Search

Variable renewable energy sources (solar, wind, etc.) are difficult to maintain efficient hierarchical operation and stable power quality from the perspective of the power system. In preparation for this increase in the proportion of renewable energy, it is necessary to prepare counterplan for power system intelligence and flexibility, such as power backup systems, power storage devices, smart control, and demand response. It is expected that control the volatility of renewable energy and supply-demand balance can be solved by producing/storing hydrogen using idle power and generating electricity using fuel cells. High-efficiency SOFC technology that can manage with daily cycle load fluctuations is the best alternative. In this work, the goal is to develop basic technologies for energy network systems that can respond to daily cycle power fluctuations of renewable energy and increase system stability through SOFC cell/stack design and durability enhancement. In this study, in order to secure the ability to cope with the variability of the power system, it is intended to present durability evaluation criteria for simultaneous heat and load cycles. Stack evaluation was performed in the current range of 0.25 ~ 0.50 A/cm2 in the case of the load cycle test and 500 ~ 700 °C in the case of the temperature cycle test.

Electrolyte-Cathode interfaces are life-threatening regions of solid oxide fuel cells where degradation phenomena occur due to chemical interdiffusion. The Buffer layer is inserted between the electrolyte-cathode to limit the cation exchange across the interface. However, state of the art buffer layer coated by screen printing does not fully prevent cation migration which results in the formation of insulating phases such as La2ZrO7 and SrZrO3. Herein, a reliable four-layered (NiO-YSZ, NiO-CeScSZ, CeScSZ, and GDC) thin film-based anode-supported SOFCs with a large-area (12 cm × 12 cm) were fabricated by sequential co-lamination, in which all cell components perform a distinct role to enhance the interfacial connectivity and packing density of electrolytes. This enhanced connectivity with a highly dense electrolyte (5-6 µm) and buffer layer (2-3 µm) was accomplished on the porous anode support without any structural defects. The single cell (144 cm2) showed a power output of 38 W at a total current of 50 A (700 °C). The Post-tested cell had exceptional micro-structural characteristics and excellent interfacial adhesion and retained its structural integrity during steady and unsteady state operation. Also, the formation of insulating phases and decomposition of the cathode were completely prevented, resulting in a remarkable improvement in durability. The cell with a four-layered structure exhibits an extreme low degradation rate of 0.2% kh-1 under 25 A current and 21 dynamic load cycling conditions, which satisfies the strict benchmark of durability for technology commercialization.

Solid oxide cell (SOC) technology is highly admissible for distributed power generation since it enables the most efficient and clean conversion of fuels into energy and heat. SOCs are also regarded as a potential technology for their decisive role in strengthening the hydrogen economy concept by storing renewable energy resources such as green hydrogen and synthetic fuels. In this work, high-performance and durable flat tubular anode-supported SOC is developed for SOC stack applications. NiO-8YSZ composite flat tubular anode support is fabricated by employing an extrusion process. Anode functional layer and electrolyte layers are deposited by the dip-coating technique, whereas the GDC diffusion barrier, LSCF-GDC composite cathode, and Ag-glass composite interconnect layers are fabricated by the conventional screen-printing process. Finally, the prepared flat tubular SOCs possess an active cathode area of 45 cm2 and demonstrated a high-power density of ~430 mW cm-2 at operating current density, voltage, and temperature conditions of 501 mA cm-2, 0.87 V, and 700 °C. During a long-term stability test at 700 °C for 1000 h, the SOC showed a voltage improvement of 0.013 % while operating at a fuel efficiency of 65%. The flat tubular anode-supported SOC’s high performance and durable operation showed its potential for commercial applications in distributed power generation and hydrogen production. Together with the research to further enhance the SOC’s performance and stability, the flat tubular SOC stack design and fabrication are also in progress.

This study improves the mechanical strength and long-term durability of Ni-8YSZ, a commonly used anode support(AS) for Solid Oxide Fuel Cells (SOFC). Instead of Ni-8YSZ, Ni-3YSZ is due to its high mechanical strength and low cost. 3YSZ alone had the disadvantage of degradation of mechanical strength in high-temperature, humidified hydrogen atmospheres due to phase transformation. The addition of nano-ZrO2 and nano-WO3 was expected to improve mechanical strength and long-term durability due to the Hall-Petch equation. For uniform dispersion, NiO and 3YSZ powders were ball-milled for 100 hours, and nano-ZrO2 or nano-WO3 was also added. The powders were sintered at 1400 oC for 5 hours. Sintered specimens were reduced at 750 oC in a hydrogen atmosphere for 8 hours. The reduced specimens were reduced for 500 and 1000 hours, respectively, at 900 oC in a humidified hydrogen atmosphere, which is an accelerated atmosphere. Ni-3YSZ with nano-ZrO2 added had greatly improved mechanical strength and long-term durability.

In the field of food and agriculture, fuel cell-based energy supply technology is gaining much attention for sustainable food systems with carbon neutrality by 2050. Previous studies have focused on the electricity balance using polymer electrolyte fuel cells (PEMFCs) without considering the temperature quality to maintain the environmental conditions required in smart farms. However, this study proposes a system that can provide all four energy sources (electricity, cooling, heating, and CO2) required by smart farms by using solid oxide fuel cells (SOFC), which can utilize high-quality heat. To confirm the feasibility of the proposed idea, we demonstrate the world's first 10 kW-class SOFC-based integrated system for a smart farm in Jinju, South Korea. The system's core components consist of a SOFC system, a hot thermal storage system, a cold thermal storage system, and a CO2 supply system. In this study, the applicability of the proposed system is verified by the experimental results of the effective production of cold and hot heat required by smart farms. In addition, the technical problems encountered during the demonstration are presented. In doing so, we suggest the direction of more economical and sustainable SOFC technology development for smart farm applications.

Since the high configurational entropy-driven structural stability of a multicomponent oxide system was proposed by Rost et al. in 2015, many experiments and simulations have been done to develop new multicomponent oxides.

Solid oxide fuel cells (SOFCs) can generate electricity through an electrochemical conversion of the chemical energy of fuels including hydrogen, hydrocarbons, and biogas because of high operation temperatures. Ammonia has recently been considered as a promising hydrogen carrier that is relatively convenient to store and transport and can be decomposed into hydrogen and nitrogen with no carbon emission via catalytic cracking. Thus, much effort has been made to utilize ammonia as a clean fuel to SOFCs for power generation at high efficiency. This review is aiming at delivering the current progress of developing high temperature ceramic fuel cells fed with ammonia, particularly more focused on the achievements of a direct ammonia fueled SOFC (DA-SOFC) to shed light on the challenges of degrading the performance and durability. The problems are primarily attributed to a lack of rational catalysts, thermal imbalance, and the evolution of nitrides on the components including the Ni based anode, Ni mesh as current collector, and stainless steels of metallic interconnect that are exposed to the ammonia fuel environment incurring microstructural deformations and electrical and electrochemical deteriorations. Lastly, strategic pathways to overcome the inadequate performance and the instability are suggested to accomplish a commercialization of DA-SOFCs.

Solid oxide fuel cell (SOFC) technology has attratced great attention because of higher efficiency, fuel flexibility and eco-friendly stationary power generation system. However, its commercialization is hindered due to the lack of durability and high cost. Herein, a facile and exceptionally reliable 4-layered anode supported SOFCs with a large area (12cm×12cm) was fabricated in a single step co-firing process at 1400 oC, in which tape-casted green films of NiO-YSZ, NiO-1CeScSZ, 1CeSxSZ, and GDC were laminated by isostatic press. The fabrication parameter such as viscosity of the slurries and mechanical strengths of the green films, etc. were optimized. As a result, finely porous anode layer, and highly dense 1CeScSZ electrolyte and GDC buffer layers on a robust porous anode-support were formed successfully. The LSC cathode was screen-printed on the GDC layer. The possibility of mass production of this process are verified through the fabrication of large area cells with an active area 100cm2. The single cell showed high power output of 38 W at total current 50A at 700°C and exhibits low degradation rate of 0.2% kh-1 at 25A for long-term test of 1000 hrs. This facile strategy is time-efficient, reproducible, cost-effective, and highly practical to produce SOFC system satisfying both high-performance and durability.

Solid oxide fuel cells (SOFCs) have attracted great interest as an alternative potential way to become the most efficient and cleanest electrochemical energy conversion system. The commercialization of SOFC technology is hindered by the degradation of component materials. The durable and high performing cathode materials is of immense importance in the durability improvement of SOFCs. Cobaltite type perovskite-based oxides have shown remarkable results but cation migration and formation of the insulating phases within and near the interface between cathode and electrolyte is often observed, which impacts greatly on the electrochemical performance and durability. Therefore, the reaction barrier layer (interlayer) typically made of doped ceria is required between cathode and electrolyte. The stability of this layer due to cations cross-migration between cathode and electrolyte and interdiffusion with electrolyte during fabrication and operation is presently one of the foremost issues (motivation) in the SOFC industry. The chemical and structural disparity associated with the cations migration and interdiffusion could affect the stability and functionality of different layers of SOFC. Understanding the formation of secondary phases and their evolution during the operating lifespan is thought-provoking because of the complexity of the system and the occurrence of numerous other processes simultaneously. In this review paper, the recent progress and advancement in this extent are presented, emphasizing the key driving forces, kinetics, analysis techniques at the micro- and nano-scale levels, and cations migration in extensively studied perovskite-based materials. An insightful understanding of the interdiffusion phenomenon taking place in the cathode/electrolyte/interlayer of SOFCs and control measures are then highlighted which is important to achieve the rational design of highly efficient SOFC with outstanding stable performance.

Solid oxide fuel cells (SOFCs) capable of operating at low to intermediate temperatures (600–750 °C) are vital for the development of robust SOFC power generation systems. In this regard, the oxygen reduction reaction is the rate-limiting step that requires new highly active catalysts or drastic improvements in the cathode microstructure when using the conventional cathode materials. Here, we report a parametric study on electrodeposition for synthesizing nanostructured cathodes for the SOFCs by producing a nanofibrous LaCoO3 cathode. The synthesis of the nanofibrous LaCoO3 involves preparing an electrically conductive template of carbon nanotubes onto the walls of a porous scaffold made of oxide-ion-conducting material followed by co-electrodeposition of La and Co hydroxides from an aqueous mixed-metal nitrate solution. Then, the deposited metal hydroxides are thermally converted to the LaCoO3 perovskite phase through low-temperature calcination performed at 800 °C. LaCoO3 microstructure is optimized as a function of deposition time, applied current, and solution concentration to obtain a nanofibrous morphology. Anode-supported SOFCs with the nanofibrous LaCoO3 cathode are tested for their electrochemical performance and durability. A durable performance obtained during the 200 h stability tests, performed at 750 and 800 °C and under a galvanostatic load of 1 A cm−2, shows the potential of the electrodeposition for producing robust nanostructured SOFC cathodes.

The effects of applied current density on the long-term performance degradation behavior of anode-supported flat-tubular type solid oxide fuel cells (SOFCs) are studied. Durability tests on the anode-supported SOFCs are conducted galvanostatically at 800 °C as a function of applied current density (200, 450, 700 and 1000 mAcm-2) for the duration of 1000 h. The performance degradation during the long-term test assessed by a voltage loss over time greatly increases with higher applied current density. The combined impedance spectroscopy and post-test characterization results show that the accelerated degradation at high current density is due to enhanced Ni particles coarsening in the anode, the formation of insulating phase between cathode and electrolyte, and evolution of fine particles in the cathode. Systematic degradation analysis conducted in the present study provides profound insight into the electrochemical performance decay of the anode-supported flat-tubular SOFCs.

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-gadolinium-doped ceria (GDC) (n-LNF-GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction. For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotube-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. Scanning electron microscopy images reveal a unique nanofibrous structure of 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 La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of 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.

A sluggish oxygen reduction reaction (ORR) is an inveterate challenge limiting the performance of solid-oxide fuel cells (SOFCs). Surface modification through the infiltration of nanoparticles is recognized as a facile technique to enhance the performance of state-of-the-art cathode materials. However, achieving stoichiometric uniformity and thermal stability of infiltrated nanoparticles needs further exploration. In this study, we demonstrate a novel ultrasonic spray infiltration technique to realize the surface modification of a La0.6Sr0.4Co0.2Fe0.8O3−δ/Gd0.1Ce0.9O2−δ composite cathode through the infiltration of a Sm0.5Sr0.5CoO3−δ cathode catalyst. Infiltration by this new technique dramatically reduces the area-specific ohmic and polarization resistances, resulting in twofold enhanced performance of the anode-supported SOFC. In contrast, only a slight increase in the performance is achieved by infiltration through a micropipette. The performance improvement through ultrasonic spray infiltration is attributed to the uniform dispersion of the catalyst in the form of a nanolayer. Moreover, TEM analysis has revealed an epitaxial deposition of Sm0.5Sr0.5CoO3−δ forming a layered perovskite structure at the La0.6Sr0.4Co0.2Fe0.8O3−δ/Sm0.5Sr0.5CoO3−δ interface leading to sustained high-performance outcomes. On the contrary, infiltration by micropipette did not produce such uniform morphology of infiltrated nanoparticles and also indicated elemental segregation giving rise to impure phase formation. The ultrasonic spray infiltration technique proposed here represents a viable and commercializable solution to produce SOFCs with high and stable performances.

The cost-effective fabrication of nanostructured cathodes for solid oxide fuel cells (SOFCs) that catalyze the oxygen reduction reaction effectively is a milestone to be achieved. Infiltration being the conventional method for the fabrication of nanostructured SOFC cathodes requires many infiltration and calcination cycles due to the low catalyst loading per infiltration cycle. Chemically assisted electrodeposition (CAED), a new means of fabricating nanostructured SOFC cathodes in a single loading step, provides the advantage of the simultaneous deposition of multiple cations while using dilute aqueous solutions of readily available salts. In this study, CAED is demonstrated by fabricating a cobalt-free LaNiO3/GDC composite cathode. The LaNiO3/GDC composite cathode prepared by CAED exhibits superior electrochemical properties compared to LaNiO3/GDC composite cathodes fabricated by sintering or self-assembly (a recently introduced low-temperature SOFC cathode fabrication method) approaches. An anode-supported SOFC with a LaNiO3/GDC composite cathode fabricated by CAED shows a high power density of 974 mW cm−2 at an intermediate operating temperature of 750 °C. Low-temperature nano-fabrication by CAED, producing a cathode with a high surface area while avoiding the formation of insulating phases, is believed to play an important role in achieving better SOFC performance.

Tubular solid oxide fuel cells (SOFCs) can be applied in a diverse range of applications, such as critical military missions, auxiliary power units, and portable power generators. In particular, portable power-generation devices may have to meet the requirements of rapid start-up, thermally self-sustaining operation, high thermal shock resistance, and high power density relative to the weight. This work presents the design and performance of a tubular SOFC stack integrated with a hybrid catalytic partial oxidation (CPOX) reformer, an afterburner (A/B), and a heat exchanger (HEX), which enables the stack operation without any external heat source with propane as a fuel. The SOFC stack that was made with four anode-supported tubular SOFCs was assembled with fuel and air chambers. The hybrid COPX reformer that was fed with a pre-mixture of propane and air acted as a start-up burner at the initial period operation to heat the stack up and then a reformer to provide a syngas to the stack when it reached an elevated temperature (700–800 °C). The A/B also provided heat energy to the stack by oxidizing the unreacted fuel and air of the stack anode and cathode exhaust, respectively. The stack first underwent a pre-treatment which reduced the anode support in a programmable furnace. The preliminary electrochemical performance of the stack was assessed while feeding a mixture gas of H2 and N2 as the fuel. Next, the pre-treated stack was integrated with the hybrid reformer, A/B, and HEX and insulated to investigate the thermally self-sustaining rapid operation capabilities by using propane as the fuel. In the integrated SOFC system, the stack reached 780 °C within an hour upon operation and generated 12 W of output power, thus demonstrating the feasibility of the system for portable power generations.

A propane-fueled solid-oxide fuel-cell-based system is an extraordinary type of technology for stationary mobile power generation given that it offers higher efficiency, silent operation and clean conversion of hydrocarbon fuels. In this study, we designed and developed a 150 W-class tubular SOFC power-generation system integrated with a catalytic partial reformer (CPOX) for the propane fuel and heat exchangers with the goal of making a robust and compact system for portable power applications. Micro-tubular SOFC cells were fabricated by ceramic processing and the cells were assembled in the form of a short stack. The CPOX nano-catalyst CeO2 Zr2O3/Pt supported on γ-Al2O3 was prepared and tested for its propane-reforming characteristics under the present operating conditions. The CPOX catalyst was used in the integrated reformer, and the performance of the 150 W-class SOFC power-generation system operating on propane fuel was studied. The rapid startup and temperature sustainability of the short stack were also monitored and stable stack temperatures were achieved within 20 min. Long-term galvanostatic operation of the power-generation system was also conducted to investigate the durability of the system. This study confirms that propane-fueled robust and compact 150 W-class power-generation systems are suitable for portable applications and that the role of efficient CPOX catalysts is crucial for high performance of the stack when operating on propane fuel.

Solid oxide fuel cell (SOFC) poses great potential for stationary power generation. Nevertheless, its full-scale commercialization has lagged due to the inadequacy of long-term durability. Along with diverse background of performance deterioration, the inter-diffusion between the cathode and electrolyte have been identified as a leading fatal factor. Herein, we introduced a robust GDC layer by sequential lamination approach that completely suppresses the detrimental phase of SrZrO3 at electrolyte interface during high temperature operation. This buffer layer is fabricated via green film sequential lamination, in which the anode support, anode functional layer, electrolyte and GDC layers were sequentially co-laminated by iso-static pressing and co-sintered at 1300-1400°C. The enhanced interfacial connectivity and desired packing density of electrolyte and buffer layer were attained by controlling the shrinkages behaviors of each component. Thus, the formation of detrimental secondary phases (SrZrO3) at interface of electrolyte and decomposition of cathode are successfully restrained during fabrication and operation at critical current density. The scale-able and mass production are also confirmed through the fabrication of large area cells (144cm2) having active area 100cm2. The sequentially co-laminated GDC layer exhibited extreme low degradation rate of 0.2%/khr, which fulfils the critical longevity benchmark for commercialization of technology. This work features a cost-effective, scalable, and reproducible method for larger scale production of robust multi-layer anode supported SOFC. Keywords: Durability, Sequential lamination, life expectancy, Detrimental phases, iso-static pressing

The ferritic stainless steel is used as interconnect materials of planar solid oxide fuel cell (SOFC) stack designs. However, the formation of a Cr2O3 oxide layer on the metallic interconnect is inevitable in the SOFC cathodic environment, and the formed layer decreases its electrical conductivity. In this study, we have investigated the effect of manganese (Mn) concentration in the cerium oxide (CeO2) dispersed ferritic stainless steels on oxidation behavior of SOFC metallic interconnect. The mixed powders with various Mn concentrations of 0.5 to 2wt.% were prepared by high-energy ball milling (HEBM), and subsequently were pelletized and sintered at 1400oC in reduction atmosphere. The area specific resistance (ASR) tests were carried out for 1,000 hrs. in air at 800 oC. The material characterization and morphology analysis of the tested samples were performed. After oxidation test, the oxide scale formed on the surface of the sample with Mn was confirmed as a Mn-Cr spinel structure. The thickness of the oxide scales increased with Mn concentration of the samples. Among the various Mn compositions, the sample with 1wt.% Mn had the lowest area specific resistance. The results show that the Mn in the ferritic stainless steel has great influence on the oxidation behavior. In this talk, we will discuss these results as related the requirements of the SOFC metallic interconnect.

Cobaltite-based perovskite materials such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) which have rapid surface activation and mixed ionic and electronic ionic conductivity (MIEC) usually mixed with ionic conducting electrolyte material to lower cathodic polarization resistance. Moreover, decreasing the particulate size of the cathode at nanoscale can effectively enhance the ORR activity of the cathode by extending the electrochemically active sites due to its high surface area. However, due the high surface energy, the nanoparticles easily aggregate before mixing into homogeneous heterophase nanoparticles, resulting in significant coarsening between adjacent particles during high-temperature sintering. In this study, GDC and LSCF-GDC composite powders were synthesized via advance sol-gel method. The physicochemical properties such as sintering behavior, phase stability, etc. of the synthesized nanopowders were investigated. The optimal sintering conditions of GDC nanopowders were evaluated based on the relative density and total conductivity of the sintered GDC pellets. Furthermore, the electrochemical performances of the LSCF-GDC nanocomposite cathodes were measured by the electrochemical impedance spectroscopy (EIS). The microstructural characteristics of the LSCF-GDC nanocomposite cathode were quantified via a 3D reconstruction techniques and related to electrochemical performance of the Ni-YSZ anode supported SOFC single cell.

For anode supported solid oxide fuel cells (SOFCs), the strength and durability of the porous cermet support during long-term operation is critical for the reliability of the cells and stacks. The effect of adding nano-Al 2 O 3 on the long-term durability of the mechanical strength of nickel-yttria stabilized zirconia (Ni-YSZ) based SOFC anode supports was investigated in this study. The SOFC anode support materials, Ni-3YSZ (3 mol% YSZ), Ni-8YSZ (8 mol% YSZ), and nano-Al 2 O 3 added Ni-YSZ composites, were subjected to a long-term degradation test at 900 °C and 30% humidity in an H 2 environment and after 1000 h exposure, the flexural strength, phase, and microstructural changes were analyzed. The results suggest that the addition of nano-Al 2 O 3 to Ni-3YSZ improves the long-term strength and durability of the cermet while its addition to Ni-8YSZ cermet did not show any significant changes in the strength degradation behavior of the Ni-8YSZ based anode support. Further analysis by SEM and XRD shows that the tetragonal to monoclinic phase transformation in partially stabilized zirconia was suppressed due to the addition of nano-Al 2 O 3 in Ni-3YSZ resulting in improved long-term stability and higher mechanical strength. Replacing the Ni-8YSZ anode support with nano-Al 2 O 3 added Ni-3YSZ might significantly reduce the material cost of SOFCs without compromising long-term strength durability, thus bringing SOFCs a step closer to commercialization.

The agglomeration of nickel (Ni) particles in a Ni-cermet anode is a significant degradation phenomenon for solid oxide fuel cells (SOFCs). This work aims to predict the performance degradation of SOFCs due to Ni grain growth by using a simplified approach. Accelerated aging of Ni-scandia stabilized zirconia (SSZ) as an SOFC anode is carried out at 900 °C and subsequent microstructural evolution is investigated every 100 h up to 1000 h using scanning electron microscopy (SEM). The resulting morphological changes are quantified using a two-dimensional image analysis technique that yields the particle size, phase proportion, and triple phase boundary (TPB) point distribution. The electrochemical properties of an anode-supported SOFC are characterized using electrochemical impedance spectroscopy (EIS). The changes of particle size and TPB length in the anode as a function of time are in excellent agreement with the power-law coarsening model. This model is further combined with an electrochemical model to predict the changes in the anode polarization resistance. The predicted polarization resistances are in good agreement with the experimentally obtained values. This model for prediction of anode lifetime provides deep insight into the time-dependent Ni agglomeration behavior and its impact on the electrochemical performance degradation of the SOFC anode.

A solid oxide fuel cell (SOFC) stack requires metallic interconnects to electrically connect unit cells, while preventing fuel from mixing with oxidant. During SOFC operations, chromia scales continue to grow on the interconnect surfaces, resulting in a considerable increase of interfacial resistance, and at the same time, gaseous Cr species released from the chromia scales degrades the cathode performance. To address these problems, in this study, protective Mn2CuO4 coatings are fabricated on metallic interconnects (Crofer 22 APU) via a plasma spray (PS) process. The PS technique involves direct spray deposition of molten Mn2CuO4 onto the interconnect substrate and leads to the formation of high-density Mn2CuO4 coatings without the need for post-heat-treatment. The thickness, morphology, and porosity of the PS-Mn2CuO4 coating are found to depend on the processing parameters, including plasma arc power, gas flow rate, and substrate temperature. The PS-Mn2CuO4 coating fabricated with optimized parameters is completely impermeable to gases and has high adhesion strength on the interconnect substrate. Furthermore, no resistive chromia scales are formed at the coating/substrate interface during the PS process. As a result, the PS-Mn2CuO4-coated interconnects show a very low area-specific resistance below 10 mΩ cm2 at 800 °C in air and excellent stability during both continuous operation and repeated thermal cycling. This work suggests that an appropriate combination of the material and coating process provides a highly effective protective layer for SOFC interconnects.

Effects of applied current density and thermal cycles on the durability of a solid oxide fuel cell (SOFC) cathode have been studied. SOFC half-cells with and without a gadolinium-doped ceria (GDC) interlayer were fabricated and tested for 1000 h at 900 °C under various current densities and thermal cycles. Performance degradation of the half-cells was assessed by increment of the area specific resistance (ASR). Initially, the ASR of the half-cells without the GDC interlayer decreased for around 150 h due to cathode activation and thereafter increased. A rapid increase in the ASR was observed at higher applied current density, which is attributed to delamination of the electrolyte/cathode interface due to the formation of Sr zirconates, and microstructural change in the cathode. However, these adverse effects were prevented by the GDC interlayer. The half-cells with the GDC interlayer exhibited a smaller degradation rate as compared to that without the GDC interlayer. During the thermal cycling test, ASR values of all GDC interlayer thickness cells increased with an increasing number of thermal cycles. The thermally cycled cell with a GDC interlayer thickness of 3.4 μm showed a lower degradation rate due to the dense GDC interlayer, which resulted in less interfacial resistance and prevented elemental diffusion towards the electrolyte. However, the half-cells with GDC interlayer thickness of 2.4 and 4.5 μm showed a higher increase in the ASR due to relatively higher Sr diffusion and delamination of the cathode/GDC interlayer interface, respectively.

In this study, we propose an improvement in the sulfur tolerance of nickel-yttria stabilized zirconia (Ni-YSZ) anodes for solid oxide fuel cells (SOFCs) by simultaneously employing optimized operating conditions and microstructural modifications. An electrolyte supported SOFC is operated at 20 ppm H2S impurity at 750 °C for 20 h degradation and 10 h recovery test. The current cycles with a higher amplitude and small pulse time during the constant current operation are beneficial for the mitigation of sulfur poisoning. The effect of humidity on the sulfur degradation of Ni-YSZ anode is also studied. The synergetic effect of microstructure modification and current cycling conditions improves the sulfur tolerance of Ni-YSZ anode. It has been found that, when an anode with a modified microstructure by infiltrated CeO2 and Yb2O3 nanoparticles is operated on 20 ppm H2S poisoned gas at 10% relative humidity and the optimum pulsed current cycling conditions, about 7 times less degradation of the SOFC performance is observed. This study shows that at lower H2S concentration, a stable operation of a SOFC with minimum degradation can be achieved with the combination of optimization of operating conditions and modification of the anode microstructure.

By using electricity from renewable sources, high-temperature solid oxide co-electrolysis cells (SOCs) can perform advantageous conversion of H2O/CO2 to high-value syngas. In this work, we investigated the performance of tubular solid oxide co-electrolysis cells for the production of syngas by electrochemical conversion of H2O/CO2. The tubular solid-oxide electrolysis cells comprise Ni-yttria stabilized zirconia (Ni-YSZ) based fuel-electrode supported cells, a yttria or scandia-stabilized zirconia (YSZ and ScSZ) electrolyte, and a composite air-electrode of (La0.85Sr0.15)0.9MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). The electrochemical performance of the tubular SOCs for various operating conditions was analyzed using I-V curves, EIS analysis, and gas chromatography. From the results, we confirm the correlation between the operating conditions and the electrochemical performance of the co-electrolysis process in the tubular SOCs. Furthermore, we found that the syngas yield of the ScSZ electrolyte-based SOC cell was better than that of the YSZ electrolyte-based SOC. The results show that using a tubular SOC offered highly efficient conversion of H2O/CO2, with high yield and good-quality syngas.

Water electrolysis based on a solid oxide electrolysis cell (SOEC) has potential to be cost-effective, environmentally friendly, and highly efficient for hydrogen production. There are two types of SOECs, depending on electrolyte materials: oxygen ion conducting SOECs (oxygen-SOECs) and proton conducting SOECs (proton-SOECs). Here we report our new findings in exploring a SOEC based on a mixed-ion conductor that can transport both oxygen ion and proton at the same time, which is denoted as “Hybrid-SOEC”. When BaZr0.1Ce0.7Y0.1Yb0.1O3-δ was used as an electrolyte, the Hybrid SOEC shows the highest efficiency, demonstrating a current density of 3.16 A cm−2 at 1.3 V and 750 °C in 10% humidified hydrogen at hydrogen electrode and 10% humidified air at air electrode. Moreover, the Hybrid SOEC exhibits no observable degradation in performance for more than 60 h of continuous operation, implying a robust system for hydrogen production.

The conversion of CO2 and steam into syngas in a pressurized solid oxide coelectrolysis (SOC) cell is considered one of the most promising pathways towards the production of sustainable fuels. In this study, a high pressure tubular SOC system was designed and developed that can efficiently convert a mixture of steam and CO2 into valuable syngas fuel. Tubular SOC cells based on a Ni-yttria stabilized zirconia (Ni-YSZ) fuel electrode, scandia stabilized zirconia (ScSZ) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Ce0.8Gd0.2O1.9−δ (GDC) composite air electrode were fabricated and tested at various high pressure conditions to determine the electrochemical and syngas production characteristics. The pressurized tubular SOC cell was first operated at the ambient pressure for various inlet gas conditions and the electrochemical performance of the tubular SOC was studied by current-voltage curves combined with electrochemical impedance spectroscopy at different H2O and CO2 mole% in the inlet gas. The pressurized SOC cell was then operated between 1 and 8 bar pressure at 800 °C in both fuel cell and coelectrolysis modes. In the fuel cell mode, the SOC showed a 44.2% increase in the maximum power density to with a pressure increase of 1–8 bar. The increase in the performance of the cell in the fuel cell mode was attributed to the higher open circuit voltage (OCV) and reduced polarization resistance of the electrodes at higher pressures. In the coelectrolysis mode, the pressure dependency of the electrochemical characteristics on the tubular SOC cell was studied and the relation between different parameters of the system and the pressure conditions was derived. It was found that the higher open circuit voltage (OCV) and the reduced polarization resistance resulted in a significant improvement in the performance of the pressurized tubular SOC cell for the production of syngas. A post-test material characterization by electron microscopy did not show any significant degradation in the tubular SOC cell microstructure during the high pressure operation at 8 bar.

In this study, a new method is developed for the fabrication of nanofibrous LaCoO3 (LCO) perovskites as cathodes (oxygen electrodes) for solid oxide fuel cells (SOFCs). The proposed method involves chemically assisted electrodeposition (CAED) of mixed metal hydroxide onto a carbon nanotube (CNT) template, followed by a low-temperature heat-treatment process. The CNT template is first fabricated on porous zirconia-based ion-conducting scaffolds (ICS) by catalytic chemical vapor deposition (CCVD) of C2H4. Perovskite-type LCO is then fabricated on the CNT template by CAED process of mixed La–Co hydroxide combined with thermal conversion of hydroxide to perovskite oxide. The method proposed here allows for the fabrication of LCO perovskites with a unique nanofibrous structure at reduced temperatures (∼900 °C), while avoiding the formation of pyrochlore phases (e.g., La2Zr2O7), which are typically observed during conventional high-temperature sintering processes of LaCoO3 with zirconia-based electrolytes. The new method also provides the precise control needed to achieve desired oxide loadings without the need for repeated deposition-annealing processes. The anode-supported SOFCs with nanofibrous LCO cathodes on zirconia and ceria scaffolds show high and stable electrochemical performance of 0.95 and 1.27 W cm−2, respectively, at 800 °C. In addition to the absence of insulating pyrochlore phases, the unique nanostructure of the LCO cathode is believed to play a beneficial role in improving the electrochemical properties by providing a large number of active reaction sites and by facilitating mass transport through the porous nanofibrous structure.

We developed oxide-dispersed alloys as interconnect materials for a solid oxide fuel cell by adding La2O3 to SUS430 ferritic steels. For this purpose, we prepared two types of La2O3 with different particle sizes and added different amounts of La2O3 to SUS430 powder. Then, we mixed the powders using a high energy ball mill, so that nano-sized as well as micro-sized oxide particles were able to mix uniformly with the SUS430 powders. After preparing hexahedral green samples using uni-axial and cold isostatic presses, we were finally able to obtain oxide-dispersed alloys having high relative densities after firing at 1,400 °C under hydrogen atmosphere. The nano-sized La2O3 dispersed alloys showed properties superior to those of micro-sized dispersed alloys in terms of long-term stability and thermal cycling. Moreover, we determined the optimum amounts of added La2O3. Finally we were able to develop a new oxide-dispersed alloy showing excellent properties of low area specific resistance (16.23 mΩ cm2) after 1000 h at 800 °C, and no degradation after 10 iterations of thermal cycling under oxidizing atmosphere.

Novel nano-oxide dispersed ferritic stainless steel alloys have been developed as potential interconnect materials for solid oxide fuel cells. Nanopowders of CeO 2 and LaCrO 3 were mixed with ferritic stainless steel powder (SUS430) using conventional ball milling. Rectangular pellets were prepared and sintered at 1400 °C in pure H 2 . The microstructural analysis of the sintered pellets showed a uniform distribution of oxide particles. Long-term area specific resistance (ASR) of the pellets was monitored using the four-probe DC method at 800 °C for 1000 h in air, revealing that an increase in the CeO 2 amount from 0.5 to 3 and 5 wt % increased the oxidation resistance of the steel. ASR values as low 32.2 and 5.5 mΩ cm 2 were observed, respectively, for 3 and 5 wt % nano-CeO 2 dispersed SUS430 steel. However, in the case of LaCrO 3 addition, no such relationship between the oxidation resistance and LaCrO 3 concentration was found. This study showed that the dispersed nano-CeO 2 particles effectively reduced the Cr 2 O 3 scale growth, likely by retarding the inward diffusion of oxygen, hence resulting in a high oxidation resistance at the SOFC operating conditions.

For long-term operation of solid oxide fuel cells, ferritic stainless steel-based metallic interconnects with high durability are considered to be one of the most viable materials. However, the formation of a thick chromia layer during the long-term operation results into an increase in the area specific resistance (ASR), ultimately shortening the lifetime of the SOFC [1, 2]. In this study, we developed novel nano-oxide dispersed ferritic steel SUS430 based alloys and tested their long-term performance as interconnect materials for SOFC application. Nano-oxides of CeO2, LaCrO3, and Y2O3 (particle size 2 at 1400 oC for 10 h. Physical properties, microstructural and phase analysis of the sintered nano-oxide dispersed stainless steel alloys were examined before the long-term testing. The developed alloy samples were tested for oxidation characteristics and long-term ASR behavior in air at 800 oC for 1000 h. Post-test analysis of the samples were conducted by SEM, EDS, and XRD techniques. The long-term ASR results show that the dispersion of nano-oxide particles significantly improved the ASR properties of the ferritic stainless steel based alloys. Especially, the total increase in the ASR of nano-CeO2 dispersed ferritic steel during the 1000h long-term test was much less than that of the SUS430, comparable to one of Crofer APU22. LaCrO3 addition also improved the ASR property but Y2O3 dispersion did not so. The dispersed nano-oxides decreased the grain size of the ferritic steel and the oxide particles were distributed at the grain boundaries of the steel. In this work, these electric and oxidation behaviors for long-term test were discussed as related to the microstructure, oxide scale formation mechanism and nano-oxide distribution of the samples. References: [1] L. Niewolak, F. Tietz, W.J. Quadakkers, Interconnects, in: K. Kendall, M. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells 21st Century, 2nd ed., Academic Press, Boston, 2016: pp. 195–254. [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.

Solid oxide fuel cells (SOFCs) require low-cost metallic components for current collection from electrodes as well as electrical connection between unit cells; however, the degradation of their electrical properties and surface stability associated with high-temperature oxidation is of great concern. It is thus important to develop protective conducting oxide coatings capable of mitigating the degradation of metallic components under SOFC operating conditions. Here, we report a conformal bi-layered coating composed of perovskite and spinel oxides on a metallic wire network fabricated by a facile electrodeposition-based route. A highly dense, crack-free, and adhesive bi-layered LaMnO3/Co3O4 coating of ∼1.2 μm thickness is conformally formed on the surfaces of wires with ∼100 μm diameter. We demonstrate that the bi-layered LaMnO3/Co3O4 coating plays a key role in improving the power density and durability of a tubular SOFC by stabilizing the surface of the metallic wire network used as a cathode current collector. The electrodeposition-based technique presented in this study offers a low-cost and scalable process to fabricate conformal multi-layered coatings on various metallic structures.

Layered perovskite oxides have received enormous attention as prospective cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their high electrical conductivities and fast oxygen kinetics. This study focuses on the structural, electrical, and electrochemical properties of layered perovskites, LnBa0.5Sr0.5Co1.5Fe0.5O5+δ (LnBSCF, Ln = Pr, Sm, and Gd), depending on the lanthanide ions in the A-site as a cathode material for IT-SOFCs. Among the evaluated perovskites, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ(PBSCF) showed the highest electrical conductivity, the highest oxygen content, and the highest values of oxygen bulk diffusion coefficient (D*) and surface exchange coefficient (k) measured by isotope oxygen exchange. The composite cathode of PBSCF and gadolinium doped ceria (GDC) is thus found to be the most suitable cathode material for IT-SOFCs among those investigated materials based on its high electrochemical properties and fast oxygen kinetics.

Solid oxide based carbon fuel cells (SO-CFCs) offer clean and efficient utilization of carbon based fuels for energy conversion. In this work, we have realized and operated 100 and 200 W-class solid oxide carbon fuel cell (SO-CFC) short stacks to investigate the fuel supply, electrochemical performance, continuous operation, long-term stability, and scale-up characteristics for SO-CFC based power generation systems. Different configurations for 100 and 200 W class short stacks were employed for integrated Boudouard gasification and carbon fuel supply at the stack level. For the 100 W class SO-CFC short stack, maximum stack power of 80.4, 93.5, and 111.5 W was achieved at 700, 750, and 800 °C, respectively, while the 200 W class SO-CFC short stack produced maximum power of 224.4 W at 750 °C when operated on carbon fuel. Both SO-CFC short stacks were operated continuously at galvanostatic conditions to study the fuel supply conditions and long-term degradation behavior of the tubular cells in the short stacks. A postmortem analysis of the SO-CFC anode was also performed by SEM and XRD to elucidate the reasons for stack performance degradation during relatively longer operation with carbon fuels. Through a detailed analysis of the dry gasification in the integrated gasifier, the electrochemical performance of the SO-CFC stacks, and the post operation diagnosis of the cells, this study provides details on the important challenges in scaling-up SO-CFC technology from a single-cell to a several hundred watt power generation system.