Current Solid Oxide Fuel Cells Research Articles

Prospective life cycle assessment to support eco-design of solid oxide fuel cells

ABSTRACT Solid oxide fuel cells (SOFCs) could have great application potential and technological development. However, there are no studies that have quantitatively and rigorously estimated the environmental impacts in the future scenario. This study fills this gap through an innovative approach consisting of patent-based technological forecasting and prospective life cycle assessment (LCA). The analysis of the 58 selected patents reveals that future SOFCs could have (on average) +53% specific power which could lead to a 56% mass reduction compared to current SOFC. The prospective LCA shows an average global warming potential (GWP) reduction of 50%. The future tubular layout is more sustainable than planar one by about 15%. GWP decreases with increasing specific power and in cells with smaller sizes and thicknesses. Finally, the ductile future SOFCs, dedicated to mobile applications and dynamic loads, have a GWP greater than future stationary SOFCs, but still equal to half of the current SOFCs. All these results therefore confirm the potential of the patented SOFC developments on environmental sustainability, arguing in favour of their industrial development and a more massive application in the future.

Degradation and recovery of solid oxide fuel cell performance by control of cathode surface acidity: Case study – Impact of Cr followed by Ca infiltration

Solid oxide fuel cells (SOFCs) have attracted attention as clean and efficient energy conversion devices with low emissions. However, several degradation mechanisms limit the electrochemical performance of current SOFCs, with cathode degradation due to Cr-poisoning from metal interconnects particularly problematic. The acidity/basicity of binary additives has been found to be a sensitive descriptor of the oxygen exchange kinetics, indicating that acidic Cr-species/basic Ca-species can be expected to deactivate/activate the cathode surface, respectively. Inspired by recent advances, the feasibility of relative acidity as a tool for reviving degraded SOFCs is demonstrated by neutralizing Cr-poisoned SOFCs by subsequent serial infiltration of Ca-species. A model mixed ionic and electronic conducting oxide, Pr0.1Ce0.9O2-δ (PCO), is selected as the cathode material. Area-specific resistances (ASR) of symmetric cells obtained by electrochemical impedance spectroscopy show that Cr-infiltration results in a seven-fold increase in ASR, while subsequent infiltration of Ca-species leads to complete recovery. Performance degradation and recovery are attributed to depressed/enhanced redox properties at the PCO surface, as supported by XPS analysis. Experiments using anode-supported fuel cells show a reduction in peak power density by 26% upon Cr-infiltration, reversed following Ca-infiltration, after which no degradation is observed during subsequent operation for 100 h.

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.

A methodological contribution to failure prediction of glass ceramics sealings in high-temperature solid oxide fuel cell stacks

Solid oxide fuel cells (SOFCs) provide electrical energy through a highly efficient direct transformation of chemical energy stored in fuels. The sealing between the stacked components of the SOFC has to prevent gas leakage towards the environment as well as mixing of fuel gas and oxidant in order to ensure a reliable long-term operability. Hence, the understanding of the sealing loading conditions and the failure assessment plays a major role regarding the improvement of current and future SOFC designs. In the present study, glass ceramics sealing failure is investigated by means of a current SOFC design. For this purpose, the stresses in the sealings are firstly examined by employing a fully parameterized three-dimensional finite element model. On the basis of a canonical example, the underlying physical mechanisms, which are responsible for the occurrence of stresses, are identified and their influence is discussed. Since the initiation of sealing failure is complex and depends on several parameters, a methodology for failure assessment is proposed. In this context, the glass transition temperature is of superordinate importance. Since the material properties differ significantly depending on whether the operating temperature is below or above the glass transition temperature, several competing failure mechanisms must be considered. • Full three-dimensional model of an SOFC stack designed by Forschungszentrum Jülich. • Identifying mechanical mechanisms in the context of high temperature sealing failure. • Proposal of a methodology for the assessment of sealing failure in SOFC stacks. • Coupled stress and energy criterion for T < T g . • Viscoelastic considerations for T > T g .

Degradation Analysis of a Commercial SOFC System

Solid Oxide Fuel Cell (SOFC) technology offers several advantages such as fuel flexibility, high efficiency, and zero criteria pollutant emissions. SOFC systems have the potential to be cheaper and provide more reliable and cleaner electrical load-following characteristics compared with other technologies by dynamic operation and control. Cost and durability are major challenges associated with current SOFC technology. Durability of Solid Oxide Fuel Cell (SOFC) technology is a key aspect for its commercialization and long-lasting deployment in different applications. Dynamic operating conditions have considerable effects on the long-term performance and durability of SOFC systems.In this study, we evaluate the performance and degradation of a 1.5 kW (AC) commercial system under steady state and dynamic load cycling conditions for over 6000 hours. We monitored and evaluated the initial and degraded performance characteristics of the SOFC stack, while testing under constant 1.6 kW load, 85% fuel utilization, and at 760°C stack temperature for 4000 hours and under dynamic cycling load for more than 2000 hours. We conducted degradation tests based upon two load cycling profiles: i) accelerated daily cycles with load changing from 0.5 kW to 1.6 kW, with stack temperatures ranging between 720°C and 760°C, and fuel utilization between 55% and 85% for 42 cycles (~1000 hours), and ii) weekly cycling test with load changing from 0.5 kW to 1.6 kW with lower slope for 10 cycles (1600 hours). A machine learning model based upon experimental data is developed to correlate the degradation rate of the system to different features of dynamic profiles to be used in the prediction of degradation rate for a wide range of dynamic load profiles.Test results show that the degradation rate is 0.025% (2mV) per 1000 hours of operation under steady state operating conditions. As the system degrades under steady state conditions, fuel consumption increases 0.3% while the efficiency drops 0.3% per 1000 hours of operation. We observe that at beginning of life and during the first 1000 hours of operation, the degradation rate is roughly twice as high as that achieved under steady state operation (i.e., 4.8mV). Results show that the system also degrades twice as fast when forced to meet daily dynamic cycling loads. The degradation rate observed under highly dynamic daily load cycling conditions is 0.58% (4.7mV) per 1000 hours of operation over 42 daily cycles.

Update on Nexceris’ Solid Oxide Fuel Cell Stack Technology

Nexceris has been active in the development of solid oxide fuel cell (SOFC) technology since 1995. In recent years, advancements have been achieved through innovations in SOFC stack materials, design, and operation. These advancements have increased technical maturity, improved durability, and reduced stack cost. With high current density (0.5–0.7 A/cm²) and single pass fuel utilization (70–80%) capabilities, Nexceris’ lightweight SOFC stacks are enabling for power systems that require both high gravimetric power density and electrical efficiency. Moreover, Nexceris’ SOFC technology has been demonstrated to be resilient against large thermal gradients and rapid load changes. Current SOFC work at Nexceris includes stack and system demonstrations, scale-up of stack manufacturing capabilities, and development of a 10-kW stack module. This paper will provide an update on the status and capabilities of Nexceris’ SOFC stack technology and cost-saving approaches to stack fabrication.

Perspective of perovskite-type oxides for proton conducting solid oxide fuel cells

Solid oxide fuel cell (SOFC) is one of the promising solid-state electrochemical device that converts chemical energy of varied fuels into electricity with high efficiency. However, its market acceptability is hindered due to its high operating temperature (800–1000 °C) that is dictated by the use of conventional oxide ion conducting yttria-stabilized zirconia electrolyte and sluggish oxygen reduction reaction properties of conventional Sr-doped LaMnO3 cathodes. Hence, major focus in the field of SOFCs has been directed towards reducing the operating temperature of current SOFCs to intermediate temperatures (500–700 °C), with the emphasis on material development for advanced electrolytes and cathodes. Due to the ease of doping on both A and B sites, structural stability, and ability to show both ionic (O2−, H+) and electronic conductivity, perovskite-type ABO3 (A = Sr, Ba; B = Ce, Zr) ceramics has been the focus of research towards development of proton conducting SOFCs (H-SOFCs). Despite significant developments, there is a general lack of understanding regarding future research directions in this field. In this review article, we first present an overview of crystal structure, dopant composition and its correlation with chemical stability and electrical conductivity followed by existing challenges associated with cathode development for H-SOFCs and achieving high fuel cell performance. We also outline the recent efforts directed towards reducing the H-SOFCs operating temperature.

Effect of Samarium Oxide on the Electrical Conductivity of Plasma-Sprayed SOFC Anodes

Solid oxide fuel cells (SOFCs) are rapidly becoming recognized as a new alternative to traditional energy conversion systems because of their high energy efficiency. From an ecological perspective, this environmentally friendly technology, which produces clean energy, is likely to be implemented more frequently in the future. However, the current SOFC technology still cannot meet the demands of commercial applications due to temperature constraints and high cost. To develop a marketable SOFC, suppliers have tended to reduce the operating temperatures by a few hundred degrees. The overall trend for SOFC materials is to reduce their service temperature of electrolyte. Meanwhile, it is important that the other components perform at the same temperature. Currently, the anodes of SOFCs are being studied in depth. Research has indicated that anodes based on a perovskite structure are a more promising candidate in SOFCs than the traditional system because they possess more favorable electrical properties. Among the perovskite-type oxides, SrTiO3 is one of the most promising compositions, with studies demonstrating that SrTiO3 exhibits particularly favorable electrical properties in contrast with other perovskite-type oxides. The main purpose of this article is to describe our study of the effect of rare-earth dopants with a perovskite structure on the electrical behavior of anodes in SOFCs. Sm2O3-doped SrTiO3 synthesized by a solid-state reaction was coated on substrate by atmospheric plasma spray. To compare the effect of the dopant on the electrical conductivity of strontium titanate, different concentrations of Sm2O3 were used. The samples were then investigated by x-ray diffraction, four-point probe at various temperatures (to determine the electrical conductivity), and a scanning electron microscope. The study showed that at room temperature, nondoped samples have a higher electrical resistance than doped samples. As the temperature was increased, the electrical conductivity correspondingly increased. The optimum value of 1.1 S/cm was found at 340°C for samples with 1.5% mol Sm2O3.

Evaluation of a Novel Perovskite-Based Conversion Coating for Corrosion Protection of 13Cr Ferritic Stainless Steels under Relevant SOFC Oxidizing Conditions

Reduction of operational temperatures from 800°C towards an intermediate temperature (IT) range of 600-750°C is one major trend in current Solid Oxide Fuel Cell (SOFC) research as a cost-effective approach to higher reliability and durability of fuel cell components and systems [1]. Intermediate temperatures expand, in fact, enormously materials selection in SOFC design allowing the possibility of using conventional ferritic stainless steels for the realization of important components such as cell housings, gas manifolds, support structures and plate interconnects (IC). In particular, 18Cr ferritic stainless steels are currently the most evaluated materials to realize cost-effective metallic IC plates due to their excellent mechanical stability, ease of fabrication and high formability characteristics. However, excessive contact resistance due to oxide scale growth and evaporation of the protective chromia scales are two primary sources of cell performance degradation that are related to an insufficient long-term corrosion resistance of 18Cr ferritic stainless steels. In order to alleviate these problems, protective ceramic oxide coatings with spinel or perovskite layers are usually applied to provide better electrical contact and reduced Cr volatility [2]. For further cost reduction, 13Cr stainless steels have received some attention in the recent literature as a potential substitution alternative at the low end of IT-SOFC operation temperatures [3,4]. At temperatures below 700°C, the oxidation of these steels gives raise to protective oxide films mainly composed of mixed (Fe,Mn,Cr) spinel oxide phases [4]. As compared to chromia-forming alloys, stainless steels that form protective (Fe,Mn,Cr) spinel oxides have an expected advantage of lower Cr volatility and contact resistance issues with only a small trade-off in corrosion resistance properties, under appropriate temperature conditions. Recently, we have proposed a novel approach for high temperature corrosion protection of stainless steels, which is based on producing LaFeO3-based perovskite layers by chemical conversion reactions taking place in a molten carbonate salt bath. Our previous results indicated that LaFeO3 perovskite coatings were able to protect stainless steels with various Cr content in typical Molten Carbonate Fuel Cell (MCFC) environments [5,6]. In order to extend the application areas of this novel coating method, the aim of this work was to evaluate the suitability of LaFeO3 perovskite coatings also for the improvement of corrosion resistance of a 13Cr ferritic stainless steel under typical IT-SOFC conditions. Techniques such as XRD and SEM/EDX analysis were used to characterize morphology and structure stability of the perovskite coating after prolonged exposure at 700°C in ambient air atmosphere. Detailed results from these studies will be presented at the conference venue. Bibliography [1] M. C. Tucker, Progress in metal-supported solid oxide fuel cells: A review, . J Power Sources 195, 2010, 4570-4582; [2] N. Shaigan, W. Qu, D.G. Ivey, W. Chen, A review of recent progress in coatings, surface modifications and alloy developments for solid oxide fuel cell ferritic stainless steel interconnects. J Power Sources 195, 2010, 1529-1542. [3] J. Fergus, Y. Zhao, Low-Chromium Alloys for Solid Oxide Fuel Cell Interconnects. ECS Trans 25, 2011, 2447-2453; [4] S. Frangini, A. Masci, S.J. McPhail, T. Soccio, F. Zaza, Degradation behavior of a commercial 13Cr ferritic stainless steel (SS405) exposed to an ambient air atmosphere for IT-SOFC interconnect applications. 144, Mater Chem Phys 2014, 491-497; [5] S. Frangini, A. Masci, F. Zaza, Molten salt synthesis of perovskite conversion coatings: A novel approach for corrosion protection of stainless steels in molten carbonate fuel cells. Corros Sci, 53, 2011, 2539-2548; [6] S. Frangini, F. Zaza, A. Masci, Molten carbonate corrosion of a 13-Cr ferritic stainless steel protected by a perovskite conversion treatment: Relationship with the coating microstructure and formation mechanism. Corros Sci, 62, 2012, 136-146.

Cell Performance of Anode-Supported BaZr0.85Y0.15O3-δ/Carbonate Composite Electrolyte at Intermediate Temperature

Recently, proton-conducting based-protonic ceramic fuel cells (PCFCs) have received great attentions as sustainable power generators at the intermediate temperature, because of their higher ionic conductivity with lower activation energy as compared to the oxygen-ion-conducting electrolytes based solid oxide fuel cells (SOFCs). Among several perovskite-type proton conducting oxides, yttrium-doped BaZrO3 (BZY) have exhibited considerable bulk proton conductivity with a high chemical resistance against CO2 and H2O in the intermediate temperature range. However, the manufacturing of porous electrode-supported dense BZY electrolyte cells virtually needs awfully difficult processes by the current SOFC technology due to its poor sinterability. Furthermore, high sintering temperature results in decreasing the proton conductivity of BZY with the BaO sublimation and low-conducting Y2O3-like phase formation. In addition, the BZY materials are still required to improve proton conductivity under the PCFC operating condition. To achieve these goals, we have designed two-phase composite electrolytes consisting of a BZY matrix phase and a binary eutectic carbonate (Li–0.5Na)2CO3 phase in previous works. The conductivity of the composite electrolytes is higher than that of the BZY under the PCFC operating condition. Moreover, dense BZY composite electrolytes are fabricated with a carbonate phase at a remarkably low sintering temperature of 670 °C. Hence, in this work, anode-supported BZY/carbonate electrolyte cells are fabricated by the co-pressing technique with the Ni-cermet anode and as lithiated NiO cathode to confirm this composite electrolyte concept and then co-sintered at 600°C for 1 h. For the physicochemical and electrochemical characterizations, the anode-supported composite PCFCs are investigated by various analysis tools such as XRD, SEM, electrochemical polarization, and impedance spectroscopy. [1] K.D. Kreuer, Annu. Rev. Mater. Res. 33 (2003) 333–359. [2] E. Fabbri, D. Pergolesi, E. Traversa, Chem. Soc. Rev. 39 (2010) 4355-4369. [3] E. Fabbri, L. Bi, D. Pergolesi, E. Traversa, Adv. Mater. 18 (2012) 195-208. [4] T. Schober, H.G. Bohn, Solid State Ionics 127 (2000) 351–360. [5] K.-Y. Park, T.-H. Lee, J.-T. Kim, N. Lee, Y. Seo, S.-J Song, J.-Y. Park, J. Alloys Comp. 585 (2014) 103–110. Keywords: Protonic ceramic fuel cell (PCFC), Composite electrolyte, Yttrium-doped barium zirconate (BZY), Carbonate, Performance. * Corresponding authors: jyoung@sejong.ac.kr (J.-Y. Park).

Tunability and Electrical Properties of Yttria-doped-ceria Films Fabricated via Atomic Layer Deposition

Current Solid Oxide Fuel Cell (SOFC) designs have operating temperatures between 800-1000 °C. Reducing this temperature to 500-600 °C would allow efficient utilization in varied applications. Yttria Doped Ceria (YDC) films show high ionic conductivity when used as fuel cell electrolytes in lower temperature ranges. This investigation shows that stoichiometric tunability of YDC film composition can be achieved through Atomic Layer Deposition (ALD). Film resistivity at room temperature is measured using a custom four-point probe sensor Film resistance analysis provides a method for evaluating the effect of doping and thickness of the film on desirable SOFC electrolyte characteristics such as high ionic conductivity.

Improved Solid Oxide Fuel Cell Performance with Nanostructured Electrolytes

Considerable attention has been focused on solid oxide fuel cells (SOFCs) due to their potential for providing clean and reliable electric power. However, the high operating temperatures of current SOFCs limit their adoption in mobile applications. To lower the SOFC operating temperature, we fabricated a corrugated thin-film electrolyte membrane by nanosphere lithography and atomic layer deposition to reduce the polarization and ohmic losses at low temperatures. The resulting micro-SOFC electrolyte membrane showed a hexagonal-pyramid array nanostructure and achieved a power density of 1.34 W/cm(2) at 500 °C. In the future, arrays of micro-SOFCs with high power density may enable a range of mobile and portable power applications.

Progress in understanding and development of Ba0.5Sr0.5Co0.8Fe0.2O3−δ-based cathodes for intermediate-temperature solid-oxide fuel cells: A review

Abstract Solid-oxide fuel cells (SOFCs) convert chemical energy directly into electric power in a highly efficient way. Lowering the operating temperature of SOFCs to around 500–800 °C is one of the main goals in current SOFC research. The associated benefits include reducing the difficulties associated with sealing and thermal degradation, allowing the use of low-cost metallic interconnectors and suppressing reactions between the cell components. However, the electrochemical activity of the cathode deteriorates dramatically with decreasing temperature for the typical La0.8Sr0.2MnO3-based electrodes. The cathode becomes the limiting factor in determining the overall cell performance. Therefore, the development of new electrodes with high electrocatalytic activity for oxygen reduction becomes a critical issue for intermediate-temperature (IT)-SOFCs. Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxide was first reported as a potential IT-SOFC cathode material in 2004 by Shao and Haile. After that, the BSCF cathode has attracted considerable attention. This paper reviews the current research activities on BSCF-based cathodes for IT-SOFCs. Emphasis will be placed on the understanding and optimization of BSCF-based materials. The issues raised by the BSCF cathode are also presented and analyzed to provide some guidelines in the search for the new generation of cathode materials for IT-SOFCs.

Recent Advances to the Development of Low‐Temperature Solid Oxide Fuel Cells

AbstractWhile existing solid oxide fuel cell (SOFC) technology has demonstrated much higher energy efficiency with minimal pollutant emission than the conventional technologies, the costs of the current SOFC systems are still prohibitive for broad commercialization. To be economically competitive, both the cost of materials and the cost of fabrication must be dramatically reduced. One effective approach to cost reduction is to reduce the operating temperature; many cell components, including interconnect, heat exchangers, and other structural or balance‐of‐plant components, can be fabricated from much less expensive materials when the operating temperature is sufficiently low. However, the interfacial polarization resistances increase rapidly as the operating temperature is reduced. This paper will address the critical issues in creating electrodes and interfaces of minimal polarization resistance in order to minimize internal electrochemical losses at low temperatures. In particular, design, fabrication, and characterization of composite electrodes consisting of silver and bismuth oxide will be discussed. Another approach to cost reduction is to reduce the cost of fabrication. Dense electrolyte films supported on porous anodes fabricated by screen‐printing and dry press will be presented.