Microscale Correlations Adoption in Solid Oxide Fuel Cell

A micro scale model of a solid oxide fuel cell (SOFC) involving the mass transfer together with the electrochemical reaction, the electron and ion transports through respective cylindrical shaped electron-and ion-conducting particles inside the electrodes was mathematically developed. The predicted cell performance was showed according to the operating and design condition. The effects of micro-scale electrode geometry on the cell performance were also taken into account. This present study reveals the working mechanisms of SOFC at the micro-scale level, while demonstrating the use of micro-scale relations to enhance the SOFC performance. The accuracy of the presented model was validated by comparing to already existing experimental results from the available literatures.

Integrated gasification fuel cell (IGFC) systems combining coal gasification and solid oxide fuel cells (SOFC) are promising for highly efficient and environmentally friendly utilization of coal for power production. Most IGFC system analyses performed to-date have used nondimensional thermodynamic SOFC models that do not resolve the intrinsic constraints of SOFC operation. In this work a quasi-two-dimensional (2D) finite volume model for planar SOFC is developed and verified using literature data. Special attention is paid to making the model capable of supporting recent SOFC technology improvements, including the use of anode-supported configurations, metallic interconnects, and reduced polarization losses. Activation polarization parameters previously used for high temperature electrolyte-supported SOFC result in cell performance that is much poorer than that observed for modern intermediate temperature anode-supported configurations; thus, a sensitivity analysis was conducted to identify appropriate parameters for modern SOFC modeling. Model results are shown for SOFC operation on humidified H2 and CH4 containing syngas, under coflow and counterflow configurations; detailed internal profiles of species mole fractions, temperature, current density, and electrochemical performance are obtained. The effects of performance, fuel composition, and flow configuration of SOFC performance and thermal profiles are evaluated, and the implications of these results for system design and analysis are discussed. The model can be implemented not only as a stand-alone SOFC analysis tool, but also a subroutine that can communicate and cooperate with chemical flow sheet software seamlessly for convenient IGFC system analysis.

Solid oxide fuel cells are among the most thermodynamically efficient energy conversion devices. They are critical for the future if we are to meet rising energy demands and increasing selectivity over our future energy mix. Traditionally, solid oxide fuel cell performance has been assessed using bulk parameters, and the microstructure-bulk properties relationship is yet to be well understood. Here, we use time-lapse 3D imaging to probe 3D electrode structure and move towards intelligently designing structures with specific performance attributes. Using 3D imaging allows for characterisation and quantification of parameters that are not well described in 2D, such as triple-phase boundary lengths, tortuosity and phase percolation. In this work, the parameters for an optimised porous nickel-scandia stabilized zirconia anode (Ni-ScSZ) were calculated using an electrochemical model to maximise triple-phase boundary length and density, gas permeation and electronic and ionic transport. Ni-ScSZ scaffolds were then produced using screen-printing and impregnation and characterized with FIB-SEM to obtain 3D microstructural parameters such as actual percolation of the phases, tortuosity and connectivity of the phases, and the length and density of triple-phase boundaries (Figure 1). The experimental microstructural parameters were then compared to the modelled optimised microstructure, allowing for an examination of the accuracy of the manufacturing parameters. Symmetrical cells were set up to compare the anode performance with the performance predicted by the electrochemical model. Early iterations of impregnated scaffolds show triple-phase boundary densities increased by approximately an order of magnitude and allowed for a critical assessment of the electrochemical model. The degraded electrode morphology was also characterized in 3D to link its changes during cycling to performance degradation. This approach enables us to move towards designing optimised electrodes with specific performance attributes. Figure 1

Integrated gasification fuel cell (IGFC) systems combining coal gasification and solid oxide fuel cells (SOFC) are promising for highly efficient and environmentally friendly utilization of coal for energy production. Most IGFC system analyses performed to date have used non-dimensional thermodynamic SOFC models that do not resolve the intrinsic constraints of SOFC operation. In this work, a one-dimensional finite volume model for planar SOFC is developed and verified using literature data. Special attention is paid to making the model capable of supporting recent SOFC technology improvements, including the use of anode-supported configurations, metallic interconnects, and reduced polarization losses. Results are presented for SOFC operation on humidified hydrogen and methane-containing syngas, under co-flow and counter-flow configurations; detailed internal profiles of species mole fractions, temperature, current density and electrochemical performance are obtained. The effects of performance, fuel composition and flow configuration on SOFC performance and thermal profiles are evaluated, and the implications of these results for system design and analysis are discussed.

The search for sustainable energy source that can compete with the existing one led to the discovery and acceptance of fuel cell technologies as a perfect replacement for fossil fuel. The ability of Solid Oxide Fuel Cells (SOFC) to capture the heat generation during the process of energy generation from electrochemical reactions favoured their recognition as a promising alternative energy source. This study therefore, focuses on the investigation of operating parameters on the SOFC performance through computer simulation of the developed mathematical model. This is achieved by simulating the effects of operating parameters on the SOFC performance. The results of computer simulation obtained reveal that pressure of the fuel, pressure of the oxidant and concentration of the fuel positively affects the SOFC performance. Analyses of these results also show that the operating temperature negatively affects the performance of the cell, for instance as cell temperature increases from 800oC to 1000oC the cell voltage decrease from 0.8402 V to 0.8400 V. The simulation of the cell efficiency also indicates that all the parameters investigated via computer simulation also affect the efficiency of the fuel cell with maximum heat generation of 19000 kJ. The developed model can be employ to predict SOFC performance at different operating conditions.Keywords:Alternative energy, technologies of fuel cells, mathematical modeling, computer simulation and solid oxide fuel cell.

The use of Solid Oxide Fuel Cells (SOFCs) continues to spread in Japan. This paper clarifies the simple linear relation between their gas consumption and their generated electric power. This means that the total amount of gas consumption only depends on the total electric power, even if plural SOFCs operate in parallel. The total gas amount doesn't depend on SOFC power distribution. To realize parallel SOFC operation, this paper presents a new current transformer (CT) circuit that realizes equal power distribution. This paper also proposes a small-scale Community Energy Management System (CEMS), where three houses share two SOFCs and one battery cell. The electric consumption of each house is hidden from the other houses to protect privacy in the proposed system. To evaluate our proposed system, a prototype CEMS was implemented, where the SOFCs and a battery cell were simulated by software. Finally, we introduced a prototype CEMS into three actual houses and conducted a social experiment that shows that providing low-priced electricity generated by a SOFC changes user awareness of energy usage and promotes energy reduction.

Introduction For many potential mobile robot applications, current power supply technology (such as the lithium ion battery technology) is in fact a key limiting factor due to its low energy density. Solid oxide fuel cells (SOFCs) are a promising alternative and can overcome limitations of current battery technology. This is because SOFCs can, in principle, use not only hydrogen but also hydrocarbon fuels which have high energy density such as gasoline and so on.Ni-YSZ cermet is the most promising anode material for SOFCs because of its low cost, chemical stability, and closely matched thermalexpansion coefficients with the dense YSZ electrolyte. Ni is an excellent catalyst for hydrocarbon fuel reforming and cracking, which leads to rapid carbon deposition inside the SOFC anode and causes coking and deactivation1). In principle, the carbon deposition on Ni can be depressed by adding steam in the hydrocarbon fuel2,3), whereas few detailed investigations of SOFCs that operate on gasoline fuel have been reported.In this work, we studied the effect of steam content and demonstrated the direct operation of SOFCs by octane which is a main ingredient of gasoline. In the case of the Ni-YSZ anode, the operation temperature must be high in order to avoid sulfur poisoning4 -6 ), because most commercially available fuels contain sulfur. Therefore, in this study, the SOFCs operation was conducted at high temperature of 950 oC. Experimental Surface-polished YSZ pellets of 2 mm in thickness were used for the electrolyte. Pt cathode electrode and Pt reference electrode were prepared on the surface and side of the pellets, respectively, by firing Pt paste at 1300 oC. Then, NiO powder and GDC powder (NiO/YSZ=6/4 (wt)) were thoroughly mixed in a vacuum using the planetary ball mill (200 rpm, 12 h), and made into NiO-YSZ pastes using ethyl-cellulose and organic solvent. The NiO-YSZ paste was screen-printed in diameter of 8 mm on the YSZ pellets and sintered at 1200 oC for 1 h.Octane and steam were supplied to the SOFC cell by bubbling carrier gas (He) at a constant rate. Octane bubbler temperature was 30 oC, and Steam/Carbon ratio (S/C) were controlled by changing the temperature of the water bubbler from 40 to 70 oC. Electrochemical properties (open circuit voltage, anode electrode resistance, I - V and I - P characteristics, stable power generation property) were measured over a temperature range of 950-700 oC. During the constant current generation, exhaust gas was analyzed by gas chromatography. Results and Discussion Figure 1 shows I - V and I - P characteristics for the cells at 950 oC in wet octane. Maximum power density of 35 mW/cm2 was obtained by S/C of 8.9. The power density decreased with S/C quickly.Figure 2 shows the time course of cell voltage at a drawn current density of 5.2 mA/cm2 for S/C of 3.5. The cell voltage was stable. That is, carbon deposit does not arise even in the cell of the Ni-YSZ anode in low S/C of 3.5 when the operation temperature is high of 950 oC. References 1) S. Mclntosh and R.J. Gorte, “Direct Hydrocarbon Solid Oxide Fuel Cells,” Chemical Reviews, 104 (2004) 4845- 4865.2) K. Sasaki and Y. Teraoka, “Equilibria in Fuel Cell Gases: I. Equilibrium Compositions and Reforming Conditions,” Journal of Electrochemical Society, 850 (7) (2003) A878-A884.3) K. Sasaki and Y. Teraoka, “Equilibria in Fuel Cell Gases: II. The C-H-O Ternary Diagrams,” Journal of Electrochemical Society, 850 (7) (2003) A885-A888.4) K. Sasaki, K. Susuki, A. Iyoshi, M. Uchimura, N. Imamura, H. Kusaba, Y. Teraoka, H. Fuchino, K. Tsujimoto, Y. Uchida, N. Jingo, “H2S Poisoning of Solid Oxide Fuel Cells,” J. Electrochem. Soc., 153 (2006) A2023–A2029.5) P. Lohsoontorn, D.J.L. Brett, N.P. Brandon, “Thermodynamic predictions of the impact of fuel composition on the propensity of sulphur to interact with Ni and ceria-based anodes for solid oxide fuel cells,” Journal of Power Sources, 175 (2008) 60–67.6) H. Kishimoto, Y-P Xiong, K. Yamaji, T. Horita, N. Sakai, M.E. Brito, H. Yokokawa, “Stability of Ni base anode for direct hydrocarbon SOFCs, ” Journal Chemical Engineering of Japan, 40 (13) (2007) 1178-1182.

Solid oxide fuel cell (SOFC) is well known as power and heat generation device which converts chemical energy directly from fuel into electricity. SOFC operate at high temperature becomes obstacle for SOFC which reducing ionic conductivity material of current electrolyte, reduce lifetime of cell components, high fabrication cost, limited durability and performance issues. This introduce to environment pollution and decrease the SOFC lifetime. The fabrication of durability and stability composite cathode are comprised from mixing of perovskite La0.6Sr0.4CO0.2Fe0.8 (LSCF) powders with nanoscale ionically conducting ceramic electrolyte materials, SDC-carbonate (SDCc) was overcome this problems. Powder preparation and composite cathode fabrication must consider which as main factors in the development of durability and stability of LSCF-SDCc composite cathode. Powders must in nanoscale to enhance the conductivity and decrease the interfacial polarization resistance and the composite cathode should in nanoporous morphology for achieve high power density over than 500 h and remarkable durability. Calcination also plays in important role and its operations will effects to the SOFC durability and performance. The necessary to prolong the lifetime and increase the SOFC performance has lead to development of durability and stability of SOFC. This paper reviews the durability and stability of the composite cathode and focus on the challenges in material technology.

Introduction With the recent enhancement of renewable energy utilization, large scale energy conversion and storage become more important to control the surplus electric power due to the unsteady power generation. Reversible hydrogen energy storage system via solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) are expected as a high efficient device because of its high operating temperature (600℃~1000℃). It is possible to unify them to one device as reversible system (RSOFC/EC), but it is necessary to understand the mechanism of FC/EC reactions and design the device with a good balance between FC and EC in order to apply them for an actual energy system. While SOFC reaction models and many electrochemical data of electrodes have been developed and reported by many researchers, there are few reports to investigate the reaction model of SOEC. Thus, it is possible to predict the performance of SOEC based on a comprehensive SOFC/EC models and experimental data of SOFC, because the reactions of SOFC and SOEC are a reversible relationship and the equal value of IR loss can be applied. However, the comprehensive SOFC/EC electrochemical model has not been established. A series of experimental data of anodic and cathodic current density vs. the potential should be investigated at various conditions to develop the SOFC/EC model. In this work, a series of anodic and cathodic electrode performance was taken using a SOFC in various conditions. Furthermore, attempting to predict SOEC performance from SOFC performances, we proposed and discussed a new model of electrolysis based on our developed SOFC model. Experimental The Disks of 8 mol% Y2O3-ZrO2 (YSZ; 0.25 mm thickness, 20 mm diameter) were used as the electrolyte and the anode was a Ni/YSZ or Ni/GDC composite, and the cathode was a La0.8Sr0.2MnO3/ScSZ composite. We measured the dependence of the current density of anodes on oxygen activity with wide range to get both power generation and electrolysis data for various gas composition (PH2=0.3~0.99 atm, PH2O=0.01, 0.03, 0.05 atm). Results and Discussion 1. Method to fit parameters on the SOFC/EC model We have developed the electrochemical reaction model on the fuel electrode (=anode) based on the equilibrium of competitive adsorption and oxygen activity, ao , specified by anode potential (Eq.1, Table.1) [1]. The SOFC model was constructed by assuming competitive adsorption equilibrium of H2, H2O and O on Ni surfaces at three-phase boundary and the rate-determining step to be Langmuir-type reactions of H with O (Table.1). We obtained an equation of the electrical current density, i, as a function of the oxygen activity (ao ) calculated from the anode potential which is simply measured from experiments. To confirm effectiveness of the model, we fitted the model to actual experimental data described by i vs. ao . From the equations of model on Table.1, each current density of SOFC (ia ) and SOEC(ic ) are described as Eq.2. To draw the plot of i vs. ao on the model, the rate constants (ka, kc ) and the equilibrium constants (KO, KH, KH2O ) need to be defined as reliable value. Thus, from the equilibrium potential vs. 1 atm O2 (Eq.3), we defined the rate constant of kc as Eq.4. When the kc became a dependent variable of ka , then we fitted ia to power generation experimental data described by i vs. ao so that the values of KHKO/KH2O were fitted approximately. Finally, i c model could be drawn on the plot of i vs. ao and the maximum value of i c was obtained by Eq.5 which is independent of ao and Eq.6 was obtained using Eq.4. 2. Experimental results and parameter fitting on the SOFC/EC model As the expreimental results, the maximum power density of SOFC with Ni/YSZ was 588.5 mW/cm2 for FC mode at PH2=0.99 atm, PH2O=0.01 atm, and ic(max) was 0.285 A/cm2 for EC mode at PH2O=0.03 atm. However, ic(max) calculated by the model (Eq.6) was 0.050 A/cm2. Also, in case of SOFC with Ni/GDC, ic(max) was 0.400 A/cm2 for EC mode at PH2O=0.03 atm, while ic(max) calculated by the model (Eq.6) was 0.055 A/cm2. The electrolysis current density measured by our RSOFC/EC showed 6 times higher than model values approximately. This result suggested the possibility that additional parallel reaction path was existed. In this presentation, we will discuss the possible electrochemical paths to explain the disagreement between the model and the experimental data. Finally, the comprehensive SOFC/EC model will be proposed to predict EC performance using SOFC data.

Numerical performance analysis of the solid oxide fuel cell for aviation hybrid power system

This research presents a thorough evaluation of an integrated system comprising a Solid Oxide Fuel Cell (SOFC), Organic Rankine Cycle (ORC), and Absorption Chiller (AC). The study employs ASPEN PLUS V10 to assess the system's energy, exergy, economic, and environmental performance. The Integrated SOFC-ORC-AC system offers trigeneration capabilities, generating electricity, cooling, and heating from a single fuel source. It demonstrates potential as an efficient and environmentally friendly energy generation method. The system can be fuelled by steam-reformed natural gas or renewable fuels like biogas or syngas. The SOFC, employing a solid electrolyte, facilitates an electrochemical reaction with hydrogen, producing electricity and heat. The exhaust gas further powers the ORC and AC units. The study builds a mathematical model, assuming steady-state, isothermal, and chemically equilibrated conditions. The SOFC and ORC simulations utilize the Peng Robinson model, while the LiBr absorption chiller employs the ELECNRTL property method for fluid thermodynamic properties. The SOFC electrical model was validated against real-world data, ensuring accuracy. The study also tested a single-effect LiBr absorption chiller, comparing results with experimental data. The operating pressure's effect on SOFC performance was evaluated, demonstrating reduced voltage losses and increased cell voltage and power density at higher pressures. Operating temperature elevation enhanced electrochemical reactions, resulting in higher cell voltage and power density, despite increased voltage losses. Augmenting the fuel utilization factor reduced voltage losses, leading to increased cell voltage and power density. The SOFC-ORC system efficiency peaked at 58.9% at the highest operating pressure, influenced by factors like compressor consumption and high fuel flow rate. Redirecting exhaust gas for waste heat recovery produced hot water, influencing the Coefficient of Performance (COP) of the LiBr absorption chiller. Mass flow rate had a smaller impact compared to hot water temperature. Exergy analysis revealed the SOFC's high efficiency (83.92%), while the steam turbine and LiBr absorption chiller demonstrated lower exergy efficiencies (70% and 32.6% respectively). Cost analysis indicated that the SOFC power plant was the most significant investment at 130,715 $, highlighting the long-term benefits of the integrated system in terms of high efficiency, low emissions, and fuel flexibility. This research offers a comprehensive assessment of the integrated SOFC-ORC-AC system, shedding light on its potential as an efficient and environmentally friendly energy generation solution. The study's findings contribute to the advancement of sustainable energy technologies, emphasizing the importance of trigeneration systems for future energy landscapes.

Coal gas fuel utilization effects on electrolyte supported solide oxide fuel cell performance

Functionally graded electrodes (FGEs) have been recently proposed to show a significant potential to improve the performance of solid oxide fuel cells (SOFC) as compared to conventional electrodes using a uniform composite layer. A mathematical model is used to mimic the FGE of a SOFC at the micro-scale level. This model is based on a comprehensive approach including the coupled mass transfer and electrochemical reactions in both the anode and cathode of a SOFC during operation. Overpotentials are solved by: the dusty-gas model (DGM) for porous-media transport in the electrodes; the modified Butler-Volmer equations for the electrochemical reactions at the triple phase boundary (TPB) layers; and ohmic law for polarization losses in the electrolyte. The current model makes use of a formulation for the active surface area such that three different kinds of graded electrodes, namely, composition graded, particle size graded, and porosity graded can be properly described. The results are then compared with available experimental data with encouraging results. Additional numerical studies explored optimum parameters for uniform conventional electrodes, the effect of the addition of an anode or cathode interlayer on cell performance, and optimum grading profiles for continuously graded electrodes. The present study reveals that micro-scale graded electrodes have the potential to enhance SOFC efficiency.

Solid oxide fuel cell (SOFC) is one of most promising types of fuel cells with advantages of high efficiencies, flexible fuel types. As a device directly converting the free energy of chemical reactant to electrical energy and heat, the performance of SOFC is strongly affected by the chemical and electro-chemical reactions occurring in the porous anode coupled with mass, momentum and heat transfer processes. A 3D CFD model has been developed by using in-house code to analyze the various processes coupled with elementary surface reactions occurring in SOFC’s anode, to identify the effects between transfer processes and some elementary reactions occurring in the anode. It shows that single step elementary reaction can affect the distribution of surface species, but not remarkable on global conditions such as temperature and gas distribution. On the other hand, global parameters including temperature, porous characteristics affect the surface species distribution and elementary reaction processes largely.

Solid oxide fuel cells (SOFCs) are being extensively researched for clean power generation from coal-derived syngas. Some of the contaminants in syngas such as phosphine (PH3) may interact with the SOFC anode material, and degrade its electrochemical performance and material properties. In this paper, a modified Sagnac interferometry method is utilized to monitor the anode surface transient temperature as a function of applied current densities under hydrogen and simulated coal syngas. Moreover, the poisoning effects of PH3 contaminant on the SOFCs performance are investigated in dry and moist conditions. The experimental results indicate that the Ni-cermet-based SOFC anode is more susceptible to degradation due to PH3 in the presence of steam than under dry conditions. These experiments are valuable for the validation and the development of SOFC electrochemical models, and understanding the anode-contaminant interaction.