bluuebunny/crossref_metadata_2025 huggingface dataset:
Dusty-Gas Model with Uniform Pressure: A Numerical Study on the Impact of a Frequent Inconsistent Assumption in SOFC Electrode Modeling
Authors: Bertei Antonio , Nicolella Cristiano
Published: July 2015

One of the most popular models adopted to describe the gas transport in porous electrodes is the dusty-gas model (DGM). However, such a model is commonly applied under the assumption of uniform pressure, which is incompatible with the DGM formulation and does not allow fluxes to obey reaction stoichiometry. In such a case, the model fails to predict partial pressure profiles. In this study, the quantification of the error in the prediction of concentration overpotential, due the inconsistent assumption of uniform pressure, is obtained by simulating the gas transport in solid oxide fuel cell anodes in a broad range of conditions. Simulations show that an inconsistent use of the dusty-gas model may lead to relative errors in the prediction of concentration overpotential as large as 60%, especially in binary H2/H2O mixtures.
Effect of Non-Uniform Electrode Microstructure in Gas Diffusion Impedance
Authors: Bertei Antonio , Arcolini Giacomo , Nicolella Cristiano , Piccardo Paolo
Published: July 2015

In this study, the impedance response of gas diffusion phenomena in anodes with non-uniform microstructure is simulated by solving the dusty-gas model in frequency domain. The microstructural parameters of the supporting and functional layers are evaluated from their tomographic reconstruction, as published in the literature. Simulations show that the gas diffusion dynamics is affected by the non-uniform microstructure, thus producing an additional feature in the Nyquist plot at high frequency. Such an additional feature may be erroneously attributed to other phenomena (e.g., charge transfer processes) when phenomenological equivalent circuits are superimposed to fit the data. The study shows that the gas diffusion fingerprint can substantially differ from the expected finite-length Warburg response in electrodes with non-uniform microstructure. The paper highlights the potential misinterpretations that can arise when interpreting impedance spectra with phenomenological models, especially when the coupling between microstructural characteristics and electrode dynamics is not properly taken into account.
An Accurate and Reliable Computational Approach for the Mechanical Stress Analysis of Planar SOFC Stack
Authors: Fang Xiurong , Li Ang , Lin Zijing
Published: July 2015

Mechanical damage is a major factor limiting the long-term stability of SOFCs. It is a common practice to perform the stress analysis by isolating the interested component of an SOFC stack. This approach is questionable as it is difficult or even impossible to properly define the boundary condition for the isolated component. Here we show that the conventional approach is prone to provide misleading results. Grid settings are tested to reveal the grid dependence of the stress analysis results. A modest grid size is shown to be computationally efficient and satisfactorily accurate, allowing for the stress analysis of 20-40-cell stack by a desktop computer. Tests also show that the common practice with a free boundary condition for the interested component yields the maximal stress that is one order of magnitude too small.
Molecular Dynamics Study of Ni/YSZ Systems Based on Improved Interatomic Model
Authors: Iskandarov Albert M , Umeno Yoshitaka
Published: July 2015

In the present paper we report development of interatomic model for molecular dynamics (MD) simulations of nickel/yttria-stabilized zirconia (YSZ) systems. The model combines the Tangney-Scandolo dipole model for YSZ, the embedded atom method for Ni, and pairwise Buckingham potentials for interface interactions between Ni and YSZ. We demonstrate that the developed dipole potential reproduces basic bulk and surface properties of YSZ. Results for oxygen diffusion suggest enhanced surface diffusion along the (110) surface. The full model was employed to simulate nickel nanoparticle migration over YSZ support. Results of MD calculations indicate the possibility of particle sliding when binding energy between the support and the particles is around 0.5 J/m2.
The Effects of Cell Parameters on SOFC Cell Unit Performance
Authors: Moon Gi Jong , Ahn Myung Mo , Choi Young Jae , Kang In Seok
Published: July 2015

The effects of cell parameters on SOFC cell unit performance have been investigated experimentally and numerically. The experiment was conducted using the anode-supported SOFC cell unit (100cm2) and the 2D and 3D CFD simulation was also performed adopting the same geometry, material properties, and cell parameters. In the experiment, the voltage of SOFC cell unit was measured under the fixed current density condition, so the same method was used in numerical simulation. Based on the good agreement of the simulation results with the experimental data, the effects of cell parameters on cell performance was investigated by changing porosity, thickness of electrode and electrolytes. The cell performance was also analyzed by calculating the activation loss, the concentration loss, and the ohmic loss. With this model, we could find the optimal cell design parameters and we expect that the current findings can provide a guideline for better design of SOFC cell unit.
Reactive Force-Field Development for Metal/Ceramic SOFC Anode Modeling
Authors: Saha Leton Chandra , Iskandarov Albert , Nakao Kazuhide , Ishimoto Takayoshi , Umeno Yoshitaka , Koyama Michihisa
Published: July 2015

We developed a reactive force field (ReaxFF) for Ni/ZrO2 system. Using ReaxFF molecular dynamics (MD) simulations, the interfacial energies, work of separation and atomic structures of Ni/ZrO2 interfaces are evaluated. It is found that low index plane is favorable to form stable interface. Among interfaces formed by high index planes, one that contains Ni(311) and ZrO2(113) planes has high interfacial energies and lower work of separation. Larger work of separation and low interface energy was obtained, when interface is composed by the low index planes, such as (111) and (220). Our developed ReaxFF parameters allow us to study metal-ceramic cermet anode for solid oxide fuel cell.
Morphological Modelling of a Metal Foam Supported SOFC Configuration
Authors: Masson David , Abdallah Bassam , Willot François , Jeulin Dominique , Mercadelli Elisa , Sanson Alessandra , Chesnaud Anthony , Thorel Alain
Published: July 2015

The present paper refers to an innovative SOFC concept named EVOLVE after a running FP7 project which integrates advanced materials and an inventive anode current collector made from a NiCrAl preoxidized foam impregnated with a conductive perovskite. Even if the concept is the beneficial combination of Metal supported cell (MSC) and Anode supported cell (ASC) technologies, strong improvements in terms of reliability and durability are expected. In order to enhance anode efficiency, the 3D microstructure needs to be precisely described at the microscopic scale. ISTEC has produced LST-GDC active anode layers using screen printing process. Back-scattered electrons (BSE) SEM images that contain relevant microstructure information have been realized by Centre des Matériaux. All the original images have been enhanced by Centre de Morphologie Mathématique using a series of morphological operators to remove artefacts. Finally, a 3D pluri-Gaussian model has been generated from 2D images, and then computed to predict volume fraction of the 3 phases, 3D tortuosity, gas permeation and ionic conductivities.
Architectured Interfaces and Electrochemical Modelling in an Anode Supported SOFC
Authors: Geagea Maya , Ouyang Jian , Chi Bo , Delloro Francesco , Chesnaud Anthony , Ringuedé Armelle , Cassir Michel , Thorel Alain
Published: July 2015

Increasing the performances of SOFC is many-fold: i/ at low currentdensity, through the enhancement of the catalytic properties of theelectrodes, ii/ in the ohmic loss region, through lower resistance, iii/ inthe high current density region, via the optimization of the electrodesmicrostructure. The present work proposes to explore how thecorrugation of electrode/electrolyte interfaces impacts the performancesof SOFCs. Taking ideas from the battery community, this approach wasapplied to the anode/electrolyte interface of a SOFC based on standardcompositions. Patterning of this interface was achieved with differentgeometries at the 10-100 μm mesoscopic scale by cold pressing. Thinelectrolyte layers have been deposited on top of these architectures bydifferent techniques. In parallel, an electrochemical model was carriedout and implemented throughout the interface in finite element method(FEM) with COMSOL Multiphysics. The results showed a 25% increase in the total current density for a certain ellipsoid geometry.
Modelling and Prediction of Deformation during Sintering of a Metal Foam Based SOFC (EVOLVE)
Authors: Xu Meng , Masson David , Ryckelynck David , Chesnaud Anthony , Thorel Alain
Published: July 2015

Stacking of cells in a SOFC stack requires that each element be perfectly flat and deprived, as much as possible, of internal stresses while maintaining their electrochemical capabilities. The EVOLVE concept introduces a metal foam based anode in which the foam plays the role of current collector, gas diffuser and thermo-mechanical deformation buffer. Owing to the different mechanical behaviour of the anode components, the deformation during sintering cannot be intuitively anticipated. Therefore, the global deformation of the cell was modelled and simulated by Finite Element considering a phenomenological approach of the anisotropic sintering. The thermo-mechanical parameters of each component were determined experimentally by dilatometry and three-point bending tests operated under conditions identical to those of the sintering. Results provide relevant indications on components composition and morphology, and on the sintering conditions for producing flat and stackable cells.
Simulation of Interfacial Cracking of the Joint between Glass-Ceramic Sealant and Metallic Interconnect in a Planar Solid Oxide Fuel Cell Stack
Authors: Lin Chih-Kuang , Shiu Wei-Hong , Wu Si-Han , Lee Ruey-Yi
Published: July 2015

Interfacial cracking in the joint between glass-ceramic sealant and metallic interconnect under thermal stresses is characterized for a prototypical planar solid oxide fuel cell (pSOFC) stack, using finite element analysis (FEA). A three dimensional FEA model is constructed for a multiple-cell stack to perform thermal stress analysis at both steady operation and shutdown stages and to locate the highly stressed region in each component. Stress intensity factor and energy release rate for fracture are calculated for each stage at the crack front of a crack placed at the highly stressed interfacial region between glass-ceramic sealant and metallic interconnect. The critical crack/defect size at the interface of such a joint in the given pSOFC stack is determined to be 70 μm by comparing the calculated energy release rates with the experimental measurements of interfacial fracture energy.
Estimation of 3D Effective Properties from 2D Cross Sections in Porous Electrodes
Authors: Ferrari Tommaso , Bertei Antonio , Nicolella Cristiano
Published: July 2015

The study summarizes the correlations between 2D and 3D microstructural properties of SOFC electrodes within the framework of stereology. 3D geometrical properties, such as the mean particle diameter, the pore size, the specific surface area and the three-phase boundary density are correlated by simple relations to 2D properties evaluated in a cross section, such as the mean diameter of the sectioned particles, the mean chord length, the particle perimeter exposed to the porous phase and the number of three-phase boundary points per unit area, respectively. The strong correlation between 2D and 3D properties predicted by stereological relations is verified by using packing algorithms in a wide range of porosity, particle size and electrode composition. The results provide practical indications that can be easily applied to SEM images of real samples for a short-cut estimation of the effective properties and of the range of confidence of the prediction.
Modeling of Solid Oxide Fuel Cell with Anisotropic Conductivity
Authors: Xu Min , Andersson Martin , Li Tingshuai , Sundén Bengt , Chen Fanglin (Frank)
Published: July 2015

In recent years, significant advances have been made in the understanding of fabricated technology of solid oxide fuel cells (SOFCs). A three-dimensional model based on the finite element method (FEM) is developed for a single planar SOFC. The uniqueness of this paper is that both anode support electrode and anode active electrode layer fabricated by the freeze-tape-casting process with anisotropic conductivity property is taken into account. The parameter study demonstrates that grading the electron conductivity (increased in both anode and cathode active layers and support layers), in the principle direction to the electrode/electrolyte interface will increase the performance. On the other hand, the results also indicate that increased conductivity perpendicular with fuel transform of active electrode could significantly enhance the gas transport current density. It is concluded that an increased electric conductivity parallel to the electrode/electrolyte and perpendicular to the fuel and gases transport path in the active electrode raises the current density efficiently. Optimization of cell performance requires consideration of anisotropic conductivity that is needed to develop three-dimensional models.
Three-Dimensional Computational Fluid Dynamics Modelling for a Planar Solid Oxide Fuel Cell of a New Design
Authors: Pianko-Oprych Paulina , Zinko Tomasz , Jaworski Zdzislaw
Published: July 2015

The aim of the work is to investigate the electrochemical processes of a planar Solid Oxide Fuel Cell and to estimate the performance of a novel SOFC design. The design involves cross-flow bipolar plates. Each of the bipolar plates has an air channel system on one side and a fuel channel system on the other side. One pair of channels in adjacent plates is used for the air flow along the cathode, the other for the fuel flow along the anode of each cell. A three-dimensional Computational Fluid Dynamics model for the anode-supported planar SOFC with complex bipolar plates has been developed. The distributions of temperature and gas flow through the channels and MEA structure were studied. The results identified the most susceptible areas for significant increase of the temperature at high current density, which can lead to hot spots formation and destruction of the electrodes.
A High Resolution Multi-Physics Numerical Model for Planar SOFC Stack
Authors: Li Ang , Fang Xiurong , Lin Zijing
Published: July 2015

We report a successful development of a high space resolution multi-physics mathematical model for full scale planar SOFC stacks which is, to the best of our knowledge, the first of its kind. This 3D 30-cell stack model takes into account the coupled physical processes, applicable for both methane and hydrogen based fuels. Every cell consists of 30 channel-rib pitches, i.e., there are 900 repeating units for the electrochemically active area of the 30-cell stack. The computational domain contains all components of the stack, including channels, internal manifolds, PEN assemblies, interconnects, seals and frames. This model is constructed using the CFD software, FLUENT®, supplemented with in-house developed external subroutines to ensure all governing equations and physical properties are correctly coupled and solved successfully. Multi-physics numerical simulations of this truly high resolution computational model of 30-cell stack have been successfully performed in a 2-CPU/16-core PC.
Stationary 2D FEM Model Framework for SOFC Stack Performance Prediction
Authors: Geisler Helge , Kromp Alexander , Joos Jochen , Weber André , Ivers-Tiffée Ellen
Published: July 2015

It is a well-known fact, that high-performing anode-supported cells (ASCs) undergo a significant power reduction when contacted in a stack by metallic interconnectors (MIC) with a specific flow field design (1,2). For profound investigations, a model framework has been presented in previous studies (3-5) which uniqueness is based on its strict use of in-house determined material parameters and validation measurements over broad range of operating conditions. Included are the physically coupled processes (i) electrical/ionic conduction in electrode/electrolyte material, (ii) electrochemical charge transfer at the electrode/electrolyte interfaces and (iii) porous media gas species transport in the porous electrodes [5]. It has become clear that O2 starvation underneath the MIC contact rips and/or electrical cross conduction limitations in the cathode material underneath the gas channel area creates performance losses, which add up additionally for each individual stack layer to the standard cell polarization losses. It will be shown in this work, why (i) by adding a current collector layer (CCL) losses are reduced, that (ii) the degree of loss reduction is highly dependable on CCL thickness and microstructure and that (iii) the overall performance can further be improved by a well-chosen MIC contact rip thickness.
Multi-scale Modeling of Biogas Fueled SOFC
Authors: Janardhanan Vinod M
Published: July 2015

This paper presents a multi-physics model for simulating solid oxide fuel cells operating directly on biogas without the aid of an external reformer. The model accounts for multi-component species transport, electrochemical charge transfer and charge transport within the electrodes and electrolyte. The model uses only 3 adjustable parameters that are fitted against a base set of experimental data and then kept constant throughout the study. The model predicted voltage fluctuations due to composition fluctuation of biogas are in very good agreement with experimentally measured voltage fluctuations. The model reveals that the assumption of H2 as the only electrochemically active species is probably inadequate for explaining the behavior of cells operating directly on biogas. It is also found that the electrochemically active thickness is independent of fuel composition and the ionic current through electrolyte under fuel rich conditions.
Detailed H2 and CO Electrochemistry for a MEA Model Fueled by Syngas
Authors: Lee Won Yong , Ong Katherine M , Ghoniem Ahmed F
Published: July 2015

SOFCs can directly oxidize CO in addition to H2, which allows them to be coupled to a gasifier. Many membrane-electrode-assembly (MEA) models neglect CO electrochemistry due to sluggish kinetics and the water-gas-shift reaction, but CO oxidation may be important for high CO-content syngas. The 1D-MEA model presented here incorporates detailed mechanisms for both H2 and CO oxidation, individually fitted to experimental data. These mechanisms are then combined into a single model, which provides a good fit to experimental data for H2/CO mixtures. Furthermore, the model fits H2/CO data best when a single charge-transfer step in the H2 mechanism is assumed to be rate-limiting for all current densities. This differs from the result for H2/H2O mixtures, where H2 adsorption becomes rate-limiting at high current densities. These results indicate that CO oxidation cannot be neglected in MEA models running on CO-rich syngas, and that CO oxidation can alter the H2 oxidation mechanism.
Three Dimensional Temperature Distribution Analysis in Directly Internal Reforming SOFC Fuelled by Methane
Authors: Ogura Teppei , Wakamatsu Katsuhiro
Published: July 2015

High SOFC operating temperature allows direct internal reforming (DIR) of methane within the SOFC anode, which is expected to be load-following simple dispersed power system. However, temperature decrease by endothermic reforming reaction leads to carbon formation and increase of thermal stress which cause decrease in the performance and durability of SOFC cells. We have developed a reactor model coupled with computer fluid dynamics and reactions to predict three dimensional temperature distributions. Calculated temperature distributions along flow direction agree with experimentally measured ones in both cases of homogeneous and functionally-graded paper structure catalysts. Detailed three dimensional analyses of temperature distributions tell us the importance of cell structures, gas inlet position, and catalyst thickness. Then, we have extended the analysis tool to more practical model where three SOFC cells are stacked. Temperature distribution in an upstream cell has steeper gradient than that in a downstream cell. Better temperature distribution was obtained by designing functionally-graded paper structure catalysts in two dimensions, along the stacking direction and the gas flow in a cell.
Simulation of Start-up of Anode Gas Recycle SOFC System Using Catalytic Combustion Method
Authors: Baba Soumei , Kobayashi Nariyoshi , Takahashi Sanyo , Hirano Satoshi
Published: July 2015

Solid oxide fuel cells (SOFCs) are the most efficient known converters of chemical to electrical energy, and simple, compact SOFC designs are actively sought. We simulated an anode gas recycle SOFC system using a catalytic combustion method during transient operations (i.e., startup and shutdown). In this system, methane fuel conversion is enabled by oxidation air that is injected by a catalytic combustion reaction in the combustor section located upstream of the pre-reformer section. The effects of the operation conditions (i.e., the stack temperature, air-to-methane feed ratio, fuel utilization, and recirculation ratio) on system performance were clarified via chemical equilibrium calculations. From the results of this simulation, we determined the operational procedures and system configurations corresponding to the stack temperature and load conditions.
A Lumped Dynamic Modelling Approach for Model-Based Control and Diagnosis of Solid Oxide Fuel Cell System with Anode Off-Gas Recycling
Authors: Marra Dario , Sorrentino Marco , Pohjoranta Antti , Pianese Cesare , Kiviaho Jari
Published: July 2015

This work focuses on the identification and validation of a Solid Oxide Fuel Cell (SOFC) stack model that accounts for anode off-gas recycling (AOGR) inclusion. A lumped dynamic modelling approach is adopted to simulate temperature and gas composition at the stack anode outlet. The model is able to simulate the dynamic response of the stack during transients. Experimental data from a real SOFC system are used in model validation and the modeling approach adopted here ensures achieving a satisfactory compromise between estimation accuracy and computational burden. These factors support using the model as state estimator in model-based control and diagnosis algorithms.
Process Analysis for Achieving Highly Enhanced Total Efficiency on Multi-Stage Fuel Supplied SOFC System
Authors: Tachikawa Yuya , Matsuzaki Yoshio , Hatae Toru , Taniguchi Shunsuke , Sasaki Kazunari
Published: July 2015

A multi-stage fuel supply SOFC system is studied, which has additional fuel supply inlets between each SOFC stack. The anode offgas from the first stack is supplied to the next stack as reformed fuel gas being mixed with additional fresh fuel. In this paper, the effect of the additional fuel flow ratio is evaluated. The electric efficiency and the fuel utilization of the system can be improved in applying multi-stage fuel supply design.
High Efficient Combined Heat and Power SOFC System for Residential Power Applications: Lifetime-Efficiency-Simulations Using AspenPlusTM
Authors: Spieker Carsten , Spitta Christian , Noponen Matti , Hallanoro Paul , Ruetten Thomas
Published: July 2015

High temperature Solid Oxide Fuel Cells (SOFC) systems are high efficient energy conversion systems with low emissions e.g. for residential power applications. The objective of this work is to provide a flexible model of a SOFC system that is capable of predicting system performance in a wide range of operating conditions as well as predicting system lifetime performance based on experimentally determined SOFC performance and endurance curves. The system model is developed using AspenPlusTM unit operation blocks and the SOFC electrochemical model is implemented using the embedded AspenPlusTM Microsoft Excel Workbook. Validation of the model is performed by comparison to experimental results. The adaption of this model to different SOFC system simulation approaches will be discussed. Furthermore for a SOFC based mCHP system development simulation results predicting an electrical efficiency higher than 50 % and an overall system efficiency higher than 85 % for the whole lifetime will be presented.
A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles
Authors: Hari Bostjan , Dhir Aman , Steinberger-Wilckens Robert
Published: July 2015

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle.The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds. The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.
FDI Oriented Simulation of an MSR Reactor for Application in SOFC Systems
Authors: Costamagna Paola , Rossi Stefano , Pugliese Federico , Gugliotta Federico , Enrico Anna
Published: July 2015

We propose a modelling approach, applied to an experimental methane steam reforming reactor, aiming at investigating carbon deposition by embedding the kinetics of the methane decomposition reaction. The results show that for a steam/methane feeding mixture with a steam-to-carbon ratio equal to 3, carbon deposition is predicted to occur in the first 0.001 m of the reactor, and this is expected to build-up during time, causing catalyst deactivation and progressive shift of the methane steam reforming and water gas shifting reactions downwards the reactor. The modelling tool is designed to be the basis of a fault detection and isolation tool, aiming at early detection and possible remediation of the coke deposition fault in methane steam reforming reactors for application in SOFC plants.
Feedforward-Feedback Control of a SOFC Power System: A Simulation Study
Authors: Vrečko Darko , Dolanc Gregor , Dolenc Bostjan , Vrančić Damir , Pregelj Bostjan , Marra Dario , Sorrentino Marco , Pianese Cesare , Pohjoranta Antti , Juričić Đani
Published: July 2015

In this paper a feedforward-feedback control design for solid oxide fuel cell (SOFC) power systems is proposed. The feedforward part of the controller reacts to the electrical current demand as well as the stoichometry of electro-oxidation and reforming processes. Feedback part performs corrections of the controlled system output by additional manipulation of system inputs. Based on relative gain analysis (RGA), it is found that two individual PI control loops turn out suitable enough to control the system. Parameters of the PI controllers are tuned on the basis of open-loop step response experiments by applying the Magnitude Optimum Multiple Integration method (MOMI). The proposed feedforward-feedback control is verified on the SOFC stack model over a one-day operation cycle using the standard load profile of residential houses. The main advantage of the proposed controller is its simple structure and easy tuning, which makes it feasible for practical implementation.
Modeling Intermediate Temperature Protonic Ceramic Fuel Cells
Authors: Albrecht Kevin J , Duan Chuancheng , O'Hayre Ryan , Braun Robert J.
Published: July 2015

Protonic ceramic fuel cells (PCFC) have emerged as a promising candidate for distributed power generation and synthetic fuel production. The cells offer the potential for reduced temperature operation (~500oC), which enables faster startup times, longer life, and lower material cost components to be used compared to their oxygen ion conducting counterparts. The development of a new protonic ceramic fuel cell computational modeling framework is presented for a predictive cell-level, interface charge transfer PCFC model capturing the mixed conducting nature of the protonic ceramic materials. The model employs a 1-D channel-level modeling strategy where fuel depletion and flow configuration effects are resolved and coupled to a semi-empirical electrochemical model. Modeling results calibrated against experimental data of a state-of-the-art PCFC composition are presented. The model is capable of simulating a fuel flexible PCFC where methane and steam without pre-reforming are fed directly into the anode gas channel.
Theoretical Study of Inorganic Carbonaceous Species Reaction with the Surfaces of BaTiO3(001)
Authors: Rivera Rocabado David Samuel , Ishimoto Takayoshi , Quang-Tuyen Tran , Shiratori Yusuke , Koyama Michihisa
Published: July 2015

In this study, the density functional theory was employed to analyze from a theoretical point of view the reaction of CO and CO2 with the surfaces of BaTiO3(001). Our results showed that the adsorption of CO is more stable on the TiO2-terminated than on the BaO-terminated slab. Additionally, this interaction led to the stable formation of CO3 on the TiO2-terminated slab. Similarly, the chemisorption of CO2 on both surfaces showed to be high stable, and it led to the CO3 formation on the BaOT slab. Moreover, in order to investigate the possibility of carbon deposition, the CO disproportionation reaction was considered to occur via the Eley-Rideal reaction mechanism. However, it was observed that the carbon deposition is quite energetically demanding, more challenging for the BaO-terminated surface than for the TiO2-terminated, and might not occur at the operating conditions of the solid oxide fuel cells.
Density Functional Theory Study of Dopant Effect on Sintering in the Anode of Solid Oxide Fuel Cell
Authors: Xu Jingxiang , Higuchi Yuji , Ozawa Nobuki , Kubo Momoji
Published: July 2015

Sintering of Ni particles in the Ni/Y-doped ZrO2 anode is a major obstacle to the widespread use of solid oxide fuel cell. In this study, we investigated the dopant effect on the diffusion of a Ni atom on the ZrO2 surface with dopants (Y and Al) by density functional theory calculations in order to inhibit the sintering. The most stable adsorption sites of the Ni atom on the Al-doped and Y-doped ZrO2 surfaces are the vicinity of the twofold-coordination oxygen atom and the vicinity of an oxygen vacancy, respectively. It is found that the most stable adsorption energy on the Al-doped ZrO2 surface is larger than that on the Y-doped ZrO2 surface. The analysis of diffusion path based on the potential energy surfaces of the Ni atom on the two surfaces shows that the energy barrier for the diffusion of the Ni atom on the Al-doped ZrO2 surface is larger than that on the Y-doped ZrO2 surface. The diffusion of the Ni atom on the Al-doped ZrO2 surface is more difficult than that on the Y-doped ZrO2 surface. This is because the Ni atom strongly bound to the twofold-coordination oxygen atom and the Ni atom is constrained in the Al-doped ZrO2 surface. Thus, the Ni sintering on the Al-doped ZrO2 surface is inhibited compared to that on the Y-doped ZrO2 surface.
Computational Materials Design of Rare-Earth-Based Fast Oxygen Ion Conductors by First-Principles Simulation Based on Density Functional Theory
Authors: Sakaue Mamoru , Kasai Hideaki
Published: July 2015

We studied atomic and electronic properties of La2GeO5-based materials by first-principles calculations based on density functional theory. We analyzed effects of doping on stable structures, electronic densities of states, oxygen migration paths and activation energies in order to evaluate their capabilities in application to electrolytes. We focus on minimum energy paths of oxygen migration based on nudged elastic band analysis in order to figure out ion conduction properties in low temperatures. Based on the results, we will discuss the potentials and hindrances of the materials as solid electrolytes operable in low temperatures and give guiding principles for the materials design.
First-Principles Study of Surface Peroxo in Oxygen-Rich Yttria Stabilized Zirconia (110)
Authors: Takemoto Seiji , Tada Tomofumi
Published: July 2015

We carried out the first principles electronic structure calculations for oxygen-rich YSZ(111), YSZ(110), and YSZ(100) surfaces, and found the two configurations of surface-peroxo structures only in oxygen-rich YSZ(110), depending on the positions of yttrium atoms. The relative surface areas for oxygen-rich YSZ(110) with the peroxo structures were also calculated by using Gibbs factors, and not so small ratio (0.8 ~ 1.1 %) of the oxygen-rich YSZ(110) with the peroxo was obtained at high temperature and oxidation conditions. The results indicate a possibility of the experimental observation of the peroxo structure on O-rich YSZ (110) surface, as already confirmed in TiO2 anatase (101) (M. Setvín et al., Science 341 (2013) 988) and cubic In2O3 (001) (D. R. Hagleitner et al., Phys. Rev. B 85 (2012) 115441).
Modeling Water Reduction on Doped Ceria Thin Films
Authors: Valdes-Espinosa Honorio , Stuve Eric M. , Adler Stuart B.
Published: July 2015

In this work, the non-linear electrochemical impedance (NLEIS) response of doped ceria thin films under reducing conditions was modeled using a stirred tank model. Two different scenarios were considered: a uniform film scenario and a surface-enriched scenario where the electron concentration in the surface was increased. Modeling results show that NLEIS is not only capable to distinguish between the different rate-determining cases, but also is sensitive to changes in the thermodynamics of the surface.
Ab Initio Molecular Dynamics Simulation of Oxygen Adsorption and Electron Transfer on SOFC Cathode
Authors: Sugiura Shinya , Shibuta Yasushi , Shimamura Kohei , Misawa Masaaki , Shimojo Fuyuki , Yamaguchi Shu
Published: July 2015

Absorption and subsequent dissociation of oxygen molecules on the cathode surface of the solid oxide fuel cell (SOFC) with various types of vacancy are investigated by the ab initio MD simulation. The oxygen molecule adsorbed on the nickelous oxide (NiO) surface with an oxygen vacancy at the surface layer and that on the surface with a nickel vacancy at the subsurface layer are dissociated. On the other hand, the oxygen molecule adsorbed on the NiO surface with a nickel vacancy at the surface layer and that on the surface with an oxygen vacancy at the subsurface are not dissociated. The change in Mulliken charge of oxygen atoms and connecting nickel atoms during the dissociation is larger during the adsorption.
Reversible Oxygen-Ion Storage for Solid Oxide Cells
Authors: Berger Cornelius M. , Hospach Andreas , Menzler Norbert H. , Guillon Olivier , Bram Martin
Published: July 2015

In a rechargeable oxide battery (ROB) a solid oxide cell (SOC) is combined with an integrated iron oxide base storage for oxygen ions. The cell is operated at 800°C alternately as fuel cell and as electrolyser and the storage material regulates the oxygen partial pressure at the fuel electrode in a range of approximately 10-21-10-18 bar. Repeated charging (electrolysis) and discharging (fuel cell mode) can lead to a degradation of the storage material (particle coarsening, layer formation). In this study the influence of additions of Al2O3, CeO2, Mn3O4, Cr2O3, TiO2, SiO2, and MgO to the Fe2O3 base on these detrimental effects is analysed. Hence, compacted samples are repeatedly oxidised and reduced in a laboratory furnace, where the conditions present in the ROB are simulated. Using XRD and laser microscopy it was found that among the tested oxides only MgO and Al2O3 could mitigate the degradation phenomena to some extent.
Reversible Fuel Cells with Tri-Layer Electrolytes
Authors: Virkar Anil V.
Published: July 2015

A tri-layer electrolyte membrane is proposed for high temperature reversible fuel cells. The tri-layer electrolyte consists of a central dense layer of a purely oxygen ion conducting material such as yttria-stabilized zirconia (YSZ), a thin dense p-type mixed oxygen ionic electronic conducting (MIEC) layer such as LSCF in contact with the oxygen electrode and a thin dense n-type mixed oxygen ionic electronic conducting layer such as rare earth oxide doped ceria in contact with the fuel electrode. In this manner, the electrochemical reactions occur at the p-type MIEC layer/oxygen electrode interface and the n-type MIEC layer/fuel electrode interface. The MIEC characteristics of the respective thin layers are expected to significantly lower the overall polarization resistances and the resistances to electronic defects transport across electrode/electrolyte interfaces. This is expected to minimize the variation of oxygen chemical potential across the tri-layer electrolyte and thus minimize degradation.
High Performance Air Electrode for Solid Oxide Regenerative Fuel Cells Fabricated by Infiltration of Nano-Catalysts
Authors: Yoon Kyung Joong , Hong Jongsup , Kim Hyoungchul , Son Ji-Won , Lee Jong-Ho , Kim Byung-Kook
Published: July 2015

A high performance air electrode was fabricated by infiltration of nano-catalysts into a porous backbone for high-temperature solid oxide regenerative fuel cells (SORFCs). The Sm0.5Sr0.5CoO3 (SSC) nano-catalysts were uniformly synthesized in a porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) – gadolinia-doped ceria (GDC) composite backbone by impregnation of nitrate precursor solution followed by homogeneous nucleation induced by urea decomposition. Significant improvement in the electrochemical performance was achieved in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes.
Thermodynamic and Exergy Analysis of Reversible Solid Oxide Cell Systems
Authors: Botta Giulia , Patel Hrishikesh C , Sebastiani Francesco , Aravind P.V.
Published: July 2015

Reversible solid oxide cell (SOC) technology could enable efficient storage of renewable energy. In literature, reversible systems have not yet been widely investigated. The main goal of the present work is to address differences and similarities among simple SOFC and SOEC systems based on the same variables. Scope of the analysis is to identify useful operating regimes for a bi-directional system, using a thermodynamic analysis. Both energetic and exergetic point of views are adopted to estimate system and components performances. Preliminary results from the ongoing research are presented in this paper. Different operating conditions are evaluated via sensitivity analysis. Results are presented first for a reversible cell and then for a complete system. Looking at system operation it is feasible to design a reversible SOFC / SOEC system. At atmospheric pressure the total reversible system energy efficiency is around 30%. This value could be increased with system modifications.
Reversible Type Solid Oxide Fuel Cells Using Ni-Fe-CeO2 Based Cermet Fuel Electrode and Applied for Metal-Air Rechargeable Battery
Authors: Ishihara Tatsumi , Inoishi Atsushi , Kim Hackho , Ida Shintaro
Published: July 2015

Effects of mixed conducting oxide added for Ni-Fe were studied as fuel electrode of Solid Oxide Reversible Cells (SORC). For SOFC operation, power density is larger as the following order, BaCe(Y)O3<<YSZ<Ce(Mn,Fe)O2<NiFe=La(Sr)Ga(Mg)O3<Ce0.8Sm0.2O2<La(Sr)Fe(Mn)O3. On the other hand, for electrolysis operation, the electrolysis current density is increased as the following order, BCY<Ce(Mn,Fe)O2 <YSZ=NiFe< La(Sr)Ga(Mg)O3<<La(Sr) Fe(Mn)O3<Ce0.8 Sm0.2O2. Therefore, for reversible operation, NiFe- Ce0.8Sm0.2O2 (SDC) seems to be the most active. Degradation of the cell using NiFe-SDC and Sm0.5Sr0.5CoO3 for fuel and air electrode, respectively, was studied at 1073 K, 100mA/cm2. The observed terminal potential was 1.13 and 1.025 V for SOEC and SOFC respectively at initial cycle and the observed potential slightly increased for SOFC and decreased for SOEC with cycle number, however, after 50 cycles, the observed terminal potential was 1.15 and 1.0 V for SOFC and SOFC, respectively. Therefore, the degradation is hardly observed for the reversible operation of the cell. Combination of SORC with metal oxidation could open a new application area for fuel cell. In this study, application of SORC for reversible metal-air battery
Energy Dense Storage Using Intermediate Temperature Reversible Solid Oxide Cells
Authors: Monti Arrigo , Wendel Christopher , Santarelli Massimo , Braun Robert J.
Published: July 2015

The development of high efficiency electrical energy storage of power produced from intermittent renewable energy sources increases the potential for their integration into the electric grid. The focus of the present study is to examine an intermediate temperature reversible solid oxide cell system (ReSOC) of distributed generation capacity (100 kW), which has been identified as a promising technology for electrical energy storage applications. Conceptualized ReSOC systems often store syngas in fixed volume tanks that can be rich in hydrogen, but have low volumetric energy density. The aim of this study is to increase syngas volumetric energy density by integrating a methanation reactor downstream of the electrolysis cell, which will thereby increase the methane content produced during charging mode and significantly raise the volumetric energy storage density of the system. It is found that integration of a methanation reactor into the system can improve volumetric energy storage density by 60% and the overall system round-trip efficiency, albeit at the expense of increased plant complexity and heat exchanger surface area requirements.
Electrolysis Operating Mode for Reversible Solid Oxide Fuel Cells
Authors: Minh Nguyen , Williams Mark Christopher
Published: July 2015

Reversible solid oxide fuel cells (RSOFCs) can operate efficiently in both fuel cell and electrolysis modes. The RSOFC has been considered for generation of electrical power from a variety of fuels and production of chemicals such as hydrogen from steam when coupled with an energy source. The RSOFC is technologically derived from the SOFC, therefore, when the cell is operated in electrolysis mode (referred to as solid oxide electrolysis cell or SOEC mode), it is critical that electrode performance is reversible and system design is configured for efficient operation in both SOEC and SOFC modes. This paper discusses certain aspects of electrode reversibility in SOEC mode for planar RSOFCs and presents a conceptual system design for electrolysis operation.
Effect of Microstructure on Performances of Hydrogen and Oxygen Electrodes for Reversible SOEC/SOFC
Authors: Uchida Hiroyuki , Puengjinda Pramote , Miyano Kohei , Shimura Kazuki , Nishino Hanako , Kakinuma Katsuyoshi , Brito Manuel E. , Watanabe Masahiro
Published: July 2015

We have developed high performance electrodes for reversible SOEC/SOFCs. Double-layer hydrogen electrodes, consisting of a mixed conducting samaria-doped ceria (SDC) with highly dispersed Ni–Co catalysts as the catalyst layer (CL) and, on top of it, a thin Ni–SDC cermet as the current collecting layer (CCL), exhibited highly reversible performance at 800°C by controlling the microstructure. We have also succeeded in enhancing the reversible performances of LSCF–SDC composite oxygen electrodes accompanied by high durability.
Oxygen Nonstoichiometry and Cathodic Property of Ce0.6Mn0.3Fe0.1O2-δ for High Temperature Steam Electrolysis Cell Using LaGaO3-Based Oxide Electrolyte
Authors: Hosoi Kohei , Sakai Takaaki , Ida Shintaro , Ishihara Tatsumi
Published: July 2015

Steam electrolysis was studied by using a new oxide cathode of Ce0.6Mn0.3Fe0.1O2-

d
(CMF). It found that this cathode showed almost same performance compared with a conventional Ni-based cathode without H2 flow and H2 generation rate obeyed the Faraday’s law at 900-700°C. The result of XRD measurement after operation, CMF phase were hardly changed after the steam electrolysis. A long-termed durability test was operated, and it revealed that CMF cathode showed the good stability over 90 h at 800 °C. The impedance spectra were measured under applied DC bias potentials. It revealed that polarization resistance and ohmic resistance were decreased with increasing DC bias potential. This decreasing of ohmic resistance was related to the increasing in electronic conductivity of CMF. CMF was n-type semiconductor and then electronic conductivity of CMF increased with decreasing of oxygen partial pressure.
Influence of the Solid Oxide Electrolysis Component Characteristics on the Electrochemical Performance of SOE Cells
Authors: Tamm Kadi , Kukk Freddy , Salvan Laur Kristjan , Kanarbik Rait , Möller Priit , Nurk Gunnar , Lust Enn
Published: July 2015

Electrochemical behavior of four solid oxide electrolysis cells (SOEC) cells with different cathode microstructures, chemical compositions and electrolyte thicknesses have been tested using cyclic voltammetry, impedance spectroscopy and other electrochemical methods. Influence of cathode composition and thickness as well as electrolyte thickness, temperature and gas composition in cathode compartment on the SOE parameters has been demonstrated. It was shown that the polarization resistance (R
P) decreases with the replacement of Ni-YSZ to Ni-GDC. The lowest R
P has been measured for single cell consisting supportive ScSZ electrolyte and thin Ni-GDC cathode layer.
Water Splitting on Model-Composite La0.6Sr0.4FeO3-δ (LSF) Electrodes in H2/H2O Atmosphere
Authors: Opitz Alexander Karl , Nenning Andreas , Kogler Sandra , Rameshan Christoph , Rameshan Raffael , Blume Raoul , Haevecker Michael , Knop-Gericke Axel , Rupprechter Guenther , Kloetzer Bernhard , Fleig Juergen
Published: July 2015

Mixed conducting cathodes for solid oxide electrolysis cells (SOECs) offer a promising alternative to the nowadays used Ni/YSZ cermet. Here, the water splitting kinetics of mixed conducting perovskite-type La0.6Sr0.4FeO3-δ (LSF) thin film electrodes was investigated in humid reducing atmospheres at 600 – 650 °C. Under equilibrium conditions an area specific surface resistance of ca. 15 Ωcm² was obtained on freshly prepared electrodes. Upon cathodic polarization of more than 20 mV a strong decrease of the surface resistance was observed. This acceleration of the water splitting kinetics was accompanied by the formation of metallic iron particles on the LSF surface, which was observed by means of near-ambient pressure XPS experiments.
Evaluation of La2NiO4 as Anode Material for Solid Oxide Electrolyser Cells
Authors: Egger Andreas , Schrödl Nina , Sitte Werner
Published: July 2015

La2NiO4 is characterised as potential anode material in solid oxide electrolyser cells (SOECs). Investigations are performed at 800°C and 0.1-0.2 bar oxygen partial pressure over a period of several thousand hours. Trends in chemical surface exchange coefficient and electrical conductivity of a densely sintered sample are identified. In addition, changes in polarisation resistance of a porous anode layer of La2NiO4 on a button cell under constant anodic current bias of -410 mAcm-2 are recorded. Special emphasis is laid on the impact of Cr-impurities in the surrounding gas phase on the oxygen transport properties and SOEC anode performance. Cr-poisoning is found to depend strongly on the level of humidity in the gas phase as well as on the polarisation conditions.