Solid Oxide Fuel Cell Devices Research Articles

Unveiling the Structural and Optical Properties of Samarium Titanates Pyrochlore, Sm2Ti2O7

A magnetic system whose geometry prevents all pairwise spin interactions from being fulfilled simultaneously to minimize the energy is said to be frustrated. These systems are prevalent throughout all disciplines of physical and chemical study. This article reports a detailed structural and optical analysis of such frustrated Sm2Ti2O7 (STO), a pyrochlore structure. The ordered pyrochlore, STO of cubic symmetry, space group Fd3¯m [no. 227], has been synthesized using the standard solid-state reaction method. The Tauc’s plot reveals a direct band gap value of 3.8 eV from ultraviolet-visible reflectance data. Photoluminescence studies for STO using 280 nm excitation wavelength show the most intense emission peak at 395 nm, 468 nm, and other weak emissions at 368 nm, 412 nm, 430 nm, 449 nm, and 514 nm corresponding to the respective electronic transitions, indicates that the materials show photoluminescence properties. However, the unique characteristics of Sm2Ti2O7, including its wide band gap, photoluminescence, and high refractive index, make it a promising candidate for various magneto-optical, solid oxide fuel cell device fabrication applications.

Efficient ion conductivity enhancement mechanism induced by metal ion diffusion of SOFCs based on Fe-doped Gd2O3 electrolyte

Considerable efforts have been made in the past several decades to search for electrolytes that can work at low temperatures for solid oxide fuel cells (SOFCs). The rare-earth oxide Gd2O3 is a thermodynamically stable semiconductor material, but it has not yet been thoroughly explored for use in SOFC devices. In this study, a series of Fe-doped Gd2O3 with varying compositions were successfully synthesized to function as electrolytes for SOFCs. The as-prepared material, 10% Fe-doped Gd2O3 (Fe0.1Gd1.9O3), exhibited an excellent peak power density of 1352 mW/cm2 at 550 ℃, while the ionic conductivity reached 0.25 S cm−1. Various spectroscopic measurements, such as X-ray photoelectron spectroscopy, ultraviolet-visible (UV–vis) spectroscopy, and density functional theory calculations, were employed to understand the enhanced ion transportation mechanism and the improved performance of Fe-doped Gd2O3. The results showed that the Fe-doped Gd2O3 and energy bandgap tuning of electrolytes can significantly improve fuel cell performance at low temperatures, which is of great significance for the future development of low-temperature ceramic fuel cells.

Water desalination plant powered by solid oxide fuel cell technology in Egypt

The unique location of Egypt makes it very promising for obtaining freshwater from the sea. After applying suitable desalination techniques integrated with solar radiation photovoltaics (PVs), freshwater can be easily produced. Integrated desalination, including solid oxide fuel cells (SOFCs), PVs, and a reverse osmosis (RO) system is proposed in this work. To demonstrate the advantages and better improve the efficiency of the integrated system, a mathematical model was established for evaluation. In this work, the model was applied in two different locations with high intensity solar radiation (El-Zafrana and El-Arish). The RO system was applied and integrated with SOFC technology then simulated and modeled using MATLAB Simulink. Results demonstrate the ability to obtain 2000 t/d freshwater production capacity with consideration of SOFC devices. The expected annual income from this plant is 750,000 USD after its sixth year of construction. In addition, the desalination process is proposed for non-stop use, over an entire day, of the used seawater. The simulation results provided in this work will help further future commercialization of such a project.

Benefits of Nanoscale Operando Experiments in Environmental Transmission Electron Microscopy for Solid Oxide Fuel Cell Devices

Benefits of Nanoscale Operando Experiments in Environmental Transmission Electron Microscopy for Solid Oxide Fuel Cell Devices

Recent progress in design and fabrication of SOFC cathodes for efficient catalytic oxygen reduction

Solid oxide fuel cells (SOFCs) are highly promising energy conversion devices. However, the performance and efficiency of current SOFC devices are still limited by inadequate oxygen reduction activity in the cathode, which has been recognized as a great challenge for SOFCs to achieve high power output at low operating temperatures. This has stimulated intensive efforts to develop more efficient cathodes for enhanced catalytic oxygen reduction. This article reviews recent advances in design and fabrication of cathodes for efficient SOFCs, with emphasis on (1) engineering cathode microstructures, (2) fabrication techniques to prepare cathode layers, and (3) strategies to address segregation and poisoning issues.

Evaluation of inkjet-printed spinel coatings on standard and surface nitrided ferritic stainless steels for interconnect application in solid oxide fuel cell devices

Inkjet printing technology was employed for the application of protective layer coatings in SOFC metallic interconnects. Aqueous-based spinel coatings were inkjet-printed on standard and surface nitrided K41 ferritic stainless-steel substrates. Inkjet-printed substrates were exposed to high-temperature oxidation and Area Specific Resistance (ASR) tests for 1000 h at 700 °C in air with 3% volume humidity, simulating SOFC cathode environment. Performance of inkjet printed coatings and effect of nitriding stainless-steel substrates were evaluated based on chromium migration/retention and Area Specific Resistance. Sol-gel infiltration was introduced to develop a scaffold layer over the porous microstructure. With the ASR reduced to a level ∼60 mΩ cm2 and chromium concentration in the getter (cathode) material below 1 atomic%, close to the detection threshold, the protective layers produced via inkjet printing present a promising solution for SOFC interconnector applications.

Coupling deep learning and multi-objective genetic algorithms to achieve high performance and durability of direct internal reforming solid oxide fuel cell

Direct internal reforming (DIR) operation of solid oxide fuel cell (SOFC) reduces system complexity, improves system efficiency but increases the risk of carbon deposition which can reduce the system performance and durability. In this study, a novel framework that combines a multi-physics model, deep learning, and multi-objective optimization algorithms is proposed for improving SOFC performance and minimizing carbon deposition. The sensitive operating parameters are identified by performing a global sensitivity analysis. The results of parameter analysis highlight the effects of overall temperature distribution and methane flux on carbon deposition. It is also found that the reduction of carbon deposition is accompanied by a decrease in cell performance. Besides, it is found that the coupling effects of electrochemical and chemical reactions cause a higher temperature gradient. Based on the parametric simulations, multi-objective optimization is conducted by applying a deep learning-based surrogate model as the fitness function. The optimization results are presented by the Pareto fronts under different temperature gradient constraints. The Pareto optimal solution set of operating points allows a significant reduction in carbon deposition while maintaining a high power density and a safe maximum temperature gradient, increasing cell durability. This novel approach is demonstrated to be powerful for the optimization of SOFC and other energy conversion devices.

Corrosion behaviour of nitrided ferritic stainless steels for use in solid oxide fuel cell devices

Plasma nitriding was applied to ferritic stainless steel substrates to improve their performances as interconnects for solid oxide fuel cell devices. The samples underwent electrical conductivity test and SEM/EDS, TEM/EDS, environmental-SEM analyses. The first stages of corrosion were recorded in-situ with the e-SEM. Nitriding is effective in limiting the undesired chromium evaporation from the steel substrates and accelerates the corrosion kinetics, but its influence of the electrical conductivity is ambiguous. No intergranular corrosion is found in the steel substrate after long time operation. Nitriding helps commercially competitive porous coating to improve chromium retention properties of metal interconnects.

Nitrous Oxide As an Oxidizer for Dual Use Fuel Cell / Thrust Systems in Space Applications

Nitrous oxide (N2O), a non-toxic chemical which can be stored in a liquefied state under moderate pressures(52 bar) without cryogenic storage, is a reactant which can be used to generate electricity or propel aspacecraft. It has been investigated as a cold gas propellant, monopropellant, and bipropellant; particularlyin the field of small satellites.[1,2] Nitrous oxide can also be used to generate electricity by acting as theoxidizer in a fuel cell where N2O reduction occurs at the cathode and a fuel such as H2 is oxidized at theanode.[3] Although the equilibrium potential in standard state aqueous electrolytes is 1.76 V vs SHE,[3] large overpotentials in aqueous electrolytes make it difficult to efficiently extract power from this reaction. Theelectrochemical reduction can be more readily achieved in a solid-oxide fuel cell (SOFC) with an oxygenion conductor for an electrolyte following the reactions in equations 1 and 2.[4] SOFCs also enable the useof alternative fuels such as hydrocarbons, CO, and NH3. Additionally, the reaction product N2 is expectedto be usable as a cold gas propellant. Cathode: \U0001d4412\U0001d442 + 2\U0001d452− → \U0001d4412 + \U0001d4422− (1)Anode: \U0001d43b2 + \U0001d4422− → \U0001d43b2\U0001d442 + 2\U0001d452− (2) We report on a SOFC device consisting of a Ni anode, a LaSrMnO3 cathode, and a Sc-doped ZrO2 electrolyte substrate. The maximum operating power which can be extracted from this system using N2Oas an oxidizer and H2 as a fuel, the conversion efficiency of N2O to N2, and a comparison of the performanceof N2O with air and O2 are all evaluated under a range of operating temperatures and flow rates.

Review of proton- and oxide-ion-conducting perovskite materials for SOFC applications

In this review, the essential use of perovskites and their structural properties associated with proton and oxide-ion conductivity are explained specifically for applications in solid oxide fuel cells (SOFCs), electrolyser cells and so on. The number of oxygen vacancies and their distribution in the crystal structure play a crucial role in perovskites, which exhibit good protonic and oxide-ion conductivity. Atmospheric stability at the operating temperature is another important factor that decides the long-term usage of the materials. Here the properties are summarised in terms of stability, proton defects, ordering and cation substitution. A basic understanding of all of these properties will give a direction to synthesis of compounds with desired proton and oxide-ion conductivity for applications in renewable and sustainable energy devices. A certain group of perovskite oxides, when prepared as nanostructures, is specifically used in fuel cell electrodes for improved performance. A few trends and highlights of current scientific advances in nanoperovskites for energy applications are discussed. The high stability of the proton conductor Ba3Ca1⋅18Nb1⋅82O8⋅73and substitution of new dopants in this compound for SOFC devices are highlighted in this review.

The Influence of Local Distortions on Proton Mobility in Acceptor Doped Perovskites

Optimizing proton conduction in solids remains the most promising solution for achieving intermediate temperature (∼750–1000 K) solid oxide fuel cell devices, and enabling selective membranes for H2 separation. Proton conduction, a thermally activated process, exhibits its highest rates in yttrium (Y) acceptor doped BaZrO3 at an optimal doping level of 20% Y. The presence of extended defects such as grain boundaries has typically generated a wide variability in reported conductivity values. This has hindered a fundamental mechanistic understanding of how (acceptor) doping levels correlate with the activation energy of protons to produce an optimal doping level for fast proton transport. While isolated dopants have been suggested as the primary source of proton trapping, our results indicate that it is the local dopant-density that matters. Here, we show that increasing the local dopant density promotes localized lattice distortions in the presence of point defects such as oxygen-vacancies or proton inters...

Defect Chemistry of Oxides for Energy Applications.

Oxides are widely used for energy applications, as solid electrolytes in various solid oxide fuel cell devices or as catalysts (often associated with noble metal particles) for numerous reactions involving oxidation or reduction. Defects are the major factors governing the efficiency of a given oxide for the above applications. In this paper, the common defects in oxide systems and external factors influencing the defect concentration and distribution are presented, with special emphasis on ceria (CeO2 ) based materials. It is shown that the behavior of a variety of oxide systems with respect to properties relevant for energy applications (conductivity and catalytic activity) can be rationalized by general considerations about the type and concentration of defects in the specific system. A new method based on transmission electron microscopy (TEM), recently reported by the authors for mapping space charge defects and measuring space charge potentials, is shown to be of potential importance for understanding conductivity mechanisms in oxides. The influence of defects on gas-surface reactions is exemplified on the interaction of CO2 and H2 O with ceria, by correlating between the defect distribution in the material and its adsorption capacity or splitting efficiency.

The heterogeneous electrolyte of CuFeO2 nano-flakes composited with flower-shaped ZnO for advanced solid oxide fuel cells

The flower-shaped ZnO was synthesized to form composite with the delafossite structure CuFeO2. The composite heterojunction formed for the ZnO-CuFeO2 composite material demonstrates a profound significance for exploring novel materials in solid oxide fuel cell (SOFC) field. At 550 °C, power outputs of 300 mW cm−2 and 468 mW cm−2 were achieved for SOFC devices using pure ZnO and composite with CuFeO2 as the electrolytes, respectively. The composite showed a good performance at low temperatures, for instance, it showed a power output of 148 mW cm−2 at 430 °C. The studies on photocurrent-time curves with visible light on/off irradiation provided an evidence for electron-hole separation. The heterojunctions separate holes and electrons, preventing short-circuiting while used in the SOFC device. These results demonstrate that introducing the heterojunctions in the electrolyte is an innovative approach for advanced SOFCs.

Battery-like Response in Solid Oxide Fuel Cell Device

The intermittency of renewable energy sources and the varying power demand throughout the day pose challenges for electrical grid stability as more and more renewable energy technologies are deployed. Existing solid oxide fuel cell technologies are slow in response to changes in current and voltage, and therefore cannot smooth out the difference between the power supply from renewables and the power demand. In this presentation, we will report a battery-like response as a new functionality incorporated into the fuel cell devices. It is realized by having in situ charge storage (e.g., metal hydrides) proximal to or integrated within the anode of the fuel cell. Electrochemical studies show a capacity density of 977 mAh g-1 in a 90-hour stable discharge. In addition, a fuel cell-battery hybrid electrochemical device was designed, and the voltage was stable at 0.86 V in the fuel cell mode and 0.73 V in the battery mode for 100 cycles over a course of 75 hours. Fuel cell with a battery mode represents a promising approach for easing the integration of intermittent renewables and enabling grid stability.

Intermediate Temperature Synthesis and SOFC Anode Application of Cerium Silicate-Based Oxy-Apatites

Oxy-apatites based on rare earth silicates (A10x(SiO4)6O2±x, A=rare earth cation) are of increasing interest for solid oxide fuel cell (SOFC) application due to the high conductivity at moderate temperatures (<1000 K). Here, we report on the intermediate-temperature synthesis (973 K) of thin film oxy-apatites and high total conductivity of the cerium silicate-based apatites at temperatures <750 K: the Ce4.67(SiO4)3O-based apatites (~80 nm-thick) were synthesized at 973 K at very low oxygen partial pressure (p(O2)<10-17atm) and the incorporation of ZnO into the cerium silicate system leads to the high total conductivity of ~0.05-0.2 S/cm. The formation of oxy-apatites was identified by in-situ conductivity measurements as a function of p(O2), x-ray diffraction analysis and x-ray photoelectron spectroscopy. In particular, the in-situ conductivity measurements confirm that the dominant conduction mechanisms of this class of materials are mainly dependent on oxygen interstitials. Since these materials are prepared at low p(O2) and are stable in reducing atmospheres, Ce4.67(SiO4)3O-based thin film apatites exhibiting high conductivity are of relevance as anodes for intermediate temperature thin film SOFC application. In order to evaluate the performance of the apatite anode in SOFC devices, thin film apatites were grown on Sc-stabilized ZrO2/LSCF electrolyte/cathode substrates. Bilayer anode of apatite/Pt and Ni-apatite composite anode were also utilized in the identical electrolyte/cathode system and the performance were compared. The noteworthy SOFC performance (e.g., peak power density of ~100 mW/cm2 at 748 K) and superior stability were observed in Ni-apatite SOFCs due to higher catalytic activity and low contact resistance at the electrolyte/anode interface compared to those with a single layer apatite anode and bilayers of apatite/Pt anode. The present study demonstrating intermediate temperature synthesis of Ce4.67(SiO4)3O-based oxy-apatites and their high conductivity may significantly contribute to the field of intermediate temperature thin film SOFC application. Figure 1

Cationic Interdiffusion at the SOFC Electrolyte/Cathode Interface in La2Mo2O9/La0.8Sr0.2MnO3‐δ

AbstractIn this work cation diffusion between a La2Mo2O9 (LM) ionic conductor and the conventional Solid Oxide Fuel Cell (SOFC) cathode material La0.8Sr0.2MnO3‐δ (LSM), was probed using secondary ion mass spectrometry (SIMS), and diffusion coefficients of Sr, Mo and Mn cations within both materials evaluated. Diffusion coefficients extracted from samples with a Sr solution deposited on the LM pellets and from a Mo solution deposited on LSM pellets were found to be orders of magnitude higher than the cross‐diffusion through the interface between two dense pellets in direct contact. These differences may be due to uncertainty in determining the interface position, or to a real dependence on the source of the diffusing cation. In the most favorable case, that of pellets in direct contact, extrapolation of diffusion coefficients down to a typical SOFC operating temperature, 800 °C, show that Mo diffusion in LSM (diffusion coefficient ∼ 10−14 cm2.s−1) is much higher than Sr or Mn diffusion in LM, and incompatible with use in a SOFC device, unless an efficient buffer layer is used.

Synthesis and characterization of La0.8Sr0.2Ni(1−x)CrxO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) system by the combustion method

This research focuses on the synthesis and characterization of six ceramic perovskite oxides based on La0.8Sr0.2Ni(1−x)CrxO3 system, with different levels of chromium modification (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), for use as anode material in solid oxide fuel cells (SOFC). The oxides were obtained in two reaction stages, starting from corresponding nitrate salts and citric acid until formation of a solid metal complex consistent with citrate species. The solid metalorganic foams were calcined at 1000°C for 120min under oxygen flow conditions and were characterized by infrared and ultraviolet spectroscopy (FTIR-UV), validating the proposed methodology in terms of purity and chemical composition. The characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX) confirms the obtention of a homogeneous perovskite structure in all analyzed phases. The evaluation of crystallite size by means of the Debye–Scherrer equation establishes a nanometric prevalence around 3.2–4.4nm along main diffraction signals. The electrical characterization of materials by solid-state impedance spectroscopy allowed identifying a particular behavior depending on the microstructure of solids for potential applications in SOFC devices.

Chemical Stability of La 1-X Sr x Mn0.8Ni0.2O3-δ x={0.1 to 0.5} Cathode Compositions with 8YSZ at High Temperature

INTRODUCTION : A one-step co-sintered solid oxide fuel cell (SOFC) stack consists of several cells sintered at high temperature at once (>1250oC). Typically, each SOFC cell is composed of a cathode (strontium-doped lanthanum manganite, LSM), an electrolyte (8YSZ), an anode (NiO/8YSZ), a ceramic interconnector and a dedicated gas distribution system [1]. It is believed that reducing the step processing should lead to cost reduction of SOFC cells fabrication and finally promote a wider use of SOFC devices. Unfortunately, several technological issues still have not had an adequate solution, mainly: thermal expansion mismatch between stack components [2] and lack of efficiency caused by formation of a high electrical resistance secondary phase at the LSM/8YSZ interface, La2Zr2O7 (LZO) or SrZrO3 (SZO) [3]. Several methods have been evaluated for reducing secondary phase formation, for instance: protector buffer layer [4], Ce addition into LSM structure [5] and A-site deficiency LSM compositions [6], etc. However, they show a limited performance or are complicated to use at the temperatures required for fabricating a one-step co-sintered SOFC stack. This work evaluates the impact of a Ni-addition, into B-site of LSM composition, on the formation of secondary phase at the LSM/8YSZ interface. Equal Ni addition (20 at%) was used in several LSM compositions, with different strontium contents, and their chemical stability with 8YSZ at 1300oC was evaluated. Moreover, a chemical stability comparison between a commercial LSM composition (La0.8Sr0.2MnO3-δ) and a similar Ni-added one (La0.8Sr0.2Mn0.8Ni0.2O3-δ) is presented. EXPERIMENTAL: La1-xSrxMn0.8Ni0.2O3-δ with x={0.1 to 0.5} compositions, hereinafter called Ni-added LSM, were fabricated by a glycine route using nitrates as reactive and glycine as fuel. Both, reactive and glycine, were dissolved in deionized water at room temperature until obtain a clear solution. Water and organic components were removed by different heat treatment at 180oC and 450oC, respectively. Afterwards, all powders were reacted and calcinated at 850oC and 1000oC for 5h, respectively. Chemical reaction with 8YSZ was evaluated by mixing Ni-added LSM powders with 8YSZ in 50/50 wt%. All samples, whatever 8YSZ mixed or not, were sintered at 1300oC for 5h. Electrical conductivity measurements were performed by using four-probe method from room temperature to 800oC in air, while chemical stability with 8YSZ was evaluated by x-ray diffraction (XRD). RESULTS AND DISCUSSION: XRD patterns from Ni-added LSM compositions showed no secondary phase formation after sintered at 1300oC for 5h (not shown). Ni-added LSM compositions with low strontium content (x≤0.3) were indexed as rhombohedral crystal structure, while at higher strontium contents (x>0.3) an orthorhombic crystal structure tends to gradually form instead of the rhombohedral one, thus at x=0.5 only orthorhombic crystal structure was indexed. Electric conductivity of La1-xSrxMn0.8Ni0.2O3-δ with x={0.1 to 0.5} compositions have a maximum (115 S cm-1) at x=0.3, well correlated with the crystal structure evolution as a function of strontium content. (not shown) Fig.1 shows XRD patterns from Ni-added LSM compositions after mixing with 8YSZ (50/50 wt%) sintered at 1300oC for 5h. No crystal structure change was observed respect to non 8YSZ mixed condition. However, at strontium contents over x≥ 0.3 a secondary phase (SZO) was observed, while below x<0.3 no secondary phase was observed. In addition, XRD patterns from a commercial La0.8Sr0.2MnO3-δ and La0.8Sr0.2Mn0.8Ni0.2O3-δ compositions mixed with 8YSZ and sintered at 1300oC for 5h were recorded. LZO secondary phase was observed only in commercial LSM composition, while it was not observed in La0.8Sr0.2Mn0.8Ni0.2O3-δ composition, even after sintering at 1300oC for 24h (not shown) Results suggest that Ni addition into the B-site of LSM (with low strontium content), could be a suitable and simple method for reducing, and eventually suppressing, the secondary phase formation at the LSM/8YSZ interface at high temperature. [1] S. Suda, J. P. Wiff and S. Shimada, ECS Trans. 57(1), 543-548 (2013) [2] B. Ahmed, S. B. Lee, R. H. Song, J. W. Lee, T. H. Lim and S. J. Park, ECS Trans. 57, 2075-2082 (2013) [3] C. Levy, Y. Zhong, C. Morel and S. Marlin, ECS Trans. 25, 2815-2823 (2009) [4] H. S. Noh, J. W. Son, H. Lee, H. R. Kim, J. H. Lee and H. W. Lee, J. Korean Ceram. Soc. 47, 75-81 (2010) [5] J. P. Wiff, K. Jono, M. Suzuki and S. Suda, J. Power Sources 196(15) 6196-6200 (2011) [6] A. Chen, J. R. Smith, K. L. Duncan, R. T. DeHoff, K. S. Jones and E. D. Wachsman, J. Electrochem. Soc. 157, B1624-B1628 (2010) Figure 1

Identification of phase in-homogeneities in Na-SrSiO3 electrolytes for low temperature SOFCs

In this work we have synthesized and characterized sodium doped SrSiO3 electrolyte, for use in low and intermediate temperature solid oxide fuel cells (SOFCs). Great interest was placed onto this material after its first report in 2012, which was later dampened by conflicting reports about the properties of this class of materials. It is imperative to resolve this issue from the viewpoint of development of low and intermediate temperature SOFCs. Here, we report the most comprehensive data till date on the properties of this class of materials. Although it is desired to synthesize a single phase material, strong evidences presented here suggest that it is a multiphase material. The reason for obtaining a multiphase material is discussed considering the reaction thermodynamics. Additional data presented here establish that at the operating temperature (~750 °C) of SOFC devices, amorphous phases in the material transforms into a crystalline phase.

Cerium silicate-based thin-film apatites: high conductivity and solid oxide fuel cell application

Abstract