bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Exsolved Structures as a Route to More Robust Anodes for Improved Biogas Utilisation in SOFCs
Authors: Cassidy Mark , Gamble Stephen , Irvine John T. S.
Published: July 2015

Biogas is a potentially readily available fuel which could be especially useful when combined with the efficient energy conversion in SOFCs. This could be especially important in rural or remote locations where grid electricity is not available. Biogas contains mixture of methane CO2 with inherently high levels of H2S, therefore to improve performance in biogas more robust anodes are required that are more tolerant to both carbon and sulphur. In this paper the use of catalyst nanoparticles exsolved onto porous as a possible method of producing more resistant structures is discussed. All of the options showed good performance in reformed biogas mixtures with the exsolved structures showing improved resistance to carbon deposition. The performance of all dropped when exposed to sulphur, however many were also observed to recover once this was removed and so give encouragement for the development of robust anodes that can withstand sulphur breakthrough without catastrophic stack failure.
The Effect of Electrode Morphology on Solid Oxide Fuel Cell Performance
Authors: Pharoah Jon G. , Handl Lisa , Schmidt Volker
Published: July 2015

Three different electrode morphologies are generated from three different starting powders, spheres representing non-aggregated powders, agglomerates of spheres and high aspect ratio cylinders modelling splats formed in plasma sprays. Electrodes from each morphology are analysed using finite volumes to predict the effective transport coefficients, the triple phase boundary length and the performance of the electrode. The same structures are also analysed using morphological characterization which can be much more efficient. It was found that high aspect ratio base particles are favourable, and that constrictivity correlates best with the finite volume transport calculations.
Development of Tailored Porous Microstructures for Infiltrated Catalyst Electrodes by Aqueous Tape Casting Methods
Authors: Cassidy Mark , Doherty David J. , Yue Xiangling , Irvine John T. S.
Published: July 2015

Recent SOFC research has shown that impregnating fine catalyst structures into porous scaffolds to be an extremely promising route for electrode development. It is clear that in optimising the advantages offered by this technique there will be an obvious link between the morphology of the porous scaffold and the infiltrated catalyst. There are significant potential benefits to using aqueous systems for the manufacture of the scaffold. They include the potential for a far larger range of pore formers which may be employed to create specific pore morphologies and also reduced environmental burdens, such as exhaust handling, worker exposure and disposal. Recent and ongoing activities to develop such systems at University of St Andrews will be described. Areas of discussion will be effects of ceramic particle size, the size ratio of pore former to ceramic particle, pore former type and loading and how these interact with other tape constituents both on the behaviour during processing and on the final fired morphology. Better understanding of these complex relationships will help in designing optimised porous structures in the future
Effective Conductivity of Solid Oxide Fuel Cell Electrodes
Authors: Zheng Keqing , Ni Meng
Published: July 2015

Effective conductivity of SOFC electrodes is an important parameter for predicting the ohmic loss in SOFC. This work investigates the effective conductivity of SOFC electrodes via numerical simulation. The microstructures of porous electrodes are reconstructed numerically by packing spherical particles in a computational domain, followed by a dilation process to simulate the sintering procedure. The effects of various parameters on the effective conductivity of the electrodes are investigated, including material composition, porosity, particle size and contact angle. The results are useful for understanding the microstructure properties of SOFC composite electrodes and for subsequent electrode optimization.
Advanced 3D Imaging and Analysis of SOFC Electrodes
Authors: Tariq Farid , Kishimoto Masashi , Cui Guansen , Yufit Vladimir , Lomberg Marina , Ruiz-Trejo Enrique , Chen Zhangwei , Brandon Nigel P.
Published: July 2015

An ability to meet our increasing energy demands will be facilitated though improving the next generation of electrochemical devices. The ability to directly image in 3D and analyse solid oxide fuel cell (SOFC) electrodes at high resolutions provides key insights in understanding structure-property relationships; as electrochemical reactions and transport phenomena are strongly affected by complex microstructure. Here we use tomographic techniques to probe 3D electrode structures at nanometer to micrometer length scales. In doing so the first characterisation of specific necks and interfaces alongside their particle sizes within SOFC electrodes is derived. Micro/nano structural changes are followed to facilitate understanding the differences which occur with shape, structures and morphology at high resolution. These are correlated with both measured experimental values and simulations to provide insight into microstructure-property relationships. We also demonstrate approaches to intelligently design electrodes through scaffolds, and potentially 3D printed structures, all towards optimising the structure for performance.
Direct Observation of the Current Distributions across SOFC by Measuring the Lateral Voltage Differences
Authors: Devaraj Abhilasha Sumangal , Yashiro Keiji , Hashimoto Shin-ichi , Kawada Tatsuya
Published: July 2015

In order to evaluate the current distribution across the SOFC, 32 probes were attached to the current collector on the cathode side to measure the lateral voltage difference at operating condition. To get the current distribution from lateral voltage differences, a charge conservation equation was used for calculation. In addition to the experiment, a simulation was also simultaneously done to compare the differences and the validity of the experimental procedures. The experimentally determined current distribution showed a big spike at near the current lead-in wires. With the simulation results, similar results were shown, which indicated this spike was an artifact in the calculation of the local current using a limited number of potential probes. Apart from this spike, this work shows the validation of the experimental results from the simulation and confirm that current distribution of SOFC can be calculated using charge conservation equation.
Methodology for Analysis of Solid Oxide Cells via Raman Spectroscopy
Authors: Manerova Jevgenija , Call Ann V , Sinclair Derek C , Elder Rachael H
Published: July 2015

Solid oxide cells (SOCs) are highly efficient electrochemical energy conversion devices capable of operating in both fuel cell and electrolysis modes. The operating temperatures of SOCs (500 – 800 °C, for IT-SOCs) create opportunities for direct utilisation of a wide variety of reactants, including low-grade fuels such as biogas, however, in-situ characterisation of evolving electrode morphologies and compositions is challenging. The design of an optically accessible experimental setup is presented alongside methodology for obtaining and interpreting in-situ Raman spectroscopic measurements. Raman spectroscopy is a valuable analytical tool for in operando monitoring of both solid oxide electrolysis (SOEC) and fuel cells (SOFC). Molecular species adsorbed on the surface can be identified, thus providing direct insight into reaction intermediates, material phase transformations and the presence of contaminants and poisons, such as carbon, chromium, sulphur and silica. Raman spectroscopic evidence of carbon deposition during CO2 electrolysis is discussed.
Analysis of Interfacial Processes at the SOFC Electrodes by I
n-Situ Raman Spectroscopy
Authors: Agarkov Dmitrii , Burmistrov Ilya , Tsybrov Fedor , Tartakovskii Ilya , Kharton Vladislav , Bredikhin Sergey , Kveder Vitaly
Published: July 2015

The present work is centered on the developments of a new technique for in-situ Raman spectroscopy studies of local chemical and electrochemical reactions, phase transitions, strains and morphological alterations in the SOFC electrodes under working conditions, combined with electrochemical measurements. An appropriate selection of the electrodes geometry makes it possible to directly collect Raman spectra from the triple-phase boundary zone by passing the beam through transparent single-crystal solid electrolyte onto the interface, varying current density, temperature and atmosphere over the working electrode. The results of case studies, focused on reduction of Ni-containing cermet anodes, are presented.
Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration
Authors: Küngas Rainer , Hertz Thomas B. , Heiredal-Clausen Thomas
Published: July 2015

A novel cell design consisting of a Ni/YSZ anode support, a Ni/YSZ anode, a zirconia-based electrolyte, and a porous stabilized zirconia backbone layer, infiltrated with a perovskite phase, is reported. The electrochemical performance of the large footprint (12 x 12 cm2) cells was tested both on single cell as well as stack level with promising results. The steady-state degradation rate of infiltrated cells in a stack was low (2.7 %/kh), despite the fact that changes in electrode microstructure and in-plane conductivity were observed, as the infiltrated cells were heat-treated to higher temperatures.
Additive Manufacturing for Solid Oxide Cell Electrode Fabrication
Authors: Lomberg Marina , Boldrin Paul , Tariq Farid , Offer Greg , Wu Billy , Brandon Nigel P.
Published: July 2015

Additive manufacturing can potentially offer a highly-defined electrode microstructure, as well as fast and reproducible electrode fabrication. Selective laser sintering is an additive manufacturing technique in which three-dimensional structures are created by bonding subsequent layers of powder using a laser. Although selective laser sintering can be applied to a wide range of materials, including metals and ceramics, the scientific and technical aspects of the manufacturing parameters and their impact on microstructural evolution during the process are not well understood. In the present study, a novel approach for electrode fabrication using selective laser sintering was evaluated by conducting a proof of concept study. A Ni-patterned fuel electrode was laser sintered on an yttria-stabilized zirconia substrate. The optimization process of laser parameters (laser sintering rate and laser power) and the electrochemical results of a full cell with a laser sintered electrode are presented. The challenges and prospects of using selective laser sintering for solid oxide cell fabrication are discussed.
Fabrication and Microstructure of Self-Supporting Thin Ceramic Electrolytes Prepared by Laser Machining
Authors: Cebollero Jose Antonio , Lahoz Ruth , Laguna-Bercero Miguel Angel , Peña Jose Ignacio , Larrea Angel , Orera Victor M
Published: July 2015

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range.
Influence of Convective Heat Transfer by Air Flow on Local Current/Temperatures along Microtubular Solid Oxide Fuel Cells In-situ Identified by Electrodesegmentation Method for Co- and Counter-flow Configurations
Authors: Aydin Ozgur , Nakajima Hironori , Kitahara Tatsumi
Published: July 2015

Contribution of spatial temperature variations to thermo-mechanical stresses along microtubular solid oxide fuel cells is often numerically estimated with local temperatures calculated by thermo-electrochemical models. This method is preferred due to the lack of experimental data. Not only to provide experimental data but also to reduce the temperature variations, in this paper we are analyzing the in-situ measured local temperatures and currents along a cell. We have measured the local properties by electrode-segmentation method for co- and counter-flow configurations at various air flow velocities. Gas flow configuration shows a substantial impact on both longitudinal temperature and current variations. Under the identical conditions, the counter-flow exhibits larger variations in both temperatures and currents. We conclude that air flow velocity determines the longitudinal temperature distributions, whereas its effect on the current distribution profile is negligible. With these findings, we anticipate larger thermo-mechanical stresses in the counter-flow configuration at high air flow velocities.
A 2D Stationary FEM Model for Hydrocarbon Fuelled SOFC Stack Layers
Authors: Geisler Helge , Dierickx Sebastian , Weber André , Ivers-Tiffée Ellen
Published: July 2015

In this study, the established model framework, where the physically coupled processes (i) charge-transfer chemistry, (ii) electron and ion conduction and (iii) gas species transport in the porous electrodes for hydrogen operation are implemented, is extended to predict local gas composition and electrochemical performance of hydrocarbon fuelled SOFC stack layers. The model geometry represents a 2D longitudinal section through a stack layer along the gas channel length. Consequently, the existing isothermal model framework is extended to meet the new requirements: (i) pressure driven gas transport in the gas channels is modeled by Navier-Stokes equations and in the porous electrodes by Darcy’s law, (ii) all existing and new gas transport equations are extended to six gas species and (iii) global reaction equations for steam reforming and water-gas shift reaction are added. The model predicts (i) where gas diffusion limitations lead to drastic performance loss and (ii) where the Ni/8YSZ anode structure most likely will suffer severe damage.
CFY-Stack Technology: The Next Design
Authors: Bienert Christian , Brandner Marco , Skrabs Stefan , Venskutonis Andreas , Sigl Lorenz S. , Megel Stefan , Becker Wieland , Trofimenko Nikolai , Kusnezoff Mihails , Michaelis Alexander
Published: July 2015

The stack concept of electrolyte supported cells is applicable for both, SOFC as well as SOEC. High power densities and efficiencies comparable to stacks based on anode supported cells can be achieved, however, in unison with higher robustness. Incorporating an electrolyte made of fully scandia-stabilized zirconia paired with chromium-base CFY interconnects of matched CTEs, a feasible stack concept was created with the focus on long-term stability in regard to high temperature corrosion and thermal cycling. Onward development of the stack design as well as stack data of more than 20,000 hours of a single stack are presented. Using the same material combinations and the same footprint as for the MK351-design, the newly developed MK352-design allows for easier stack assembling and system integration. Slight modifications in interconnect design enable lower pressure drops over the stack, which, paired with enhanced tolerance chains lead to enhanced stack performance, especially in regard to system cycling.
The Impact of Pressurization on Anode-Supported and Electrolyte-Supported Planar Solid Oxide Fuel Cells at 750oC ~ 850oC
Authors: Shy Shenqyang Steven , Hsieh Y.D. , Liang Jyun-De
Published: July 2015

The impact of pressurization on anode and electrolyte-supported cells (ASC/ESC) is measured in a high-pressure SOFC test facility using the same single-cell stack setup, a planar fuel cell with rib-channel flow distributors, under the same experimental conditions (i.e. same flow rate, temperature, pressure). Results show that at T= 850°C and 0.7 V, power densities of ASC/ESC increase from 309/193 mW cm-2 to 476/250 mW cm-2, as p increases from 1 atm to 5 atm. As T increases from 750°C to 850°C at 0.7 V, power densities of ASC/ESC increase from 175/97 mW cm-2 to 309/193mW cm-2 at p = 1 atm, while at p = 5 atm, the corresponding increases of power densities are 281/137 mW cm-2 to 476/250 mWcm-2. It is found that ASC is more sensitive to pressurization than ESC, while the latter is more temperature-sensitive. Corresponding electrochemical impedance spectra explain these results.
Direct Utilization of Methane in Microtubular-SOFC
Authors: Majewski Artur Jacek , Dhir Aman
Published: July 2015

Liquefied natural gas (LNG) is receiving increased interest as a fuel for trucks. This is also an ideal fuel for SOFC. The work presented here is part of a project utilising LNG in microtubular SOFC (mSOFC) in a truck APU application and the issues associated with this fuel. The paper mainly focuses on solving problems with temperature distribution along and across the mSOFC cell. The key problem in the proposed system is the temperature distribution (TD). Despite the good resistance to thermal shock, the long-term operation with unequal TD can cause cell damage. The TD was measured along and across the cell (internally and externally) under different operating conditions. H2 and CH4 were used as fuels in the first instance. CH4 was converted into syngas using semi-internal catalytic partial oxidation catalyst (CPOX) located at the entrance of the cell. Different mixtures of fuel and air and different forms of the catalyst were tested for the CPOX of hydrocarbons.
Performance Degradation Analysis of Different Type SOFCs
Authors: Yoshikawa Masahiro , Yamamoto Tohru , Asano Koichi , Yasumoto Kenji , Mugikura Yoshihiro
Published: July 2015

Long term durability tests of six different type SOFCs, which have been developed by Mitsubishi Hitachi Power Systems (MHPS), Kyocera, TOTO, NGK SPARK PLUG (NTK), NGK INSULATORS (NGK), and Murata Manufacturing (Murata) have been started under the New Energy and Industrial Technology Development Organization (NEDO) project from FY2013. 2012 model of the Kyocera’s stack which was operated until 10,000 hours, showed stability compared with 2008 model. The voltage decay rate was 0.2%/1000hr. The dominant degradation factors of this stack were IR drop and cathode overvoltage. 2012 model of the NTK’s stack showed that it has an initial voltage drop up to 1,000 hours and the degradation factors were IR drop and cathode overvoltage. The voltage decay rate was 0.6%/1000hr including thermal cycling. The stacks of MHPS’s, TOTO’s, NGK’s, and Murata’s were still in the middle of durability test. In this study, we report our recent activities toward the durability and the dominant performance factors, such as IR drop and overvoltage of anode and cathode, for the six types of SOFCs.
Direct Current Distribution Measurement of an Electrolyte-Supported Planar Solid Oxide Fuel Cell under the Rib and Channel by Segmented Electrodes
Authors: Koshiyama Takahiro , Nakajima Hironori , Karimata Takahiro , Kitahara Tatsumi , Ito Kohei , Masuda Soichiro , Ogura Yusuke , Shimano Jun
Published: July 2015

In the planar SOFCs, the fuel/oxidant distributions and current collecting resistance cause current and temperature distributions over the electrodes under the separator ribs and flow channels. Optimized design of the separator is hence required to improve the output power and chemical/thermo-mechanical durabilities of practical stacks. To clarify the distributions, we prepare planar cells having three segmented cathodes. Current-voltage characteristics are measured with voltage control using three electric loads to reproduce the electrode potentials of a single cell at around 800°C. We find significantly small in-plane oxygen transport rate under the cathode rib and higher current collecting resistance under the channel. Increased anode rib width gives large overpotential under the rib due to fuel starvation. Finite element modeling supports the above experimental results. We demonstrate an improved separator design of a practical stack, taking advantage of this model. Thereby ca. 17% higher maximum power is given in the finite element simulation.
Performance Degradation Prediction of a Low-Temperature SOFC via Impedance Spectroscopy and CFD Modelling
Authors: Boigues Muñoz Carlos , Pumiglia Davide , Santoni F , McPhail Stephen J. , Comodi Gabriele , Carlini Maurizio
Published: July 2015

The present work encompasses the immediate performance characterization of a first generation LSC-based SOFC single cell by means of polarization curves, electrochemical impedance spectroscopy (EIS), the distribution relaxation times (DRT) method and equivalent circuit modeling (ECM). Besides, an endurance performance characterization based on the FCTESQA testing protocols along with EIS measurements, the aforementioned ECM and computational fluid dynamics (CFD) modelling theory has enabled to generate a time-dependent model capable of predicting performance degradation of the single cell when operating under predetermined conditions.
Performance Characteristics of a Micro-tubular Solid Oxide Fuel Cell Operated with a Fuel-rich Methane Flame
Authors: Wang Yuqing , Shi Yixiang , Cai Ningsheng , Ye Xiaofeng , Wang Shaorong
Published: July 2015

A micro-tubular solid oxide fuel cell (SOFC) is directly combined with a fuel-rich methane flame in a simple, "no-chamber" setup. The flame serves as a fuel partial oxidation reformer and a quick starter for the SOFC in the system. Experiments were performed using an anode supported micro-tubular SOFC and a multi-element diffusion flame burner for various equivalence ratios and gas flow rates. The SOFC was directly heated up by the flame from room temperature to operating temperature in less than 120 s. The maximum power generated by the fuel cell reached 0.45 W at the equivalence ratio of 1.2. The cell was operated at a fixed voltage of 0.45 V for three thermal cycles in 18 hours without significant performance degradation when the equivalence ratio was 1.2.
Development of Intermediate Temperature (550 - 650oC) Metal Supported Solid Oxide Fuel Cells (SOFCs) Using Plasma Processes
Authors: Rupa Pantula K. P. , Goli V. R. , Balasubramanian Krishnamurty , Tomov R I , Kumar R Vasant , Glowacki B A , Krishnan Venkatesan Venkata
Published: July 2015

An entire cycle for fabricating a metal supported cell is developed, using porous SS430L as anode substrate, NiO-GDC as the anode, GDC as electrolyte and LSCF as cathode, as follows - - Tape Casting of porous SS430L substrate layers, followed by vacuum sintering (1100 C)- Brush painting of anode (NiO + GDC) layers, followed by a high heat flux treatment to induce rapid sintering - Plasma Spray (powder) deposition of GDC electrolyte layer leading to sintering- Ink-Jet printing of GDC colloidal suspension to give better finish to the ‘rough’ electrolyte surface, followed by high heat flux treatment- Brush painting of cathode (LSCF) layers on the electrolyte surface followed by high heat flux treatment The cells are characterized for their microstructure and have shown highly dense electrolytes, and fine microstructures for anodes and cathodes. Process refinements are underway (with electrochemical characterization) to enhance cell performance and stack assembly.
A Novel Micro-Tubular Solid Oxide Fuel Cell with a Porous Zirconia Support for Intermediate-Temperature Operation
Authors: Panthi Dhruba , Choi Bokkyu , Tsutsumi Atsushi
Published: July 2015

To improve current collection efficiency and prevent cell degradation under reduction–oxidation (redox) cycling, we have proposed a novel micro-tubular solid oxide fuel cell (SOFC) with a configuration of inert support/current collector/inner electrode/electrolyte/outer electrode/current collector. In this work, we applied multi-step dip coating and low-temperature co-sintering methods to fabricate a micro-tubular SOFC based on the proposed design using yttria-stabilized zirconia (YSZ), Ni, Ni-scandia-stabilized zirconia (ScSZ), ScSZ, strontium-doped lanthanum manganite (LSM)–ScSZ, and LSM as the inert support, anode current collector, anode, electrolyte, cathode, and cathode current collector, respectively. The electrochemical performance of the fabricated cell was characterized in an intermediate temperature range, which allows for the use of cheap stack materials and also slows down the performance degradation mechanisms. Our results indicate that the performance of the proposed micro-tubular SOFC can be improved considerably in the intermediate temperature range using conventional materials when YSZ is substituted with ScSZ as the electrolyte and ion-conducting phase in the electrodes.
Tubular SOFC with Hollow Fiber Ceramic Support and Inner Coating
Authors: Yang Zhibin , Zhu Tenglong , Han Minfang
Published: July 2015

In this work, porous ceramic supported tubular cell with inner coating was studied. The hollow fiber support tube was fabricated through phase-inversion method using 3%mol Y2O3 doped ZrO2
(TZP). Then the NiO-8%mol Y2O3 stabilized ZrO2 (YSZ) anode layer, YSZ electrolyte layer, (La0.8Sr0.2)0.95MnO3-δ(LSM)-YSZ cathode layer and LSM current collected layer were applied by screen printing and high-temperature sintering in proper orders. Finally, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ-Gd0.1Ce0.9O1.95 composite layer was coated on the inner side of the support tube. Cell performance characterization was conducted using room-temperature humidified hydrogen and methane at a gas flow rate of 40 mL min-1 inside the tube and ambient air at cathode side. Results show that, the maximum power density was 96 and 106 mW cm-2 at 850 oC under H2 and CH4, respectively. No obvious degradations were observed in the stability test under humidified H2 for 50 h and CH4 for 250 h.
SOFC Stack Operation: Effects of Electrode-Interconnect Contacts
Authors: Minh Nguyen , Budur Abhijith , Dogan Fatih
Published: July 2015

Planar SOFC multi-cell stacks incorporating metallic interconnects generally exhibit average cell performance lower than that observed for out-of-stack cells under similar conditions. It has been suggested that electrode-interconnect, especially cathode-interconnect, contacts (and their ohmic resistances) are the main cause for this observed difference. In addition, cathode-interconnect contacts can evolve in long-term operation, resulting in stack performance reduction/degradation with time. Experiments using current interruption, AC electrochemical impedance and other characterization techniques have been conducted on single-cell stacks and button cells in contact with interconnect materials. The data obtained to date confirmed the hypothesis that contact ohmic resistance significantly contributes to stack performance losses. This paper summarizes and discusses experimental results on the effects of cathode-interconnect contacts on stack performance.
Micro-SOFC with High Performance and Fast Thermal-Cycling Ability
Authors: Kim Kun Joong , Park Byung Hyun , Kim Sun Jae , Bae Hongyeul , Choi Gyeong Man
Published: July 2015

Miniaturized solid-oxide fuel cells (micro-SOFCs) have received growing attention for use in portable devices. Conventional design of micro-SOFC has adopted a freestanding membrane supported by Si substate and used pure metal electrode which has shown poor thermomechanical-stability. In this study, we have developed a new design of micro-SOFC with porous stainless-steel (STS) as a substrate to support a thin-film membrane electrode assembly (MEA) to achieve thermally-robust cell. A composite of nano-porous (La,Sr)(Ti,Ni)O3 conductor and electrolyte is applied as a contact layer between the macro-porous STS and the thin-film MEA. Excellent electrochemical performance and thermal cycling ability at or below 550oC for this novel cell are demonstrated.
Suppression of Carbon Deposition on Ni Films by Redox Treatment of Ceria Substrates
Authors: Wang Fangfang , Kishimoto Haruo , Bagarinao Katherine Develos- , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: July 2015

The carbon deposition behavior on Ni film supported on the two types of GDC, as-sintered and redox-processed, is investigated under dry 5% CH4 at 800 oC for 1 h. Totally different carbon deposition behaviors were observed. Large amount of carbon was deposited on the Ni film supported on as-sintered GDC, while there is no carbon deposition on the Ni film supported on GDC with redox treatment. It seems that the redox treatment for GDC substrate plays an important role in suppressing the carbon deposition on Ni film, which would be related to high concentration of the oxygen vacancies on the GDC surface.
Evaluation of a Metal Supported Ni-YSZ / YSZ / La2NiO4 IT-SOFC Elaborated by Physical Surface Deposition Processes
Authors: Fondard Jérémie , Bertrand Pierre , Billard Alain , Skrabs S , Franco Thomas , Fourcade Sébastien , Batocchi Pierre , Mauvy Fabrice , Bertrand Ghislaine , Briois Pascal
Published: July 2015

The elaboration of the last generation metal supported IT-SOFC complete cell by dry surface deposition processes is really challenging. Atmospheric Plasma Spraying (APS) and Reactive Magnetron Sputtering (RMS) processes are respectively adapted to deposit Ni-YSZ anode and YSZ electrolyte layers. RMS is also used to coat a thin and dense La2NiO4 (LNO) cathode layer. In this work, we have elaborated a complete cell on metallic support (ITM) produced by PLANSEE SE. The innovative LNO cathode layer was compared with screen-printed LNO layers, with and without RMS bonding layer. Electrochemical and Voltametry tests were performed on these samples. It reveals lower performances than literature due to the high density of the RMS cathode layer, and too high temperature during sintering step which deteriorate layers manufactured by RMS and metallic substrate. Nevertheless, using LNO bonding layer manufactured by RMS seems to be an interesting way to improve the polarization resistance of the cell.
Three-dimensional Modeling of Internal Reforming SOFC with a Focus on the Interconnect Size Effect
Authors: Sun Qiong , Ni Meng
Published: July 2015

A three-dimensional (3D) model of methane fed SOFC stack has been developed to investigate interconnect size effect on stack performance. Different from the existing studies on interconnect size effect which only consider hydrogen (H2) as a fuel, we considered direct internal reforming (DIR) of methane and water gas shift reaction (WGSR) in anode. In addition, both H2 and carbon monoxide (CO) are considered as electrochemically active fuel in this model. Parametric simulations are performed to study the geometric effect of interconnect on stack performance. Different from H2 fuel case, the temperature decreases along the gas channel of methane fed SOFC. It is also found that the interconnect rib size has obvious effect on the current density distribution. The results also show that the optimum ratio Ra is 0.3 for stacks with different ratio of the inlet methane to steam, while the optimum ratio is 0.2 for SOFC running on H2.
Shape Forming of Ceramic Tubes for Electrochemical Reactors by Gel-Casting Method
Authors: Chalkia Vasiliki , Pandis Pavlos , Stathopoulos Vassilis
Published: July 2015

Ceramic powders of an oxygen ion conductor such as apatite-type lanthanum silicate La9.83Si4.5Fe1.5O26±δ and a proton conductor such as BaZr0.8Y0.2O3±δ where prepared, by solid state chemistry. These single phased materials after powder processing were used in shape-forming by gel-casting into tubes of the range of 5-14 cm length and 0.6-2 cm diameter. Powder properties were verified by XRD, SEM and laser particle size distribution analysis. In addition, rheological measurements were performed in order to report the viscosity of the slurries used for a successful shape-forming casting. Different sintering protocols were applied all leading to high porosity structures suitable for electrode supported electrochemical reactors even after sintering at 1500oC. The porosity of the produced tubes was evaluated by Archimedes method while the microstructure was studied by SEM.
Design of New Power Source Based on Micro-SOFC for Mobile Electronic Devices
Authors: Murayama Shoya , Iguchi Fumitada , Shimizu Makoto , Tanaka Shuji , Yugami Hiroo
Published: July 2015

A package consisted of a vacuum insulator and a heat exchanger was designed to enable power sources based on micro-SOFCs fueled by liquid fuels thermal sustainability and consistency with other electronics in mobile electronic devices. Gas-liquid heat exchanger worked for cooling the edge of the thermal insulator and recovering the latent and sensible heat of exhaust gases. Numerical analysis using a finite element method and experiment using a prototype package revealed that applying of liquid fuels based on methanol could reduce the surface temperature of the package lower than 85 oC at the operation temperature lower than 500 oC, and thermal sustain operation could be archived by heat recovering at this range.
Effects of Lamination Conditions on the Performance of Anode-Supported Solid Oxide Fuel Cells
Authors: Timurkutluk Bora , Timurkutluk Cigdem , Ciflik Yelda , Korkmaz Hatice , Kaplan Yuksel
Published: July 2015

Solid oxide fuel cells (SOFCs) operate at high temperatures and produce electricity and heat energy from fuels in an electrochemical way. Membrane electrode assembly (MEA) composed of a dense electrolyte coated with two porous electrodes on each side is generally constructed on the electrolyte. However, high operation temperatures are required to obtain acceptable performance values due to high electrolyte resistance as a result of the use of thick electrolyte layer as a mechanical support for MEA. Alternatively, the cells can be fabricated as anode-supported where the anode is responsible for supporting the cell mechanically. By doing so, the operation temperature can be lowered due to reduced electrolyte thickness. In this study, the effects of isostatic press parameters i.e. temperature and pressure for NiO/YSZ anode support on the anode-supported cell performance and the microstructure of the anode support are investigated. The experimental results reveal that the cell performance is strongly influenced by the pressing parameters. In this aspect, the optimum pressing temperature and pressure are found to be 50 °C and 40 MPa, respectively.
Electro-Chemical Potential Analysis of Zirconium Based on the Reaction-Diffusion Equations of Oxygen Ion and Electron Considering Phase Transformation
Authors: Muramatsu Mayu , Kishimoto Haruo , Yamaji Katsuhiro , Yashiro Keiji , Kawada Tatsuya , Terada Kenjiro , Yokokawa Harumi
Published: July 2015

Phase transformations induced by the precipitation of Ni in Ni-doped 8Yttria-Stabilized Zirconia (8YSZ), which is a typical electrolyte material, have recently been known to cause electrochemical degradation of Solid Oxide Fuel Cells (SOFC). Numerical simulations are conducted to evaluate the oxygen potential distributions and then to estimate the degree of transformation during long-term operations that can be determined by the equilibrium partial pressure between Ni and NiO. The simulation results indicate that the oxidation-reduction front inside the electrolyte tends to move towards the anode side reflecting the difference in electrical conductivities with different time constants between the oxidation and reduction regions.
Towards the Next-Generation of Solid Oxide Fuel Cell Systems
Authors: Singh Vaibhav , Wagner Patrick Hubert , Wuillemin Zacharie , Diethelm Stefan , Schiffmann Jürg , Van herle Jan
Published: July 2015

To improve the industry benchmark of solid oxide fuel cell systems (SOFC), we consider anode off-gas recirculation using a blower as an add-on to our next-generation SOFC system. Evolutionary algorithms compare the different design alternatives, i.e. co-flow or counter-flow stack operation with hot or cold recirculation. The system performance is evaluated through multi-objective optimization criteria, i.e. maximization of electrical efficiency and cogeneration efficiency. The results obtained suggest that improvements to the best SOFC systems, in terms of net electrical efficiency, are achievable.
Electrochemical Model of a Triode Solid Oxide Fuel Cell
Authors: Caliandro Priscilla , Diethelm Stefan , Nakajo Arata , Van herle Jan
Published: July 2015

A Triode Solid Oxide Fuel Cell is a novel cell architecture that consists of two circuits: an auxiliary circuit, operated in electrolysis mode, and a conventional main fuel cell circuit. During triode operation, performance enhancement can be expected especially when a significant electrode overpotential is present. A two-dimensional stationary isothermal model is implemented in a commercial software, COMSOL Multiphysics. The model, able to predict conventional and triode operation, gives guidelines for the electrodes geometry design that needs to be adopted in order to favor the expected improvements. The interaction between the main and auxiliary circuits is then discussed in terms of equipotential and current lines in a cross section of the cell for two different geometries: anode and electrolyte supported cells. The improvements achievable in triode operation are also calculated in terms of electric current surplus that is possible to obtain in the fuel cell circuit.
Prediction of SOFC Performance with or without Experiments: A Study on Minimum Requirements for Experimental Data
Authors: Yang Tao , Sezer Hayri , Celik Ismail Bektas , Finklea Harry O. , Gerdes Kirk
Published: July 2015

In the present study, a physics-based procedure combining experiments and multi-physics numerical simulations is developed for overall analysis of SOFCs operational diagnostics and performance predictions. In this procedure, essential information for the fuel cell is extracted first by utilizing empirical polarization analysis in conjunction with experiments and refined by multi-physics numerical simulations via simultaneous analysis and calibration of polarization curve and impedance behavior. The performance at different utilization cases and operating currents is also predicted to confirm the accuracy of the proposed model. It is demonstrated that, with the present electrochemical model, three air/fuel flow conditions are needed to produce a set of complete data for better understanding of the processes occurring within SOFCs. After calibration against button cell experiments, the methodology can be used to assess performance of planar cell without further calibration. The proposed methodology would accelerate the calibration process and improve the efficiency of design and diagnostics.
Performance Characteristics of 100 W Carbon Fuel Cell Stack Based on SOFC Technology
Authors: Mushtaq Usman , Kim Sun-Kyung , Song Rak-Hyun , Lim Tak-Hyoung , Lee Jong-Won , Lee Seung-Bok , Park Seok-Joo
Published: July 2015

Carbon Fuel Cells (CFCs) run on carbon-rich fuels such as coal and biomass. Owing to their high theoretical efficiencies, they have been studied as new stationary power generation. This work presents the fabrication and operation of a 100W SOFC-based CFC stack, consisting of 5 bundles with 6 tubular cells per bundle. 8 mol%Y2O3-stabilized ZrO2 (8YSZ) electrolyte and layers of La0.8Sr0.2MnO3/La0.6Sr0.4Fe0.8Co0.2O3 cathode were coated on Ni-8YSZ anode support, with an active electrode area of 60cm2 per cell. Six cells were embedded vertically on a fuel gas manifold and interconnected electrically in parallel within a bundle. Five bundles were sealed and stacked in series electrically. The stack was connected to carbon fuel chambers containing mixture of activated carbon and potassium carbonate. The carbon fuel mixture was agitated with carbon dioxide to promote reverse Boudouard reaction and thus providing carbon monoxide as stack fuel. The stack and the fuel chambers were operated simultaneously in a heating furnace. The CFC stack showed 111.5W at 850oC and its average voltage degradation rate is 0.55 V/kh for 200hours. The CFC stack degradation during long-term operation was analyzed and discussed as related to microstructural change, poisoning by impurities and electrochemical cell polarization losses.
Influence of Small Defects Produced in Electrolytes during Manufacturing Processes on Operated SOFCs
Authors: Onuki Shoma , Iguchi Fumitada , Shimizu Makoto , Kawada Tatsuya , Yugami Hiroo
Published: July 2015

The influence of gas leakage through penetrated holes introduced during fabrication was experimentally evaluated using in-situ Raman scattering spectroscopy. Gas chromatography analysis of pressure differences between the anode and the cathode revealed that the gas leakage through the holes was dominated by gas diffusion through the anode, and that the pressure difference did not influence the amount of gas leakage. In-situ measurements in an operated cell with a hole revealed combustion between leaked H2 and air occurred around the hole, the O2 partial pressure at this hole was not sufficiently low to reduce NiO, and the temperature increased by almost 10°C around the hole. In contrast, no influence on stress distributions was observed.
Effect of Cathode Contacting on Anode Supported Cell Performances and Degradation
Authors: Spotorno Roberto , Piccardo Paolo , Schiller Guenter
Published: July 2015

The contact geometry effect on anode-supported cells (ASC) has been evaluated comparing the use of platinum meshes and Crofer 22 APU bipolar plates as current collectors. Additionally, the application of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) paste between the electrode and the current collector allowed to estimate the beneficial effect of the contacting layer enhancing the current distribution at the cathode side. Cells have been electrically loaded for 100 hours to investigate the polarization effects on their performances by means of current-voltage curves and electrochemical impedance spectroscopy. Post-experiment analyses have been carried out to support the electrochemical observations.
Understanding the Electrochemical Performance of SOFC Stacks
Authors: Lang Michael , Auer Corinna , Braniek Gabor , Wenz Franziska , Hauler Felix
Published: July 2015

In the past much effort was spent for the detailed understanding of the electrochemical behavior of SOFC single cells. However, these results cannot be transferred to the entire SOFC stack technology because of huge differences in fuel utilization, temperature distribution, gas flow design and electrical current load. Therefore, proper and detailed understanding of the electrochemical behavior of the SOFC stacks is necessary for the successful introduction and acceptance of the SOFC technology into the global energy market. The paper presents the electrochemical behavior of SOFC stacks with anode supported cells (ASC) in the cassette design at different operating conditions. The focus lies on the investigation of the resistances of the stack repeat units as a function of operating temperature and fuel gas flow rate. The stacks were investigated by current-voltage curves, electrochemical impedance spectroscopy (EIS) and gas analysis.
Anomalous Ohmic Loss in Solid Oxide Fuel Cells with Doped Ceria Interlayers
Authors: Zhou Xiao-Dong , Lu Z , Templeton J , Stevenson J W
Published: July 2015

The ohmic resistances were characterized in anode-supported and electrolyte-supported single cells by using electrochemical impedance spectroscopy from 500 to 850 °C. Ceria layers with various porosities were employed, which were found to play a governing role on the accelerated ohmic resistance reported in literature. The ohmic resistance with a porous doped ceria barrier layer was as large as three times of that contributed by YSZ. Further research was carried out by using a variety of YSZ electrolyte thicknesses, which were fabricated by tape casting and lamination. A linear relationship was found between the ohmic resistance of the fuel cell and the YSZ electrolyte thickness. Calculations of the contribution of the YSZ electrolyte to the total ohmic resistance show that (1) YSZ is still a satisfactory electrolyte at temperatures above 600 °C, (2) if there is no doped ceira layer, the total ohmic loss is governed by YSZ while the interfacial resistance is negligible, and (3) explorations should be directed to reduce the interception resistance to achieve significant improvement in cell performance with a doped ceria interlayer.
Microstructural Characterization of SrZrO3 Formation and the Influence to SOFC Performance
Authors: Kanae Shu , Toyofuku Yasuhiro , Kawabata Tsutomu , Inoue Yuko , Daio Takeshi , Matsuda Junko , Chou Jyh-Tyng , Shiratori Yusuke , Taniguchi Shunsuke , Sasaki Kazunari
Published: July 2015

One of the major phenomena to shorten SOFC durability is the formation of insulating phases, such as SrZrO3, between the cathode and the electrolyte. It is known that SrZrO3 is formed and grown during sintering processes as well as during long-term operation. A systematic study is made to examine the SrZrO3 formation mechanisms and their influence on electrochemical properties.
Theoretical Analysis of Cation Diffusion Pathway in SOFC Interlayer
Authors: Lin Ching-Tang , Ishimoto Takayoshi , Koyama Michihisa
Published: July 2015

Cation diffusions in solid oxide fuel cell (SOFC) interface causes degradations of cell performance. We investigated the cation diffusion mechanism in yttria stabilized zirconia (YSZ), as a first step to clarify the cation diffusion mechanism in SOFC interface. Molecular dynamics simulation combined with metadynamics method were used to simulate cation jumps in this study. Cation jumps were confirmed by using metadyanamics method. Y and Sr diffusion mechanisms in YSZ were duscussed in this study.
Electrochemical Performance of SOFC Components Fabricated by Spray Pyrolysis Method
Authors: Tsimekas George , Papastergiades Efthimis , Kiratzis Nikolas Euripides
Published: July 2015

The method of Spray Pyrolysis (SP) was applied to prepare thin films of electrodes for Solid Oxide Fuel Cell (SOFC) components. Film microstructure was analyzed by scanning electron microscopy (SEM) and was found that thin defect-free films with excellent adhesion to the substrate could be produced on dense substrates. X-ray diffraction (XRD) analysis showed that the films were crystalline after the deposition at relatively low (i.e. 700 °C) post-deposition sintering temperatures. Electrochemical tests of structures of Cu-LSCM/YSZ/LSM, Cu-LSCM/CGO/LSCF, Cu-CeO2/YSZ/Pt and Co-CeO2/ScSZ/LSM where the electrodes deposited on top of electrolytic CGO, YSZ and ScSZ dense substrates showed that it is possible to obtain SOFC electrodes with sufficient electrochemical performance fabricated by spray pyrolysis.