Degradation Of Solid Oxide Fuel Cells Research Articles

Multiphysics Simulation for the Performance of Tubular Solid Oxide Fuel Cells Operated on Coal Syngas

Solid oxide fuel cells (SOFCs) can be operated directly on coal syngas, but the various contaminants in coal syngas affect the performance and durability of the device. In the present study, three-dimensional multiphysics simulations were developed to investigate the performance degradation of tubular SOFCs operated on coal syngas. The numerical model includes charge conservation, species transport within the electrodes and the channels, and heat transfer within the device. These physical processes are coupled by the chemical/electrochemical reactions, which are represented by a Butler-Volmer type formula. Based on the thermodynamic database about impurities interaction with the Ni-YSZ composite anode, the contaminants are assumed to be adsorbed on the anode surface and form secondary phases. These formed phases affect the microstructural properties, electrical conductivity, and the number of active sites available for electrochemical reactions (i.e., hydrogen and carbon monoxide oxidation). During the cell operation, the contaminants diffuse from the fuel channel/anode interface to the anode/electrolyte interface, causing further irreversible degradation. The in-house developed multiphysics simulation is designed to be robust for prediction of interaction between anode materials with different types of contaminants (e.g., PH3, H2S, H2Se, AsH3, and user-defined). With the model parameters calibrated in the previous study, the performance of the tubular SOFCs with different levels/types of contaminants is predicted. The tolerance limits of the SOFC cell on single and multiple contaminants are also predicted with the simulations. Furthermore, the degradation resulted from Ni coarsening and redistribution, are also implemented into the model to mimic the performance of realistic SOFCs operating on coal syngas. The performance degradation investigation in this study provides guidance for experimental testing with syngas exposure, which is eventually beneficial to the cost reduction of the coal syngas clean-up technology.

Eco-Technoeconomic Analyses of Natural Gas-Powered SOFC/GT Hybrid Plants Accounting for Long-Term Degradation Effects Via Pseudo-Steady-State Model Simulations

Abstract In this study, four solid oxide fuel cell (SOFC) power plants, with natural gas (NG) as the fuel source, that account for long-term degradation were designed and simulated. The four candidate SOFC plants included a standalone SOFC plant, a standalone SOFC plant with a steam bottoming cycle, an SOFC/ (gas turbine) GT hybrid plant, and an SOFC/GT hybrid plant with a steam bottoming cycle. To capture dynamic behaviors caused by long-term SOFC degradation, this study employed a pseudo-stead-state approach that integrated real-time dynamic 1D SOFC models (degradation calculation embedded) with steady-state balance-of-plant models. Model simulations and eco-techno-economic analyses were performed over a 30-year plant lifetime using matlab simulink R2017a, aspen plus V12.1, and python 3.7.4. The results revealed that, while the standalone SOFC plant with a steam bottoming cycle provided the highest overall plant efficiency (65.0% LHV), it also had high SOFC replacement costs due to fast degradation. Instead, the SOFC/GT hybrid plant with a steam bottoming cycle was determined to be the best option, as it had the lowest levelized cost of electricity ($US 35.1/MWh) and the lowest cost of CO2 avoided (−$US100/ton CO2e).

Multiphysics Simulation for the Performance of Tubular Solid Oxide Fuel Cells Operated on Coal Syngas

Solid oxide fuel cells (SOFCs) can be operated directly on coal syngas, but the various contaminants in coal syngas affect the performance and durability of the device. In the present study, three-dimensional multiphysics simulations were developed to investigate the performance degradation of tubular SOFCs operated on coal syngas. The numerical model includes charge conservation, species transport within the electrodes/channels, and heat transfer within the device. These physical processes are coupled by the chemical/electrochemical reactions, which are represented by a Butler-Volmer type formula. Based on the thermodynamic database of impurity interactions with the Ni-YSZ composite anode, the contaminants are assumed to be adsorbed on the anode surface and form secondary phases. These formed phases affect the microstructural properties, electrical conductivity, and the number of active sites for electrochemical reactions. During the operation, the contaminants diffuse from the channel/anode interface to the anode/electrolyte interface, causing further irreversible degradation. The in-house developed multiphysics simulation is robust for prediction of interaction between anode materials with different types of contaminants (e.g., PH3, H2S, AsH3, etc.). With the calibrated model parameters, the performance of the tubular SOFCs with different levels/types of contaminants is predicted. The tolerance limits of the cells are also predicted. Furthermore, the degradation resulted from Ni redistribution, are also implemented into the model to mimic the performance of realistic SOFCs operating on coal syngas. The performance degradation investigation in this study provides guidance for experimental testing with syngas exposure, which is eventually beneficial to the cost reduction of the coal syngas clean-up technology.

Phase Field Study of Cr-Oxide Growth Kinetics in the Crofer 22 APU Alloy Supported by Wagner’s Theory

The Crofer 22 APU alloy is a frequently used metallic material to manufacture interconnects in solid oxide fuel cells. However, the formation and evaporation of Cr2O3 not only increases the electrical resistance but also leads to the Cr-related degradation over the service time. In order to investigate the growth kinetics of Cr-oxide, i.e., Cr2O3, the multi-phase field model coupled with reliable CALPHAD databases is employed. The phase field simulation results are benchmarked with the predictions of Wagner’s theory. Moreover, we evidence the influence of the temperature and Cr concentration on the ferritic matrix phase and the oxygen concentration at the Cr2O3/gas interface on the growth kinetics of Cr-oxide, paving the way for further investigations of Cr-related solid oxide fuel cell degradation processes.

Degradation behavior under alternating constant-current/constant-voltage discharge for flat-tube solid oxide fuel cells inside stack

An alternating constant-current (CC)/constant-voltage (CV) discharge for the optimal operation mode of solid oxide fuel cells (SOFCs) inside stack is carried out, and the degradation of SOFCs is discussed. The SOFCs are operated alternately in CC/CV mode for 985 h at 750 °C. The results show that the degradation rate of SOFCs first decreases and then increases in the CC/CV alternating operation mode. And the lowest degradation rate is 3.64%/100 h in the CV operation mode at ∼0.85 V, which is about one order of magnitude higher than the average degradation rate (0.36%/100 h) in the corresponding CC operation mode. The EIS analysis indicates that the ohmic resistance increases and the polarization resistance decreases after the CV operation mode, while the impedance change after CC discharge shows the opposite trend.

Identification of internal polarization dynamics for solid oxide fuel cells investigated by electrochemical impedance spectroscopy and distribution of relaxation times

Reliability and durability are two major problems restricting for Solid oxide fuel cells (SOFCs) industrial applications. To ensure the long-term stability, understood the internal operation mechanism of SOFC was necessary. The polarization curve combined with the distribution of relaxation times (DRT) method to analyze the electrochemical impedance spectroscopy (EIS) was used to identify the SOFCs modulation and degradation effect through the excitation frequency. Dynamic evolution of carbon deposition process and specific time constants were determined employing EIS and DRT. Special attention was paid to the dependency between the complex reaction processes that occur during the different operation of SOFC. The corresponding frequencies of concentration and activation polarization resistances in EIS were investigated under various gas compositions. The high concentration polarization resistance caused by the addition of nitrogen and hydrogen starvation was the key limiting factor for high cell power density. The total polarization resistance increased from 1.50 Ω/cm2 to 5.26 Ω/cm2 when the H2:N2 ratio decreased from 1:0 to 1:5. The anode did not deteriorate due to the poisoning of Ni particles in a short-term tested under 0.5 A/cm2 current density when the fuel was methane.

Long-Term Degradation Trend Prediction and Remaining Useful Life Estimation for Solid Oxide Fuel Cells

During the actual operation of the solid oxide fuel cell (SOFC), degradation is one of the most difficult technical problems to overcome. Predicting the degradation trend and estimating the remaining useful life (RUL) can effectively diagnose the potential failure and prolong the useful life of the fuel cell. To study the degradation trend of the SOFC under constant load conditions, a SOFC degradation model based on the ohmic area specific resistance (ASR) is presented first in this paper. Based on this model, a particle filter (PF) algorithm is proposed to predict the long-term degradation trend of the SOFC. The prediction performance of the PF is compared with that of the Kalman filter, which shows that the proposed algorithm is equipped with better accuracy and superiority. Furthermore, the RUL of the SOFC is estimated by using the obtained degradation prediction data. The results show that the model-based RUL estimation method has high accuracy, while the excellence of the PF algorithm for degradation trend prediction and RUL estimation is proven.

Dynamic life cycle assessment of solid oxide fuel cell system considering long-term degradation effects

In this work, we conduct a detailed cradle-to-product life cycle analysis in order to quantify the environmental impact of generating electricity using a conventional natural gas-fueled solid oxide fuel cell (SOFC). In contrast to previous studies, we account for SOFC degradation using a model previously developed by the authors to simulate deterioration in performance of SOFC over operating time. Midpoint environmental impacts were quantified using the ReCiPe 2016 and TRACI 2.1 US-Canada 2008 characterization methodologies in SimaPro. The resulting global warming potential was higher than those reported for SOFCs, which are underestimated because they neglect degradation. The results were compared with the environmental burdens associated with power generation using two conventional combined heat and power systems (i.e., gas turbines and internal combustion engines of various capacities), showing that even when accounting for long-term SOFC degradation impacts, the environmental performance of SOFCs is superior. This is true even though the analysis used a conservative approach in which SOFC system waste heat was not utilized. This means that if waste heat was utilized, the next environmental impact per unit energy produced would be even lower.

Study on extremely high temperature gradient at entrance of solid oxide fuel cell by preheating model

<sec>The degradation or failure caused by thermal stress is a serious problem for solid oxide fuel cell (SOFC), especially in preheating process. The common working temperature for SOFC is more than 700 ℃, so it should be preheated to startup temperature (e.g. 600 ℃). The thermal stress induced by temperature gradient in SOFC is a crucial factor that results in the degradation or failure of SOFC, therefore there are many studies on the optimization of preheating process.</sec><sec>Numerical model is an important tool in the study of SOFC preheating process, however there exists a serious discrepancy between the model results and experimental results. The numerical model always gives a very high temperature gradient in the SOFC which can result in SOFC crack according to the material permissible stress, and this result disagrees with the practical experimental result. In this paper, a hot gas preheating model of SOFC is developed and the model is verified by comparing with model results from the literature. Then, the location of maximum temperature gradient and distribution of temperature gradient in the SOFC are studied by this model, and the extremely high temperature gradient at entrance is analyzed. Some conclusions are given below.</sec><sec>1) The maximum temperature gradient is always located at the edge of SOFC nearby the gas entrance. The variation of temperature rise rate and velocity of hot gas show negligible effect on the position of maximum temperature gradient in the gas flow direction. For single channel preheating method, the maximum temperature gradient is at the gas entrance. For the dual channel preheating method, the maximum temperature gradient is always at the cathode gas entrance whatever gas feeding way is co-flow or counter-flow, because the thermal conductivity of cathode is lowest.</sec><sec>2) There is an extremely high temperature gradient at the gas entrance, and the temperature gradient sharply decreases along the gas flowing direction at the small entrance section. The extremely high temperature gradient may result from the uniform inlet temperature and velocity set in the model, and the entrance effect can greatly enhance the heat transfer between gas and SOFC component due to the large difference in velocity and temperature at the entrance section.</sec><sec>3) The entrance extension of gas channel can give rise to a fully developed velocity distribution and reduce the temperature gradient at SOFC entrance, however, there is always a high temperature gradient at the entrance section of SOFC due to the uniform inlet gas temperature. Therefore, the maximum temperature gradient given by numerical model as a criterion of SOFC safety can overestimate the thermal stress, and the distribution of temperature gradient in SOFC should be analyzed together to optimize the preheating process.</sec>

Performance Evolution of Ni-YSZ Anode-Supported SOFCs During Initial-Stage Operation

Solid oxide fuel cell (SOFC) is a clean and efficient power generation device, which has been widely used in recent years. However, its operation lifetime still needs to be improved to meet the requirements of further commercialization. The performance degradation of SOFCs is affected by many factors. It is meaningful to distinguish these factors and determine the dominant factor(s) for extending the operation lifetime. In this work, the initial operation stage (<100 h) of Ni-YSZ anode-supported SOFCs is mainly focused, since it has been found that the electrochemical performance changes most significantly in this stage. The electrochemical impedance spectroscopy (EIS) is continuously monitored during the operation of cells. Different electrode processes are distinguished through coupled distribution of relaxation time (DRT) and equivalent circuit model (ECM) analysis. Accordingly, the changes of different electrode processes in the initial-stage operation are obtained by detailed comparative analysis of EIS. It’s found that SOFCs go through activation stage and aging stage in turn: i) In the activation stage, the residual NiO in the anode is further reduced, so the porosity of the anode increases and the gas phase diffusion is enhanced, resulting in the performance improvement of the cell. ii) In the aging stage, the Ni particles in the anode agglomerate, so the effective three phase boundary (TPB) density decreases, which leads to the degradation of anode interface reactions and the drop of cell performance. Besides, we speculate that the dominant degradation mechanism in long-term operation (>100 h) is the continuous increase of the anode interface reaction-related resistance, which is mainly caused by gradual agglomeration of Ni particles. This evolution mechanism of electrochemical performance is then confirmed by detailed microstructure characterization. Figure 1

Influence of Surface Modification Using a Rare Earth Element on Properties of Ferritic Stainless Steel Metallic Interconnects

Iron and chromium based ferritic stainless steels have been considered to be a promising material for the metallic interconnect of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). However they have a drawback of chromium evaporation led by a scale growth at the steel surface when exposed at a high temperature oxidation atmosphere, which results in chromium poisoning of the air electrode and subsequent performance degradation of SOFCs and SOECs. Application of a surface modification or protective coating onto the metallic interconnects has been introduced to prevent the degradation by mitigating the chromium evaporation. In this study, ferritic stainless steels modified with a rare earth element of neodymium was investigated on the properties of high temperature oxidation and electrical conductivity. Detailed analyses on phase formation, microstructure evolution, and area specific resistance were carried out to figure out effects of the surface modification on the steels. Accordingly, the surface modified steels revealed decrease in the area specific resistance which was led by the reduction of scale growth since the rare earth element altered the chromium oxidation behavior.

On the dependence of interfacial resistance on contact materials between cathode and interconnect in solid oxide fuel cells

The dependence of interfacial contact resistance (ICR) on contact materials between cathode and interconnect is systematically studied under both isothermal oxidation and thermal cycling conditions. Three kinds of cathode current-collecting layer (CCCL) are used, (La,Sr) (Co,Fe)O3 (LSCF), LSCF+10%Ag, and Ag, and tested in a SUS430/CCCL/SUS430 sandwich structure to simulate the actual operation of the solid oxide fuel cells (SOFCs). Experimental results show that the ICR of LSCF+10%Ag exhibits the smallest value, in comparison with the specimens with LSCF and Ag paste, as well as the sample without a CCCL. For LSCF+10%Ag contact, the ICR increases from 0.0069 mΩ cm2 to 3.74 mΩ cm2 under an isothermal condition for 150 h, then increases from 3.74 mΩ cm2 to 10.79 mΩ cm2 after 15 thermal cycles. This work provides information for the understanding of possible mechanisms of performance degradation of SOFCs.

Pressurized SOFC System Fuelled by Biogas: Control Approaches and Degradation Impact

Abstract This paper shows control approaches for managing a pressurized solid oxide fuel cell (SOFC) system fuelled by biogas. This is an advanced solution to integrate the high efficiency benefits of a pressurized SOFC with a renewable source. The operative conditions of these analyses are based on the matching with an emulator rig including a T100 machine for tests in cyber-physical mode. So, this paper presents a real-time model including the fuel cell, the off-gas burner (OFB), and the recirculation lines. Although the microturbine components are planned to be evaluated with the hardware devices, the model includes also the T100 expander for machine control reasons. The simulations shown in this paper regard the assessment of an innovative control tool based on the model predictive control (MPC) technology. This controller and an additional tool based on the coupling of MPC and proportional integral derivative (PID) approaches were assessed against the application of PID controllers. The control targets consider both steady-state and dynamic aspects. Moreover, different control solutions are presented to operate the system during fuel cell degradation. The results include the system response to load variations, and SOFC voltage decrease. Considering the simulations including SOFC degradation, the MPC was able to decrease the thermal stress, but it was not able to compensate the degradation. On the other hand, the tool based on the coupling of the MPC and the PID approaches produced the best results in terms of set-point matching, and SOFC thermal stress containment.

High spatial resolution temperature profile measurements of solid-oxide fuel cells

Temperature gradients resulting from local electrochemical reactions, current distribution and geometry of gas flow channels in solid oxide fuel cells (SOFCs) create thermal stresses, localized thermophysical property gradients and uneven property evolution, contributing to SOFC degradation. This paper presents a new method to perform temperature measurements (up to 800 °C) at high spatial resolutions to monitor the operation of SOFCs. Using femtosecond laser irradiation, distributed fiber sensors were hardened for high temperature environment applications. Distributed fiber sensors were embedded in interconnected plates using an additive manufacturing method to perform temperature measurements with 4-mm spatial resolution during the operation of a planar fuel cell. The measurement revealed the impact of various H2 fuel concentrations and current loads have on temperature profiles of the SOFC tested. Temperature variation on the anode side was found to be less than 5 °C, and 3 °C on the cathode side. The measurements were compared to results from a multiphysics fuel cell performance model simulating similar conditions. These simulations predicted similar temperature gradients, indicating the experimental data obtained is reasonable. The model also predicts that the effect of the embedded sensor has on the local temperature will be minimal and that the gradient of temperature in the gas channels will be captured despite the separation between the sensor and the gas flow. The high spatial resolution data harnessed by these distributed fiber sensors provides experimental support for model-based design and optimization to improve the operational efficiency and longevity of solid oxide fuel cells and fuel cell assemblies.

Development of mathematical transfer functions correlating Solid Oxide Fuel Cell degradation to operating conditions for Accelerated Stress Test protocols design

This work presents an innovative model-based approach for the development of mathematical transfer functions capable of correlating Solid Oxide Fuel Cells (SOFCs) degradation rate to the applied operating conditions. Such functions can be used for fuel cell lifetime prediction and Accelerated Stress Test (AST) protocols design. The proposed approach relies on multiscale modelling methodology and links local degradation to high level performance models to evaluate the key operating variables accelerating voltage decay over time. A thorough simulation analysis is performed to convey the correlation among operating variables and degradation rate into mathematical transfer functions. To better illustrate the overall design and application process of such functions, a case study accounting for Ni agglomeration is addressed. The multiscale modelling framework is applied to correlate microscale (i.e., Ni particles size change) and macroscale (i.e., SOFC voltage reduction) levels through the most affected mesoscale parameters. The model is then used to simulate voltage decay over time and link degradation rates to the applied operating conditions. Afterwards, a parametric analysis is performed to investigate the influence exerted by each operating variable on the degradation rate and derive the transfer functions. An example of application for Accelerated Stress Test (AST) protocols design is then given.

A Mathematical Model for Prediction of Long-Term Degradation Effects in Solid Oxide Fuel Cells

A mathematical model of long-term solid oxide fuel cell (SOFC) degradation is proposed based on a cross-cutting meta-study of SOFC degradation research available in the open literature. This model ...

Current Status of Solid Oxide Fuel Cell Technology Research and Development at National Energy Technology Laboratory

The DOE Office of Fossil Energy Solid Oxide Fuel Cell (SOFC) Program is interested in the near-term commercialization of high-temperature SOFC and solid oxide electrolyzer cell (SOEC) technologies that are robust, reliable, and resilient. A recent report delivered to the United States Congress highlighted several development recommendations including the design of pilot-scale units, continued early stage research and development, increased industrial engagement, and the exploration of reversible operation of SOFC technology.The National Energy Technology Laboratory (NETL) SOFC research group currently addresses most of these recommendations. NETL’s in-house research efforts focus on the characterization, simulation, and mitigation of high temperature degradation of fuel cell components. The capstone of these efforts is NETL’s SOFC degradation modeling framework, which uses NETL supercomputing facilities to simulate SOFC performance degradation of thousands of possible electrode configurations experiencing multiple simultaneous degradation modes under a broad array of relevant operating conditions. The models for the different degradation modes are based upon experimental data (1) generated in-house, (2) referenced from available scientific publications, and (3) shared from collaborations with other industrial, academic, and national laboratory partners within the SOFC Program. The team then employs techniques in data analytics to select optimal electrodes to maximize the SOFC performance for given operating conditions. These modeling efforts guide electrode engineering efforts in-house and through external collaborations by identifying (1) which degradation modes contribute the most to overall performance degradation for given operating conditions and (2) which electrode features will have the greatest impact on lowering cell degradation and system costs. Additionally, the development on non-invasive in situ high temperature fiber optic sensors for temperature and gas composition measurement provides valuable data for inclusion in degradation models as well as informing technology development at the commercial scale. Finally, the wealth of experience gained in development degradation models and materials for reducing the cost of SOFC technology is being readily applied to reducing the cost of SOEC technology.NETL will report on its most recent progress in the field of SOFC and SOEC development, including degradation modeling, in situ fiber optic sensor development, electrode engineering, and relevant systems-level analyses.

An overview of degradation in solid oxide fuel cells-potential clean power sources

Solid oxide fuel cells (SOFCs) have emerged as the potential power generating devices, being profoundly effective, biofuel-based, and causing negligible harm to the environment. The commercialization of this device would introduce a new revolution in the field of electronic devices and power age. The performance of SOFCs is subject to the efficient working of its significant segments like anode, cathode, electrolyte, interconnect, and sealant. The mechanism of working of a SOFC, the kinetics and thermodynamics involved, as well as the composition of the fuel utilized are other vital variables in-charge of the performance of SOFCs. The serious issue with these devices has been the degradation of the components at high temperatures because of both intrinsic and extrinsic factors. Plenty of researchers have attempted to address this issue of degradation. Despite the fact that there are a large number of articles and reviews on corrosion, very few comprehensive reports have been published. In this review, various aspects of degradation have been covered including the mechanism, remedies, and alternatives as proposed by various researchers. It is a comprehensive review of degradation in SOFCs covering the most recent advances in the study of degradation and its mitigation measures.

A Model of Solid Oxide Fuel Cell Degradation on a Microstructural Level

The growth of nickel (Ni) particles in the porous anode is one of the most critical issues in solid oxide fuel cells (SOFC). It reduces the density of triple-phase boundaries (TPBs) over time and increases the polarization resistance of SOFC. Most of the three-dimensional models that are used to simulate this phenomenon in detail are numerically exhausting and as such intractable for on-line applications. This work presents a two-dimensional, microstructural model of reduced complexity as a trade-off between the numerical load and the level of detail. The model of Ni agglomeration is based on the power-law coarsening theory. The resulting model was validated by comparing the relative density of TPBs and the cell voltage to the experimentally measured values. It was shown that the calculated values closely fit the measured data. The advantage of the proposed model is that it takes lower computational load during the simulation compared to the complex phase field models and is suitable for estimation of SOFC electric performance over time.

Effect of inhomogeneous oxidation on the mechanical degradation of anode supported solid oxide fuel cell

A typical failure mode of the anode-supported solid oxide fuel cell (SOFC) is the cracking of electrolyte due to the excessive tensile stress caused by the expansion of anode during re-oxidation. This paper builds a three-dimensional model based on the finite element method (FEM) to investigate the effect of inhomogeneous oxidation on mechanical degradation of SOFC. The stress distributions and critical oxidation strains with considering inhomogeneous oxidation are compared to those of supposed homogeneous oxidation. The results indicate that the gradient of oxidation strain induces a large stress gradient and bending moment in anode, which increase the stresses and curvature of the cell, leading to the deterioration of SOFC degradation. The critical oxidation strains are increased in the SOFC with considering the inhomogeneous oxidation except for the anode. By calculating the stress under homogeneous re-oxidation, the resistance to failure is underestimated for cathode, electrolyte and glass-ceramic (GC), but the resistance to failure of the anode is overestimated. The effects of creep and thickness of the graded-oxidized zone on the redox stability are also investigated. This study helps to understand the effect of inhomogeneous oxidation and enhance the performance and lifetime of SOFC.