Solid Oxide Fuel Cell Electrodes Research Articles

Electrochemical performance of La0.8A0.2TiO3-δ (A = Li, Mg) based perovskites for solid oxide fuel cell electrode

ABSTRACT For potential use as an electrode in SOFCs, the effects of lithium and magnesium doping for phase development and conductivity of LaTiO3 have been investigated. Using a 1000°C sintering temperature, dense ceramics are created via the traditional solid oxide reaction method. Phase study shows the presence of perovskite phase with monoclinic crystal assembly. Structural characteristics of doped and undoped perovskites were calculated using the VESTA tool. Through the computed XRD spectral analysis, unit cell dimensions are established. To quantify sub-atomic characteristics and examine lattice components, CrystalMaker software also calculates electron density and lattice range. CrystalMaker program is useful for simulating porosity distributions and analysing impure inclusions in crystallisation.The electrical conductivity of the perovskites was analysed using impedance spectrometry and Li-doped structures display a significant increase in conductivity in the phase borderline of disordered perovskite.

Ni/GDC Fuel Electrode for Low-Temperature SOFC and its Aging Behavior Under Accelerated Stress

The microstructural integrity of Ni-based fuel electrodes is important for long-term solid oxide fuel cell (SOFC) operation. Degradation due to microstructural changes such as Ni-agglomeration, coarsening, and densification must be prevented by an appropriate microstructure. Here, the performance of four types of nickel-ceria-based fuel electrodes, which differ concerning layer sequence and manufacturing processes, was evaluated by electrochemical impedance spectroscopy at the nominal operating temperature of 600 °C. Electrodes produced through screen-printed GDC exhibited an acceptable polarization resistance (0.260 Ωcm2), whereas electrodes with an additional printed Ni/GDC layer demonstrated inferior performance (0.550 Ωcm2). Electrodes formed through infiltration of GDC into the printed GDC-layer displayed unreproducible performance values ranging from 0.16 to 1.20 Ωcm2 despite similar processing. Conversely, electrodes with an extra layer of GDC infiltrated into the Ni-backbone exhibited good performance (0.195 Ωcm2) and stability. Accelerated degradation tests under OCV at increased operating temperatures of 700 and 900 °C were performed on the sample based on a GDC infiltrated Ni-backbone that performed best among reproducible samples. The polarization resistance at 600 °C recorded at the beginning and the end of life increased by up to 100%. Microstructural analysis of the electrodes at different aging states revealed strong microstructural changes of fine-infiltrated GDC structures and Ni agglomeration at higher operating temperature.

Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions

Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can switch reversibly between power generation as a solid oxide fuel cell (SOFC) and hydrogen production as a solid oxide electrolysis cell (SOEC). It is important to systematically understand the electrode reaction processes and degradation factors in these two modes to tailor high-performance and durable r-SOC electrodes. The dependence of polarization resistance on cell fabrication conditions and operating conditions has been individually investigated for SOFC and SOEC by impedance measurement and distribution of relaxation times (DRT) analysis [1-4], but it is necessary to evaluate r-SOC as a whole [5]. Here in this study, we aim to systematically clarify the similarities and differences in the electrode reaction processes at the fuel electrodes of both SOFC and SOEC modes of r-SOCs, with respect to fuel electrode fabrication conditions. Experimental Several types of cells were fabricated with different fuel electrode constituent materials, thicknesses, and sintering temperatures. Three types of fuel electrode materials were used: Ni-GDC cermet, a composite of Ni and mixed ionic-electronic conductor Gd0.9Ce0.1O3 (GDC); Ni-YSZ cermet, a composite of Ni and pure ionic conductor YSZ (8 mol% Y2O3 - stabilized ZrO2); and Ni-GDC co-impregnated electrode with LST-GDC as a backbone support (LST: La0.1Sr0.9TiO3). Scandia-stabilized zirconia (ScSZ) was used as the electrolyte plate, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode. GDC buffer layer was prepared between the electrolyte and the air electrode to suppress the formation of interfacial insulting layers.Electrochemical impedance measurements were performed for the fuel electrode of the fabricated cell under SOFC and SOEC modes by supplying H2-H2O mixture and varying operating temperature, fuel humidification, and current density. The DRT analysis was conducted to separate various polarization resistance components of the fuel electrode with different relaxation times. The area of each DRT peak corresponds to the resistance of each electrode reaction process. In this study, activation energy was derived based on the assumption that the electrical conductance is of an Arrhenius-type thermally activated character. Its dependence on the fuel electrode fabrication conditions was investigated. Furthermore, electrode microstructure was observed by using focused-ion beam scanning electron microscopy (FIB-SEM). Results and Discussion Figure 1 shows typical DRT peaks of the Ni-GDC cermet fuel electrode in (a) SOFC and (b) SOEC modes, measured at different temperatures. In the range of 10-1 to 106 Hz where the frequency response was measured, three DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all with a DRT peak area decreasing with increasing operating temperature. This indicates that there are at least three electrode reaction processes with different relaxation times, which are thermally active processes. Activation energies of 0.1-0.3 eV (SOFC mode) and 0.2-0.5 eV (SOEC mode) were obtained for P1, and 0.9-1.0 eV (SOFC mode) and 1.1-1.3 eV (SOEC mode) for P2. The activation energies in SOEC mode were higher than those in SOFC mode for both P1 and P2. In the presentation, the dependence of activation energies on the fuel electrode constituent materials and related electrode reaction processes will be discussed.

The Evolution of Solid Oxide Fuel Cell Materials

Solid oxide fuel cells (SOFCs) are a key component of the future energy landscape. Although there is considerable research on the physical properties and technology of classic oxide materials for electrode and electrolytes in SOFCs, the field is very active as new experimental and theoretical techniques are now available that can improve these systems. In the present review, we consider key systems such as perovskite-related materials, the impact of strain and interfaces and advanced concepts that can improve the properties of SOFC materials. In particular, we consider the oxygen diffusion properties of perovskite-related materials and focus on La2NiO4+δ and the double perovskites such as GdBaCo2O5.5. Then, we review the importance of interfaces and strain as a way to engineer defect processes. Finally, we consider advanced concepts to form designed structures that explore the effect of local high entropy on lattice stabilization.

Structural and electrochemical performance of (Sr1.8Ln0.2)FeMoO6 (Ln = Sr, La, Sm, Eu) anode for solid oxide fuel cell

Different electronic structure on 4 f shell endows rare earth with variable of catalytic activity. In order to explore the catalytic effect of rare earth on solid oxide fuel cell (SOFC) electrode, we prepare electrolyte-supported (Sr1.8Ln0.2)FeMoO6/SDC/LSGM/SBCO single cell with Ln = Sr, La, Sm and Eu, and investigate their electrochemical performance based on X-ray diffraction (XRD), DC four-point probe, I-V and electrochemical impedance spectra. XRD results show that (Sr1.8Ln0.2)FeMoO6 are of single phase and belong to I4/m space group. Owing to the increased density of states, electronic conductivity of (Sr1.8La0.2)FeMoO6 (SLFM), (Sr1.8Sm0.2)FeMoO6 (SSFM) and (Sr1.8Eu0.2)FeMoO6 (SEFM) increases significantly, where SEFM exhibits the highest value in the measuring range. The higher conductivity and the smaller activation energy favor the power output of the investigated cell. The maximum power density of Sr2FeMoO6 (SFMO)-based cell is 772 mW·cm−2 at 850 ℃, that of SLFM- and SSFM-based cell increases to 890.8 mW·cm−2 and 861.6 mW·cm−2, while SEFM-based cell exhibits the highest value of 964.6 mW·cm−2. Electrochemical Impedance Spectroscopy (EIS) finds that SEFM-based cell possesses the smallest electrode resistance, charge transfer resistance, the fastest surface exchange and oxygen diffusion process, which favors its highest power output. These results demonstrate that the synergistic reaction in catalytic activity between rare earth atoms and SFMO lattice is different to a large degree, and our innovative discovery is the good catalytic activity of SEFM anode, which is conducive to comprehensively understanding the catalytic properties of rare earth for SOFC electrodes.

Quantitative estimation of triple phase boundaries in solid oxide fuel cell electrodes via artificial neural network

Virtual solid oxide fuel cell (SOFC) electrode microstructures composed of pore, electrolyte and catalyst phases with various particle sizes and volume fractions are reconstructed to design high-performance electrodes by investigating the role of microstructural properties on the electrodes and thereby the cell performance. The active TPB (triple phase boundary) densities in these microstructures are numerically measured and the data are used to train numerous artificial neural networks established with different model parameters and learning methods. Based on the results of 10,000 trainings of each model, the network that employs a backpropagation method of Bayesian regulation and has 2 hidden layers with 15 neurons is found to be the best one. It is then used to simulate new cases, whose parameters are in the range of those used in training. Further validation of the best network is also performed by considering a few randomly selected cases. The simulation results providing active TPB densities quantitatively are discussed regarding the microstructural properties. The overall results reveal that active TPBs can be increased by reducing the particle size of the phases and volume fraction of any phase should be selected according to the particle size to improve the number of active TPBs.

Advanced Manufacturing of Unique Solid Oxide Fuel Cell Electrode and Electrolyte Microstructures through Aerosol Deposition

Development of various additive manufacturing technologies over the years has given an opportunity for highly customizable and unique structures to be fabricated with applications towards several different industries. For ceramic manufacturing, techniques such as direct ink writing (DIW), stereolithography (SLA), and fused deposition modeling (FDM) have been utilized to construct very complex structures. These technologies have also been developed for use towards solid oxide fuel cells (SOFCs) where they have been utilized to manufacture components greater than 200 µm in thickness. Some components of the SOFC such as the electrodes, electrolyte, and barrier layer are much smaller and consist of thicknesses from 1 µm to 50 µm. Along with the reduced thickness, the electrodes of a SOFC are often comprised of a composite material where the previously mentioned technologies struggle with achieving both the required high resolution and compositional change needed to manufacture these specific components. This project’s goal is to develop an additive manufacturing technique that suits both requirements for manufacturing the electrodes, electrolyte, and barrier layer of a SOFC.The technology that has been developed to complete the manufacturing of highly customizable electrodes along with the electrolyte and barrier layer is Aerosol Deposition. The Aerosol Deposition system contains several different elements that lead to consistently tailored microstructures for the various 3-D printed parts including the use of syringe pumps, an ultrasonic atomizing nozzle from Sonaer Ultrasonics, an infrared heater, and a flexible automation system. The ultrasonic atomizing nozzle is used to convert a stream of liquid into a fine mist via mechanical vibrations. The liquid that is supplied to our ultrasonic atomizing nozzle is low solids loading solvent-based suspension containing approximately 1 - 5 vol% of solids and polymer pore formers. Suspensions are supplied to the nozzle by mechanical pressure provided from a programmable syringe pump. This technology accompanied with a flexible automation system gives the potential for highly customizable and repeatable microstructures that can aid in evaluating variables associated with the different components of the SOFC.Development of the additive manufacturing system to fabricate the anode functional layer, electrolyte, barrier layer, and cathode active and current collector layers through an automated process have been studied. For the electrodes, a microstructure that contains approximately 30% - 40% porosity is suitable to enhance the electrochemical performance of the electrode. Sintering temperatures for the electrodes typically range from 1000 °C to 1300 °C which can typically densify the microstructure and restrict the amount of porosity present. To implement porosity within the microstructure poly(methyl methacrylate) was incorporated into electrode suspensions due to their ability to diffuse out of the electrode microstructure at temperatures of ~450 °C. The electrical and mechanical properties of the separate components have been characterized accordingly utilizing electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Acknowledgements: This work was performed in support of the US Department of Energy’s Solid Oxide Fuel Cell Program. The authors would like to acknowledge the WVU Shared Research Facilities (SRF) and thank Dr. Thomas Kalapos from Leidos Research Support Team for his assistance.

Reliable Lab-Scale Evaluation for Enhanced SOFCs Electrode Performance - Influence of Electronic Transport

Understanding and optimizing electrochemically active zone for oxygen reduction reaction (ORR) in solid oxide fuel cells (SOFCs) cathodes are indispensable to maximize device’s performance. For a mixed ionic and electronic conducting electrode, the range of this zone depends on the oxygen surface exchange and solid-state oxygen/electron transport properties of electrode materials and the oxygen gas transport through porous electrode. This implies that electrode microstructure, including surface area, porosity, and tortuosity, needs to be carefully designed and controlled to maximize electrochemically active electrode volume. This aspect is also critical to realize valid characterization of the electrode’s electrochemical activities. For instance, when a material’s electronic conductivity is low or the electrical contact points are spaced beyond a critical distance, the electrode polarization resistance measured by electrochemical impedance spectroscopy will be controlled by the sheet resistance not the oxygen exchange resistance. In this presentation, we will discuss our synthesis approach of lanthanum strontium cobalt ferrite (LSCF) and spinel powders by using co-precipitation with a continuous stirred-tank reactor, in order to precisely control powder’s chemistry and morphology (ultimately, electrode microstructure). And, we will discuss the influence of electrode microstructure and current collecting method on electronic conduction in porous electrode and, eventually, on electrochemical performance and its reliable evaluation in a lab-scale button cell configuration.This work was supported by the US Department of Energy (DOE), Office of Fossil Energy, (Office of Fossil Energy & Carbon Management), “Solid Oxide Fuel Cell Manufacturing in Support of Office of Fossil Energy” program through Argonne National Laboratory under FWP No. 27327.1.

Enhancing the Cathodic Performance of LSM Via Nanostructured Surface Decoration with Infiltrated Sm0.5Sr0.5CoO3-Δ

The Solid Oxide Fuel Cell (SOFC) is getting attention from next-generation electrochemical energy conversion devices with high efficiency and low pollutant emission. But the high operating temperature in SOFC can lead to problems like high cost, difficult sealing, and fast degradation. To alleviate this problem, Intermediate temperature SOFC (IT-SOFC) has become an adequate alternative. But, as the operating temperature decreased, the Oxygen reduction reaction (ORR) also decreased, contributing to performance degradation and efficiency loss. The infiltration method, effectively improving the performance of the SOFC electrode, is one of the most effective ways. However, this method has been limited due to the multi-step process and instability of long-term operation. In this study, we suggest a new process that combines the infiltration and spray method with co-sintering to diminish the multi-step. We fabricated a cathode in which the LSM and Sm0.5Sr0.5CoO3-δ infiltration solvent coated simultaneously by the spray process and co-sintered. And we measured the cell performance and stability. Consequently, when applied as electrolyte-supported cells at 1073K, performance is measured by exhibiting a maximum power density of 0.986W cm-2 in fuel cell mode and electrolysis performance of 0.878A cm-2 at 1.3V. The result of this study was 0.724W higher than that of the bare LSM electrode. Figure 1

Computational Modeling for Cr and S Poisoning Pathways on La0.6Sr0.4Co0.2Fe0.8O3 Surfaces

Perovskite oxygen electrode degradation caused by cation segregation sets the limit of performance and lifetime of solid oxide fuel cells (SOFC) [1][2]. For the state-of-art perovskite oxygen electrode, (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF), the commonly known degradation mechanism is through Sr segregation, which can be further poisoned by Cr and as well as by S impurities to form insulating layers, limiting the oxygen evolution reaction (ORR) [3][4]. In order to advance our understanding of Cr and S poisoning pathways on LSCF surfaces, we will combine ab initio density functional theory (DFT) reaction energetics, defect chemistry, and microkinetic modeling to establish a quantitative model to find the deposition reaction on different termination slabs. To predict the reaction mechanism and kinetics of Cr and S poisoning reactions, we will study CrO3 and SO2 molecules deposition pathways on pristine LSCF, and surface-modified (eg. Hf, Zr, Pr, Nd, Ce surface-doped) LSCF slabs. I will correlate adsorption energies with LSCF surface characteristics to explain the origin of the deposition, and use these characteristics to evaluate the effectiveness of the surface infiltration. Ab initio molecular dynamics (AIMD) will be applied at different ensembles to investigate further steps of the reaction, and show how the surface modification will inhibit poisoning reactions. These findings will help to guide the design of better performance and more durable oxygen electrodes for SOFCs.[1] Neagu, D., Tsekouras, G., Miller, D. N., Ménard, H., & Irvine, J. T. (2013). In situ growth of nanoparticles through control of non-stoichiometry. Nature Chemistry, 5(11), 916–923.[2] Lee, K. T., & Wachsman, E. D. (2014). Role of nanostructures on SOFC performance at reduced temperatures. MRS Bulletin, 39(9), 783–791.[3] Jiang, S. P., & Chen, X. (2014). Chromium deposition and poisoning of cathodes of solid oxide fuel cells – a review. International Journal of Hydrogen Energy, 39(1), 505–531.[4] Chen, K., & Jiang, S. P. (2020). Surface segregation in solid oxide cell oxygen electrodes: Phenomena, mitigation strategies and electrochemical properties. Electrochemical Energy Reviews, 3(4), 730–765.

Determination of the effective conductivities of solid oxide fuel cell electrodes using the first‐order homogenization method

AbstractApproximately 80% of the world's primary energy supply consists of fossil fuels. In order to reduce the CO2 consumption in the world, fuel cells will be indispensable for the environmentally friendly generation of electrical energy. Many experimental and numerical studies show that the composition and the microstructure morphology of porous electrodes have a great influence on the durability and conversion efficiency of fuel cells. In order to establish a relationship between the specific microstructure of the electrodes and the performance of the overall fuel cell, the macroscopic physical quantities need to be determined. In this work, the first‐order computational homogenization method capable of capturing anisotropic effects is applied in order to estimate different types of homogenized conductivities. The effective conductivities can be used to conduct numerical simulations on the fuel cell level in order to obtain correlations between the microstructure characteristics (e.g., volume fraction of pores, morphology) and the performance.

A Surrogate Model of the Butler-Volmer Equation for the Prediction of Thermodynamic Losses of Solid Oxide Fuel Cell Electrode

Solid oxide fuel cells are becoming increasingly important in various applications, from households to large-scale power plants. However, these electrochemical energy conversion devices have complex behavior that is difficult to understand and optimize. A numerical simulation is a primary tool for analysis and optimization-design. One of the most significant challenges in this field is improving microscale transport phenomena and electrode reaction models. Two main categories of simulation are black-box and white-box models. The former requires large experimental datasets and lacks physical constraints, while the latter inherits the inaccuracy of typical electrochemical reaction models. Here we show a micro-scale artificial neural network-supported numerical simulation that allows for overcoming those issues. In our research, we substituted one equation in the system, an electrochemical model, with an artificial neural network prediction. The data-driven prediction is constrained and must satisfy all reminded balance equations in the system. The results show that the proposed model can simulate an anode-electrode’s thermodynamic losses with improved accuracy compared with the classical approach. The coefficient of determination R2 for the proposed model was equal to 0.8810 for 800 °C, 0.8720 for 900 °C, and 0.8436 for 1000 °C. The findings open a way for improving the accuracy and computational complexity of electrochemical models in solid oxide fuel cell simulations.

Facile Construction of Nanostructured Cermet Anodes with Strong Metal-Oxide Interaction for Efficient and Durable Solid Oxide Fuel Cells.

Nanostructured anodes generate massive reaction sites to oxidize fuels in solid oxide fuel cells (SOFCs); however, the nonexistence of a practically viable approach for the construction of nanostructures and the retention of these nanostructures under the harsh operating conditions of SOFCs poses a significant challenge. Herein, a simple procedure is reported for the construction of a nanostructured Ni-Gd-doped CeO2 anode based on the direct assembly of pre-formed nanocomposite powder with strong metal-oxide interaction. The directly assembled anode forms heterointerfaces with the electrolyte owing to the electrochemical polarization current and exhibits excellent structural robustness against thermal ripening. An electrolyte-supported cell with the directly assembled anode produces a peak power density of 0.73W cm-2 at 800°C, while maintaining stability for 100h, which is in contrast to the drastic degradation of the cermet anode prepared using the conventional method. These findings provide clarity on the design and construction of durable nanostructured anodes and other electrodes for SOFCs.

Numerical analysis of the relation between the porosity of the fuel electrode support and functional layer, and performance of solid oxide fuel cells using computational fluid dynamics

The development of the hydrogen industry brings new technological challenges. Solid oxide fuel cells (SOFCs) seem to be one of the leading devices for hydrogen conversion and its production while operating in its reverse mode (as an electrolyser). Fine-tuning of SOFC microstructure might extend cells life and boost their performance. The article presents original numerical studies of the performance of solid oxide fuel cells, based on the OpenFuelCell model, extended by fuel and oxidant concentration loss equations. Transport phenomena in the porous structure of the anode functional layer (AFL) and the anode support layer (ASL) were simulated using the modified Fick's law (MFL) and the Knudsen diffusion coefficient. The presented research focuses on the influence of fuel distribution in fuel electrode of SOFC together with reacting zones and on the influence of AFL and ASL microstructure characteristics on cell performance. The studies included porosity in the range of 30%–60% for both types of anode layers. The obtained results showed a significant impact of the porosity characteristics on the SOFC performance and indicated the possible direction for further improvement. Numerical studies have shown that an increase in anode layers porosity of 30% allows for an increase in cell efficiency of even 15%. Experimental, as well as numerical results, showed that above a porosity of 49%, further increasing the porosity has no strong effect on the results. Also, a novelty in the work and an important part of it is the comparison of the impact of microstructure manipulation of the two anodic layers. Improvement of ASL microstructure allows to better, more homogeneous, fuel distribution inside the anode. Additionally, it increases the concentration of the fuel in the functional layer by up to 8%, which leads to increase in SOFC performance.

High-Performance Sr0.95Fe0.8Mo0.1Ni0.1O3−δ Electrode for Reversible Symmetrical Solid Oxide Cells

Reversible symmetrical solid oxide cells (RS-SOCs) have attracted much attention due to their high energy conversion efficiency and fabrication simplicity. In this study, 10% Fe was substituted with Ni in the B-site of Sr0.9Fe0.9Mo0.1O3−δ to enhance the electrochemical performance of H2O electrolysis. The characterization results and theoretical calculations indicated that Ni doping decreased the adsorption and reaction energy barrier of intermediates of H2O electrolysis on the Sr0.95Fe0.8Mo0.1Ni0.1O3−δ’s (111) surface, which promoted the kinetics of the electrode reaction, thus fabricating electrochemical activity and resulting in higher reaction dynamics. Consequently, a high power density of 1.145 W cm−2 at 850 °C on a symmetrical cell was achieved in the solid oxide fuel cell (SOFC) mode, and a current density of 3.995 A cm−2 was obtained at 850 °C and 1.6 V in the solid oxide electrolysis cell (SOEC) mode, indicating the Sr0.9Fe0.8Mo0.1Ni0.1O3−δ oxide to be a promising SOFC electrode for power production and SOEC electrode for H2 production.

Proton-coupled electron transfer at SOFC electrodes.

Understanding the charge transfer processes at solid oxide fuel cell (SOFC) electrodes is critical to designing more efficient and robust materials. Activation losses at SOFC electrodes have been widely attributed to the ambipolar migration of charges at the mixed ionic-electronic conductor-gas interface. Empirical Butler-Volmer kinetics based on the transition state theory is often used to model the current-voltage relationship, where charged particles transfer classically over an energy barrier. However, the hydrogen oxidation/water electrolysis reaction H2(g) + O2- ⇌ H2O(g) + 2e- must be modeled through concerted electron and proton tunneling events, where we unify the theory of the electrostatic surface potential with proton-coupled electron transfer kinetics. We derive a framework for the reaction rate that depends on the electrostatic surface potential, adsorbate dipole moment, the electronic structure of the electron donor/acceptor, and vibronic states of the hydrogen species. This theory was used to study the current-voltage characteristics of the Ni/gadolinium-doped ceria electrode in H2/H2O(g), where we find excellent validation of this novel model. These results yield the first reported quantification of the solvent reorganization energy for an SOFC material and suggest that the three-phase boundary mechanism is the dominant pathway for charge transfer at cermet electrodes.

Microstructural design of solid oxide fuel cell electrodes by micro-modeling coupled with artificial neural network

Artificial neural network (ANN) is used to model active three/triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) electrodes composed of phases with various particle sizes for the first time in the literature. Electrode microstructures comprising catalyst, electrolyte and pore phases with the same volume fraction, but various mean particle sizes are synthetically generated via Dream.3D software and the active TPB densities are measured by COMSOL software to obtain input data for training the ANN models as well as to validate the network results. In this regard, three learning methods of Bayesian regulation (BR), Levenberg-Marquardt (LM) and Scaled conjugate gradient (SCG) with various hidden layer and neuron numbers are examined. Among ANN models with three inputs and one output, the model with BR including one hidden layer and five neurons performs the best. This model revealing an average relative error of only 0.036 is then employed to simulate SOFC electrodes microstructures with new particle sizes not introduced in the learning process. The active TPB densities estimated by ANN are found to agree well with the computed ones. Therefore, ANN modeling is considered as a useful tool for the prediction of active TPB density in SOFC electrodes after a careful selection of backpropagation method and network structure.

π Learning: A Performance‐Informed Framework for Microstructural Electrode Design

AbstractDesigning high‐performance porous electrodes is the key to next‐generation electrochemical energy devices. Current machine‐learning‐based electrode design strategies are mainly orientated toward physical properties; however, the electrochemical performance is the ultimate design objective. Performance‐orientated electrode design is challenging because the current data driven approaches do not accurately extract high‐dimensional features in complex multiphase microstructures. Herein, this work reports a novel performance‐informed deep learning framework, termed π learning, which enables performance‐informed microstructure generation, toward overall performance prediction of candidate electrodes by adding most relevant physical features into the learning process. This is achieved by integrating physics‐informed generative adversarial neural networks (GANs) with convolutional neural networks (CNNs) and with advanced multi‐physics, multi‐scale modeling of 3D porous electrodes. This work demonstrates the advantages of π learning by employing two popular design philosophies: forward and inverse designs, for the design of solid oxide fuel cells electrodes. π learning thus has the potential to unlock performance‐driven learning in the design of next generation porous electrodes for advanced electrochemical energy devices such as fuel cells and batteries.

Three-dimensional numerical simulation of oxygen isotope transport in lanthanum strontium manganese - Yttria-stabilized zirconia cathode of solid oxide fuel cell

Distribution of oxygen isotope 18O concentration which was labeled in lanthanum strontium manganese (LSM) – yttria-stabilized zirconia (YSZ) cathode of a solid oxide fuel cell (SOFC) is predicted through numerical simulations using a three-dimensional microstructure which was reconstructed by a focused ion beam-scanning electron microscopy (FIB-SEM). The electrochemical reaction under the SOFC operation is first numerically simulated, then the unsteady 18O transport is simulated by coupling self-diffusion by concentration gradient, migration by the electrochemical potential field, and electrochemical reaction at the triple phase boundaries. Predicted results were compared with the measured 18O concentration by a secondary ion mass spectrometry taken at the intermediate plane of the reconstructed 3D microstructure, which showed qualitative consistency between them. Thus, from the direct correlation of the electrochemical reaction and 18O concentration in an actual electrode microstructure, influence of electrochemical reaction was discussed. The present approach provides useful information for the interpretation of the oxygen labeling experiment results, which can cultivate better understanding of the electrochemical reaction mechanism in the SOFC electrodes.

3D microstructures of solid oxide fuel cell Ni-YSZ anodes with carbon deposition

Carbon deposition is a critical problem for operating solid oxide fuel cells (SOFCs) with carbon containing fuels such as natural gas, biogas, etc. When steam to carbon ratio is below the critical threshold, carbon may form on the surface of nickel (Ni) catalyst. Carbon covers the active triple boundaries and deteriorates the electrochemical performance. In most severe cases, carbon may even lead to an irreversible deformation of a porous cermet. However, quantitative investigations of carbon deposition have been limited due to the difficulties in observing the microstructures. In the present study, the 3D structures of carbon deposition in the SOFC electrode are quantitatively reconstructed for the first time by a machine learning assisted image processing framework. Focused ion beam - scanning electron microscope (FIB-SEM) measurements of anode samples are conducted without resin infiltration. A U-net neural network with multiple inputs is developed to identify the unfilled pores, from which phase segmentations of raw SEM images without resin filling became possible. The mild and severe carbon deposition conditions are tested by exposing the electrodes to humidified and dry methane conditions. It is revealed from the 3D reconstruction that carbon layer formed over Ni particles and Ni pulverizes due to high temperature corrosion (metal dusting). At the same time, YSZ network deformed by the internal stress. The observed microstructural changes are in good agreement with the performance recovery after the regeneration process. The developed microstructure evaluation framework will enable quantitative investigations of carbon deposition and developments of mitigation strategies for SOFC anodes.