Solid Oxide Fuel Cell Research Research Articles

On Three Fundamental Questions Concerning Activity and Stability in Solid Oxide Cells

The aim of this presentation is to address three fundamental questions related to solid oxide cells: Are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) indeed the rate-limiting steps in the high-performance of solid oxide cells, and how can we accurately quantify the area specific resistance of the oxygen electrode?What causes the phenomenon known as “electrochemically driven phase transformation,” and how can our understanding of this process be applied to create electrodes that are both high-performing and durable?How can we develop reliable accelerated testing protocols for both solid oxide fuel cells and solid oxide electrolysis cells, and which physical processes are being accelerated through these tests? The accurate quantification of electrode polarization in fuel cells and electrolyzers holds critical importance but presents a significant challenge due to the extensive overlap in polarizations from both the anode and cathode, whether in DC or AC measurements. This overlap creates a notable gap in our understanding of electrode behavior and in the development of electrochemical devices that are both high-performing and durable. In this presentation, I will introduce a reliable method for measuring the polarization of individual electrodes within a solid oxide cell. This technique is versatile and can be easily adapted for use in various types of electrochemical cells. Additionally, we will explore the limitations associated with using the distribution of relaxation times analysis for determining the polarization of individual electrodes.We will then address the origin for the phase transformation observed in an oxygen electrode during operation, as opposed to what is seen with thermally annealed materials. By integrating electronic conduction at the interface layer, we can significantly reduce the occurrence of phase transformation. This understanding of “electrochemically driven phase change” is crucial for the development of reliable accelerated testing protocols. Such protocols are essential in solid oxide fuel cell research to speed up the investigation of durability issues, quickly identify potential failure mechanisms, and ultimately estimate the lifespan of electrochemical cells. In our study, we compared solid oxide fuel cells operated at constant current density with those subjected to accelerated testing methods, which involve intermittent current injections. We have formulated a general accelerated testing framework, which will be presented in detail.Finally, we will present a theoretical model that underlies those three questions and can be used to address stability and durability issues in solid oxide cells. Acknowledgements: The presenter would like to thank Prof. Anil Virkar, Dr. Emir Dogdibegovic, and Dr. Yudong Wang, for their invaluable contributions to the work presented. This work was made possible through the support of projects DE-FE0026097, DE-FE0031667, DE-AR0001346, and DE-FE0032110.

Operando analysis of a solid oxide fuel cell by environmental transmission electron microscopy

Correlating the microstructure of an energy conversion device to its performance is often a complex exercise, notably in solid oxide fuel cell research. Solid oxide fuel cells combine multiple materials and interfaces that evolve in time due to high operating temperatures and reactive atmospheres. We demonstrate here that operando environmental transmission electron microscopy can identify structure-property links in such devices. By contacting a cathode-electrolyte-anode cell to a heating and biasing microelectromechanical system in a single-chamber configuration, a direct correlation is found between the environmental conditions (oxygen and hydrogen partial pressures, temperature), the cell open circuit voltage, and the microstructural evolution of the fuel cell, down to the atomic scale. The results shed important insights into the impact of the anode oxidation state and its morphology on the cell electrical properties.

On Electrochemically Driven Phase Change and Accelerated Test Protocols in Solid Oxide Cells

The aim of this talk is to address three fundamental questions in solid oxide fuel cells and solid oxide electrolysis cells:(1) Whether or not the oxygen reduction reaction is indeed the limiting step in solid oxide cells and how to quantify it definitely?(2) What is the origin for the so-called “electrochemically driven phase transformation and how to translate the understanding to achieve a high-performance and highly stable electrode?(3) How to develop reliable accelerated test protocols and what’s the physical process that was accelerated?Quantifying electrode polarization in fuel cells and electrolyzers is of significant importance. It, however, remains difficult because of the substantial overlap of polarizations from both negative and positives electrodes either in a dc or an ac measurement. This challenge leads to a compelling gap in our scientific understanding of electrode phenomena and designing high-performance and durable electrochemical devices. In this talk, we will describe a reproducible method to quantify the polarization of an individual electrode of a solid oxide cell. This method is generic and can be applied readily to other electrochemical cells.We will then address the greater phase transformation of an oxygen electrode during operation when compared to thermally annealed powders. Theoretical analysis suggests that the presence of a reduced oxygen partial pressure at the interface between the oxygen electrode and the electrolyte is the origin for the phase change in an oxygen electrode. Guided by the theory, an addition of the electronic conduction in the interface layer leads to the significant suppression of phase change, while improving cell performance and performance stability.Reliable accelerated test protocols are needed for solid oxide fuel cell research to facilitate rapid learning on key durability issues, identify potential modes of failure expeditiously, and eventually predict the calendar lifetime of an electrochemical cell. In this work, solid oxide fuel cells operated at a constant current density were compared to cells undergoing accelerated measurements, which are composed of intermittent current injection to the cell. A general accelerated test profile was developed by cycling a solid oxide fuel cell from open circuit to a predetermined operating current density that is the same as the current density during a steady-state operation, to accelerate the local redox environment. Up to 1,320,000 cycles were generated in this work. The cell degradation was accelerated by nearly 10×, suggesting the feasibility of using this protocol for acceleration test to predict life performance of solid oxide fuel cells.Finally, we will present a theoretical model that underlies those three questions and can be used to address stability and durability issues in solid oxide fuel cells and solid oxide electrolysis cells.

Accelerated test protocols to predict service life and durability of solid oxide fuel cells

Reliable accelerated test protocols are needed for solid oxide fuel cell research to facilitate rapid learning on key durability issues, identify potential modes of failure expeditiously, and eventually predict the calendar lifetime of an electrochemical cell. In this work, solid oxide fuel cells operated at a constant current density were compared to cells undergoing accelerated measurements, which are composed of intermittent current injection to the cell. A general accelerated test profile was developed by cycling a solid oxide fuel cell from open circuit to a predetermined operating current density that is the same as the current density during a steady-state operation, to accelerate the local redox environment. The following parameters were studied: current density, operation temperature, moist level, sintering temperature, cycling current, cycling frequency, and operation time. Up to 1,320,000 cycles were generated in this work. The cell degradation was accelerated by nearly 10 times, suggesting the feasibility of using this protocol for acceleration test to predict life performance and durability of solid oxide fuel cells.

On the Technology of Solid Oxide Fuel Cell (SOFC) Energy Systems for Stationary Power Generation: A Review

This paper presents a comprehensive overview on the current status of solid oxide fuel cell (SOFC) energy systems technology with a deep insight into the techno-energy performance. In recent years, SOFCs have received growing attention in the scientific landscape of high efficiency energy technologies. They are fuel flexible, highly efficient, and environmentally sustainable. The high working temperature makes it possible to work in cogeneration, and drive downstream bottomed cycles such as Brayton and Hirn/Rankine ones, thus configuring the hybrid system of a SOFC/turbine with very high electric efficiency. Fuel flexibility makes SOFCs independent from pure hydrogen feeding, since hydrocarbons can be fed directly to the SOFC and then converted to a hydrogen rich stream by the internal thermochemical processes. SOFC is also able to convert carbon monoxide electrochemically, thus contributing to energy production together with hydrogen. SOFCs are much considered for being supplied with biofuels, especially biogas and syngas, so that biomass gasifiers/SOFC integrated systems contribute to the “waste to energy” chain with a significant reduction in pollution. The paper also deals with the analysis of techno-energy performance by means of ad hoc developed numerical modeling, in relation to the main operating parameters. Ample prominence is given to the aspect of fueling, emphasizing fuel processing with a deep discussion on the impurities and undesired phenomena that SOFCs suffer. Constituent materials, geometry, and design methods for the balance of plant were studied. A wide analysis was dedicated to the hybrid system of the SOFC/turbine and to the integrated system of the biomass gasifier/SOFC. Finally, an overview of SOFC system manufacturing companies on SOFC research and development worldwide and on the European roadmap was made to reflect the interest in this technology, which is an important signal of how communities are sensitive toward clean, low carbon, and efficient technologies, and therefore to provide a decisive and firm impulse to the now outlined energy transition.

Computational Optimization of Functionally Graded Electrodes for Solid Oxide Fuel Cells

Solid Oxide Fuel Cells (SOFCs) are widely considered to be an ideal power source across a range of industries in the near future due to their high efficiency, high power density, and fuel flexibility. However, for widespread usage of SOFCs to be feasible, certain disadvantages, such as their high operating temperature, electrochemical losses, and high cost of manufacturing, must be solved. In particular, the field of materials research occupies a unique position of being able to quickly and simultaneously solve many of these issues through the development of material compositions and structures that do not currently exist in the industry. Especially relevant to solid oxide fuel cells in particular, is the impact that the electrodes’ geometries and compositions have on the operating performance. The electrodes’ ability to quickly move reactants to the interface of the electrolyte and remove products to the bulk flow comes into play as the fuel cell operates at higher current densities and concentration losses become prominent. Therefore, the microstructures present throughout the electrodes’ depth plays a vital role in improving overall cell performance. However, current fuel cell research has not yet effectively captured and defined the connections of the microstructure parameters and measured their impact on cell behavior. Additionally, homogeneous electrode design and implementation have dominated the research and commercial space thus far. The technique of functional material grading, which has begun to see wide research and commercial usage for such problems as acoustic impedance matching, thermal control, and mechanical design will be leveraged for the enhancement of SOFC electrodes. Functionally graded electrodes have been used in solid oxide fuel cell research in recent years in an effort to improve the cell performance by altering the microstructure including porosity, particle size, and composition of electronic and ionic conductors near the triple phase boundary region. Normally the functional grading process adds additional fabrication steps making it less desirable as an optimization process and easy manufacturing method. However, by using an additive manufacturing process it eliminates the need for multiple discrete graded layers to be deposited to obtain a graded electrode functional layer. This study seeks to explore the correlations of geometry and structure parameters from the meso-scale through to the micro-scale level, together with mass transfer, ionic and electronic transport, and gas-surface electrochemical reactions inside the electrodes to guide future additive manufacturing of SOFCs. Outlined is the development of an effective medium model for simulating the performance of fuel cell microstructures as a function of specific operating ranges in temperature, pressure, and in fuels used. Smooth and continuous linear and nonlinear functional gradation profiles of porosity and material composition are studied within the framework of an effective medium boundary value problem where the electrochemical relations, such as the Butler-Volmer equation, percolating conduction paths, and gas diffusion are solved using the finite difference method. The form of these relations for homogeneous electrodes was analyzed by Costamagna, et. al [1], who also defined outstanding problems with regards to optimizing SOFC electrodes [2]. Globally optimal linear and nonlinear gradation profiles and cell parameters are derived as a function of particle sizes, ratio of conductivities, and desired operating conditions and scored based on their reduction of cell overpotentials.[1] Costamagna, P., P. Costa, and V. Antonucci, Micro-modelling of solid oxide fuel cell electrodes. Electrochimica Acta, 1998. 43(3-4), pp.375-394.[2] Costamagna, P., P. Costa, and E. Arato, Some more considerations on the optimization of cermet solid oxide fuel cell electrodes. Electrochimica Acta, 1998. 43(8), pp.967-972. Figure 1

Suppression of Sr surface segregation in La0.8Sr0.2Co0.2Fe0.8O3-δ via Nb doping in B-site

Sr surface segregation has been one of the main reasons for the cathode performance degradation during the long-term operation of solid oxide fuel cells (SOFC). Investigation on Sr segregation mechanism and proposing strategies on suppressing the Sr surface segregation are significant for SOFC development. In this paper, La 0.8 Sr 0.2 Co 0.2 Fe 0.8-x Nb x O 3-δ (LSCFNb, x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) are prepared via sol-gel method. The electrochemical performance and long-term stability are tested through electrochemical impedance spectroscopy (EIS) and constant current polarization. The results show that the long-term stability of LSCFNb cathodes are strongly affected by Nb content. Combining the results of ICP and XPS, it's revealed that the Sr surface segregation can be effectively suppressed with the increase of Nb content. The LSCFNb cathodes gain the optimal electrochemical performance when x = 0.04, with minimum polarization resistance of 0.27 Ω cm 2 at 750 °C and oxygen reduction reaction activation energy of 1.54 eV. After cathodic polarization for 144 h, the polarization resistance and activation energy of LSCFNb4 cathode increase slightly, revealing it a promising cathode material for SOFC research.

Swarm Intelligence-Based Methodology for Scanning Electron Microscope Image Segmentation of Solid Oxide Fuel Cell Anode

Segmentation of images from scanning electron microscope, especially multiphase, poses a drawback in their microstructure quantification process. The labeling process must be automatized due to the time consumption and irreproducibility of the manual labeling procedure. Here we show a swarm intelligence-driven filtration methodology performed on raw solid oxide fuel cell anode’s material images to improve the segmentation methods’ performance. The methodology focused on two significant parts of the segmentation process, which are filtering and labeling. During the first one, the images underwent filtering by applying a series of filters, whose operation parameters were determined using Particle Swarm Optimization upon a dedicated cost function. Next, Seeded Region Growing, k-Means Clustering, Multithresholding, and Simple Linear Iterative Clustering Superpixel algorithms were utilized to label the filtered images’ regions into consecutive phases in the microstructure. The improvement was presented for three different metrics: the Misclassification Ratio, Structural Similarity Index Measure, and Mean Squared Error. The obtained distribution of metrics’ performances was based on 200 images, with and without filtering. Results indicate an improvement up to 29%, depending on the metric and method used. The presented work contributes to the ongoing efforts to automatize segmentation processes fully for an increasing number of tomographic measurements, particularly in solid oxide fuel cell research.

Progress in Material Development for Low-Temperature Solid Oxide Fuel Cells: A Review

Solid oxide fuel cells (SOFCs) have been considered as promising candidates to tackle the need for sustainable and efficient energy conversion devices. However, the current operating temperature of SOFCs poses critical challenges relating to the costs of fabrication and materials selection. To overcome these issues, many attempts have been made by the SOFC research and manufacturing communities for lowering the operating temperature to intermediate ranges (600–800 °C) and even lower temperatures (below 600 °C). Despite the interesting success and technical advantages obtained with the low-temperature SOFC, on the other hand, the cell operation at low temperature could noticeably increase the electrolyte ohmic loss and the polarization losses of the electrode that cause a decrease in the overall cell performance and energy conversion efficiency. In addition, the electrolyte ionic conductivity exponentially decreases with a decrease in operating temperature based on the Arrhenius conduction equation for semiconductors. To address these challenges, a variety of materials and fabrication methods have been developed in the past few years which are the subject of this critical review. Therefore, this paper focuses on the recent advances in the development of new low-temperature SOFCs materials, especially low-temperature electrolytes and electrodes with improved electrochemical properties, as well as summarizing the matching current collectors and sealants for the low-temperature region. Different strategies for improving the cell efficiency, the impact of operating variables on the performance of SOFCs, and the available choice of stack designs, as well as the costing factors, operational limits, and performance prospects, have been briefly summarized in this work.

Recent Activities of Solid Oxide Fuel Cell Research in the 3D Printing Processes

Recent Activities of Solid Oxide Fuel Cell Research in the 3D Printing Processes

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.

(High Temperature Materials Division Outstanding Achievement Award Address) Electrochemical Engineering of Cells for Conversion of Renewable Energy

Electrochemical engineering may be regarded as comprised of two fields:1) Electrochemical engineering science2) Electrochemical engineering art/technologyElectrochemical engineering science is based on fundamental laws of electrochemistry. It deals with electrochemical systems and processes according to scientific principles, and deals with systems related to industrial electrochemical technologies. Its aim is analysis and mathematical description (modeling), which will allow us to design electrochemical devices and processes, and to operate them under full control at optimal conditions in a profitable manner.Electrochemical engineering art/technology is based on good intuition and intelligent trial-and-error, which both need broad empirical knowledge and theoretical insight into a number of scientific disciplines. Besides electrochemistry, disciplines such as electro-physics, solid state physics, physical chemistry, chemistry, catalysis, interface science, materials science, quantum mechanics, density functional theory, and mechanical physics are important. None of the above mentioned disciplines can stand alone.The main difference is that the engineering science needs a coherent and exact mathematical description, while the engineering art “just” needs to show resulting hardware that functions with good performance. However, there is no sharp border between the two fields of electrochemical engineering.This presentation deals with electrochemical engineering of cells for conversion of renewable electric energy (from solar photovoltaics, wind, and hydropower) into chemical energy and reverse using devices such as electrolysis cells – fuel cells and batteries. Examples are taken from the area of reversible solid oxide cells (RSOCs), which are cells that work well in both solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode, and from the area of proton exchange membrane electrolysis cells (PEMECs).Electrochemical engineering science would obviously seem to be the tool to use for development of a perfect RSOC, whether the application is for electrolysis or fuel cell. However, when the latest international era of SOFC research and development (R&D) took off about 1990, the fundamental knowledge about all the possible materials for cell and stack components was not available, nor were the mechanisms and kinetics of the electrode reactions, as well as the degradation mechanisms and degradation rate well known. As one example, impurities at interfaces in the cell and on grain boundaries in the materials play a huge role in context of degradation. This means that it has been necessary to deal with a big number of the elements in the periodic table. Even after 30 year we still do not have enough knowledge to do proper electrochemical engineering science on SOCs, and the good progress in R&D has been carried out by electrochemical engineering art. Materials science and engineering art have become main disciplines as part of the electrochemical engineering in the continued R&D of RSOCs. However, the very broad area have resulted in some research groups that understand only part of the science behind SOC technology.In spite of the very comprehensive and complex nature of electrochemical engineering science of RSOC it is still helpful to try to do a full mathematical description using the little knowledge available. All the unknowns are then assumed. When such modeling attempt is combined with detailed operando characterization of electrodes, single cells and stacks this may provide a basis for an empirical model that can simulate a cell or a stack of cells of a given type with fair approximation. Comparison between modeling and measurements will give information about which detailed knowledge is still missing. This will give inspiration to new experiments with cell and stack components and lead to new cell and stack designs with new or improved components for further studies. Such iterative R&D strategy is very resource and time consuming, but the international SOC R&D results from the latest 30 - 40 years strongly indicate that this is the most successful strategy. This statement will be illustrated with selected examples of SOC strategies carried out by various R&D groups over decades of work.Also, examples of slow progress of PEMEC and alkaline electrolysis cells due to a strategy with far too much emphasis on only few aspects forgetting other important aspects will be presented.These examples indicate that the use of the holistic nature of electrochemical engineering is the best cure against an unbalanced R&D strategy.

Recent advances and perspectives of fluorite and perovskite-based dual-ion conducting solid oxide fuel cells

High-temperature solid-state electrolyte is a key component of several important electrochemical devices, such as oxygen sensors for automobile exhaust control, solid oxide fuel cells (SOFCs) for power generation, and solid oxide electrolysis cells for H2 production from water electrolysis or CO2 electrochemical reduction to value-added chemicals. In particular, internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs, hypothetically based on either oxygen-ion-conducting electrolytes or proton-conducting electrolytes. Up to now, some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability, while in available electrolyte database, particularly in the field of SOFCs, such dual-ion conductivity was seriously overlooked. Actually, few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature. Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics. On the other hand, exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs. In this review, we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs. The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced, and then (mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed. Following on, recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes, are reviewed. Finally, the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

A New High‐Performance Proton‐Conducting Electrolyte for Next‐Generation Solid Oxide Fuel Cells

Conventional solid oxide fuel cells (SOFCs) are operable at high temperatures (700–1000 °C) with the most commonly used electrolyte, yttria‐stabilized zirconia (YSZ). SOFC research and development activities have thus been carried out to reduce the SOFC operating temperature. At intermediate temperatures (400–700 °C), barium cerate (BaCeO3) and barium zirconate (BaZrO3) are good candidates for use as proton‐conducting electrolytes due to their promising electrochemical characteristics. Herein, two widely studied proton‐conducting materials with two dopants are combined and an attractive composition for the investigation of electrochemical behaviors is discovered. Ba0.9Sr0.1Ce0.5Zr0.35Y0.1Sm0.05O3−δ (BSCZYSm), a perovskite‐type polycrystalline material, has shown very promising properties to be used as proton‐conducting electrolyte at intermediate temperature range. BSCZYSm shows a high proton conductivity of 4.167 × 10−3 S cm−1 in a wet argon atmosphere and peak power density of 581.7 mW cm−2 in Ni–BSCZYSm | BSCZYSm | BSCF cell arrangement at 700 °C, which is one of the highest in comparison with proton‐conducting electrolyte‐based fuel cells reported until now.

Cobalt and Titanium substituted SrFeO3 based perovskite as efficient symmetrical electrode for solid oxide fuel cell

One of the key tasks in solid oxide fuel cell research is to develop cost-competitive electrodes that work efficiently in wide range of air and fuel utilizations. Herein, we promote our study to a series of Cobalt and Titanium substituted La0.4Sr0.6Fe0.7Ti0.3-xCoxO3-δ (LSFTC, x = 0, 0.05, 0.1, 0.2) perovskite oxides. It is shown that Cobalt doping effectively improves the electrical conductivity and oxygen electrochemical reduction activity, yielding decreased cathode polarization resistance and lower dependence of pO2 change. For example, σ600°C = 81 S/cm and Rp,C750°C = 0.1 Ω cm2 for LSFTC-5 are obtained in pO2=0.21atm. In anode conditions of wet H2, the LSFTC cubic perovskites are partially reduced to hybrid structure of ABO3-A2BO4-metal with Cobalt doping amount less than 10% and are fully decomposed to A2BO4-metal with 20% doping. The higher Cobalt substitution generates more nano particles exsolution, which promotes anode processes at low temperatures. However, the generated AO-rich compositions are shown detrimental to anode performance in both conducting property and anode catalytic activity under low H2 partial pressures. In current study, the electrodes are evaluated under practical working conditions with broad pO2 and pH2, which provides guidelines for industrial-applicable SrFeO3 based symmetrical electrode development.

Progress in SolidOxide Technologies: From Fundamentals to Systems – EFCF2018

AbstractNo abstract.

Nanoscale Surface and Interface Engineering of Solid Oxide Fuel Cells by Atomic Layer Deposition

Recently, atomic layer deposition (ALD) has drawn much attention as a suitable tool for fabrication and engineering of high performance fuel cell catalysts and electrodes. Intrinsic merits of ALD enable synthesis of conformal and uniform film even at a sub-nm scale with excellent stoichiometry control and reproducibility. Leveraging the unique characteristics, ALD has proven its promising potential as a solution to achieve two major challenges of solid oxide fuel cell research: sluggish kinetics at low operational temperatures and long-term stability. In this review, recent efforts to address the challenges by the use of ALD-based functionalization of surfaces and interfaces of cell components are discussed.

Application oriented multiple-objective optimization, analysis and comparison of solid oxide fuel cell systems with different configurations

With the development of SOFC (solid oxide fuel cell) technology, especially in terms of cell manufacture and stack assembly, recent SOFC research has focused on system integration and control. Various SOFC system configurations presented in the literature can be applied to various application scenarios for their unique advantages. A thorough evaluation and comparison of those SOFC systems in terms of performance, cost and efficiency is very important for optimal system design, taking the environment and conditions into consideration. In this paper, four typical 10 kW-scale SOFC-based systems are investigated, a hydrogen-fueled SOFC system, an external steam-reforming SOFC system, an SOFC/gas turbine hybrid system and SOFC/SOEC (solid oxide electrolysis cell) combined system. First, physical system models were constructed according to physical conservation laws and chemical kinetics and validated using experimental data. In addition, an exergoeconomic analysis was carried out based on these models. Then the optimal operating points of the four systems, which can be used for system performance comparison under the same operating conditions, are acquired through a multiple-objective optimization process based on an improved genetic particle swarm optimization algorithm. Then the systems were compared in aspects of technical and exergoeconomic performance under the same net output power, and comprehensive system marking was performed. Finally, analysis and predictions of application scenarios for these systems were proposed based on the scores. This paper provides a theoretical foundation for the design, analysis and application of SOFC systems.

Evaluation of PEMFC Impedance Spectra By Using the Distribution of Relaxation Times

Electrochemical impedance spectroscopy (EIS) is one of the most valuable characterization methods for complex electrochemical systems such as fuel cells. The measured impedance spectra are commonly analyzed by a complex nonlinear least square (CNLS) fit, delivering a model function represented by an equivalent circuit model (ECM). In this case the ECM has to be defined a priori, without knowing number, size and time constants of the contributing polarization processes. The assessment of a physico-chemically motivated ECM remains challenging, especially if polarization processes with close time constants occur. This leads to an overlap of processes in the frequency domain and thus makes it difficult to separate them, which may result in wrong model assumptions and instable and ambivalent fitting results. To overcome this issue we will present an alternate approach, where ECM and starting parameters for the CNLS fit are obtained by a pre-identification of the impedance response by the distribution of relaxation times (DRT) method [1],[2]. This approach was established in the framework of our solid oxide fuel cells research [3], later on transferred to lithium-ion batteries [4] and recently to high temperature polymer electrolyte fuel cells (HT-PEMFC) [5]. A typical result of our approach on a low-temperature PEM fuel cell is displayed in Figure 1: Whereas in the imaginary part of the spectrum only one broad peak is visible, the DRT facilitates a deconvolution of up to five clearly separable peaks (P1 - P5). In order to assign each peak to a physicochemical mechanism, systematic and comprehensive variations of operating parameters as current density, humidity and gas composition at anode and cathode have been conducted. By that we are able to distinguish between (i) charge transfer kinetics at the Pt-catalyst, (ii) the proton transport coupled therewith in the ionomer of the catalyst layer and (iii) the gas transport mechanisms in the porous media of the electrode and gas diffusion layer (GDL). Furthermore, our analysis enables us to assign the polarization processes to the respective electrode and to quantify their share to the overall polarization.

Performance investigation of a micro-tubular flame-assisted fuel cell stack with 3,000 rapid thermal cycles

Solid oxide fuel cell research and development has faced challenges with slow startup, slow shutdown and a limited number of thermal cycles, which hinders the technology in areas like micro-combined heat and power. A novel micro combined heat and power system, based on a boiler/hot water heater with integrated micro-tubular flame assisted fuel cells (mT-FFCs), is proposed which requires rapid startup, shutdown and thousands of thermal cycles. A 9 cell mT-FFC stack is developed and operated in a two-stage combustor. Rapid startup and shutdown of the fuel cells is demonstrated. The first-stage combustor is ignited, turned off and re-ignited for a total of 3000 on/off, thermal cycles. A maximum heating rate of 966 °C.min−1 and a maximum cooling rate of 353 °C.min−1 is achieved while thermal cycling. Despite the presence of CO in the exhaust, the anode remains porous and crack free after ∼150 h of thermal cycling testing. The mT-FFC stack continues to generate significant power, even after completing the cycling test, and a low voltage degradation rate is reported.