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Cr poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi

High-temperature solid oxide electrolysis cells (SOECs) provide greater efficiency and may potentially provide future technology to meet the enormous energy storage needs generated by the surge in the availability of intermittent solar and wind electricity. However, in implementing this SOEC technology, the high polarization losses and long-term degradation of the SOEC electrodes are the bottlenecks. In this research, we tailored the microstructure of SOEC air electrode to improve electrochemical efficiency and increase the stability of the air electrode. The optimization of the microstructure culminated in a 30% improvement in SOEC electrochemical performance at 800 °C for H2O conversion and considerably improved long-term stability for >1000 hours. The Post-test SEM and TEM investigations suggested that delamination of the air electrode was prevented due to effective microstructure tailoring, and resistive interfaces forming Sr diffusion were suppressed inside the barrier layer and electrolyte. Due to the increased triple phase boundary density, porosity at the interface, and greater active surface area of the electrode, the buildup of the oxygen partial pressure over the electrolyte/barrier layer/air-electrode was decreased.

Iron and chromium based ferritic stainless steels have been considered to be a promising material for the metallic interconnect of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). However they have a drawback of chromium evaporation led by a scale growth at the steel surface when exposed at a high temperature oxidation atmosphere, which results in chromium poisoning of the air electrode and subsequent performance degradation of SOFCs and SOECs. Application of a surface modification or protective coating onto the metallic interconnects has been introduced to prevent the degradation by mitigating the chromium evaporation. In this study, ferritic stainless steels modified with a rare earth element of neodymium was investigated on the properties of high temperature oxidation and electrical conductivity. Detailed analyses on phase formation, microstructure evolution, and area specific resistance were carried out to figure out effects of the surface modification on the steels. Accordingly, the surface modified steels revealed decrease in the area specific resistance which was led by the reduction of scale growth since the rare earth element altered the chromium oxidation behavior.

In solid oxide fuel cells (SOFC), strontium zirconate (SrZrO3) insulating phase formation between Sr-containing cathode and yttria-stabilized zirconia (YSZ) electrolyte was a long-standing unsolved problem. Though a bilayer strategy with gadolinium doped ceria (GDC), or the use of samarium doped ceria (SDC) as a protective layer have been reported to improve stability and performance, the effectiveness of these processes at preventing secondary phase formation is still open to debate. In this study, focusing on Sc and Ce co-doped ZrO2 (ScCeSZ), we found that nanometer-scale Sc-segregation layers are present at co-sintered GDC/ScCeSZ interfaces. Utilizing atomic-column resolved scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical measurements, we successfully demonstrate that SOFC cells consisting of Sc-segregated interfaces show a remarkable increment of long-term durability.

High-temperature solid oxide electrolysis cells (SOECs) offer higher efficiency compared to other electrochemical water splitting technologies and potentially could provide future technology to tackle the huge energy storage requirements created by the surge of intermittent solar and wind electricity availability. However, the lower electrochemical performance and long-term degradation of the SOEC electrodes are bottlenecks in the implementation of this technology. Herein, we report microstructure tailoring of a solid oxide cell air electrode via a simple method to significantly enhance the electrochemical performance and boost the air electrode stability. The air electrode microstructure was tailored by employing a graphite pore former and the cells were tested for SOEC performance and long-term durability under fuel cell (FC)-electrolysis cell (EC) cycles and a 1000 h chronopotentiometry test. The microstructural optimization resulted in a 30% increase in the SOEC performance for H2O conversion at 800 °C and significantly improved the long-term durability. Post-test SEM and TEM analyses indicated that, due to the microstructure tailoring, delamination of the air electrode was avoided and resistive interfaces forming Sr diffusion was suppressed within the barrier layer and electrolyte. Due to air electrode microstructure optimization, the buildup of the oxygen partial pressure across the electrolyte/barrier layer/air-electrode was reduced owing to increased triple phase boundary density, porosity at the interface, and larger active surface area of the electrode.

The purpose of this study was to fabricate a porous supporting cathode for direct carbon solid oxide fuel cells (DCFC). Therefore, the effect of Gd0.1Ce0.9O2−δ (GDC) addition on the phase stability, sintering behavior, thermal expansion, and porosity of La0.65Sr0.3MnO3−δ/(Y2O3)0.08(ZrO2)0.92 (LSM/YSZ) composite was evaluated. The sintering temperature and the porosity of the LSM/YSZ composite were observed to increase with increase in the amount of GDC. An LSM/YSZ/GDC tri-composite with optimized properties was selected to fabricate the tubular cathode-supported DCFCs (LSM/YSZ/GDC|YSZ|NiO/YSZ) through extrusion, slurry coating, and co-firing. A special chamber was designed for the DCFC operation of the tubular cell. Electrochemical characterization was performed by measuring the polarization curves and electrochemical impedance spectroscopy, using the syngas produced by in situ steam gasification of carbon black.

There is increasing demand for versatile catalysts for direct hydrocarbon utilization with the coming of hydrocarbon economy. The catalysts are required to possess both high catalytic activities and excellent carbon coking tolerance for the hydrocarbon oxidation process. In this regard, we considered Ni-based alloy catalysts, e.g . Ni-Co, Ni-Cu, and Ni-Fe, which are expected to provide synergistic effects from the high catalytic activities of Ni and the high carbon coking tolerance of transition metals. We conduct a systematic investigation of catalytic effects on the electrochemical properties and the carbon coking tolerance of the candidates. Moreover, the binding strengths of H, O, and C species with each alloy catalyst were examined via density functional theory (DFT) calculations, providing insight into the trend of catalytic activity and carbon coking tolerance. In this study, the single cell for the solid oxide fuel cell with Ni-Fe catalyst shows the best electrochemical performance, 0.81 and 0.30 W cm −2 at 700 °C under H 2 and C 3 H 8 , respectively, with excellent tolerance against carbon deposition.

We investigated the long-term performance degradation in a solid oxide carbon fuel cell (SO-CFC) integrated with a steam gasifier that used activated carbon as a fuel. The steam gasifier-integrated SO-CFC was continuously operated for 2000 h at 750 °C under galvanostatic conditions. Fuel analysis, in-situ electrochemical tests, and post-mortem characterization were performed to determine the dominant degradation factors during the extended operation of the SO-CFC. During the 2000 h continuous operation, the overall degradation rate of the SO-CFC was 0.108 V per 1000 h. Electrochemical impedance spectroscopy analysis showed that the polarization and ohmic resistance of the SO-CFC increased gradually with the operation time. The post-mortem diagnosis via SEM, XRD, EDS, and XPS analyses revealed that the increased Ni particle coarsening and carbon deposition at the anode functional layer induced increased performance degradation in the SO-CFC. The long-term durability study of the SO-CFC with a steam gasifier confirmed that conventional anode materials result in rapid performance degradation during 2000 h continuous operation, and further development of anode materials will be necessary for the long and durable operation of SO-CFCs.

In this work, the effects of different sintering inhibitors added to La 0.8 Sr 0.2 MnO 3-∂ (LSM) were studied to obtain an optimum cathode material for cathode-supported type of Solid oxide fuel cell (SOFC) in terms of phase stability, mechanical strength, electric conductivity and porosity. Four different sintering inhibitors of Al₂O₃, CeO₂, NiO and gadolinium doped ceria (GDC) were mixed with LSM powder, sintered at 1300℃ and then they were evaluated. The phase stability, sintering behavior, electrical conductivity, mechanical strength and microstructure were evaluated in order to assess the performance of the mixture powder as cathode support material. It has been found that the addition of Al₂O₃ undesirably decreased the electrical conductivity of LSM; other sintering inhibitors, however, showed sufficient levels of electrical conductivity. GDC and NiO addition showed a promising increase in mechanical strength of the LSM material, which is one of the basic requirements in cathode-supported designs of fuel cells. However, NiO showed a high reactivity with LSM during high temperature (1300℃) sintering. So, this study concluded that GDC is a potential candidate for use as a sintering inhibitor for high temperature sintering of cathode materials.

We investigated the operating characteristics of solid oxide carbon fuel cells (SO–CFCs) integrated with a steam gasifier that used carbonaceous fuels, including activated carbon and biomass driven charcoal. Steam gasification was carried out in a specially designed gasifier, which was directly integrated with a solid-oxide based carbon fuel cell. We studied the effects of gasification temperature, steam flow rate and catalyst addition on the electrochemical performance of SO–CFC, and the results showed that among the three tested fuels, activated carbon with a K 2 CO 3 catalyst performed the best. At 850 °C, maximum power density values of 108 mW/cm 2 , 161 mW/cm 2 and 181 mW/cm 2 were achieved when the SO–CFC was operated using activated carbon, biomass driven charcoal and activated carbon with a K 2 CO 3 catalyst, respectively. The SO–CFC operated continuously for 100 h and it showed relatively stable performance. This study suggests that by using a catalytic steam gasifier integrated with the SO–CFC, solid carbon fuel resources can be used for power generation with higher efficiency and minimal carbon footprint.

Equal amounts of Gd 0.1 Ce 0.9 O 2− δ (GDC) were added to La 0.65 Sr 0.3 MnO 3− δ /(Y 2 O 3 ) 0.08 (ZrO 2 ) 0.92 (LSM/YSZ) powder either by physical mixing or by sol–gel process, to produce a porous cathode support for solid oxide fuel cells (SOFCs). The effect of the GDC mixing method was analyzed in view of sinterability, thermal expansion coefficient, microstructure, porosity, and electrical conductivity of the LSM/YSZ composite. GDC infiltrated LSM/YSZ (G-LY) composite showed a highly porous microstructure when compared with mechanically mixed LSM/YSZ (LY) and LSM/YSZ/GDC (LYG) composites. The cathode support composites were used to fabricate the button SOFCs by slurry coating of YSZ electrolyte and a nickel/YSZ anode functional layer, followed by co-firing at 1250 °C. The G-LY composite cathode-supported SOFC showed maximum power densities of 215, 316, and 396 mW cm −2 at 750, 800, and 850 °C, respectively, using dry hydrogen as fuel. Results showed that the GDC deposition by sol–gel process on LSM/YSZ powder before sintering is a promising technique for producing porous cathode support for the SOFCs.

A small, stationary reformer designed as a stand-alone and self-sustaining type was developed for on-site hydrogen (H2) production. We created a compact reformer to produce H2 at a rate of 1 Nm3/h using the previously reported reaction kinetics of steam methane reforming (SMR). Both catalysts for the compact reformer - i.e., 15 wt% and 20 wt% Ni/γ-Al2O3 - showed good activity, with CH4 conversion exceeding 90% at 655 °C and a contact time of 3.0 gcath/mol, which were considered critical thresholds in the development of a small, compact stationary reformer. At an H2 production rate of 1 Nm3/h, the catalyst amount was calculated to be 167.8 g and the reformer length required to charge the catalyst was 613 mm, with a diameter of 1 inch. The CH4 conversion and H2 production rates achieved with the compact reformer using the 20 wt% Ni/γ-Al2O3 catalyst at 738 °C were 97.9% and 1.22 Nm3/h, respectively. Furthermore, a heat-exchanger type reformer was developed to efficiently carry out the highly endothermic SMR reaction for on-site H2 production. This reformer comprised a tube side (in which the catalysts were charged and the SMR reaction took place by feeding the reactants) and a shell side (in which the heat for the endothermic reaction was supplied by CH4 combustion). Reforming activities were evaluated using the active 20 wt% Ni/γ-Al2O3 catalyst, depending on the reactants' gas hourly space velocity (GHSV). The H2 production rate increased as the GHSV increased. Finally, the reformer produced a CH4 conversion of 98.0% and an H2 production rate of 1.97 Nm3/h at 745 °C, as well as a high reactants' GHSV of 10,000 h−1. Therefore, the heat-exchanger type reformer proved to be an effective system for conducting the highly endothermic SMR reaction with a high reactants' GHSV to yield a high rate of H2 production.

Long-term performance degradation of solid oxide fuel cell (SOFC) cathode as a function of gadolinium doped ceria (GDC) interlayer thickness has been studied under accelerated operating conditions. For this purpose, SOFC half-cells with GDC interlayer thicknesses of 2.4, 3.4 and 6.0 µm were fabricated and tested for 1000 h at 900 °C under constant current density of 1 A/cm 2 . The half-cells consisted of lanthanum strontium cobalt ferrite (LSCF)/GDC composite cathode, GDC interlayer, scandia-ceria stabilized zirconia electrolyte and platinum anode as a counter electrode. Area specific resistance (ASR) of the half-cells was continuously measured over time. Higher increase in ASR was observed for the half-cells with GDC interlayer thickness of 2.4 and 6.0 µm, which is attributed to higher strontium (Sr) diffusion towards electrolyte and to cathode/GDC interface delamination coupled with small Sr diffusion, respectively. However, half-cell with GDC interlayer thickness of 3.4 µm showed smaller degradation rate due to highly dense GDC interlayer which had less interfacial resistance and suppressed Sr diffusion towards electrolyte.

The H2O–CO2 electrochemical conversion process in solid oxide coelectrolysis (SOC) cells is potentially an efficient way to reduce CO2 emissions and to store renewable power simultaneously. In this study, a tubular solid oxide coelectrolysis (SOC) cell based on a general electrode support solid oxide fuel cell was fabricated and investigated. We fabricated tubular electrode support tubes through an extrusion process, and the essential SOC cell components, i.e., the electrolyte and the electrode, were then coated onto the surface of a ceramic support consecutively using a vacuum slurry and dip-coating method. The cell was operated while varying the operating temperature, cathode gas flow rate, and the supplied amount of H2O. The results demonstrate that the fabricated tubular SOC cell is a promising candidate for many practical applications, such as technology to mitigate climate change and power fluctuations associated with renewable energy.

The Cr-poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi0.6Fe0.4O3-δ (LNF) has been developed as an alternative cathode material owing to its superior chemical stability in Cr-environments. In this study, we develop a hybrid electrochemical deposition technique to fabricate a nanostructured LNF-GDC (n-LNF-GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction (ORR). For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotubes (CNT)-modified GDC backbone by electroplating, whereas La cations are successively deposited through a chemically assisted electrodeposition method. The proposed method involves a low-temperature (900 °C) calcination step of electrodeposited cations which avoids the need of fabricating a GDC diffusion barrier layer which is otherwise needed to avoid the formation of insulating phases (e.g., La2Zr2O7) when fabricating by conventional high temperature (≥1000 °C) sintering. SEM images reveal a unique nanofibrous structure of the n-LNF-GDC, which is believed to play an instrumental role in enhancing the electrochemical characteristics by increasing the active triple-phase boundaries. An anode-supported SOFC with the n-LNF-GDC cathode showed the superior performance of 0.984 W cm-2 at an intermediate temperature of 750 °C as compared to the power densities of 0.495 and 0.874 W cm-2 produced by LNF-GDC and state of the art LSCF (La0.6Sr0.4Fe0.8Co0.2O3-δ)-GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of the n-LNF-GDC, whereas LSCF exhibited severe degradation. The electrochemically engineered nanostructured n-LNF-GDC can serve as an effective cathode for SOFCs to achieve high performance and long-term durability.

This paper summarizes various mechanisms involved in the degradation of Solid Oxide Fuel Cells (SOFCs) anode. Ni–YSZ is the most commonly used anode material in SOFCs, since it has various advantages such as high catalytic activity for H2, methane reforming, stability and high electronic conductivity. However, this material shows various types of degradations when used at high temperatures for prolonged time periods. The different types include Ni grain growth by sintering, carbon coking, sulfur poisoning and redox cycling. The in-detail mechanism of each type of degradation followed by different controlling mechanisms has been presented in greater detail. Modifications in the Ni–YSZ microstructure and optimization of operating conditions can effectively increase the life time of SOFCs and help in their commercialization.

A segmented-in series (SIS) SOFC consists of segmented unit cells connected in electrical series and shows improved stack efficiency over conventional SOFCs. In this design, a thin interconnect film provides both electrical contact and sealing between the anode of one cell and the cathode of the next; thus, it should have high conductivity and chemical/structural stability in both reducing and oxidizing atmospheres as well as impermeability to gases. Here, we report a dual-layer interconnect film for SIS–SOFCs comprising perovskite-type oxides, Sr 0.7 La 0.2 TiO 3 (exposed to a reducing atmosphere) and La 0.8 Sr 0.2 FeO 3 (exposed to an oxidizing atmosphere). The interconnect film is not only very dense but also highly conductive and stable under SOFC operating conditions; in particular, it shows an area-specific resistance of 19.6 mΩ cm 2 at 800 °C, which is much lower than the generally accepted limit for SOFCs. A flat-tubular SIS–SOFC fabricated using these interconnect films exhibits a power density as high as 340 mW cm −2 , which proves the feasibility of the dual-layer interconnect design.

An interconnect is the key component of solid oxide fuel cells that electrically connects unit cells and separates fuel from oxidant in the adjoining cells. To improve their surface stability in high-temperature oxidizing environments, metallic interconnects are usually coated with conductive oxides. In this study, lanthanum nickelates (LaNiO₃) with a perovskite structure are synthesized and applied as protective coatings on a metallic interconnect (Crofer 22 APU). The partial substitution of Co, Cu, and Fe for Ni improves electrical conductivity as well as thermal expansion match with the Crofer interconnect. The protective perovskite layers are fabricated on the interconnects by a slurry coating process combined with optimized heat-treatment. The perovskite-coated interconnects show area-specific resistances as low as 16.5 - 37.5 m Ω·㎠ at 800℃.

Evaporation of Ni in the form of Nickel Hydroxide (Ni(OH)2) in Solid Oxide Fuel Cell (SOFC) anodes (Ni-YSZ) is one of the major causes of anode degradation. Transition metals such as Fe, Cr and Co can act as sacrificial anodes for Ni, because of lower Gibbs Free Energy values for the formation of their corresponding volatile hydroxides as compared to Ni (OH)2. The transition metals were added to porous Ni-YSZ anode scaffold by infiltration method. Nano-sized particles were sporadically dispersed on the Ni-YSZ surface, confirmed by Scanning Electron Microscopy (SEM). X-Ray Diffraction (XRD) patterns show a very good chemical compatibility between the added metals and Ni-YSZ anodes. Symmetric cells were then prepared and the Area-Specific Resistance (ASR) was monitored at 1000 °C, with a fuel gas containing 25 vol.% H2, 75 vol.% N2, for more than 250 h . To control accelerated evaporation condition of anode, relative humidity in anode gas was fixed at 12 %. The difference in the amount of the added metal before and after long-tern test was determined by EDS analysis. Change in the grain size distribution of Ni particles and Triple Phase Boundary (TPB) density, before and after long term test were calculated by image analysis. Well-defined relations were obtained among ASR change rate determined from electrochemical measurements and grain size distribution, TPB density change rate calculated from image analysis.

Sintering of Ni in solid oxide fuel cell (SOFC) anodes (Ni-YSZ) is a major cause of anode degradation. To reduce this growth rate, several sintering inhibitors (SiC, SiN, Al2O3, AlN, CeO2 and GDC) were added into Ni-YSZ anode using powder methods. The modified anodes were screen printed on YSZ electrolyte to prepare symmetric half-cells and their performance was investigated by long term stability test at high temperature. X-ray diffraction (XRD) analysis showed that the most sintering inhibitors were chemically compatible with anode materials except Al2O3 and AlN. During the long term test, area specific resistance (ASR) was measured at 1000 °C in 25vol% H2 and 75vol% N2 environment. Triple phase boundary (TPB) density was calculated by image analysis techniques before and after operation. A clear relation was found between ASR change rate determined from electrochemical measurements and TPB density change rate calculated from image analysis. Moreover, among the various sintering inhibitors, CeO2 and GDC exhibited the best performance by showing the lowest ASR and TPB density change rates. ASR change rate has been discussed in view of loss in TPB density during operation.

To develop small stationary reformers for on-site H 2 production, the active catalyst and its reaction kinetics were examined in order to study the steam methane reforming reaction. A 20 wt% Ni/γ-Al 2 O 3 was found to be a highly active catalyst within the investigated range of contact time from 1.16 to 3.64 g cat h/mol, which was good for developing the small stationary reformers. BET, XRD, and TEM analysis revealed that the high activity of the 20 wt% Ni/γ-Al 2 O 3 catalyst compared to the 15 wt% Ni/γ-Al 2 O 3 catalyst was strongly ascribed to the high number of Ni metal particles and the ratio of the number of the Ni metal species between the catalysts was calculated to be 1.33. Furthermore, the SMR reaction kinetics of the reversible first-order reaction between reactants and products was applied. This showed that the activation energies obtained by the two catalysts were the same because of the similar pore diffusion and heat transfer restrictions, and the similar Ni particle size in the catalyst pores. Also, it was found that the ratio of the pre-exponential factor was 1.30, which was exactly proportional to the ratio of Ni loading in the catalysts because it was strongly related to the collision density.

Metal oxides with a perovskite structure have attracted great interest in a wide range of technical applications, including solid oxide fuel cells (SOFCs), owing to their unique electronic, chemical, and structural features. Recently, significant efforts have been put into developing simple and cost-effective methodologies to controllably produce perovskite oxide layers for SOFC applications. In this study, we demonstrate the fabrication of a perovskite-type lanthanum cobaltite (LaCoO3) film via a facile electrochemical route and its feasibility as a conductive coating for metallic interconnects in SOFCs. A uniform, dense, and adhesive LaCoO3 film with a thickness of about 1 μm (mixed with a small amount of Co3O4) is formed on a cobalt-coated stainless steel substrate through an electrodeposition process involving nitrate reduction and hydroxide precipitation, followed by thermal conversion in air. The fabricated perovskite film serves as an efficient conductive coating that can mitigate degradation in the electrical properties of metallic interconnects under typical SOFC operating conditions.

High-temperature coelectrolysis of H2O and CO2 by using solid oxide coelectrolysis cells (SOC) is considered to be among the most efficient processes for CO2 conversion as these SOCs can efficiently utilize both heat and renewable electrical energy. One of the key components is the development of highly efficient, modular SOC cells and stacks to further scale up the CO2 conversion process towards industrial applications. In this study, we developed highly efficient and durable flat-tubular solid oxide coelectrolysis cells (FT-SOCs) and investigated the electrochemical performance (I-V, EIS, long-term galvanostatic test) of single cells and a 6-cell bundle for CO2-H2O coelectrolysis to produce syngas with controllable H2/CO ratios. The FT-SOC with an active area of 40 cm2 reached a maximum current density of −3.2A/cm2 at 1.6 V at 800 °C and an H2O/CO2 ratio of 2. In the 6-cell FT-SOC bundle, 90% CO2 conversion was achieved by producing high-quality syngas with flexible H2/CO ratios and stable long-term operation for continuous 500 h. The results of this study show that by using an FT-SOC bundle, scalable and controllable syngas quality could be produced and integrated with the multitude of downstream processes.

Offering fast oxygen reduction kinetics and high electrical conductivities relative to those of ABO3-type perovskite oxides, layered perovskite cathode materials have received considerable attention for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this study, we have investigated the effects of Ni substitution for the Co site in SmBa0.5Sr0.5Co2O5+δ in terms of structural characteristics, electrical properties, and electrochemical performance of SmBa0.5Sr0.5Co2−xNixO5+δ (x = 0, 0.1, and 0.2) in relation to its application as an IT-SOFC cathode material. At the given temperature, the electrical conductivities of SmBa0.5Sr0.5Co2−xNixO5+δ (x = 0, 0.1, and 0.2) decrease with increasing Ni content. For x = 0.1, the lowest ASR value, 0.125 Ω cm2, and the highest single cell performance, 1.78 W cm−2 at 600 °C, are obtained.

The effect of gadolinium-doped ceria (GDC) interlayer on the cathode degradation of solid oxide fuel cell (SOFC) during accelerated current load cycling was investigated. The SOFC half-cells with and without GDC interlayer were prepared and tested under 400 rapid current load cycles. The half-cells consisted of lanthanum strontium cobalt ferrite (LSCF)GDC composite cathode, GDC interlayer, scandia ceria stabilized zirconia (ScCeSZ) electrolyte, and platinum anode as a counter electrode. The area specific resistance (ASR) of the half-cell was measured every 10 current load cycles. The ASR of the half-cell without GDC interlayer greatly increased with current load cycling, which is attributed to the delamination of the cathode/electrolyte interface due to SrZrO3 formation during sintering. On the other hand, the half-cell with GDC interlayer showed a minute increase in ASR during current load cycling due to very small elemental diffusion across the GDC interlayer/ electrolyte interface. These results mean that the GDC interlayer produced high resistance to cathode degradation under the current load cycling due to effective suppression of Sr diffusion across the interface.

A carbon gasified carbon-based fuel cell (CFC) short stack was fabricated and investigated for generating effective carbon fuel cell reactions. Anode-supported tubular CFC cells with a 45 cm 2 active electrode area were used to manufacture the CFC short stack, which was coupled with a dry gasifier induced by a reverse Boudouard reaction. Activated carbon (BET area 1800 m 2 /g) powder was mixed with K 2 CO 3 powder (5 wt.%) and used to fill a dry gasifier as a solid carbon fuel, and pure CO 2 gas was supplied to the gasifier. The CO fuel generated by the reverse Boudouard reaction in the dry gasifier increased the performance of the CFC short stack. The tubular CFC short stack showed a maximum power of 29.4 W at 800 °C. It was operated under a range of operating conditions by changing the operating temperature, flow rate of the pure CO 2 and the thermal cycle operation. The results indicate that the fabricated tubular CFC is a promising power generation system candidate for many practical applications, such as residential power generation (RPG) and stationary power systems.

A unit bundle of a flat tubular segmented-in-series (SIS)-solid oxide fuel cell (SOFC) for intermediate temperature (650–800 °C) operation was fabricated and operated in this study. We fabricated flat tubular ceramic supports through an extrusion process and analyzed the basic properties of the flat tubular ceramic support: the visible microstructure, porosity, mechanical strength, and pore size distribution. After that, we manufactured a flat tubular SIS-SOFC single cell using screen printing and a vacuum slurry dip-coating method for the electrode/interconnect and electrolyte. In addition, to make a unit bundle for a flat tubular SIS-SOFC, five SIS-SOFC single cells with an effective electrode area of 0.8 cm2 were coated onto the surface of the prepared ceramic support and were connected in series using an Ag + glass interconnect between each single SIS-SOFC cell. The performance of the 5-cell unit bundle for a flat tubular SIS-SOFC in 3% humidified H2 and air at 800 °C had a maximum power of 2.5 W.

An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The interconnects can be divided broadly into two categories – ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. This paper provides a short review on ceramic materials for SOFC interconnects. After a brief discussion of the key requirements for interconnects, the article describes basic aspects of chromites and titanates with a perovskite structure for ceramic interconnects, followed by the introduction of dual-layer interconnects. Then, the paper presents protective coatings based on spinelor perovskite-type oxides on metallic interconnects, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation.

Direct carbon fuel cells (DCFCs) have recently attracted great interest because they could provide a considerably more efficient means of power generation in comparison with conventional coal-fired power plants. Among various types of DCFCs under development, a hybrid system offers the combined advantages of solid oxide and molten carbonate electrolytes; however, there is a significant technical challenge in terms of power capability. Here, we report an experimental study demonstrating how anode microstructure influences the power-generating characteristics of hybrid DCFCs. The anode microstructure (pore volume and surface area) is modified by using poly(methyl methacrylate) (PMMA) pore-formers. Polarization studies indicate that cell performance is strongly dependent on the anode surface area rather than on the pore volume. The incorporation of PMMA-derived pores into the anode leads to improved power capability at typical operating temperatures, which is attributed to an enlarged active zone for electrochemical CO oxidation.

Herein, ferritic stainless steel alloys are developed with the dispersion of nano-oxides of reactive elements to improve their oxidation characteristics for solid oxide fuel cell (SOFC) interconnects. Nano-oxides of yttrium, cerium, and lanthanum chromite are homogeneously dispersed in a ferritic stainless steel base powder and specimen pellets are prepared by pressing the powder and sintering it in hydrogen at 1400 °C. The nano-oxide dispersed alloys are tested for oxidation characteristics and electrical properties at 800 °C for 1000 h in air. The results show that the ferritic stainless steel with 3 wt% nano-ceria exhibits significantly improved area-specific resistance (ASR) characteristics. The increase in the ASR for this alloy is found to be only 15 mΩ cm2/kh and is ascribed to the thin dense oxide layer (~0.4 μm), the presence of spinel (MnCrO4) at the outer side of the oxide layer, and the improved oxide layer adherence to the metal substrate. The addition of reactive element oxides altered the oxidation kinetics of the Fe-Cr alloys, thus making nano-oxide dispersed ferritic stainless steel highly durable and most suitable for SOFC interconnects. The oxidation kinetics of the nano-oxide dispersed steel was also discussed as related to cation diffusion.

Nano-size Sm and Nd-doped ceria (SNDC) that has the higher ionic conductivity than that of Gd-doped ceria (GDC) was applied to a commercial cathode of solid oxide fuel cells by using an infiltration process in order to improve electrochemical performance and durability. SNDC nano-particles were synthesized via an in situ sol–gel process on Sr- and Fe-doped LaCoO3 (LSCF) and GDC composite cathode. The microstructure and electrochemical property of the tailored cathode to oxygen reduction reaction were evaluated. It appeared that the application of the SNDC infiltrated cathode decreased the electrode polarization resistance and thus increased the power density, which was attributed for the conductive nanoparticles to expand the reactive sites and promote the cathode reaction.

We developed a new method for the fabrication of La1-xSrxCoO3-GDC composite cathodes in a nanofibrous morphology combining chemically assisted electrodeposition and infiltration techniques for solid oxide fuel cells. Fabrication method of nanofibrous La1-xSrxCoO3-GDC composite cathode for solid oxide fuel cells consists of chemically assisted electrodeposition of La0.6CoO3 into a porous GDC scaffold followed by an infiltration of Sr to produce a La1-xSrxCoO3 phase after a heat treatment at 900 °C. The fabrication method for La1-xSrxCoO3-GDC composite cathode involves following steps: fabrication of a highly porous GDC scaffold on a dense ScCeSZ electrolyte of an anode supported button cell by screen printing a GDC ink containing 30 wt % PMMA pore former and then sintering at 1300 °C; infiltration of 0.5 M cobalt nitrate solution into porous GDC scaffold to act as seed for CNT growth by catalytic chemical vapor deposition of carbon 750 °C using ethylene as carbon source; deposition of La0.6CoO3 by chemically assisted electrodeposition of La and Co from an aqueous electrolyte containing La(NO3)3-6H2O and Co(NO3)2-6H2O; heat treatment of the electrodeposited GDC scaffold is in air at 750 °C for 5 h to remove the CNT; infiltration of strontium and heat treatment at 900 °C to form the La1-xSrxCoO3 phase. A detailed schematic of the fabrication of nanofibrous La1-xSrxCoO3-GDC composite cathode is shown in figure 1. The new fabrication method for nanofibrous La1-xSrxCoO3-GDC composite cathode uses a low fabrication temperature (900 °C) as compared to the conventional sintering which may avoids the formation of secondary phases with ScCeSZ electrolyte. The new fabrication method for nanofibrous La1-xSrxCoO3-GDC composite cathode also provides excellent control over La1-xSrxCoO3 loading and a desired loading can be achieved in a single electrodeposition step. Nanofibrous morphology of new cathode can provide large surface area and can also assist in transport of oxidant through nanoporous structure. The complete anode supported button cells produced by the new fabrication technique have shown a high electrochemical performance (613 mW cm-2 at 750 °C) while using humidified hydrogen as fuel

aInterdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea bSchool of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA cFuel Cell Laboratory, New and Renewable Energy Research Division, Korea Institute of Energy Research, Daejeon 305-343, Korea dDepartment of Mechanical Engineering, Dong-Eui University, Busan 614-714, Korea

Layered perovskites have attracted abundant interest as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their high electrical conductivity and excellent catalytic properties for the oxygen reduction reaction (ORR). However, cobalt related layer perovskite oxides generally suffer from larger thermal expansion co-efficiency (TEC) than that of electrolyte materials. In this study, we have prepared a thin interlayer, SmBa0.5Sr0.5Co2O5+δ (SBSCO) layered perovskite, via pulsed laser deposition (PLD) on a Sr- and Mg- doped LaGaO3 (LSGM) thin film electrolyte to prevent the formation of a micro-gap arising from the thermal mismatch between the SBSCO cathode and LSGM electrolyte. A Samaria-doped ceria (SDC) buffer layer was prepared between the cathodic interlayer and LSGM electrolyte in order to prevent interdiffusion of cations. The cathodic interlayer of SBSCO is helpful for overcoming the thermal mismatch between the SBSCO powder cathode and the LSGM electrolyte, and also shows high power generating properties and small area specific resistance under typical fuel cell operating conditions.

We have investigated the comparable performance of raw and ash-free coal in the operation of a direct carbon fuel cell (DCFC). The various structural and morphological analyses using SEM, TEM, EDX, XPS, XRD, and TGA are carried out to study the distinct physicochemical properties of coals. Due to contained volatile organic compounds, raw coal generates about a two-fold higher fuel cell performance compare to ash-free coal below a reaction temperature of 750 °C. However, over a cell temperature of 900 °C, both of them reach a similar power density of 170 mW cm −2 . In the long-term operation of a DCFC, we observe a distinctly more durable power performance using ash-free coal than that of raw coal.

In present work, optimized the manufacturing process of anode-supported tubular SOFCs cell and stack were studied. For this purpose, we first developed a high performance tubular SOFC cell, and then made electrical connection in series to get high voltage. The gas sealing was established by attaching single cells to alumina jig with ceramic bond. Through these process, we can obtain such high OVP as around 15V, which means that the electrical connection and gas sealing were optimized. Finally we developed a new tubular SOFC stack which shows a maximum power of 65W @ 800℃.

In this study, tubular SOFC unit cell with advanced anode current collector was fabricated to improve the cell performance. First, we prepared two types of single cells having the same manufacture processes such as the same electrolyte, electrode coating condition and sintering processes. And then to compare the developed single cell performance with conventional cells, we changed the anode current collecting methods. From the impedance analysis and I-V curve analysis, the cell performance of advanced cell is much higher than that of conventional cell.

Rechargeable lithium–oxygen batteries have attracted considerable attention due to their high energy density. The critical challenges that limit the practical use of this technology include sluggish kinetics of the electrochemical oxygen reactions on the cathode during discharging and charging. Here, urchin-like α-MnO2 materials decorated with Au and Pd nanoparticles are developed for use as a cathode catalyst for rechargeable Li–O2 batteries with hybrid electrolytes. Au and Pd particles as large as 3–8 nm are uniformly dispersed on the vertically aligned nanorods of α-MnO2. The Au/α-MnO2 and Pd/α-MnO2 catalysts show excellent bi-functional activity for both oxygen reduction and evolution. A rechargeable Li–O2 battery with a hybrid electrolyte is constructed using the nanostructured composite catalysts. Charging and discharging experiments of the batteries indicate that the metal-decorated, urchin-like α-MnO2 can be used as an efficient bi-functional catalyst for rechargeable hybrid Li–O2 batteries.

In a segmented-in-series solid oxide fuel cell (SIS-SOFC), an interconnect (IC) provides electrical contact and sealing between the anode of one cell and the cathode of the next. A metallic silver-glass composite (SGC) is considered a promising alternative to ceramic IC materials in SIS-SOFCs. In this work, a simulation study is performed on a tubular SIS-SOFC to assess the effectiveness of the SGC-IC design and to predict the SOFC performance characteristics for various IC geometries and conductivities. The developed model provides detailed information on cell behavior, such as the internal resistance, the potential/current distribution, and the local gas species concentration. The results demonstrate that the SGC material greatly reduces a potential drop across the IC film. Thus, it provides the following substantial advantages over conventional ceramic IC materials: (i) increased power density and (ii) a larger degree of flexibility in the cell design. Moreover, the validation test, i.e., comparison of the simulated results with the experimental data, indicates that the model could serve as a valuable tool for design optimization to achieve the required SOFC performance.

(La0.8Sr0.2)0.95MnO3−δ (LSM)–Gd0.1Ce0.9O2−δ (gadolinium-doped ceria, GDC) composite cathode material was developed and characterized in terms of chemical stability, sintering behaviour, electrical conductivity, mechanical strength and microstructures to assess its feasibility as cathode support applications in cathode-supported fuel cell configurations. The sintering inhibition effect of LSM, in the presence of GDC, was observed and clearly demonstrated. The mechanical characterization of developed composites revealed that fracture behaviour is directly affected by pore size distribution. The Weibull strength distribution showed that for bimodal pore size distribution, two different fracture rates were present. Furthermore, the contiguity of LSM and GDC grains was calculated with image analysis, and correlation of microstructural features with mechanical and electrical properties was established. Subsequently, an LSM/GDC-based cathode-supported direct carbon fuel cell (DCFC) with Ni/ScSZ (scandia-stabilised zirconia) anode was successfully fabricated via slurry coating and co-firing techniques. The microstructures of electrodes and electrolyte layers were observed to confirm the desired morphology after co-sintering, and a single cell was electrochemically characterized in solid oxide fuel cell (SOFC) and DCFC mode with ambient air as oxidant. The higher values of open-circuit voltage indicated that the electrolyte layer prepared by vacuum slurry coating is dense enough. The corresponding peak power densities at 850 °C were 450 and 225 mW cm−2 in SOFC and DCFC mode, respectively. Electrochemical impedance spectroscopy was carried out to observe electrode polarization and ohmic resistance.

A tubular direct carbon fuel cell based on an anode support solid oxide fuel cell was fabricated and studied. Carbon black and molten carbonate were filled in the inner part of the tubular DCFC cell. The performance of the tubular DCFC cell at 800 oC had a maximum power density of 97 mW/cm2; this result indicates that the fabricated tubular DCFC is a promising candidate for many other practical applications, such as residential power generation (RPG) and auxiliary power unit (APU) systems.

A novel composite cathode material for cathode-supported direct carbon fuel cells (DCFCs) was developed and characterized in terms of phase stability, sintering behavior, electrical conductivity, mechanical strengths and microstructures. It was found that the newly developed LSM/GDC composite provides sufficient level of mechanical strength, electrical conductivity and porosity after sintering at 1300 °C and does not form any undesirable secondary insulating phases. The sintering behavior study showed that GDC inhibits sintering of LSM and thermal expansion coefficient (TEC) is compatible with other cell components. The preliminary results showed that LSM/GDC composite is suitable for cathode support applications.

(Mn,Cu)3O4-based conductive oxides are examined as protective coatings to improve the surface stability of metallic interconnects for solid oxide fuel cells at high temperatures. Nano-sized Mn3 − x Cu x O4 materials with various Cu contents (x = 1.0–1.5) are synthesized and a composition-structure–property relationship is experimentally determined. The Cu content (x) has a significant influence on phase stability as well as sintering, electrical, and thermal expansion characteristics. Thin and dense Mn3 − x Cu x O4 coatings are fabricated on the interconnects (Crofer 22 APU) by a slurry coating process and subsequent heat treatment. The coated interconnects exhibit area-specific resistances as low as 7.1–15.0 mΩ cm2 at 800 °C. The electrochemical cell shows no performance degradation in the presence of the Mn3 − x Cu x O4-coated interconnect. The results indicate that the Mn3 − x Cu x O4 coatings act as an effective barrier to high-temperature oxidation of the metallic interconnects.

The effects of Sr substitution for Ba on the structural properties, oxygen content, electrical conductivity, and electrochemical performance of a cation-ordered perovskite LaBaCo2O5 + δ (LBCO) oxide have been investigated in relation to the application of LBCO as a cathode material for IT-SOFC applications. The electrical conductivity of LaBa0.5Sr0.5Co2O5 + δ (LBSCO) in air decreases with increasing temperature. At the temperature range of 100–850 °C, the electrical conductivity of LBSCO is much higher than that of Sr-free LBCO. The minimum area specific resistance value is achieved at LBSCO composite with 40 wt.% Ce0.9Gd0.1O2 − δ (GDC). The best performance of LBSCO–40GDC based on a GDC electrolyte reaches 1.254 W cm−2 at 600 °C. These data allow us to propose that the LBSCO–40GDC is a good candidate for IT-SOFC applications. Keywords: Solid oxide fuel cells, Cathode, Ordered perovskite, Electrochemical performance

An interconnect in solid oxide fuel cells electrically connects unit cells and separates fuel from oxidant in the adjoining cells. Metallic interconnects are usually coated with conductive oxides to improve their surface stability and to mitigate chromium poisoning of a cathode. In this study, Mn 1.5 Co 1.5 O 4 (MCO) spinel oxides doped with Cu and Ni are synthesized and applied as protective coatings on a metallic interconnect (Crofer 22 APU). Doping of Cu and Ni into MCO improves sintering characteristics as well as electrical conductivity and thermal expansion match with the Crofer interconnect. The dense layers of Cu- and Ni-doped MCOs are fabricated on the interconnects by a slurry coating process and subsequent heat-treatment. The coated interconnects exhibit area-specific resistances as low as 13.9–17.6 mΩ cm 2 at 800 °C. The Cu-doped MCO coating acts as an effective barrier to evaporation and migration of Cr-containing species from the interconnect, thereby reducing Cr poisoning of a cathode.

In this study, successive coating and co-sintering techniques have been used to fabricate LSM/GDC based cathode supported direct carbon fuel cells. The porous LSM/GDC cathode substrate, dense, thin and crack free GDC and ScSZ layers as bi-layer electrolyte, and a porous Ni/ScSZ anode layer was obtained by co-firing at . The porous structure of LSM/GDC cathode substrate, after sintering at , was obtained due to the presence of GDC phase, which inhibits sintering of LSM because of its higher sintering temperature. The electrochemical characterization of assembled cell was carried out with air as an oxidant and carbon particles in molten carbonate as fuel. The measured open circuit voltages (OCVs) were obtained to be more than 0.99 V, independent of testing temperature. The peak power densities were 116, 195 and at 750, 800 and , respectively.

>> The correlation between NiO-YSZ microstructure and its electrical property used for SOFC anode was critically evaluated with image processing and direct measurement techniques. These innovative processing techniques were employed to quantify the contiguity of the anode constituent phase. The calculated contiguitieswere then correlated with electrical conductivity attained from 4-probe DC method. This investigation describedthat contiguity of nickel oxide phases of an anode has a linear relationship with its electrical conductivity. We observed that the contiguity of NiO increased from 0.18 to 0.50 then electrical conductivity attained was significantly increased from 520 S/cm to 1468 S/cm at 900°C. Key words : SOFC(고체산화물연료전지), Microstructure(미세구조), Anode(연료극), NiO-YSZ, Contiguity(연결도), PMMA † Corresponding author : sblee@kier.re.kr [ 접수일 : 2013.6.14 수정일 : 2013.6.28 게재확정일 : 2013.6.30 ]Copyright ⓒ 2012 KHNES 1. Introduction Anode support for a solid oxide fuel cells (SOFCs) is desired to have high electrical conductivity and mechanical stability at its operating temperature range (650 – 1000°C)