Solid Oxide Fuel Cell Stack Research Articles

Numerical analysis of natural gas, hydrogen and ammonia fueled solid oxide fuel cell based micro cogeneration units with anodic gas recirculation

The energy sector is actively transitioning towards climate-neutral solutions, emphasizing advancements in clean power generation technologies. Cogeneration systems based on solid oxide fuel cells (SOFC) currently exhibit higher electrical efficiencies than conventional plants, but their operation can still be improved. One of the approaches to increase its efficiency is implementing anodic off-gas recirculation. In this work, a numerical model of a 10 kW SOFC installation with anodic gas recirculation was analyzed using Aspen HYSYS software. System fueled with three alternative fuels (natural gas, hydrogen, and ammonia) was tested. In this paper it was proven that anode-off gas recirculation improves the electrical and total efficiency of the system for each fuel type. The cogeneration unit with a SOFC stack can operate safely over a wide range of recirculation ratios without need for additional modifications. Ammonia-fueled units achieve electrical efficiency (55%) higher than hydrogen-based system (47.6%) but lower than installation fueled with natural gas (61.8%).

The thermodynamic and life-cycle assessments of a novel charging station for electric vehicles in dynamic and steady-state conditions

The current study performs the thermodynamic and life-cycle assessments (LCA) of a novel charging station in two system designs. The goal is to design an efficient charging station for electric vehicles with high efficiencies and low environmental impacts using Solid Oxide Fuel Cell (SOFC) technology. SOFC is considered a sustainable and environmentally friendly technology to generate electricity compared to combustion engines. To ameliorate the performance, the exhaust heat of the SOFC stacks will be recovered for hydrogen production in an electrolyzer. The system uses four SOFCs to charge the electric vehicles while the output heat is recovered by an Organic Rankine Cycle (ORC) to generate further electricity for hydrogen production in an electrolyzer. In the first design, it is assumed that the SOFC stacks will work full-load during the 24 h of the day, while the second design considers full-load operation for 16 h and part-load (30%) operation for 8 h. The second design of the system analyzes the possibility of integrating a {mathrm{LiMn}}_{2}{mathrm{O}}_{4} lithium-ion battery stores the excessed electricity once the power load is low and acts as a backup in high power demands. Results of the thermodynamic analysis calculated the overall efficiencies of 60.84% and 60.67% for the energy and exergy, respectively, with the corresponding power and hydrogen production of 284.27 kWh and 0.17 g/s. It was observed that higher current density would increase the output of SOFC while reducing the overall energy and exergy efficiencies. In dynamic operation, the use of the batteries can well balance the change of the power loads and improve the dynamic response of the system to the simultaneous changes in the power demand. LCA results also showed that the 284.27kWh system leads to global warming (kg {mathrm{CO}}_{2} eq) of 5.17E+05, 4.47E+05, and 5.17E+05 using Solid Oxide Electrolyzer (SOE), Proton Exchange Membrane Electrolyzer (PEME), and Alkaline Electrolyzer (ALE), respectively. In this regard, the usage of PEME has the lowest impact on the environment in comparison to SOEC, and ALE. A comparison between the environmental impacts of different ORC’s working fluids also suggested against the usage of R227ea while R152a showed promising results to be used in the system. The size and weight study also revealed that the battery benefits from the lowest volume and weight in comparison to the other components. Among the considered components in this study, the SOFC unit and the PEME have by far the highest volume.

Structural design and optimization for a 20-cell solid oxide fuel cell stack based on flow uniformity and pressure drop

This study analyzed the influence of channel resistance, inlet flow rate, manifold depth and other related parameters on the gas distribution uniformity and pressure drop in an external 20-cell solid oxide fuel cell stack by computational fluid dynamics (CFD) technique. It provides a basis for determining the physical and geometric parameters of the stack. Furthermore, the flared inlet tube structure shows the effect of controlling the initial velocity of gas inflow and buffering; the flared outlet tube structure has the benefit of reducing the local pressure loss and the pressure drop. Combined with the perforated sheet structure, the gas in the inlet manifold is redistributed to improve the uniformity of gas flow. Compared with the basic model, the pressure drop of perforated sheet stack was reduced by 17.6% from 349.5 Pa to 288.5 Pa, and the gas flow uniformity index of that was reduced from 4.06% to 0.22%.

Thermoelectrical comprehensive analysis and optimization of multi-stack solid oxide fuel cell system

Solid oxide fuel cell (SOFC) is one of the most promising power generation technologies for its high efficiency, low emission, and fuel adaptability. The power of a single SOFC stack is usually limited to about 1 kW to guarantee its reliability, and stacks are therefore integrated in series or parallel to meet load power demand. However, the performance of a multi-stack SOFC system predominantly depends on the configuration (electrical and gas path structure) of the stack module. Consequently, it is important for the development of SOFC to explore the influence of stack integration structure on system performance and thermal safety, and to further grasp the multi-stack design principles by analyzing the input-output characteristics of the system. The existing studies mainly focus on the electric performance-related parameters analysis and optimization of multi-stack, without considering the thermal safety, the laws of the integration structure influence on system performance and comprehensive optimization on system level. In this work, general multi-stack SOFC systems with four gas distribution structures constructed by four validated stacks are considered and their thermoelectrical performance is systematically investigated and optimized under operational constraints based on a completed multi-SOFC system model. Moreover, the input-output characteristics, thermoelectrical performance and operation rules of the multi-stack SOFC system analysis are conducted, and finally, the stack module design principles and optimal stack topology are obtained. The results show that the parallel connection of two serial stack branches is preferred and can reach the maximum net system efficiency of 42.90 % and maintain the maximum temperature gradient within 6.04 K/cm at a low cost.

Numerical performance analysis of solid oxide fuel cell stacks with internal ammonia cracking

Ammonia-fueled operation of solid oxide fuel cells is a promising alternative to their hydrogen-fueled operation. However, high ammonia decomposition rates at elevated operating temperatures of the solid oxide cells lead to a significant temperature drop at the stack inlet, causing increased thermal stresses. A multi-scale model is used in this study to investigate stack performance under direct feed and external pre-cracking of ammonia. Additionally, the effects of co- and counter-flow configurations, gas inflow temperatures, current density, and air flow rate on the stack performance under direct ammonia feed are examined. The simulation results show that for gas inlet temperatures above 750 °C, the power densities with direct feed and external cracking of ammonia differ by less than 5%. Moreover, it is indicated that the thermal stresses are lowest for the co-flow case, which decrease with decreasing gas inlet temperature and current density and with increasing air flow. Finally, this study shows that under practically applicable operating conditions, the risk of mechanical failure of the cells under direct ammonia feed operation is small.

Thermal management of Ammonia-fed Solid oxide fuel cells using a novel alternate flow interconnector

Ammonia is a promising fuel for solid oxide fuel cells (SOFCs) as it is carbon-free and easy to store at high volumetric energy densities. However, the endothermic decomposition of ammonia in an SOFC stack significantly reduces the temperature at the entrance of the fuel flow, leading to temperature shock and nitriding. Designing a suitable interconnector for the stack to obtain a flatter temperature distribution is an efficient strategy to overcome this problem. This article proposes a novel interconnector design using an alternate flow concept for both fuel and air. A three-dimensional SOFC model was used for the thermal investigation of the proposed design under different operating conditions, including temperature, current, and fuel utilization. The results indicated that the alternate flow design exhibited a 40% lower temperature difference and up to 53 K higher average temperature than a typical cross-flow design. In addition to a flatter temperature profile, the proposed design exhibited a higher ammonia conversion rate than the conventional design, demonstrating its promise for use in robust and efficient ammonia-fed SOFC stacks.

Transport Phenomena in a Banded Solid Oxide Fuel Cell Stack—Part 1: Model and Validation

This paper primarily focuses on the formulation and validation of mathematical and numerical models for a new electrolyte-supported solid oxide fuel cell stack. By leveraging numerical modeling, the main goal is to deepen the understanding of the operational aspects and transport phenomena within this system. The developed models are implemented in ANSYS, Inc., Fluent software, which enables a range of simulations. To validate the models, a stack fabrication methodology, a prototype construction, and conducted electrochemical tests were proposed. The simulated current-voltage characteristics for two different operating temperatures and three different fuel compositions were compared with the experimental measurements with satisfactory agreement. The counter-flow configuration was simulated and compared to the co-flow arrangement. The numerical simulation has demonstrated its efficacy in identifying possible design imperfections and enhancing the operational conditions of the prototype stack. Moreover, the developed model was further used, in Part 2 of this paper, to analyze the improvement options implementation for the next stage of the prototype.

Transport Phenomena in a Banded Solid Oxide Fuel Cell Stack—Part 2: Numerical Analysis

Solid oxide fuel cells are recognized as a promising energy conversion technology. Crucial to the field is the opportunity to reduce the costs of prototyping methodology. Due to the difficulty of conducting direct measurements inside the electrodes and fuel cell’s channels, numerical modeling remains the primary tool for improving the understanding and analyzing a fuel cell operation. Here, a computational fluid dynamic simulation of a banded solid oxide fuel cell’s stack, applied to enhance the geometrical design, is shown. A mathematical model, which includes momentum, heat, mass, and charge transport phenomena, was developed and used for the numerical simulation. The model was validated against the experimental study and confirmed its accuracy. The gas flow rate influence on the performance was investigated in details. Various arrangements of fuel and air channels were simulated and analyzed, including extending the system into a short stack. The proposed design modifications led to an increase in the volumetric power density of the stack compared to the existing prototype design. The proposed mathematical and numerical models were shown to be useful for testing further design modifications to the stack, including performance analysis, by changing the operating parameters of the system or applying new materials.

Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as an onboard bipropellant thruster can create enhanced operational flexibility. If a spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If a spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for SOFCs, as in situ thermal NH3 cracking will generate H2 and N2O decomposition will generate O2. A 5 cell SOFC stack produced 89 W when fueled with NH3 and N2O. The results of this study demonstrate the potential for a bifunctional spacecraft system that can satisfy both operational power and on-orbit maneuverability requirements.

Direct Ammonia SOFC-Gas Turbine Hybrid Systems Modeling for Heavy-Duty Transportation Sector

Solid oxide fuel cells (SOFCs) have the potential to run on ammonia without the need for any pre-reforming and therefore enable effective energy conversion of ammonia to power. In this work, an ammonia based SOFC-Gas turbine (GT) system concept is proposed and assessed for the mobility sector. The model integrates a three-dimensional multiscale SOFC stack simulation based on a validated Ni-GDC/GDC/SSC button cell model with balance-of-plant component modeling. This work discusses the thermodynamics of SOFC operation and system concepts to utilize ammonia in a hybrid system for a kW-scale transportation application. System indicators and performance metrics such as efficiency, electrochemical utilization and turbine inlet temperature are evaluated and optimized. The proposed hybrid system is computationally predicted to reach efficiencies of up to 60% for pressurized operation.

Model Based Comparative Analysis of GDC and YSZ Based Solid Oxide Fuel Cells

Although solid oxide fuel cells (SOFC) offer high fuel-to-electric energy conversion efficiencies, their relatively low power-to-weight ratios make it difficult to integrate them with aircraft propulsion systems. This paper explores the feasibility of designing high throughput SOFCs for hybridization with gas turbines in aircraft powerplants. This paper explores and compares two SOFC technologies for achieving high specific power (kW/kg) with different membrane electrode assembly architectures, one with thin-film yttria-stabilized zirconia (YSZ) electrolytes and the second with high-power density gadolinia doped-ceria (GDC) electrolytes. The studies explore the operation of the respective SOFC stacks with synthetic CH4 as a carbon-neutral aviation fuel. Down-the-channel SOFC models are calibrated to experimental measurements of YSZ- and GDC-electrolyte cells at Elcogen and at the University of Maryland respectively. The model results provide a basis for determining the flow inlet conditions that enable each cell type to achieve high specific powers. The results also indicate the requirement of high airflows and upstream fuel preprocessing to sustain the high specific powers with sustainable cell operating conditions.

Novel SOFC Repeating Unit Design for the Uniform Distribution of Temperature and Thermo-Electrochemical Reaction Zone in a Commercial Scale Stack

Solid oxide fuel cells (SOFC) have been spotlighted as eco-friendly energy sources due to their various advantages, but performance degradation occurring in high-temperature operations and hydrocarbon-based fuel conditions have become obstacles to commercialization. In this study, a novel SOFC stack design is proposed to alleviate the nonuniform distribution of temperature and chemical reaction which can accelerate the degradation of the conventional crossflow type stack. We compared the conventional and the novel SOFC stack design through three-dimensional multiphysics simulation analysis. Compared to the conventional design, the standard deviation of temperature, chemical reaction rate, and fuel species concentration in the novel design decreased by 65.07%, 20.28%, and 25.14%, respectively, showing the advantage of the novel design.

Interface Design Development for High Durability of SOFC Interconnectors Using Electrodeposition Coating

Solid Oxide fuel cell (SOFC) mounted in ENE-FARM type S has been commercialized since 2012. For further market expansion of ENE-FARM type, higher efficiency, higher durability, and lower cost of SOFC stacks are required. A key technology to advance its performance is a coating on SOFC metallic interconnector for the long-term durability of SOFC stacks. We achieved significant reduction in resistance and improved durability by improving the highly mass producible electrodeposition coating method. In this research, the coating technology of the SOFC interconnector has been developed. Long-term durability was confirmed through high-temperature acceleration evaluation, and the electrodeposition coating on the SOFC interconnector was installed in the ENE-FARM type S.

Rapid and durable oxygen reduction reaction enabled by a perovskite oxide with self-cleaning surface

The growth of electrochemically inert segregation layers on the surface of solid oxide fuel cell cathodes has become a bottleneck restricting the development of perovskite-structured oxygen reduction catalysts. Here, we report a new discovery in which enriched Ba and Fe ions on the near-surface of Nd1/2Ba1/2Co1/3Fe1/3Mn1/3O3−δ spontaneously agglomerate into dispersed Ba5Fe2O8 nanoparticles and maintain a highly active and durable perovskite structure on the surface. This unique surface self-cleaning phenomenon is related to the low average potential energy of Ba5Fe2O8, which is grown on the near-surface layer. The electrochemically inert Ba5Fe2O8 segregation layer on the near-surface of the perovskite catalyst achieves self-cleaning by regulating the formation energy of enriched metal oxides. This self-cleaned perovskite surface exhibits an ultrafast oxygen exchange rate, high catalytic activity for the oxygen reduction reaction, and good adaptability to the actual working conditions of solid oxide fuel cell stacks. This study paves a new way for overcoming the stubborn problem of perovskite catalyst surface deactivation and enriches the scientific knowledge of surface catalysis.

Evaluation of an Energy Separation Device for the Efficiency Improvement of a Planar Solid Oxide Fuel Cell System with an External Reformer

Due to the high operating temperature of solid oxide fuel cells (SOFC), the system efficiency depends on efficient thermal integration and the effective construction of system configuration. In this study, nine configurations of system integration design were investigated to evaluate the possible improvement of system efficiency with energy separation devices. The models were developed under the Matlab/Simulink® platform with Thermolib® module. The reference layout of the simulation included an SOFC stack, a compressor, an external reformer with a burner, a three-way valve, a heat exchanger, and a water pump. From the reference case, eight cases extended layouts for the capability of thermal energy utilization with a catalytic converter, SOFC hybridization, and an energy separation device. Since the energy separation device was beneficial to thermal energy utilization via a boost to the gas temperature, electric efficiency, and combined heat and power (CHP) efficiency was improved with the thermal integration of the energy separation device with a turbo generator.

Performance characterization of metal-supported solid-oxide fuel cell stacks at elevated pressure

In this paper, we present results on performance characterization of solid-oxide fuel cell stacks at elevated pressures up to 6 bara. Stacks are designed and built by Ceres Power, Ltd., and are rated at 1- and 5- kWe. Fuel streams include H2/N2 mixtures, synthetic natural-gas reformate, and simulated anode tail-gas recycle. Elevated operating pressure serves to increase stack electrochemical performance, with the most-pronounced gains found up to 4 bara. Pressurized operation reduces the extent of methane conversion, promoting more-uniform internal reforming and cooling within the stack. Such cooling is critical at higher-current conditions. A previously developed one-dimensional computational stack model is used to provide insight into stack operation. Pressurization is found to slightly increase internal thermal gradients, while promoting more-uniform reactant-concentration profiles across the cell, reducing the likelihood of local fuel starvation. The high fuel dilution brought by anode recycle can modestly decrease stack performance; however, this decrease is recovered through elevated-pressure operation at 3 bara. Anode recycle further promotes compositional uniformity across the cell. These results reflect that pressurized operation can promote stack performance, while potentially promoting long-term stack durability through uniformity in stack environmental conditions.

Elucidating the sensitivity to key operating parameters of a commercial-scale solid oxide fuel cell stack with open cathode manifolds

Solid oxide fuel cell (SOFC) is considered a promising eco-friendly energy conversion technology due to its high efficiency and fuel flexibility resulting from its high-temperature operation and ceramic structure. However, nonuniformities in thermal and electrochemical distribution within the SOFC stack can lead to performance degradation and hinder its market competitiveness. This study aims to identify optimal operating conditions to minimize these nonuniformities by investigating the effects of key operating conditions on the internal phenomena and local thermodynamic states of a commercial-scale stack. A highly reliable hydrocarbon-fueled SOFC model is developed and used to investigate the response of a 1-kW commercial-scale stack with open cathode manifolds to changes in key operating conditions. A parametric study is conducted on the air inlet temperature, air utilization, external reforming rate, and operating current density. Results show that increasing the air inlet temperature improves the uniformity of in-plane temperature distribution but deteriorates the uniformity of current density distribution. Air utilization and air inlet temperature have an identical mechanism to alter the internal distribution, thus showing a similar effect on local thermodynamic states. However, when altering the air utilization, the rate of decrease in uniformity of vertical temperature and current density is 5.39 times and 2.47 times larger than the change in the air inlet temperature. Increasing the external reforming rate exacerbates the overall distribution of local thermodynamic states. Among the selected operating parameters, the operating current density has the greatest influence on the in-plane temperature and current density distribution. This study provides guidance on the desired internal conditions inside the stack by quantitatively analyzing the effects of key operating conditions on the internal phenomena and local thermodynamic states of the stack through performance parameters and sensitivity analysis.

Transient thermomechanical analysis of a 1 kW solid oxide fuel cell stack based on 3D multiphysical field model

ABSTRACT In this paper, a model of a complete structured methane (CH4) internal reforming solid oxide fuel cell (SOFC) stack is developed. Material properties are extracted from experiments to establish a numerical simulation model to elucidate the mechanical failure mechanism of the stack under the combined effect of multiple factors. The steady-state and transient temperature and stress distributions of the stack are investigated. Results show that the higher the number of stacked layers, the more inhomogeneous the temperature distribution, the lower the fuel and oxygen (O2) utilization and potential of the cell, and the reduced flow rate in the top layer. The maximum temperature difference decreases rapidly during the first 50 mins of the stack shutdown. The first principal stress at the anode of the co-flow stack first decreases in the first few minutes of shutdown, then increases rapidly and is higher than the value at time 0. The first principal stress in the anode of the counterflow stack first increases and then decreases, with an increase of about 100 MPa. The maximum first principal stresses of the electrolyte and cathode decrease nearly monotonically, and the first principal stresses are smaller than the steady-state values.

Low-cost, high-density Mn–Co spinel coatings for stainless steel interconnect via efficient microwave heating

The high preparation cost and poor density of spinel coatings for stainless steel interconnect have always been puzzling conundrums for the solid oxide fuel cell stack developers. Herein, the microwave heating technology for fabricating Mn–Co spinel coating is developed to address these issues. We designed a device spontaneously providing reducing atmospheres and realized the low-cost, high-efficiency reduction of Mn–Co spinel via microwave heating. Dense coatings (MnO + Co) are formed on the steel surface at ∼1100 °C. The excellent density is related to the melting of Co particles induced by microwave selective heating. At initial, microwave heating is dominated by dipolar polarization, interfacial polarization, and natural resonance. After forming metallic Co, conductive loss and the lens effect further accelerate the reduction process. High-quality spinel coatings are formed during the subsequent oxidation at 800 °C, exhibiting an extremely low area-specific resistance increase rate.

Investigate the effect of a parallel-cylindrical flow field on the solid oxide fuel cell stack performance by 3D multiphysics simulating

In this paper, the 3D electrochemical-multiphysics coupling models for the one-cell solid oxide fuel cell (SOFC) stacks with the parallel flow field and a new parallel-cylindrical flow field have been developed and verified to evaluate their working characteristics. Firstly, the 3D model is established based on the realistic component structures including the solid, fluid, and porous components. Secondly, the momentum, mass, species, and energy transports, and the electrochemical reactions are coupled to the corresponding regions for carefully considering their effects on the performance. The analyzing result shows that a typical SOFC using the parallel-cylindrical rib configuration is concluded to be proper designing in achieving a good stack performance. The SOFC stack adopting the new parallel-cylindrical flow field would increase the electric current density by 38 % and improve the reactant distribution uniformity by 60 % than that with the traditional parallel flow field.