal analyses, scanning electron microscopy, x-ray diffraction. The electrical properties of the sintered samples were studied by electrochemical impedance spectroscopy as a function of dopant concentration x and temperature. The spark plasma sintering is effective to sinter the ZrO2-In2O3 nanoparticles, and sample with x = 8 were found to be pure ionic conductor at temperatures above ~ 300 °C.
ZrO2-CeO2 Interface Properties: A First-Principle Investigation
Authors: Fronzi Marco , De Vita Alessandro , Tateyama Yoshitaka , Traversa Enrico
Published: April 2011

In the present work we present a Density Functional Theory approach to investigate the structural and electronic properties of the low index ZrO2-CeO2 interface. Optimizations of the crystal geometry for the separate ZrO2 and CeO2 bulks as well as the interfaces are carried out and the structural morphology is analyzed. The energy formation of the oxygen vacancies are analyzed at different values of the lattice parameter, in order to verify its dependency on the strain. This eventually allow us to identify the vacancy concentration difference between bulks and interfaces. Activation energy of the oxygen migration are also calculated in the optimized bulk as well as under strain condition as at the interfaces level, to identify eventual preferential migration channel. The effect of the doping on the lattice geometry is analyzed for the low index interfaces in order to verify its influence on the morphologic disorder and consequently on vacancy concentration.
Electrical Properties of Tb and Sm Co-Doped Ceria Electrolyte at Different Oxygen Partial Pressures
Authors: Vestli Mihkel , Nurk Gunnar , Lust Enn
Published: April 2011

Tb and Sm co-doped ceria was studied as electrolyte membrane for intermediate temperature solid oxide fuel cell single cells. The ceramic doped ceria powders with different compositions such as Ce0.9Sm0.1O2-δ and Ce0.9Sm0.1Tb0.05O2-δ were synthesized using glycine-nitrate process and characterized using XRD and impedance methods. The conductivity measurements of the pellet like bulk samples were conducted at different temperatures and gas environments.
BaCe0.8Zr0.1Y0.1O3-α Thin Film Elaborated by Reactive Magnetron Sputtering
Authors: Arab Pour Yazdi Mohammad , Briois Pascal , Billard Alain
Published: April 2011

BaCe0.8Zr0.1Y0.1O3-α protonic conductor coatings were co-sputter deposited from Ba, Zr and Ce0.9Y0.1 metallic targets in argon-oxygen reactive gas mixtures. The targeted composition of the coatings is obtain by fixing the discharge current applied on Zr and Ce0.9Y0.1 targets and adjusting the discharge current applied on Ba target. As deposited coatings are amorphous and present a good chemical stability against carbonation under air up to 573 K. The coatings crystallise after annealing treatment around 873 K for 2 hours under air in a mixture of BaCO3 and CeO2 in spite of the targeted double substituted BaCeO3 perovskite structure. Nevertheless, the crystallization in the convenient perovskite structure was obtained after annealing treatment under vacuum (5 ×10-3 Pa) at 873 K during 2 hours to prevent the carbonation of the coating. Such crystallized coatings kept mainly their initial morphological properties.
Development of Novel Fe-Doped Barium Calcium Niobates as Promising Mixed Conductors for Solid Oxide Fuel Cells (SOFCs)
Authors: Kan Wang Hay H. , Trinh Trang T. , Fürstenhaupt Tobias , Thangadurai Venkataraman
Published: April 2011

Synthesis, structural analysis, chemical stabilities and electrochemical measurements of a new Fe-doped barium calcium niobates (Fe-BCNs) family as promising mixed conductors for SOFCs were reported. The Fe-BCNs, prepared by conventional solid state method, exhibited as single phases which can be indexed as Fm-3m (space group no. 225) structure with cell parameter a ~ 8.4 Aå by PXRD and SAED. The Fe-BCNs showed superior chemical stability in pure CO2 gas at 800oC for 24 h, boiling H2O for 72 h, 30 ppm H2S at 600oC for 24 h and pure CH4 gas at 600oC for 12 h, confirmed by PXRD. The highest total conductivity of 1.3 × 10-2 Scm-1 (Ea~0.5eV) was found for Ba2Ca0.787Fe0.566Nb0.646O6-δ at 400oC in air.