High Temperature Solid Oxide Fuel Research Articles

Characterization of Sr2Fe1,5Mo0,5O6-δ Based Solid Oxide Electrolysis Cells

Hydrogen electrodes of solid oxide electrolysis cells (SOEC) are typically made of Ni-YSZ cermet. Despite having excellent catalytic activity Ni-based electrodes suffer from poor redox stability and Ni volatility [1]. Sr2Fe1,5Mo0,5O6-δ (SFM) mixed ionic- and electric conducting (MIEC) double perovskite has been proposed as promising hydrogen electrode material for solid oxide electrolysis cells (SOEC) because of its excellent catalytic properties and good conductivity. In this study SOEC single cells were prepared using SFM hydrogen electrode and (La0,6Sr0,4)0,99Co0,96Ti0,04O3-δ (LSCT) as well as (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) air electrodes [2, 3].Studied cells were prepared using 19 mm 10Sc1CeSZ electrolyte substrates. Screen printed 6 μm thick Ce0.9Gd0.1O1.95 (GDC) layer was applied to both sides of the cell to prevent formation of insulating SrZrO3 layer. GDC layer was sintered to the electrolyte at 1300°C for 5h. SFM or 50%SFM/50%GDC electrode layer with 0,52cm2 surface area was screen printed to the GDC layer and was sintered at 1200°C and at 1150°C to optimize electrode composition and thermal treatment program of electrode. Afterwards LSCT or LSCF oxygen electrodes were screen printed to the other side of the cell and sintered at 1100°C for 2 h. Finally, cells were characterized using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and time-of flight secondary ion mass spectrometry (TOF-SIMS).Impedance spectroscopy analysis showed that cells with 50%SFM/50%GDC hydrogen electrode sintered at 1150°C and LSCT oxygen electrode had highest current densities, reaching 1,59 A/cm2 at 1,5V and 850°C with 67,5% water in hydrogen electrode compartment. However, stability of the cells needs to be further investigated. With TOF-SIMS analysis it became apparent that Sr is moving through GDC intermediate layer and poorly conducting phases are formed in the GDC/10Sc1CeSZ boundary.[1] C. Singhal, K. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications, Elsevier, Oxford, 2003.[2]Bernadet, C. Moncasi, M. Torell, A. Tarancon, High-performing electrolyte-supported symmetrical solid oxide electrolysis cells operating under steamelectrolysis and co-electrolysis modes, Int. J. Hydrogen Energy 45 (2020)14208–14217[3]Sanna, W. Zhang, P. Costamagna, P. HoltappelsSynthesis and electrochemical characterization of electrospun nanofiber cathodes for intermediate- temperature solid oxide fuel cells Int. J. Hydrog. Energy (2020), pp. 1-14

The optimal design of solid oxide and molten carbonate fuel cells integration with a CO2 recycling unit: An attempt to reach a clean transition process

High-temperature Solid Oxide Fuel Cell (SOFC) technology has great potential as a clean and effective energy source. However, several issues have prevented their widespread adoption, like high operating costs, difficulty integrating with other components, and being sensitive to fuel contamination. In order to address these challenges, the main novelties of the present work are carbon capture and utilization for clean energy production, using the flue gas condensation process as a cost-effective and energy-efficient strategy, and the combination of Molten Carbonate Fuel Cells (MCFC) for increased energy efficiency and most effective component integration. The proposed novel system is also equipped with a gasifier and vanadium chloride unit for syngas and clean hydrogen production. The system's practicality is evaluated by analyzing the key performance indicators from thermodynamic, exergo-economic, exergo-environmental, and sustainability viewpoints. Also, the Sankey diagram is presented to investigate each component's effectiveness from the exergy destruction facet. According to the findings, at the most optimum design condition, the acceptable energy and exergy efficiencies of 61.06% and 50.66%, respectively, are achieved, revealing the system's effectiveness. The suggested system is also financially attractive since it achieves a reasonable levelized power cost of 17.6 $/MWh at a total cost of 44.1 $/h. The findings show that carbon dioxide recovery is crucial in reducing the pollutants due to the low emission index of 5.01 kg/GWh. Finally, the exergo-environmental index, environmental damage effectiveness, and exergy stability factor have equivalent values of 0.012, 0.59, and 0.54.

Investigation of Heat Distribution in SOC-Stacks By Multiphysical Modeling

In the scope of clean energy, the solid oxide cell (SOC) offers a promising solution for different applications. The electrolyte, the air electrode and the fuel electrode of an SOC are typically based on yttrium stabilized zirconia (YSZ), lanthanum strontium cobaltite (LSC) or manganite (LSM) and nickel cermet, respectively. It typically operates in a temperature range of 600 – 1000 oC and can be operated as a fuel cell (SOFC), an electrolysis cell (SOEC) or reversibly (rSOC).An SOC-stacks consists of several repeating units, each of which is assembled by various components. Among them, the sealants are important to maintain the reliability and long-term operations of a stack. Several issues lead to high stress in the sealants, including the mechanical load, mismatch of thermal expansion coefficients, and thermal gradients 1. It was indicated that a small temperature gradient near the manifolds results in excessively high tensile stress. This may lead to glass ceramics sealing failure, which is critical in SOC designs 2. Therefore, the authors carry out the elastic stress simulations in an operating SOC-stack due to non-uniform temperature distributions.A previously introduced CFD model 3 is further developed to address coupled chemical and electrochemical reactions in rSOC-stacks. This model has been implemented in the open-source library, OpenFOAM. It considers the major multiphysical phenomena e.g. heat, mass, momentum and charge transport as well as heat radiation and electrochemical reactions and employs a volume-averaged approach 4. The computational requirements can be greatly reduced, which offers the possibility to simulate large stacks in reduced computing time. The temperature distributions derived from the stack simulation are used as inputs for thermal stress analysis, by mapping the interconnect temperatures to the detailed repeating unit. An open-source, finite element method (FEM) based software, Calculix, is applied to simulate the stress distributions. It is assumed all layers are tightly connected without slipping.The SOC-stack design considered in the multiphysical simulation as well as the FEM stress analysis is an in-house design, Mark-F20. It consists of 18 repeating units, each with an active area of approximately 320 cm2. The stack operates in the furnace condition, at a temperature of 700 oC, with CH4 mixture being supplied to the anode in the SOFC-mode (i=0.5 A/cm², U=0.8 V). The flow is in a counter-flow regime. A comparison of temperature distributions in interconnect is conducted between simulation and experiment. A maximum deviation of 10 K can be observed near the fuel inlet. It is acceptable providing the overall temperature variations of 80 K and the uncertainties in the measurements. This low-temperature zone results from the fast endothermic methane steam reforming reaction. The zone near the fuel outlet is cooled down by the inlet airflow on the cathode side. The stress-free temperature is 800 oC. It can be found that the maximum stress appears around the fuel inlet manifold with a magnitude of 100 MPa. The stress is also large near the air inlet manifold with a magnitude of 70 MPa. These areas show higher possibilities of mechanical failure.Consequentially, the stack model that has been developed enables to investigate the heat distribution in SOC-stacks. By comparing temperature distribution and the IV-curve predicted by the model with experimental measurements, good agreements were found.In the future, the sealant failure will be investigated 2 and attention has to be paid to future stack designs. References(1) Blum, L.; Groß, S. M.; Malzbender, J.; Pabst, U.; Peksen, M.; Peters, R.; Vinke, I. C. Investigation of Solid Oxide Fuel Cell Sealing Behavior under Stack Relevant Conditions at Forschungszentrum Jülich. Journal of Power Sources 2011, 196 (17), 7175–7181.(2) Bremm, S.; Dölling, S.; Becker, W.; Blum, L.; Peters, Ro.; Malzbender, J.; Stolten, D. A Methodological Contribution to Failure Prediction of Glass Ceramics Sealings in High-Temperature Solid Oxide Fuel Cell Stacks. Journal of Power Sources 2021, 507, 230301.(3) Zhang, S.; Peters, R.; Varghese, B. A.; Deja, R.; Kruse, N.; Beale, S. B.; Blum, L.; Peters, R. Modeling of Reversible Solid Oxide Cell Stacks with an Open-Source Library. ECS Trans. 2021, 103 (1), 569.(4) Beale, S. B.; Zhubrin, S. V. A Distributed Resistance Analogy for Solid Oxide Fuel Cells. Numerical Heat Transfer, Part B: Fundamentals 2005, 47, 573–591. Figure 1

Influence of the Ti Content on the Electrochemical Performance and Surface Properties of (La0.6Sr0.4)0.99Co1− xTixO3− δ Oxygen Electrode

Mixed ionic and electronic conducting (MIEC) oxides are being used as solid oxide fuel cell (SOFC) electrode materials [1, 2]. La1− xSrxCoO3− δ (LSC) oxygen electrode has perovskite-type (ABO3) structure. The properties of these materials are determined by chemical composition, crystallographic structure and oxidation state of B-site elements. These electrode materials have good catalytic activity towards oxygen reduction reaction and oxide ion oxidation, but they have limited durability if carbon dioxide or humidity are presented in the electrode gas compartment. It is important to increase the long-term durability of these electrode materials at natural gas conditions, i.e. in gas from the external environment with micro-concentrations of impurities like water and carbon dioxide [3, 4, 5].The SOFC oxygen electrode powders with different stoichiometry ((La0.6Sr0.4)0.99Co1− xTixO3− δ , x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were prepared by using the thermal combustion method [6]. X-ray diffraction (XRD) analysis was used to characterize the crystallographic structure of the synthesized powders. Symmetrical cells for Electrochemical Impedance Spectroscopy (EIS), Focused Ion Beam Time of Flight Secondary Ions Mass Spectrometry (FIB-TOF-SIMS) and X-Ray Photoelectron Spectroscopy (XPS) were made using synthesized powders. Prepared symmetrical cells were characterized at different temperatures, potentials, gas compositions i.e. conditions.Systematic impedance analysis showed that materials with bigger cation (Ti4+), doped into the LSC B-site, increase the material long-term stability against impurities like carbon dioxide and water. As a result of the work, the optimal amount of dopant (Ti4+) was found, which increased the stability of the material in the environment with impurities.[1] C. Singhal, K. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications, Elsevier, Oxford, (2003).[2] Weber, E. Ivers-Tiffée, J. Power Sources 127, 273 (2004).[3] Kivi, J. Aruväli, K. Kiresimäe, A. Heinsaar, G. Nurk, E. Lust, J. Electrochemical Society, 160, F1022 (2013).[4] Kivi, J. Aruväli, K. Kirsimäe, P. Möller, A. Heinsaar, G. Nurk, E. Lust, J. Solid State Electrochem, 21, 361 (2017).[5] P. Jiang, Int J. Hydrogen Energy, 44, 7448 (2019).[6] P. Bansal, Z. Zhong, J. Power Sources, 158, 148 (2006).

Micro-cogeneration based on solid oxide fuel cells: Market opportunities in the agriculture/livestock sector

Bio-waste embeds an extraordinary renewable potential, and it becomes a source of energy savings when transformed into a valuable resource, like biogas. Cogeneration (CHP) from biogas employing high-temperature Solid Oxide Fuel Cells (SOFCs) scores a high sustainability level, thanks to improved environmental and energy performances. The synergy between the niche market of small/micro biogas producers and SOFCs might act as a springboard to open market opportunities for both SOFC commercialization and business upgrade of small farms. However, local regulations, waste management, renewable energy subsidies and, above all, availability of eligible sites, determine real chances for on-the-ground implementation.Through a detailed analysis of the application scenario, this research aims at investigating opportunities for the experimentation of SOFC–CHP in small biogas plants and identifying the possible bottlenecks for future deployment. When it becomes relevant, energy conversion of livestock (especially cattle and swine) and agriculture waste requires SOFC modules from 10 kWe to 35 kWe. This is in line with the current status of SOFC suppliers. Moreover, considering the fuel cell market roll-out, the average levelized cost of electricity is expected to decrease from 0.387 €/kWh to 0.115 €/kWh, when electricity is produced from livestock waste available on-site.

Applicability of the SOFC technology for coupling with biomass-gasifier systems: Short- and long-term experimental study on SOFC performance and degradation behaviour

Coupling biomass gasification with high temperature Solid Oxide Fuel Cells (SOFCs) is a promising solution to increase the share of renewables and reduce emissions. The quality of the producer gas used can, however, significantly impact the SOFC durability and reliability. The great challenge is to ensure undisturbed operation of such system and to find a trade-off between optimal SOFC operating temperature and system thermal integration, which may limit the overall efficiency. Thus, this study focuses on experimental investigation of commercial SOFC single cells of industrial size fueled with different representative producer gas compositions of industrial relevance at two relevant operating temperatures. The extensive experimental and numerical analyses performed showed that feeding SOFC with a producer gas from a downdraft gasifier, with hot gas cleaning, at an operating temperature of 750 °C represents the most favorable setting, considering system integration and the highest fuel utilization. Additionally, a 120 h long-term test was carried out, showing that a long-term operation is possible under stated operating conditions. Local degradation took place, which can be detected at an early stage using appropriate online-monitoring tools.

Optimization of an integrated biomass gasifier-fuel cell system: An experimental study on the cell response to process variations

Coupling biomass gasification with high temperature Solid Oxide Fuel Cells (SOFCs) is a promising solution to increase the share of renewables and raise energy efficiency. Optimal system integration and high durability of its components are both required for this purpose. Moreover, system optimization may ask for a compromise between optimal SOFC operating temperature and system thermal integration. Nevertheless, the producer gas quality and operating temperature have a noticeable impact on SOFC performance, which has to be considered.In order to address the challenges mentioned, this study focuses on experimental investigation of commercial SOFC single cells of industrial size fuelled with different gas mixtures. Namely, typical producer gas compositions from downdraft fixed bed gasification with air (with and without drying) and fluidized bed gasification with steam are considered. In addition to that, the effect of temperature variation is analysed. The results show that, although a higher cell temperature (800°C) and a dry product gas composition lead to higher efficiencies, it is feasible to run the SOFC on wet producer gas at lower cell temperatures (750°C). Despite a decreased efficiency, this would optimize the gasifier-SOFC coupling. Moreover, the presence of water in the producer gas (when drying is not included) reduces the possibility of carbon deposition, thus increasing the cell durability. Therefore, cases with low cell temperatures and presence of water in the gas should be considered as viable alternatives for the system coupling and possible SOFC degradation in such cases is going to be extensively analysed.

High Performance Low Temperature Solid Oxide Fuel Cells with Alkali Metal Carbonate Additives in Co-Doped Ceria Electrolyte

Doped ceria-carbonates composites are a new class of electrolytes for low temperature solid oxide fuel cells, these show very high ionic conductivity due to fast interfacial transport [1-2]. As reported by Chockalingum and Basu [3], 25 wt% (LiNa)2CO3-GDC electrolyte exibited an ionic conductivity of 0.17 S cm−1 at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550–800 °C. To further improve the ionic conductivity, a series of calcium gadolinium/neodymium/samarium co-doped cerium oxide, M0.2CaxCe0.8-xO2 (x = 0.01 to x = 0.1) (M= Gd, Nd, Sm) have been synthesised by solgel method. The electrolytes have been physically and electrochemically characterized with respect to their thermal behaviour, phase, microstructure, elemental analysis and electrochemical performance using thermogravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy, Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy and electrochemical impedance spectroscopy respectively. The particle size of as synthesized electrolyte powders is ~ 20 nm as observed from the TEM. XRD results of the prepared electrolytes show that the powders are phase pure. The gadolinium calcium co-doped ceria lithium sodium carbonate (25% (LiNa)2CO3-Gd0.2Ca0.05Ce0.75O2) composite electrolytes exhibit high ionic conductivity (0.3 Scm-1 at 650°C), as it combines both the advantages of co-doping and the composite effect. Co-doped composite electrolytes show higher conductivity and stability due to the presence of calcium than the previously investigated composite electrolytes of (LiNa)2CO3-GDC [4, 5].

Design of a High Temperature Solid Oxide Fuel Cell: A Review

Design of a High Temperature Solid Oxide Fuel Cell: A Review

Modelling Microstructural and Chemical Degradation of Ferritic Stainless Steels for SOFC Interconnects

Ferritic Fe-based (FeCrX) alloys forming a protective chromium oxide film are used for providing electrical interconnection in high temperature Solid Oxide Fuel Cells (SOFC) are susceptible to degradation mechanisms in the presence of high temperatures (>600oC), and humid air. These translate by the increase in interconnect electrical contact resistance and the formation of volatile chromium species causing poisoning of the adjacent cathode. Modelling tools and techniques are increasingly becoming popular to gain better understanding of the degradation mechanisms that lead to the formation of volatile chromium species. This research work examines the oxidation behaviour of uncoated ferritic stainless steels system operated at temperature of 700oC in both wet (3% humidity) and dry conditions. A model is presented based on the physical processes involved. The model is able to predict the weight gain of the samples upon oxidation, the oxide film thickness, the volatilization of chromium and the useable lifetime of interconnects based on chromium depletion. Parameter determination from standard experiments is discussed along with the physical and design insights from the model. Perhaps most importantly the model provides recommendations regarding accelerated testing of FeCrX interconnects and control of the Chromia film thickness. Acknowledgements: This work was supported by the European FCH JU in project SCORED 2:0 under contract no. 325331 and the EPSRC.

Numerical modeling of an indirect internal CO2 reforming solid oxide fuel cell energy system fed by biogas

High-temperature Solid Oxide Fuel Cells have a flexible fuel supply and high energy performance. When fed with biofuels, such as biogas, they provide an attractive, ecofriendly and efficient energy system.The Internal Reforming that uses the high temperature of the same fuel cell makes them suitable to biogas, whose carbon dioxide content can be exploited.The fuel cell is characterized by an Internal CO2 Dry Reforming that converts the CH4 in the biogas into an H2 rich stream, owing to the role of CO2, acting as reforming promoter.The paper presents the formalization and the implementation in Matlab of a steady state-zero dimensional numerical model which describes the various processes of a global self-sustained Indirect Internal CO2 Reforming Solid Oxide Fuel Cell System fed by biogas. In addition to the energy core of the system with reforming and electrochemical section, the plant scheme considers the preheating of fresh gases, partial recirculation of the fuel cell exhausted gases and combustion of the expelled ones.The model aims at assessing energy performance and at monitoring carbon deposition.

Understanding the Current-Voltage Behavior of High Temperature Solid Oxide Fuel Cell Stacks

High temperature solid oxide fuel cell (SOFC) stacks are highly efficient and environmentally friendly electrochemical systems, which convert the chemical energy of fuel gases with oxygen from air directly into electrical energy. During operation of SOFC stacks under system operating conditions pronounced temperature and fuel gas composition gradients along the cell area and along the height of the stack occur. Therefore, in contrast to SOFC cells, the electrochemical behavior of SOFC stacks is much more complex and has not sufficiently been studied. Specially, a shortcoming exists in terms of understanding the homogeneity, performance loss mechanisms, and various resistances and overvoltages within the stack repeat components. Therefore, this paper focuses on the improvement of the understanding and of the interpretation of different current-voltage curves of solid oxide fuel cell stack repeat units. Three different cases are discussed: repeat units with high power performance, with high cell contact resistance and with high fuel utilization. The stacks were investigated by current-voltage curves, electrochemical impedance spectroscopy and gas analysis. In order to understand the electrochemical behavior of these three cases both experimental and modeling results are presented, compared and discussed.

Modeling and techno-economic analysis of the integration of a FC-based micro-CHP system for residential application with a heat pump

This work aims to analyse the techno-economic performance of an integrated system for a residential CHP (Combined Heat and Power) application, based on the integration of a Fuel Cell (FC) micro-cogeneration device coupled with an Heat Pump (HP).The main components of the system are: the Fuel Cell unit, the Heat Pump and the thermal storage – required to cover the thermal peaks, mainly due to the domestic hot water demand. The analysis will be focused on the most diffused FC technologies for residential applications: a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) and a high temperature Solid Oxide Fuel Cell (SOFC).FC-based cogeneration systems usually produce an electric power surplus respect to the thermal production, because of their high electrical efficiency. Currently, however, the households heating load exceeds significantly the electricity requirements, thus making difficult the sizing of a FC system for a single family house without including large electrical and thermal storages or high grid/boiler integration. The combination of a Fuel Cell and an Heat Pump has been found to be an optimal solution to manage this problematic while achieving a reduction in the primary energy consumption and avoiding energy overproduction.In the proposed scenario the heat is exploited by feeding both the domestic hot water and a low-temperature radiant floor heating system operating between 35 °C and 45 °C.An energy and economic analysis has been performed to understand and to evaluate the plant feasibility.Results have pointed out that the best economic choice, with the current energy tariff scenario, is related to a small size FC-based CHP system able to produce enough electrical power to feed the HP plus a low electrical consumption (<1 kW electrical size), which corresponds to the base electrical household consumption (the electrical power which is near-always requested by the house). The electrical load is in fact deeply changing during the day (with one-minute variable peaks) and with a higher electrical production from the FC, most of the electrical power would be sold to the grid without no energy advantages.The best PEMFC configuration was able to reach a total efficiency of 75%: if compared to the case with separated energy generation (electricity from the grid and heat from a boiler) the saving is estimated in three years of payback for the current scenario (2015).With the SOFC system, thanks to its higher total efficiency equal to 81%, the primary energy consumption was reduced (−30% respect to PEMFC) with a consequent reduction in the operating costs. However, from an economic point of view, the payback still results extended because of its not competitive investment cost.

Biomass integrated gasifier-fuel cells: Experimental investigation on wood syngas tars impact on NiYSZ-anode Solid Oxide Fuel Cells

The aim of this work is to assess the feasibility of a Biomass Integrated Gasifier Fuel Cell (B-IGFC) plant. High temperature Solid Oxide Fuel Cells (SOFC) are the most efficient energy systems currently being developed and they show good fuel flexibility thanks to their high operational temperature. For the application here discussed, the fuel major active species are H2,CO and CH4; yet, in wood-derived syngas small amounts of higher hydrocarbons are produced too. Among them, tars are claimed to be biomass Achille’s heel, causing severe issues in internal combustion engines and turbines. Conversely, SOFCs might be able to decompose tars with a gain on cell performance. However, in order to avoid fast degradation, tars concentrations have to be below a critical threshold. In this work, SOFC operation with real wood syngas from a pilot batch gasifier is firstly demonstrated. Then, longer tests are repeated under controlled conditions, artificially reproducing wood syngas with and without tars. Tests demonstrated that commercial NiYSZ-anode cells are able to work on syngas with a model tar (toluene) concentration up to 10g/N m3, exhibiting a voltage gain with regard to performances on syngas without model tar. No material degradation was observed after the experiments. As a final result, this paper aims at providing a proof of concept of a simplified B-IGFC system design, in order to reach its cost-effectiveness on small-scale installations.

Development of Intermediate Termperature Fuel Cells for Direct Conversion of Methane to Liquid Fuels

An electrochemical route to upgrade methane to liquid products, such as methane is being investigated. The process is based on an oxide conducting electrolyte and a metal/metal oxide redox couple, to partially oxidize methane to oxygenates. The objective of this project is development of a durable, low-cost, and high performance Low Temperature Solid Oxide Fuel Cell (LT-SOFC) for direct conversion of methane to methanol and other liquids, characterized by: a) operating temperature < 500°C, b) current density of > 100 mA/cm2 in liquid hydrocarbon production mode, c) continuous operation of > 100 h, d) cell area > 100 cm2, e) cell cost per rate of product output < $100,000/bpd, f) process intensity of > 0.1 bpd/ft3, g) product yield and carbon efficiency > 50%, and h) volumetric output per cell > 30 L/day.

From hydrogen production by water electrolysis to its utilization in a PEM fuel cell or in a SO fuel cell: Some considerations on the energy efficiencies

Ultra-pure hydrogen to feed a low temperature Proton Exchange Membrane Fuel Cell (PEMFC) or a high temperature Solid Oxide Fuel Cell (SOFC) can be produced by water electrolysis, either in a Proton Exchange Membrane Electrolysis Cell (PEMEC) working at low temperatures (25–110 °C) or in a Solid Oxide Electrolysis Cell (SOEC) working at high temperatures (600–950 °C). Both processes will be presented and discussed comparatively in terms of energy efficiencies, taking into account the working conditions at a low (70–80 °C) or a high (800 °C) temperature and at a given current density, conditions which are far from the thermodynamic equilibrium (no current flowing). Conversely to what is often written in the literature, the electrical energy efficiency of a SOEC never exceeds 100% and is comparable to that of a PEMEC, reaching in both cases 60–70% depending on the working conditions. In addition the electrical efficiency of a hydrogen/oxygen fuel cell working at a low temperature (PEMFC) or high temperature (SOFC) will be calculated allowing us to evaluate the round-trip energy efficiency of a hydrogen redox battery, such as a Unitized Regenerative Fuel Cell (URFC) for storage of intermittent energy. Some experimental examples of URFC working at low (PEM) or high (SOC) temperatures from recent publications will be presented and their energy efficiency will be estimated according to our theoretical calculations.

Developing Low-Intermediate Temperature Fuel Cells for Direct Conversion of Methane to Methanol Fuel

The objective of this project is development of a durable, low-cost, and high performance Low Temperature Solid Oxide Fuel Cell (LT-SOFC) for direct conversion of methane to methanol and other liquids, characterized by: a) operating temperature < 500oC, b) current density of > 100 mA/cm2 in liquid hydrocarbon production mode, c) continuous operation of > 100 h, d) cell area > 100 cm2, e) cell cost per rate of product output < 100,000/bpd, f) process intensity of > 0.1 bpd/ft3, g) product yield and carbon efficiency > 50%, and h) volumetric output per cell > 30 L/day

Three-Dimensional Analysis of Coarsening Dynamics in Porous Materials for Electrochemical Energy Conversion and Storage: Direct Measurement and Visualization of Changes in Local Surface Curvature

High operating temperature affords solid oxide fuel cells (SOFCs) fuel flexibility, favorable kinetics, enhanced transport properties and high quality heat for secondary thermodynamic cycles.1 Elevated temperatures, however, present challenges to ensuring cell durability.2 Coarsening of nickel in the Ni-YSZ anode is one such challenge that can lead to significant performance degradation. The fundamental driving force Δμ for coarsening phenomena is given by Eq. 1.3 The expression, which assumes isotropic interfacial energy, indicates that the chemical potential μ of a curved interface differs from that of a flat interface μ 0 by the factor VmγH, where H is mean curvature, γ interfacial energy and Vm molar volume. Δμ = μ - μ 0 = VmγH (1) Eq. 1 makes evident that variations in interface curvature, i.e., interface shape, directly correspond to variations in chemical potential. Furthermore, it follows from Eq. 1 that microstructural coarsening is fundamentally related to variations in interface shape. The link between interface shape and coarsening propensity is well known and methods have been developed to directly measure interfacial curvature distributions for complex morphologies in 3-D.4,5 In this work, these techniques are applied to 3-D images obtained by x-ray nanotomography to study coarsening in microstructures obtained from Ni-YSZ solid oxide fuel cell anodes aged for varying lengths of time. This work builds on a previous characterization of the same samples.6 The curvature measurements collected suggest that a combination of coarsening and morphological instability, which leads to channel pinch-off, severely diminish the connectivity of the anode’s Ni network and, in addition, lead to a significant loss of both nominal and effective triple-phase boundary (TPB) density. Both the loss of connectivity and TPB density coincide with cell performance degradation that was observed in the aging experiment7 from which the anode samples were taken. References Singhal, S. C.; Kendall, K. High Temperature Solid Oxide Fuel Cells, Elsevier, 2003.Yokokawa, H.; Tu, H.; Iwanschitz, B.; Mai, A. Fundamental mechanisms limiting solid oxide fuel cell durability. J. Power Sources 2008, 400-412.Voorhees, P. W. The Theory of Ostwald Ripening. J. Stat. Phys. 1985, 231-252.Glicksmann, M. E.; Voorhees, P. W. Ostwald Ripening and Relaxation in Dendritic Structures. Metall. Trans. A, 1984, 995-1001.Mendoza, R.; Savin, I.; Thornton, K.; Voorhees, P. W. Topological complexity and the dynamics of coarsening. Nat. Mater., 2004 385-388.Nelson, G. J.; Grew, K. N.; Izzo, J. R. Jr.; Lombardo, J. J.; Harris, W. M.; Faes, A.; Hessler-Wyser, A.; Van herle, J.; Wang, S.; Chu, Y. S.; Virkar, A. V.; Chiu, W. K. S. Three-dimensional microstructural changes in the Ni-YSZ solid oxide fuel cell anode during operation. Acta Mater., 2012 3491-3500. 7. Faes, A.; Hessler-Wyser, A.; Presvytes, D.; Vayenas, C. G.; Van herle, J. Nickel-Zirconia Anode Degradation and Triple Phase Boundary Quantification from Microstructural Analysis. Fuel Cells, 2009 841-851. Acknowledgements Financial support from the National Science Foundation (Award CBET-1134052) and an Energy Frontier Research Center on Science Based Nano-Structure Design and Synthesis of Heterogeneous Functional Materials for Energy Systems (HeteroFoaM Center) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award DE-SC0001061) is gratefully acknowledged. X-ray nanotomography was performed with Dr. Steve Wang at the Advanced Photon Source supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Ni-YSZ samples were provided by MER Dr. J. Van herle (Ecole Polytechnique Federale de Lausanne, Switzerland).

Developing Low-Intermediate Temperature Fuel Cells for Direct Conversion of Methane to Methanol Fuel

The direct conversion of methane to liquid fuels and chemicals is highly sought, especially at low-scale to more effectively utilize remote natural gas resources. The objective of this project is development of a durable, low-cost, and high performance Low Temperature Solid Oxide Fuel Cell (LT-SOFC) for direct conversion of methane to methanol and other liquids, characterized by: a) Operating temperature < 500oC, b) Current density of > 300 mA/cm2, in fuel cell mode and > 100 mA/cm2 in liquid hydrocarbon production mode, c) continuous operation of > 100 h, d) cell area > 100 cm2, e) cell cost per rate of product output < 100,000/bpd, f) process intensity of > 0.1 bpd/ft3, g) product yield and carbon efficiency > 50%, and h) volumetric output per cell > 30 L/day

A Brief Description of High Temperature Solid Oxide Fuel Cell’s Operation, Materials, Design, Fabrication Technologies and Performance

Today’s world needs highly efficient systems that can fulfill the growing demand for energy. One of the promising solutions is the fuel cell. Solid oxide fuel cell (SOFC) is considered by many developed countries as an alternative solution of energy in near future. A lot of efforts have been made during last decade to make it commercial by reducing its cost and increasing its durability. Different materials, designs and fabrication technologies have been developed and tested to make it more cost effective and stable. This article is focused on the advancements made in the field of high temperature SOFC. High temperature SOFC does not need any precious catalyst for its operation, unlike in other types of fuel cell. Different conventional and innovative materials have been discussed along with properties and effects on the performance of SOFC’s components (electrolyte anode, cathode, interconnect and sealing materials). Advancements made in the field of cell and stack design are also explored along with hurdles coming in their fabrication and performance. This article also gives an overview of methods required for the fabrication of different components of SOFC. The flexibility of SOFC in terms fuel has also been discussed. Performance of the SOFC with varying combination of electrolyte, anode, cathode and fuel is also described in this article.