Efficient Solid Oxide Fuel Cells Research Articles

Enhancing Sr-deficient Sr(Ti0.3Fe0.7)O3–δ Cathode Performance through Sm0.5Sr0.5CoO3–δ Infiltration

The development of cathodes with improved polarization, aimed at reducing the operating temperature of solid oxide fuel cells (SOFCs), is an important avenue of research toward more efficient SOFCs. Sr(Ti0.3Fe0.7)O3–δ recently emerged as an active and stable cathode material; although its oxygen transport capability was shown to be further improved by introducing a Sr deficiency, the accompanying increased sinterability creates challenges in optimizing cathode microstructure. One facile approach may be single-step infiltration with highly active materials, such as Sr0.5Sm0.5CoO3–δ (SSC). However, there is limited knowledge regarding the impact of SSC on the electrochemical mechanisms within Sr-deficient Sr(Ti0.3Fe0.7)O3–δ . In this study, we systematically investigate the electrochemical characteristics of SSC-infiltrated Sr0.95(Ti0.3Fe0.7)O3–δ (STF) cathodes. Transmission line model-based impedance analysis provides a mechanistic understanding of STF and the role of SSC infiltrants in polarization improvement. The results reveal that SSC effectively reduces the resistance associated with key electrode processes, including oxygen diffusion, surface exchange, and dissociative adsorption/desorption. Consequently, using SSC infiltration, the power density of a Ni–Zr0.84Y0.16O2–δ (YSZ) anode-supported full cell with thin (∼2.5 μm) electrolyte increased from ∼1.88 to ∼2.47 W cm–2 at 800 °C.

Smart Dual-Exsolved Self-Assembled Anode Enables Efficient and Robust Methane-Fueled Solid Oxide Fuel Cells.

Perovskite oxides have emerged as alternative anode materials for hydrocarbon-fueled solid oxide fuel cells (SOFCs). Nevertheless, the sluggish kinetics for hydrocarbon conversion hinder their commercial applications. Herein, a novel dual-exsolved self-assembled anode for CH4 -fueled SOFCs is developed. The designed Ru@Ru-Sr2 Fe1.5 Mo0.5 O6-δ (SFM)/Ru-Gd0.1 Ce0.9 O2-δ (GDC) anode exhibits a unique hierarchical structure of nano-heterointerfaces exsolved on submicron skeletons. As a result, the Ru@Ru-SFM/Ru-GDC anode-based single cell achieves high peak power densities of 1.03 and 0.63Wcm-2 at 800°C under humidified H2 and CH4 , surpassing most reported perovskite-based anodes. Moreover, this anode demonstrates negligible degradation over 200h in humidified CH4 , indicating high resistance to carbon deposition. Density functional theory calculations reveal that the created metal-oxide heterointerfaces of Ru@Ru-SFM and Ru@Ru-GDC have higher intrinsic activities for CH4 conversion compared to pristine SFM. These findings highlight a viable design of the dual-exsolved self-assembled anode for efficient and robust hydrocarbon-fueled SOFCs.

Thermal management of Ammonia-fed Solid oxide fuel cells using a novel alternate flow interconnector

Ammonia is a promising fuel for solid oxide fuel cells (SOFCs) as it is carbon-free and easy to store at high volumetric energy densities. However, the endothermic decomposition of ammonia in an SOFC stack significantly reduces the temperature at the entrance of the fuel flow, leading to temperature shock and nitriding. Designing a suitable interconnector for the stack to obtain a flatter temperature distribution is an efficient strategy to overcome this problem. This article proposes a novel interconnector design using an alternate flow concept for both fuel and air. A three-dimensional SOFC model was used for the thermal investigation of the proposed design under different operating conditions, including temperature, current, and fuel utilization. The results indicated that the alternate flow design exhibited a 40% lower temperature difference and up to 53 K higher average temperature than a typical cross-flow design. In addition to a flatter temperature profile, the proposed design exhibited a higher ammonia conversion rate than the conventional design, demonstrating its promise for use in robust and efficient ammonia-fed SOFC stacks.

Enhancing coking tolerance of flat-tube solid oxide fuel cells for direct power generation with nearly-dry methanol

The state-of-the-art Ni/yttria-stabilized zirconia (YSZ) anodes in direct methanol solid oxide fuel cells (SOFCs) are vulnerable to carbon deposition. We propose two strategies to enhance coking tolerance of the cell, focusing on promoting the oxygen storage capacity of the Ni/YSZ anode and the methanol conversion in flat-tube SOFCs with an active area of 60 cm2. The Ni/YSZ anodes are decorated with nanosized gadolinia-doped ceria (GDC) by wet impregnation method and the fuel channels are filled with extra GDC-Ni/YSZ catalyst. Through these measures, carbon deposition in the modified cells is mitigated, and therefore the steam/carbon (S/C) ratio for successful long-term cell operation is significantly lowered, and the cell durability is improved. A GDC-Ni/YSZ cell with extra catalyst is operated for over 1200 h directly on methanol under low S/C ratios at 750 °C and carbon deposition is considerably suppressed. In addition, the degradation mechanism of the cell directly fueled with nearly-dry methanol (S/C = 0.1) is investigated. This work provides insight into efficient and durable SOFCs using biofuels, towards renewable energy conversion in large-scale commercial applications.

Ruthenium Doped Lscf Based Cathode for Enhanced Performance of Solid Oxide Fuel Cells

Recently, a tremendous upsurge in the research of Solid oxide fuel cells (SOFCs) has been documented due to cheap electricity production and without harming the environment. The development of efficient SOFCs requires more robust cathode for oxygen reduction. Until yet a copious amount of research has been done on varieties of materials including LSCF. In this work, Ruthenium is doped on the LSCF forming nanostructured Ru-LSCF with various Ru stoichiometric quantities. The Ru-LSCF catalyst is prepared via simplistic technique “Glycine combustion process”, producing evenly embedded Ru in LSCF perovskite materials leading to increased oxygen reduction reaction (ORR). The nanostructured Ru-LSCF cathode showed polarization resistance of approximately 0.031 Ωm2 at 750 0C. The peak powers of approximately 1760.5, 1480.1, 893.3 mW/cm2 were recorded at 750, 700, and 650 0C, respectively. Ru LSCF was quantitatively optimized for enhanced power production with high precision calculation. The results show that the Ru-LSCF optimum fabricated nanostructured cathode is promising catalyst for the reduction of oxygen at the cathode side for highly durable SOFCs.

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.

Optimization of Operating Conditions of a Solid Oxide Fuel Cell System with Anode Off-Gas Recirculation Using the Model-Based Sensitivity Analysis

Designing a configuration of an efficient solid oxide fuel cell (SOFC) system and operating it under appropriate conditions are important for achieving a highly efficient SOFC system. In our previous research, the system layout of a SOFC system with anode off-gas recirculation was suggested, and the system performance was examined using a numerical model. In the present study, the system operating conditions were optimized based on the system configuration and numerical model developed in the previous paper. First, a parametric sensitivity analysis of the system performance was investigated to demonstrate the main operating parameters. Consequently, the fuel flow rate and recirculation ratio were selected. Then, the available operating conditions, which keep the system below the operating limits and satisfy the desired system performance (Ufuel > 0.7 and ηelec > 45%) were discovered. Finally, optimized operating conditions were suggested for three operating modes: optimized electrical efficiency, peak power, and heat generation. Depending on the situation, the demand for electricity and heat can be different, so different proper operating points are suggested for each mode. Additionally, using the developed model and the conducted process of this study, various optimized operating conditions can be derived for diverse cases.

Infiltration of nickel and copper catalysts into a GDC backbone assisted by supercritical CO2 for efficient SOFC anodes

This study describes an original method developed for the shaping of composite solid oxide fuel cell (SOFC) anodes including either nickel or copper as metal.

Highly Active and Stable a-Site Deficient La0.4Sr0.4Ti0.94Ni0.06O3-δ SOFC Anode Material with in-Situ Exsolved of Ni Nanoparticles

La-doped strontium titanates with a perovskite structure are promising candidates of the anode materials for solid oxide fuel cells (SOFCs) owing to their good chemical compatibility with other components and superior redox-stability. Among these La-doped SrTiO3 (LST), A-site deficient LST materials have attracted much interest due to their improved electrochemical characteristics. Recently, exsolution in A-site deficient LST has been intensively studied, because catalytic active and durable metal nanoparticles can be exsolved on the LST surface. In this study, we developed the A-site deficient Ni-doped La0.4Sr0.4TiO3 (LSTN)-Ce0.9Gd0.1O1.95 (GDC) composite anodes, and investigate their electrochemical performance and redox stability on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte-based SOFCs. The maximum power density(MPD) of LSTN44-GDC anode based cell was 0.698 mW cm-2 at 900℃ in wet H2 fuel (3% H2O). Also, during redox cyclic tests combined with long-term stability test, The LSTN44-GDC cell maintained its performance without any degradation. All these results demonstrate that the A-site deficient LSTN-GDC is a promising material for an efficient and stable SOFC anode.

Basic Study of Anode Off-Gas Recycling Solid Oxide Fuel Cell Module with Fuel Regenerator

In recent years, with the rise of global environmental protection activities, it is becoming necessary to reduce CO2 emissions in social activities. In the field of power generation, it is very important to capture CO2 emissions and increase the conversion efficiency from chemical energy to electrical energy. Because the increased electrical efficiency can lead to the increased power, it is likely to reduce the consumption of fossil fuels for power generation, resulting in reduced CO2 emissions. In our previous report, the effect of a fuel regenerator in a two-stage solid oxide fuel cell (SOFC) module on the electrical efficiency was studied. The results showed that the electrical efficiency was considerably improved by removing H2O and CO2 from the anode off-gas by the fuel regenerator. The highest electrical efficiency was obtained when 100% of H2O and CO2 were removed from the anode off-gas, and it was estimated to be a net alternating current (AC) of 71.8% (lower heating value (LHV)). Although it is necessary to maintain the module at a high temperature in order to realize the system, a 4.8 kW two-stage SOFC module with a fuel regenerator was developed and confirmed to have the electrical efficiency equivalent to a net AC of 66.0% (LHV) with the thermal self-sustainability. In 2020, a demonstration test using a highly efficient two-stage SOFC system has started. In this study, we focused on an anode off-gas recycling SOFC module with a fuel regenerator. The reason why we studied the module is that it can generate highly efficient power and capture a large amount of CO2 at the fuel regenerator. Therefore, the effect of the fuel regeneration on both the electrical efficiency and capture of CO2 was examined. The authors are presently not aware of any reports of examining the effect of the fuel regenerator, which removes CO2 and/or H2O extensively from the anode off-gas, on the electrical efficiency and CO2 capture in an anode off-gas recycling SOFC module. The calculation was carried out under the following conditions. CH4 was used as a fuel, and the ratio of steam to carbon of the inlet fuel was 2.5 or more in order to avoid the carbon deposition. The temperature of both the reformer and SOFC stack was set at 700°C. The area specific resistance and current density of the SOFC stack were assumed to be 0.383 ohm cm2 and 0.25 A cm–2, respectively. The lowest available fuel concentration, which is assumed to be the ratio of the partial pressure of hydrogen to water vapor (= p(H2) / p(H2O)), was set by calculating the outlet fuel concentration when operating a single-pass SOFC stack with a maximum fuel utilization rate of 80%. For estimating the system performance, the inverter efficiency and auxiliary device loss rate were assumed to be 95% and 6%, respectively. The Nernst voltage was determined from the inlet and outlet gas composition of the stack which is calculated by a process simulation software. The electrical efficiency was estimated from the cell voltage and fuel utilization rate. The highest electrical efficiency was obtained when both the fuel utilization rate and recycle rate were 100%, and the removal rates of CO2 and H2O at the fuel regenerator were 100% and 44.4%, respectively. The reason to remove only 44.4% of H2O from the anode off-gas is to keep the ratio of steam to carbon of the inlet fuel at 2.5. The electrical efficiency was a net AC of approximately 75.5% (LHV) with 100% of CO2 capture at the fuel regenerator. In addition, the CO2 removal rate was studied to reduce to 63.9% because there is a margin in the fuel concentration of the SOFC stack. Even if the removal rates of CO2 and H2O at the fuel regenerator were 63.9% and 44.4%, respectively, the electrical efficiency was estimated to be a net AC of approximately 74.9% (LHV), and the CO2 capture at the fuel regenerator was 100%. These results show that the anode off-gas recycling SOFC module can generate highly efficient power as well as the two-stage SOFC module when using the fuel regenerator. Furthermore, the anode off-gas recycling SOFC module has advantage of capturing CO2 at the fuel regenerator. Although it is not easy to generate highly efficient power with the thermal self-sustainability, it is expected that the anode off-gas recycling SOFC module with the fuel regenerator is developed and put into practical use in the future.

A comparison of steam reforming concepts in solid oxide fuel cell systems

Various concepts have been proposed to use hydrocarbon fuels in solid oxide fuel cell (SOFC) systems. A combination of either allothermal or adiabatic pre-reforming and water recirculation (WR) or anode off-gas recirculation (AOGR) is commonly used to convert the fuel into a hydrogen rich mixture before it is electrochemically oxidised in the SOFC. However, it is unclear how these reforming concepts affect the electrochemistry and temperature gradients in the SOFC stack. In this study, four reforming concepts based on either allothermal or adiabatic pre-reforming and either WR or AOGR are modelled on both stack and system level. The electrochemistry and temperature gradients in the stack are simulated with a one-dimensional SOFC model, and the results are used to calculate the corresponding system efficiencies. The highest system efficiencies are obtained with allothermal pre-reforming and WR. Adiabatic pre-reforming and AOGR result in a higher degree of internal reforming, which reduces the cell voltage compared to allothermal pre-reforming and WR. Although this lowers the stack efficiency, higher degrees of internal reforming reduce the power consumption by the cathode air blower as well, leading to higher system efficiencies in some cases. This illustrates that both stack and system operation need to be considered to design an efficient SOFC system and predict potentially deteriorating temperature gradients in the stack.

(Invited) Sputtered Thin Films for Very High Power, Efficient, and Low-Cost Commercial SOFCs

Sputtering of thin electrolyte layers has been demonstrated to increase solid oxide fuel cell (SOFC) performance in very small-scale, e.g., button cells. The few cases where thin film techniques were brought in to early stages of commercialization (e.g., Lilliputian and SiEnergy) showed remarkable low temperature SOFC performance, but required sophisticated cell designs processed with Si and MEMs type technologies. This work takes advantage of low cost, conventional ceramic processing to build large format (10 cm x 10 cm) half-cells upon which the sputtered layers above are added to dramatically increase SOFC performance. In this work, an electron-blocking layer which increases the open circuit cell voltage of the GDC electrolyte based cell and a Gd doped ceria (GDC) buffer layer which mitigates reactions between the cathode and electron blocking layer are deposited by sputtering. This presentation will present progress towards developing increased SOFC performance using this sputtering technology at the commercial-scale. Challenges encountered or expected with thin film development for SOFC commercialization will be discussed.

A-site deficient La0.4Sr0.4TiO3-Ce0.9Gd0.1O1.95 composites as efficient and redox stable anodes for solid oxide fuel cells

La-doped strontium titanates have attracted much interest as promising reliable ceramic anodes for solid oxide fuel cells (SOFCs) owing to their superior redox-stability. Moreover, recent studies demonstrated that A-site deficiency of the La-doped SrTiO3 perovskite could effectively promote conductivity and catalytic activity, simultaneously. In this study, we developed the LST44-Ce0.9Gd0.1O1.95 (GDC) composite anodes, and investigated their electrochemical performance and redox stability on La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte-based SOFCs. During galvanostatic long-term stability tests combined with in situ redox cycles, power out-put performance of the LST44-GDC employed SOFC was initially increased by ∼53% to 0.26 W cm−2 and maintained the high performance over 350 h at 800 °C. Analysis of the accumulated electrochemical impedance spectra during the long-term stability test showed that the electrochemical activity of the LST44-GDC anode was promoted at the initial redox cycling. Consequently, this study demonstrates that A-site deficient LST44-GDC is a promising material as an efficient and redox stable SOFC anode.

Development of a Highly Efficient SOFC Module Using Two‐stage Stacks and a Fuel Regeneration Process

AbstractA solid oxide fuel cell (SOFC) module using two‐stage stacks and a fuel regeneration process between them was developed in this study for the first time, to the best of the authors' knowledge. Upon configuring the first‐stage and second‐stage stacks and a steam reformer between them in the SOFC module, a gross output power of DC 2.27 kW was generated with gross power generation efficiency of DC 69.2% (lower heating value (LHV)), at a total fuel utilization rate of 86.3%. This technology enables operation at a very high total fuel utilization rate even while operating the stacks at a moderate fuel utilization rate (below 70%). Considering an auxiliary device loss (6%) and inverter loss (5%), the net power generation efficiency is estimated to be AC 61.8% (LHV); hence, the module is considered to exhibit a high power generation efficiency. Further increases in the power generation efficiency could be realized in the future by removing the CO2 from the anode off‐gas during the fuel regeneration process and/or operating the stacks at higher temperatures by decreasing heat leakage from the module.

Toward Lower Temperature and More Efficient Solid Oxide Fuel Cell: The Effect of Gibbs Phase Rule on the Triple Phase Boundary

Stationary SOFCs are source of green electricity to power future electrically powered vehicles. In SOFC the ionic conductivity determines the efficiency. It is obvious that a shift in the operating temperature of solid oxide fuel cells (from 1000 down to around 750–800 degree C) is desired. However, better electrolyte and electrode materials are required for lower temperature operation in order to maintain their high temperature performance. It had been known that both phase purity (single phase) and microstructure of, for example LSGM materials, depend on synthesis procedure and processing and, as a matter of fact, the synthesis of a pure single phase material is rather difficult [1,2]. Two important conclusions are the objective of this research work: 1-The cathode, anode or electrolyte become ionically conducting at a sharp phase transition temperature (the operating T of the SOFC). Below such T the materials loses its ionic conductivity [3] 2-The Gibbs phase rule (single phase and two components of the air) may be applied at the triple phase boundary (TPB) where the number of phases of the MIEC (single or two phases) are in contact with single and pure phase electrolyte [4]. 1. Djurado, E. and Labeau, M., J. Europ. Ceram. Soc., 1998, 18, 1397–1404 2. Tas, A. C., Majewski, P. and Aldinger, F.,. J. Am. Ceram. Soc., 2000, 83, 2954–2960 3. S. Hall, Superionics: crystal structures and conduction process,.Rep. Prog Physics, 2004, 67, 1233-1314 4. S. B. Adler, Factors Governing Oxygen Reduction in Solid Oxide Fuel Cell Cathodes, Chem. Rev. 2004, 104, 4791−4843.

High oxide ion conductivity below 500∘C in the garnets LaxY3−xFe5O12+δ

We address the issue of achieving high oxide ion conductivity at low temperatures $(\ensuremath{\le}500{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C})$ in stable electrolytes for solid oxide fuel cell (SOFC) techonology. We report here a high oxide ion conductivity $(\ensuremath{\sim}{10}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{S}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})$ in the La substituted yttrium iron garnets $\mathrm{L}{\mathrm{a}}_{x}{\mathrm{Y}}_{3\text{\ensuremath{-}}x}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12+\ensuremath{\delta}}$ at low temperatures $(\ensuremath{\sim}450{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C})$. The judicious substitution of high electropositive $\mathrm{L}{\mathrm{a}}^{3+}$ ions in the yttrium iron garnet $(x\ensuremath{\le}0.45)$ affords continuous and easy oxide ion conduction pathways through polyhedral networks even at a low temperature of $\ensuremath{\sim}127{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. The conduction pathways have been visualized from the maximum entropy method analyzed soft bond valence sum distribution, obtained from neutron diffraction data. Our study also shows that these iron garnets have high structural stability over a broad range of temperature (at least over $27\text{--}800{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C})$, and compatible thermal expansion coefficient $(\ensuremath{\sim}10.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}{\mathrm{C}}^{\ensuremath{-}1})$ with that of the commonly used interconnect and electrode SOFC materials. We reveal that the oxide ion conduction in the present garnet is based on an excess oxide ion concentration mechanism. The observed high oxide-ion conductivity at low temperatures in the present trivalent substituted garnets is a remarkable finding for the development of an efficient SOFC technology.

Perspectives in Solid Oxide Fuel Cell-Based Microcombined Heat and Power Systems

Abstract Fuel cell technology has undergone extensive research and development in the past 20 years. Even though it has not yet made a commercial breakthrough, it is still seen as a promising enabling technology for emissions reduction. The high electrical efficiency (Powell et al., 2012, “Demonstration of a Highly Efficient Solid Oxide Fuel Cell Power System Using Adiabatic Steam Reforming and Anode Gas Recirculation,” J. Power Sources, 205, pp. 377–384; Föger and Payne, 2014, “Ceramic Fuel Cells BlueGen—Market Introduction Experience,” 11th European SOFC & SOE Forum 2014, Lucerne, Switzerland, Paper No. A0503; and Payne et al., 2009, “Generating Electricity at 60% Electrical Efficiency From 1-2 kWe SOFC Products,” ECS Trans., 25(2), pp. 231–240) of an solid oxide fuel cell (SOFC)-based fuel cell system and the ability to operate on renewable fuels make it an ideal platform for transition from fossil-fuel dependency to a sustainable world relying on renewable energy, by reducing emissions during the transition period where fossil fuels including natural gas remain a major source of energy. Key technical hurdles to commercialization are cost, life, and reliability. Despite significant advances in all areas of the technology cost and durability targets (Papageorgopoulos, 2012, “Fuel Cells, 2012 Annual Merit Review and Peer Evaluation Meeting,” U.S. Department of Energy, Washington, DC, accessed May 14, 2012, http://www.hydrogen.energy.gov/pdfs/review12/fc_plenary_papageorgopoulos_2012_o.pdf) have not been met. The major contribution to cost comes from tailor-made balance of plant (BoP) components as SOFC-based systems cannot be optimized functionally with off-the shelf commercial items, and cost targets for BoP and stack cannot be met without volume manufacturing (Föger, 2008, “Materials Basics for Fuel Cells,” Materials for Fuel Cells, M. Gasik ed., Woodhead Publishing, Cambridge, UK, pp. 6–63). Reliability issues range from stack degradation and mechanical failure and BoP component failure to grid-interface issues in a grid-connected distributed generation system. Resolving some of these issues are a key to the commercial viability of SOFC-based microcombined heat and power (CHP) systems. This paper highlights some of the technical and practical challenges facing developers of SOFC-based products.

Effect of Exchange Current Density on Current Distribution at Planar-Type SOFC Anodes

Cell stack structure of solid oxide fuel cells (SOFCs) affects to their performance. Its optimization is important to realize highly efficient SOFCs. In this study, we focus on the numerical simulation method combined with experimentally obtained exchange current density. Deriving the anode exchange current density for fully pre-reformed methane-fueled SOFCs, the effect on the current distribution is evaluated. Current distribution was calculated using variable anode exchange current density after taking into account the pressure of CO and CO2.

Reduced Temperature Sintering of GDC Electrolyte for IT-SOFCs

Lanthanide material- (gadolinium or samarium) doped ceria (GDC or SDC) is considered one of the most advanced electrolyte materials for intermediate temperature (below 700 oC) SOFC (IT-SOFC) because of its high ionic conductivity at these temperatures. However, a high sintering temperature (above 1400 oC) is a disadvantage of the doped ceria. Metal oxides such as Fe oxide, Co oxide, Mn oxide, Li oxide, Ga oxide and Cu oxide were used as sintering aids to obtain the fully sintered electrolytes at a lower sintering temperature. In this study, the effect of a copper additive as a sintering aid to lower the sintering temperature for the construction of solid oxide fuel cells (SOFCs) was investigated. Gd-doped ceria (GDC) electrolyte with 0.25-10 mol% CuO sintering aid was prepared by reacting GDC power and copper nitrate solution followed by heating at 600 oC. The sintering of CuO-coated GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy of CuO-GDC electrolytes at temperatures ranging from 1100 to 1400 ¢ªC. The addition of Cu additive in GDC powder led to a decrease in the sintering temperature from 1400 to 1100 oC, which can result in the reduction of SOFC fabrication costs. For the GDC powder with 0.25 mol% Cu additive, linear shrinkage rates over the range of 1100 to 1400 oC were the highest (ca. 16.79-17.34 %). Regarding ionic conductivity, the 0.25 and 0.5 mol% Cu-added samples showed a higher value than the untreated GDC powder in the range of 550 to 750 oC, while the value for the 0.75 mol% Cu-added sample was lower. This result was evidenced by the occurrence of mechanical defects in body of the GDC samples with higher Cu contents (≥ 0.75 mol%). In addition, the activation energy of the CuO-GDC prepared in this work remained unchanged significantly. These results obtained in this study suggest that further investigations of proper sintering aids with the combination of different metal oxides and the optimization of GDC-electrolyte synthesis conditions may enable more stable and efficient SOFCs based on GDC. Figure 1

Bilayered BaZr0.1Ce0.7Y0.2O3-δ/Ce0.8Sm0.2O2-δ electrolyte membranes for solid oxide fuel cells with high open circuit voltages

Bilayered electrolyte membranes composed of BaZr0.1Ce0.7Y0.2O3−δ (BZCY) and Ce0.8Sm0.2O2−δ (SDC) were evaluated for solid oxide fuel cells (SOFCs), and the influence of the membrane architecture on the cell performance was investigated. The electrochemical testing results showed that the electron-blocking ability of BZCY layer depends on its exact location in the fuel cell. The partial internal short circuit was nearly totally eliminated for the cell with BZCY layer located at the anode side, and the corresponding cell exhibited a high open circuit voltage (OCV) of 1.0V at 700°C. In contrast, the cell with BZCY layer located at the cathode side still exhibited significant internal short-circuit behavior. The different electron-blocking ability can be ascribed to the atmosphere-dependent charge transport behavior of BZCY. The present results demonstrate that the bilayered BZCY/SDC membrane with BZCY layer located at the anode side is a promising electrolyte for highly efficient low-temperature SOFCs. Besides, the BZCY layer should be as thin as possible to achieve desirable power performance for the fuel cell.