Solid Oxide Fuel Cell Stack Research Articles

A numerical study of the performance of solid oxide fuel cell with bi-layer interconnector

Solid oxide fuel cell (SOFC) has attracted wide attention because its efficiency is not limited by the efficiency of Carnot cycle. The structure of flow channel in SOFC has great effects on the internal mass distribution, which influences current density. In this paper, the height of flow channel and the position, arrangement, number and height of the fin which is placed in channel, are changed to get different structures of bi-layer interconnector, and they are applied to three layers SOFC stack. The effects of each structural parameter on the current density are studied by numerical simulation. The results show that, increasing the number of fins and bi-layer interconnector height can make more reactant gas enters the electrode. In addition, compared with the conventional structure, the current density can be increased by the bi-layer interconnector up to 31.256%, and the bi-layer interconnector structure could save n-1 layers of interconnector, which reduces the volume of SOFC stack. Among the five structural parameters, the position of fins has the least influence on temperature distribution and current density, while the arrangement of fins has the highest influence on volume current density, reaching 30%. Using a staggered arrangement and higher bi-layer interconnector can also improve the temperature distribution.

Finite element modeling of the glass sealing process for solid oxide cell stacks

The sealing process for solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) stacks is a vital step in the assembly and manufacturing of these systems. The cell seal and stack seal serve to prevent leakage and the mixing of air with hydrogen and steam during operation. Good seals are critical for reporting accurate cell and stack performance and durability, as leaks can mask degradations and manifest as performance improvement. Predictive modeling of seal materials during sealing processes for SOFC and SOEC stacks has been largely unexplored and could provide design and manufacturing insights for these systems. In this work, finite element modeling was conducted to simulate the assembly and stack sealing of planar cells to capture the densification, viscous flow, and crystallization behavior of the G18 glass ceramic seal material during full scale stack fabrication. The Skorohod-Olevsky viscous sintering material model was implemented in the ANSYS finite element program and modified to account for crystallization effects to simulate the response of the G18 seal material. The effects of initial cell/stack curvature were captured via preliminary stack manufacturing simulations, and its influence on stack sealing quality was studied. Effects of compressive loading sequence and configuration were investigated.

Coupling a thermoelectric-based heat recovery and hydrogen production unit with a SOFC-powered multi-generation structure; an in-depth economic machine learning-driven analysis

This study presents a comprehensive technical, environmental, and economic analysis of a thermal power plant utilizing solid oxide fuel cells (SOFC) to meet urban demands for electrical power, fresh water, and hydrogen. The integrated system includes SOFC with anode and cathode recycling, multi-effect desalination, a power generation cycle with a heat recovery unit using a thermoelectric generator, and a hydrogen compression unit. A detailed parametric analysis was conducted to identify optimal conditions for key outputs such as total cost rate and exergy efficiency, employing genetic algorithms and artificial neural networks. According to the economic evaluation, the SOFC stack accounts for 65.11 % of total costs at 139.8 $/h, with the inverter contributing 11.9 %. The environmental analysis shows that the proposed system emits the least CO2 per energy unit compared to SOFC/GT and SOFC/GT/RC systems. The parametric study indicates that increasing the pressure ratio enhances the output power of the SOFC and the production of the gas turbine. However, this also leads to higher compressor consumption, thereby reducing net power. Furthermore, increasing the current density results in greater production of electricity, hydrogen, and freshwater, while also raising the exhaust gas temperature, which aids in the desalination process. The optimization results show an exergy efficiency of 61.38 % and a total cost rate of 132.9 $/h, with artificial neural networks reducing optimization time from 124 h to 14 min.

A High-Temperature, High-Speed, Oil-Free Syngas Compressor for Small-Scale Combined Heat and Power

Abstract For low-emission, small-scale combined heat and power generation, integrating a biomass gasifier with a downstream solid oxide fuel cell system is very promising due to their similar operating conditions in terms of temperatures and pressures. This match avoids intermediate high-temperature heat exchangers and improves system efficiency. However, to couple both systems, a high-temperature and oil-free compressor is required to compress and push the low-density, high-temperature bio-syngas from the gasifier to the solid oxide fuel cell stack. The design and development of this high-temperature, high-speed, and gas-bearing supported compressor is presented in this work. An iterative process involving preliminary design, meanline analysis using commercial tools and in-house models is used for the design, which is then numerically analyzed using computational fluid dynamics. The goal is to achieve a design with a wide operating range and high robustness that withstands extreme working conditions. The 727 W machine is designed to run up to 210 krpm to compress 18.23kg/h of syngas at 350°C and 0.81bar. The centrifugal compressor has a tip diameter of 38 mm and consists of 9 backswept main and splitter blades. The impeller is made of Ti6Al4V and coated to prevent hydrogen embrittlement from the hot and highly reactive bio-syngas. The results obtained from the established models suggest a good concordance with the results from numerical analyses, despite the high temperatures and small scale of this design.

Multiscale multiphysics modeling of ammonia-fueled solid oxide fuel cell: Effects of temperature and pre-cracking on reliability and performance of stack and system

Ammonia is a promising carbon-free fuel for solid oxide fuel cells (SOFCs). However, direct feeding of ammonia into the SOFC may lead to serious degradation due to the nitriding. Conversely, the pre-cracking of ammonia introduces complexity to the system design and causes increased power losses in the system. Therefore, it is crucial to explore all these aspects simultaneously. In this context, this study introduces a novel multiscale modeling approach by integrating a 3D multiphysics simulation of the ammonia-fueled SOFC stack with system-level modeling to investigate the reliability and performance of the stack and system. Two different cell technologies developed for low temperature (LT) and high temperature (HT) operation are investigated at LT (600 – 700°C) and HT (700 – 800°C) ranges. The results indicate that fuel inlet temperature should be 55°C and 18°C higher than the minimum temperature in 0% pre-cracking case for HT and LT cases, respectively. The increase in the required air flow rate for cooling in the 100% pre-cracking case compared to the 0% pre-cracking case is around 100% and 216% for the HT and LT cases, respectively. However, stack power production and power losses in the system components are comparable for LT and HT cases which leads to similar system performance. A larger share of the active area is affected by nitriding in LT cases than HT ones. However, a smaller cracking ratio at LT (∼ 82%) compared to HT conditions (∼ 92%) is needed for elimination of nitriding. While the LT and HT cases are comparable in terms of system power production, the lower stack outlet temperatures in LT cases require novel and more expensive catalysts for ammonia pre-cracking and HT cases need more expensive steels.

Highly robust and porous cathode current collecting layer for flat-tubular solid oxide fuel cell stack applications

Solid oxide fuel cells (SOFCs) have gained great attention as a stationary power generation application due to their high efficiency, fuel flexibility and environmental friendliness. The devices and power age could be revolutionized with the commercialization of these technologies. The SOFC-based stationary power generator is one step closer to commercialization however, it is delayed due to the inherent bottleneck of insufficient long-term durability. The cathode current collecting layer (CCCL) is crucial in stack applications to minimize the contact loss between cell and metallic interconnects. Herein, we report an easy-to-fabricate and highly robust CCCL to boost electrochemical performance and long-term durability of flat tubular (FT) short stack. The tailored structure of the CCCL was employed in the fabrication of the FT short-stack. The G/Ag porous structure exhibited increased porosity of 61.2 %, thereby enhancing the mass transport and improving the overall performance and long-term durability. The four-cell FT stack was manufactured without an interconnect and open air-gas channel. Subsequently, the FT short-stack is tested for performance and long-term durability for elapsed 5000 h at a chronopotentiometry test. The porous layer of graphite/Ag on the cathode layer maintained structural integrity without defects and mechanical failure. Consequently, the stack voltage remains stable throughout operation owing to improved structural stability and uniform temperature distribution across four FT cell stack.

Development of an ammonia decomposition reactor, afterburner and post-decomposition reactor for 1 kW solid oxide fuel cells using ammonia

Solid oxide fuel cells can overcome the poor flammability of ammonia by directly converting the chemical energy of ammonia into electricity. However, thermal stress by internal decomposition, nitriding at the solid oxide fuel cells stack and nitrogen oxides emissions must be considered when using ammonia in solid oxide fuel cells. In this study, an ammonia fuel processor was developed for stable operation and low emissions of solid oxide fuel cells using ammonia. The ammonia fuel processor consisting of an ammonia decomposition reactor, an afterburner and a post-decomposition reactor was tested using simulated off-gases of solid oxide fuel cells using ammonia. The ammonia conversion of the decomposition reactor varied from 32 % to 84 % with off-gas temperatures from 360 °C to 670 °C. When ammonia conversion after the solid oxide fuel cell stack was 99.70 %, nitrogen oxides emissions of the afterburner was 1.05 g/kWh, which is higher than the regulatory limit of 0.26 g/kWh. High fuel utilization and excess air ratio made nitrogen oxides emission even worse. The regulatory limit was successfully satisfied by using the post-decomposition reactor even when ammonia conversion after the solid oxide fuel cell stack was 99.10 %. The developed ammonia fuel processor could supply fuel at the optimal hydrogen-to-ammonia ratio and prevent nitrogen oxides emissions in solid oxide fuel cells using ammonia.

Optimal energy management based on real-time performance analysis for the solid oxide fuel cell-combined heat and power system

In order to realize the efficient and stable operation of the solid oxide fuel cell (SOFC)-combined heat and power (CHP) system in the typical applied scenario, three different energy management schemes are proposed in this study. First, a coupled calculation model of the solid oxide fuel cell-gas turbine-combined heat and power (SOFC-GT-CHP) system with a rated power of 30 kW for the SOFC stack is constructed. The inlet temperature and inlet pressure of the SOFC stack are optimized. The recommended design for the proposed system is thence obtained. Second, three operation schemes of SOFC-GT-CHP are proposed. They consist of the operation scheme of single-stack, multi-stack and optimal operation scheme coupled with vanadium redox flow battery (VRB). Finally, four types of typical applied scenarios in North China are selected. The real-time performance of the SOFC-GT-CHP system when applying three different operation schemes is obtained and comparatively analyzed. The results are presented as follows. First, the SOFC-GT-CHP system achieves a rated power of 44.50 kW and a rated system efficiency of 47.20 % when the inlet temperature and pressure of the stack are preferably 505 °C and 709.1 kPa. Second, the application of the multi-stack SOFC-GT-CHP system has the advantage of high efficiency in the low-load operation domain. With a net output power at 20 kW, the time average efficiency of SOFC-GT-CHP is increased from 38.37 % to 46.96 %. Finally, the SOFC-GT-CHP system achieves the highest time average generation efficiency of 46.13 % in the hotel applied scenario when applying the optimal operation scheme coupled with VRB. This meets the practical operation requirement of the SOFC stack. The reduction of the net output power range of SOFC-GT-CHP is 67.87 %. It shows that the optimal operation scheme is efficient and stable. The study can provide a reference for the energy management of the SOFC-GT-CHP system in typical applied scenarios.

Thermal stress and contact analysis utilizing tested temperature data in a kW-class external-manifold solid oxide fuel cell stack

Thermal stress and contact are two pivotal factors influencing the operational lifespan and performance of solid oxide fuel cell (SOFC) stacks. In practical kW-MW SOFC systems, stack boxes are typically constructed using kW-class stack blocks comprising dozens of cells. Temperature distribution affects the thermal stress distribution, thus affecting the contact of the stack. In this work, the thermal stress distribution and contact of a 2.5 kW external-manifold stack composed of 60 repeat units are investigated by using finite element analysis (FEA). To get a more accurate and realistic results, temperature data of a stack measured in an ongoing SOFC system is incorporated into the computational model. The influences of the clamp loads from manifolds, the structure of current collectors, the number of spacer plates, and the thickness of interconnects on the thermal stress distribution and contact of the stack are investigated. In the basic stack, the tensile stress induced by the temperature gradient appears to be the primary cause of the high thermal stress in the air inlet region of top cells. Due to the high-temperature strength of the seal material and endplates, the contact is inferior in cells near endplates. Increasing the clamp loads of manifolds within specified limits leads to a reduction in both the magnitude and area of high thermal stress, concurrently enhancing the stack contact. Strengthening the current collector structure induces more high-stress regions and simultaneously increases the stack contact. The introduction of overmuch spacer plates results in more high stress regions and a deterioration in stack contact. Moreover, increasing the thickness of interconnects introduces more high stress regions, negatively impacting stack contact.

In-situ electrochemical impedance analysis of a commercial SOFC stack fueled by real wood gas

The combination of solid oxide fuel cells (SOFCs) and wood gasification has the potential to significantly increase renewable electricity production and decrease emissions. Depending on the quality of the wood gas, degradation processes have a significant impact on the reliability and lifetime of the SOFC. Using electrochemical impedance spectroscopy (EIS) and subsequent distribution of relaxation times (DRT) analysis, the impact on the degradation of coupling wood gasification with a commercial SOFC stack is determined in this study. The thermal behavior of the SOFC stack under various operating conditions, as well as various synthetic wood gas mixtures classified by their hydrogen-to-carbon (H/C) ratio, was assessed. The decrease in the H/C ratio from 8 to 1, observed during syngas and real wood gas operation, leads to a rightward shift in the Nyquist plots, suggesting an increase in the SOFC stack's impedance. Correlations between variations in the H/C ratio and their effects on anodic electrooxidation, ionic conduction, gas transport, and diffusion were identified using DRT analysis to interpret the EIS results. By incorporating an upstream desulfurization system and ensuring an H/C ratio greater than 2, the coupling of biomass gasification with the SOFC stack was stable to degradation issues.

Solid oxide fuel cell stack with enhanced performance and durability utilizing a porous Ag coating layer as the current collector

This study focuses on reducing the weight of the stack applied to the unit cell during the structuring process of a solid oxide fuel cell (SOFC) stack. By using a porous Ag coating layer as a current collector, separator plates and connectors are eliminated and the manufacturing cost of the stack can thereby be reduced. Additionally, the performance and stability of the stack are significantly improved by reducing the contact resistance between cells. The Ag coating layer used in this study can be optimized by adjusting the coating thickness and the ratio of graphene and Ag paste, which affects dispersibility and porosity. The optimized Ag porous coating layer makes it possible to manufacture a stack cell with a simple structure without requiring a separator, and excellent performance is confirmed in a long-term test of 4000 h.

Direct oxidative coupling of methane into ethylene in a catalyst-enhanced planar solid oxide fuel cell stack reactor

This study presents an efficient method to convert methane into valuable olefins using a Solid Oxide Fuel Cell (SOFC) membrane reactor. Methane, abundant in natural and shale gas, serves as a sustainable feedstock due to its favorable carbon-hydrogen ratio. The SOFC membrane reactor eliminates costly air separation units and safety risks associated with explosive methane-oxygen mixtures. A planar SOFC stack achieves over 30 % methane conversion, 40 % ethylene selectivity, and power generation capabilities. Optimization with mixed-conducting ceramics enhances electrical performance without compromising catalytic activity. The stack's scalability is demonstrated, with the 5-cell configuration surpassing the 2-cell setup. This innovative approach offers a sustainable solution to methane waste, producing high-value chemicals while reducing environmental impact.

Thermal Stress in Full-Size Solid Oxide Fuel Cell Stacks by Multi-Physics Modeling

Mechanical failures in the operating stacks of solid oxide fuel cells (SOFCs) are frequently related to thermal stresses generated by a temperature gradient and its variation. In this study, a computational fluid dynamics (CFD) model is developed and further applied in full-size SOFC stacks, which are fully coupled and implemented for analysis of heat flow electrochemical phenomena, aiming to predict thermal stress distribution. The primary object of the present investigation is to explore features and characteristics of the thermal stress influenced by electrochemical reactions and various transport processes within the stacks. It is revealed that the volume ratio of the higher thermal stress region differs nearly 30% for different stack flow configurations; the highest probability of potential failure appears in the cell cathodes; the more cells applied in the stack, the greater the difference in the predicted temperature/thermal stress between the cells; the counter-flow stack performs the best in terms of output power, but the predicted thermal stress is also higher; the cross-flow stack exhibits the lowest thermal stress and a lower output power; and although the temperature and thermal stress distributions are similar, the differences between the unit cells are bigger in the longer stacks than those predicted for shorter stacks. The findings from this study may provide a useful guide for assessing the thermal behavior and impact on SOFC performance.

To study the effect of geometric parameters on the performance of a typical cone-shaped tubular segmented-in-series solid oxide fuel cell stack

Long electric current transfer path has been a common problem with tubular series cells. Cone-shaped tubular segmented-in-series solid oxide fuel cells (SIS-SOFCs) have attracted much attention due to their special advantages, such as short electric current path, unsealed requirement, small thermal stress, low operating electric current, and so on. In this paper, the electrochemical and multiphysics coupling model of a typical SIS-SOFC is developed. Then, the relationship between the geometric structure and the working characteristics within the SIS-SOFC is investigated. The results show that the size of the active reaction region in the downstream cone-shaped cell depends on the length of the interconnectors. Thus, increasing the length of the interconnectors increases the active reaction area of the series cell while decreasing the current transmission path. The ratio between the interconnector length and total cell length equals 0.5 is found to be a proper geometric factor for the SIS-SOFC to achieve a good overall performance and reaction uniformity.

Thermal dynamic analysis and multi-objective optimization of a 10 kW dual preheating solid oxide fuel cell system

The increasingly serious environmental problems caused by the excessive development of fossil fuels necessitate the promoting of novel and effective energy technologies. As an environmentally friendly and effective promising solution in terms of its low emission, and fuel adaptability, the solid oxide fuel cell (SOFC) system has attracted widespread attention. To better promote the progress of SOFC, the SOFC testing system (SOFC TS) is very important. In this paper, we have established a dual preheating SOFC TS configuration where the fuel is first preheated by exhaust gas, and then preheated by the electric heater to the setting temperature. A comprehensive thermodynamic analysis is conducted to investigate the characteristic of this SOFC TS. Building upon this designed testing system, a multi-objective optimization approach is adopted to enhance the performance of the thermal management subsystem. The results showed that the SOFC stack is the main exergy component in the SOFC TS, the selected point of multi-objective optimization can reduce the thermal management costs by 60$ and improve system efficiency by 4.5%.

Long-term thermo-mechanical performance evolution of a 15-cell solid oxide fuel cell stack

Understanding mechanical performance evolution and failure mechanism of solid oxide fuel cell stack (SOFCs) during long-term operation period are essential to prolong operation life and advance commercialization. In this study, based on the structural mechanical model, the evolution characteristics of thermal stress, failure probability, strains, and deformation of SOFCs fueled by partially pre-reformed CH4 during 3000 h' operation are revealed. It's found the maximum thermal stresses of anodes, sealants, and frames/ICs decease respectively by 82.9%, 74.1%, and 88.4%, while those of electrolytes and cathodes firstly fluctuate then increase. The failure probabilities of sealant and anode decrease by 6∼10 orders of magnitude, while increase by 1 order of magnitude and 1.5 times for electrolyte and cathode. 300 h later, sealant may fracture by creep strain, while the component most likely to fail due to thermal stress changes from sealant to cathode. The maximum deformation of positive electrode-electrolyte-negative electrode (PEN) locates in anode of cell 15. It is suggested creep resistance of sealant be improved to avoid creep fracture, mechanical strength of cathode/sealant be increased to decrease failure probability, and the temperature unevenness be decreased to avoid larger deformation.

A Solid Oxide Fuel Cell Stack Integrated With a Diesel Reformer for Distributed Power Generation

A Solid Oxide Fuel Cell Stack Integrated With a Diesel Reformer for Distributed Power Generation

A comprehensive survey of artificial intelligence-based techniques for performance enhancement of solid oxide fuel cells: Test cases with debates

Since installing solid oxide fuel cells (SOFCs)-based systems suffers from high expenses, accurate and reliable modeling is heavily demanded to detect any design issue prior to the system establishment. However, such mathematical models comprise certain unknowns that should be properly estimated to effectively describe the actual operation of SOFCs. Accordingly, due to their recent promising achievements, a tremendous number of metaheuristic optimizers (MHOs) have been utilized to handle this task. Hence, this effort targets providing a novel thorough review of the most recent MHOs applied to define the ungiven parameters of SOFCs stacks. Specifically, among over 300 attempts, only 175 articles are reported, where thirty up-to-date MHOs from the last five years are comprehensively illustrated. Particularly, the discussed MHOs are classified according to their behavior into; evolutionary-based, physics-based, swarm-based, and nature-based algorithms. Each is touched with a brief of their inspiration, features, merits, and demerits, along with their results in SOFC parameters determination. Furthermore, an overall platform is constructed where the reader can easily investigate each algorithm individually in terms of its governing factors, besides, the simulation circumstances related to the studied SOFC test cases. Over and above, numerical simulations are also introduced for commercial SOFCs’ stacks to evaluate the proposed MHOs-based methodology. Moreover, the mathematical formulation of various assessment criteria is systematically presented. After all, some perspectives and observations are provided in the conclusion to pave the way for further analyses and innovations.

SOFC stack modeling: a hybrid RBF-ANN and flexible Al-Biruni Earth radius optimization approach

Abstract This study introduces a novel hybrid methodology for model identification of solid oxide fuel cell (SOFC) stacks by integrating a radial basis function-based artificial neural network (RBF-ANN) with a flexible Al-Biruni Earth radius optimizer (FA-BERO). The primary objective of the proposed method is to augment the precision and efficiency of SOFC stack modeling by considering the advantages of both RBF-ANN and FA-BERO algorithms. The main purpose of using these two methods is to optimize the structure of the RBF-ANN based on the suggested FA-BERO algorithm. The other contribution of this study is improving the efficiency of the Al-Biruni Earth radius optimizer (A-BERO) by applying two improvements on it, including constriction factor and elimination phase to increase the exploration and exploitation strength of the basic A-BERO. To validate the effectiveness of the proposed model, it is compared with some state-of-the-art models in the field, such as the artificial neural network and multi-armed bandit algorithm (ANN/MABA) and rotor Hopfield neural network and grey wolf optimization (RHNN/GWO). Furthermore, the model is validated by experimental data, and the final results demonstrate the efficacy of the hybrid approach in accurately representing the intricate behavior of SOFC stacks. The proposed model achieves lower error rates (ERs) and root mean squared errors (RMSEs) than the comparative methods across different network arrangements and temperature conditions. The results show that, for instance, for the 2/12/1 network arrangement at 900°C, the proposed model attains an ER of 6.69% and an RMSE of 2.13, while the ANN/MABA and RHNN/GWO methods obtain ERs of 9.67% and 8.54%, as well as RMSE values of 24.48 and 9.23, respectively. The proposed model also exhibits superior accuracy and convergence speed compared to the comparative methods, as shown by the current–voltage curves and the convergence analysis. Consequently, this novel hybrid methodology offers a valuable tool for researchers and engineers working in the domain of fuel cell technology, enabling them to better understand and optimize SOFC stack performance.

Analysis on temperature uniformity in methane-rich internal reforming solid oxide fuel cells (SOFCs)

Temperature uniformity is a critical parameter in solid oxide fuel cells (SOFCs) since it directly impacts thermal stress, material degradation and output performance. Effective thermal management typically aims to achieve a minimal temperature gradient, especially within a SOFC stack assembled by numerous single cells. In this study, numerical simulations of various boundary conditions and cell designs are performed to investigate thermal uniformity in methane-rich internal reforming SOFCs, which can be utilized as a guidance for design and operation in practical application. The results indicate that the fuel gas with a 5 % mole fraction of methane is more effective in enhancing thermal uniformity through reforming cooling effect at the electrolyte compared to only a 1 % mole fraction. It is strongly recommended in cell design to maintain the ratio of the cell's length to its width (Rcell) greater than or equal to 1.0 considering its better thermal uniformity. However, both increasing the ratio of channel width to rib width (Rc-r) and decreasing the ratio of channel height to channel width (RH-W) have been demonstrated to deteriorate temperature uniformity. Within this study, increasing the backpressure to 1.5 bar is found to result in a 16.7 % reduction in the maximum temperature difference across the electrolyte when compared to that at atmospheric pressure. It is also advisable to operate at the inlet temperature ranging from 973 K to 1023 K for a more uniform temperature distribution within the SOFC.