Anode-supported Solid Oxide Fuel Cells Research Articles

Performance Evaluation of an Anode-Supported SOFC Short-Stack Operating with Different Fuel Blends as Stationary-CHP System

Abstract In the perspective of the transition of gas grids towards hydrogen/natural gas blends or even pure hydrogen, Solid Oxide Fuel Cells “SOFC” could play a crucial role as efficient and clean stationary Combined Heat and Power systems, flexibly operating on different feedstocks. A solid oxide fuel cell short stack is analyzed experimentally under different fuel gas compositions which emulate different gas grid transition scenarios. The testing campaign is defined with the aid of a preliminary system-level simulation which assesses system architecture and operating strategy (off-gas recirculation, external reforming, etc.). Experimental tests (polarization curves and performance/efficiency maps) are run in different operating conditions in terms of fuel utilization and temperature in three gas composition scenarios. 
To assess the efficiency of the SOFC unit under the different feedstock operation, different formulations of stack and system efficiencies are proposed and analyzed, based on the boundary conditions considered for the input/output energy streams. 
Experimental results were key to evaluate the different efficiency definitions proposed; albeit the highest voltage/power is obtained with the 100% H2 scenario, the efficiency may be higher with 100% NG and blend scenarios, due to the lower energy content of the input fuel.

Modeling and characterization of sintered YSZ/NiO porous electrode structural properties using coarse-graining molecular dynamics method

In solid oxide fuel cell (SOFC), sintering of YSZ and NiO powders into porous anode plays a crucial role in determining its overall performance. In this study, a coarse-graining (CG) molecular dynamics (MD) model is developed to capture sintered half-cell composed of porous functional layer with NiO/YSZ particles and dense YSZ ceramic electrolyte layer with applied in anode-supported SOFC. The sintering process is simulated in two stages, i.e., heating process followed by temperature-holding process. This study also explores effects of sintering parameters (e.g., temperature, powder size and material compositions) on structural characteristics, including distribution of sintered triple-phase boundary (TPB) length, porosity, and pore size. It is found that structural properties vary mainly during the heating stage of sintering, while a higher sintering temperature leads to a larger TPB length and a lower porosity, while increasing in diameter ratio of the NiO powders to YSZ powders is advantageous for increasing TPB length, porosity and size pores for promoting electrode electrochemical activity. This work provides a bottom-up approach for potential optimization of SOFC fabrication condition and parameters.

Ru-Ce0.7Zr0.3O2-δ as an Anode Catalyst for the Internal Reforming of Dimethyl Ether in Solid Oxide Fuel Cells.

The development of direct dimethyl ether (DME) solid oxide fuel cells (SOFCs) has several drawbacks, due to the low catalytic activity and carbon deposition of conventional Ni-zirconia-based anodes. In the present study, the insertion of 2.0 wt.% Ru-Ce0.7Zr0.3O2-δ (ruthenium-zirconium-doped ceria, Ru-CZO) as an anode catalyst layer (ACL) is proposed to be a promising solution. For this purpose, the CZO powder was prepared by the sol-gel synthesis method, and subsequently, nanoparticles of Ru (1.0-2.0 wt.%) were synthesized by the impregnation method and calcination. The catalyst powder was characterized by BET-specific surface area, X-ray diffraction (XRD), field emission scanning electron microscopy with an energy-dispersive spectroscopy detector (FESEM-EDS), and transmission electron microscopy (TEM) techniques. Afterward, the catalytic activity of Ru-CZO catalyst was studied using DME partial oxidation. Finally, button anode-supported SOFCs with Ru-CZO ACL were prepared, depositing Ru-CZO onto the anode support and using an annealing process. The effect of ACL on the electrochemical performance of cells was investigated under a DME and air mixture at 750 °C. The results showed a high dispersion of Ru in the CZO solid solution, which provided a complete DME conversion and high yields of H2 and CO at 750 °C. As a result, 2.0 wt.% Ru-CZO ACL enhanced the cell performance by more than 20% at 750 °C. The post-test analysis of cells with ACL proved a remarkable resistance of Ru-CZO ACL to carbon deposition compared to the reference cell, evidencing the potential application of Ru-CZO as a catalyst as well as an ACL for direct DME SOFCs.

Application of Yttria Stabilized Zirconia (8YSZ) and NiO Precursors for Fabrication of Composite Material for Anode-Supported SOFCs

Application of Yttria Stabilized Zirconia (8YSZ) and NiO Precursors for Fabrication of Composite Material for Anode-Supported SOFCs

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

Cubic-stabilized zirconia doped with 8 mol% Y2O3 (8YSZ) is a highly popular electrolyte material for solid oxide fuel cells (SOFCs) due to its exceptional oxide ionic conductivity, which remains consistent across a broad range of oxygen partial pressures. However, previous studies [1,2] have shown that the addition of nickel oxide (NiO) to 8YSZ can expedite the phase transformation process (from cubic to tetragonal) when exposed to a reducing atmosphere at relatively high temperature as 900℃. This phase transformation is closely related to the degradation of 8YSZ's conductivity. Therefore, it is crucial to investigate whether NiO, which should dissolve into the YSZ electrolyte during the co-sintering process with the NiO-YSZ anode at high temperatures, can lead to a similar phenomenon in anode-supported cells (ASCs). Hence, investigating the NiO solid solution phenomenon and its effect on the phase transformation in the YSZ electrolyte of ASCs can offer insights into its degradation behavior.In this study, NiO-YSZ anode support and YSZ electrolyte were co-sintered at 1370℃, 1450℃, and 1550℃, respectively, for 2 hours to fabricate the half-cell samples. Subsequently, these samples were reduced at 900℃ and 700℃, respectively, with a flow of 50ccm dry H2. High-resolution secondary ion mass spectrometry (SIMS) was used to detect the presence of NiO in YSZ, and Raman spectroscopy was used to detect the phase transformation (cubic to tetragonal) occurring in the YSZ.The SIMS results showed that the amount of NiO in the YSZ electrolyte increased with higher sintering temperatures. Moreover, after reducing the cells at 900℃, phase transformation was detected in all samples. However, there was no significant difference among those cells in terms of the degree of phase transformation, which indicated that phase transformation was not accelerated by the increase of dissolved NiO in YSZ. On the other hand, no phase transformation was observed for the cells reduced at 700℃. The mechanism of phase transformation of YSZ in anode-supported SOFCs and its related conductivity degradation will be discussed in the presentation.

Exploring B-site high-entropy configuration of spinel oxides for improved cathode performance in solid oxide fuel cells

High-entropy engineering is an emerging strategy to enhance material properties beyond their individual components. In this study, we synthesized a high-entropy spinel oxide cathode material, Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4, for solid oxide fuel cells (SOFCs) using a solution combustion method. The material exhibits a spinel structure with diverse surface metal valence states and a high concentration of oxygen vacancies. Density functional theory calculations reveal the B-site high-entropy design can significantly improve the oxygen adsorption capability. Electrochemical tests demonstrate that Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4 has superior conductivity and oxygen reduction activity compared to binary spinel oxides. An anode-supported SOFC with Ni(Fe0.2Mn0.2Co0.2Cr0.2Ni0.2)2O4 cathode achieved a peak power density of 583 mW cm-2 at 800 °C. Impedance and relaxation time distribution (DRT) analyses indicate that the oxygen molecular dissociation and oxygen atom diffusion dominates the cathode polarization. This study demonstrates that high-entropy engineering of the B-site in spinel oxides is a promising strategy to optimize cathode performance for SOFCs.

Facile preparation of patterned anode substrate for solid oxide fuel cells by direct-writing 3D printing technology

3D printing has revolutionized solid oxide fuel cell (SOFC) by introducing complicated structure and new functionalities that cannot be realized using traditional preparation process. This work provides guide and insights into the application of direct-writing 3D printing to fabricate the patterned electrolyte|electrode interface for the anode-supported SOFC using 3 mol % yttria-stabilized zirconia-nickel oxide (3YSZ-NiO) as the anode substrate material. The parameters that affected the shaping and performance of SOFC including the rheological properties of 3YSZ-NiO anode paste, the printing parameters, and the heat treatment process of the pre-sintered anode substrate were evaluated. The prepared 3YSZ-NiO paste exhibited a typical shear-thinning characteristic, “yielding” solid-like behavior, and time- and temperature-independent stability performance, which ensured the paste suitable for extrusion while allowing the shape of the printed body to be maintained after extrusion during the direct-writing printing process. The as-prepared anode paste, combined with the obtained values of 0.1 MPa, 100 mm s−1, 100 rpm, and 0.3 mm for printing parameters of the extrusion pressure, the printing speed, the screw speed, and the nozzle diameter, respectively, as well as the devised heat treatment program for the pre-sintered 3YSZ-NiO anode substrate, successfully produced defect-free corrugated anode substrates. The cell made from the as-mentioned anode substrate showed an open circuit voltage of 1.02 V and a maximum power density of 619.44 mW cm−2 at 850 °C, which was comparable to the other identical cells fabricated by traditional and other 3D printing processes. Using the 3D printing process shown here, the preparation time of patterned anode substrate can be reduced and simplified.

Highly dense and ultrathin gadolinia-doped ceria interlayer for enhanced performance of large-area anode-supported solid oxide fuel cell

The fabrication of a highly dense and ultrathin Gd doped ceria (GDC) interlayer on a large-area, porous electrolyte-coated planar anode support using vacuum slurry coating is studied for application in solid oxide fuel cells (SOFCs). The electrolyte-coated planar anode support body is fabricated by tape casting and pre-sintering is performed at 1100, 1150, and 1200 ​°C. The GDC interlayer is coated onto the pre-sintered electrolyte-coated anode support using a vacuum slurry coating process with different immersion times (30–60 ​s). A highly dense and ultrathin GDC interlayer with a thickness of 1.48 ​μm is produced after co-sintering at 1400 ​°C. The 1200 ​°C pre-sintered electrolyte-coated anode support showed a thin and highly dense GDC interlayer which is attributed to a lower shrinkage difference between the coated GDC interlayer and pre-sintered body. The electrochemical performance of a vacuum slurry-coated GDC interlayer cell is 38 ​% higher compared to that of the screen-printed GDC-coated cell at 700 ​°C due to the greatly reduced Ohmic and electrode polarization resistances. The considerable improvement in the performance is attributed to the ultrahigh GDC density which has prevented the secondary phase formation between the cathode and electrolyte. This study presents the economical, scalable, and reproducible process for the fabrication of highly robust GDC interlayer for the large-area planar anode-supported SOFCs.

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

The addition of nickel oxide (NiO) to 8 mol% yttria-stabilized zirconia (8YSZ) accelerates the phase transformation from cubic phase to tetragonal phase when exposed to a reducing atmosphere at relatively high temperatures such as 900 ℃, resulting in the degradation of oxide ion conductivity.In this study, NiO-related phase transformation of 8YSZ electrolyte is investigated for anode-supported cells (ASCs). 8YSZ electrolyte co-sintered with NiO-YSZ anode at high temperatures exhibited NiO dissolution into the 8YSZ electrolyte during the sintering process and the amount of dissolved NiO increased with increased sintering temperatures. After reducing the cells at 900 ℃, phase transformation is observed in the 8YSZ electrolyte and resulted in a decrease of the oxide ion diffusion coefficient (D*). On the other hand, no phase transformation is observed for the cells reduced at 700 ℃for 5 hours.

Modeling and microstructural study of anode-supported solid oxide fuel cells: Experimental and thermodynamic analyses

Developing novel solid oxide fuel cells (SOFCs) with high stability running at low temperatures is an important objective in SOFC science. In the current paper, a comprehensive physics-based microstructure modeling using scanning electron microscope (SEM) image analysis was performed on several anode-support SOFCs operating at low temperatures with high stability. To bridge the gap in the literature regarding an accurate and realistic modeling, a new model was developed based on the variable fuel and air utilization factors and updated microstructure values (e.g., tortuosity, porosity, pore size, grain size). The model accuracy was verified by a thorough point-to-point validation for eight different cells with the configuration of Ni-YSZ (anode), YSZ (electrolyte), and GDC/PNO (cathode). Different temperatures, hydrogen, and air mass flow rates were used, for which an average error of less than 3% in the I-V curves was achieved. The microstructure of the cells, including cathode thickness (15–26 μm), anode-support thickness (350–460 μm), porosity (39 and 43%), grain size (1.1–1.4 μm), and pore radius (0.9–1.1 μm) were varied. Moreover, the effects of the critical operational and design parameters on the overpotential losses and cell performance were studied. The results show that a hydrogen flow rate of 43 sccm was ideal when the cell operated at 0.9 A/cm2 and 700 °C. Moreover, an average anode-support pore radius of 1.75 μm resulted in the best cell performance. It was also concluded that the electrolyte thickness has a higher effect on the cell performance compared to the cathode thickness.

Design and Experimental Investigation of Temperature Control for a 10 kW SOFC System Based on an Artificial Neuronal Network

For a future carbon-neutral energy economy, fuel cells play an important role due their high efficiency. Especially the Solid Oxide Fuel Cell (SOFC) with demonstrated efficiencies beyond 60 % 1 can contribute to reasonable roundtrip efficiencies for hydrogen and e-fuels 2.To match the fluctuating electricity demand in a future electricity grid, dominated by renewable energy sources like wind and photovoltaic, dynamic operation of fuel cells is required. The research has shown that the degradation und therefore the lifespan of Solid Oxide Cell (SOC) stacks shows a significant dependency on the operating conditions and dynamic load changes 3. However, some research suggests that the degradation is not caused by the load changes itself but spatial temperature gradients during load changes 4–6.Therefore, controlling the temperature gradients in the stack during load changes can have a significant impact on the lifespan of SOC stacks. This is typically more dramatically for stacks with larger cell sizes or multiple cells per layer. Furthermore, a tight temperature control allows for running the stack at maximum efficiency without the risk of stack damage due to exceeding temperature limits.In this work the authors designed and experimentally evaluated different controller topologies for fuel cell operation (SOFC) of a reversible solid oxide cell (rSOC) system described previously 7. The controller design incorporates an artificial neuronal network (ANN) for real time state predictions. The training data for the ANN was generated by a dynamic model of this system. This model is implemented in Matlab Simulink and was validated against experimental data. The generated training data consists of about 1,000 simulated days of dynamic system operation with a sample interval of 10 s. Additionally, data for 16,000 different steady state operating conditions of the system were generated.One focus of this work is the robustness of the controller under real world conditions despite inaccuracies of the underlying model and SOC degradation effects over time. To compensate the aging of the stack, the ANN is trained on variable degradation states. The degradation state is then tracked by the controller during operation to maintain an accurate prediction. First system experiments showed promising results in this respect (Fig. 1).Fig 1. Maximum temperature (red) and its setpoint (red, dashed) as well as 8 other temperatures distributed over the stack (black) in response to a given current density profile (green) and the air flow (blue) set by the controller AcknowledgmentsThe authors would like to thank their colleagues at the Forschungszentrum Jülich GmbH, who helped realize this work, and the Helmholtz Society for financing these activities as part of the Living Lab Energy Campus. References(1) Peters, Ro.; Frank, M.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Long-Term Experience with a 5/15kW-Class Reversible Solid Oxide Cell System. J. Electrochem. Soc. 2021, 168 (1), 014508. https://doi.org/10.1149/1945-7111/abdc79.(2) Heydarzadeh, Z.; McVay, D.; Flores, R.; Thai, C.; Brouwer, J. Dynamic Modeling of California Grid-Scale Hydrogen Energy Storage. ECS Trans. 2018, 86 (13), 245–258. https://doi.org/10.1149/08613.0245ecst.(3) Kim, Y.-D.; Lee, J.-I.; Saqib, M.; Park, K.-Y.; Hong, J.; Yoon, K. J.; Lee, I.; Park, J.-Y. Degradation of Anode-Supported Solid Oxide Fuel Cells under Load Trip and Cycle Conditions and Their Degradation Prevention Operating Logic. J. Electrochem. Soc. 2018, 165 (9), F728–F735. https://doi.org/10.1149/2.1391809jes.(4) Hagen, A.; Høgh, J. V. T.; Barfod, R. Accelerated Testing of Solid Oxide Fuel Cell Stacks for Micro Combined Heat and Power Application. Journal of Power Sources 2015, 300, 223–228. https://doi.org/10.1016/j.jpowsour.2015.09.054.(5) Nakajo, A.; Wuillemin, Z.; Van herle, J.; Favrat, D. Simulation of Thermal Stresses in Anode-Supported Solid Oxide Fuel Cell Stacks. Part I: Probability of Failure of the Cells. Journal of Power Sources 2009, 193 (1), 203–215. https://doi.org/10.1016/j.jpowsour.2008.12.050.(6) Jiang, W.; Luo, Y.; Zhang, W.; Woo, W.; Tu, S. T. Effect of Temperature Fluctuation on Creep and Failure Probability for Planar Solid Oxide Fuel Cell. Journal of Fuel Cell Science and Technology 2015, 12 (5), 051004. https://doi.org/10.1115/1.4031697.(7) Peters, R.; Tiedemann, W.; Hoven, I.; Deja, R.; Kruse, N.; Fang, Q.; Blum, L.; Peters, R. Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich. ECS Trans. 2021, 103 (1), 289–297. https://doi.org/10.1149/10301.0289ecst. Figure 1

Performance Evaluation of an Anode-Supported Solid Oxide Fuel Cell Short-Stack Operating with Different Hydrogen-Natural Gas Blends as Stationary Combined Heat and Power System

One of the most promising characteristics of Solid Oxide Fuel Cells (SOFCs) is the possibility to process a wide variety of fuels with high electrical efficiencies, when compared to other types of fuel cells. Considering the prospected transition of the Natural Gas (NG) grid to hydrogen to decarbonize the gas sector, SOFCs could play a crucial role as efficient and clean stationary Combined Heat and Power (CHP) systems.In this work a 15-cell SOFC short-stack (Anode Supported, cell area 121 cm2) has been analysed experimentally under different compositions resembling possible short-, medium- and long-term gas grid scenarios (100% NG, 67%H2 blend in NG and 100%H2) which have been obtained by a preliminary system-level simulation which takes into account operating conditions of the stack and fine-tuning of the system parameters (e.g. Recirculation Rate RR, once through Fuel Utilization FUot, global Fuel Utilization FUtot) to optimize the overall system-level efficiency. Several tests were run at different temperatures (640-710 °C), Fuel Utilization (FU, 50%-70%) and at current loading (15-30 A - part/full load), characterizing in detail the stack response from an electrochemical (polarization curves and short-term stability tests) and chemical conversion point of view (gas chromatographic analyses in OCV and under load), as well as mapping its performances in stationary conditions (output power and stack-level efficiency). The conversion efficiency has been assessed in detail with different approaches at both stack and cell level, considering both once-through (stack-level) and total (system) FU rates.After having confirmed that the stack performances in reference testing conditions are fully aligned to the stack manufacturer data, confirming the test bench setup validity, the foreseen testing campaign has been carried out showing compatibility of the SOFC stack in the investigated conditions. The results show that from a pure performance point of view the 100%H2 composition obtains highest voltage and power at nominal conditions due to losses of the reformate compositions due to lower OCV values and kinetic behaviour of the chemical reaction chains. Instead, from an efficiency point of view the reformate conditions obtain higher stack-level efficiency (72.02% for the 67%H2+NG; 69.45% for the 100%NG) respect to the 100%H2 compositions (68.61%) due to the lower input fuel calorific value. The comparison of the different efficiency definitions provides further insight on the process and system level. By comparing reference testing conditions before and after the testing campaign it is possible to confirm that no significant degradation has occurred at global stack level in all the compositions. Figure 1

Electrochemical Performance and Mechanical Stress Evaluation of Metal-Supported Solid Oxide Fuel Cells Fabricated By Plasma Spray Method

At present, the most common type of SOFC is anode-supported SOFC (AS-SOFC), in which the cell is mechanically supported by the thick fuel electrode layer. Recently, Metal-supported SOFCs (MS-SOFCs) have attracted attention because of their potential for low cost and high mechanical robustness. However, the fabrication process of MS-SOFCs has not been established. The mechanical behavior of the cells under high temperature operation has not been clarified. In this study, we fabricated prototype MS-SOFCs using the plasma spray method. The cell was tested by electrochemical measurements, residual stress measurements, and SEM/EDX to clarify the mechanical behavior of MS-SOFCs under high temperature operation.The layers of anode (NiO-YSZ), electrolyte (LSGM9182), and cathode (LSCF6428) were formed on a metal substrate (SUS430) by atmospheric pressure plasma spraying (APS) to fabricate a single cell of MS-SOFC.Open circuit voltage, AC impedance, and I-V measurements were performed at 600°C, 650°C, and 700°C. The residual stress of LSGM9182 electrolyte was evaluated by cosα method [1] under the cell operation condition using specially designed chamber.The MS-SOFC with thicker electrode layers showed the much lower OCV than that of theoretical. In addition, the electrolyte had vertical cracks between cathode and anode after the 2nd thermal cycle. However the MS-SOFC with thinner electrode layers showed the higher OCV, which was nearly theoretical value, and much better I-V characteristics than the cell with thicker electrodes. Electrochemical impedance measurement revealed the plasma sprayed electrodes showed acceptable performance even though its microstructure was not optimized. The residual stress of LSGM electrolyte in the cell did not change so much during the cell operation. This might be caused by existence of small cracks in the electrolyte layer.This research was financially supported by NEDO.[1] K.Tanaka, Journal of the Society of Materials Science,japan,vol.66,No.7 (2017) 479-487

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

The integration of Solid Oxide Fuel Cells (SOFCs) in hybrid power generation systems offers the opportunity to achieve higher electric efficiencies. In the SOS-CO2 cycle [1], a newly developed cycle for blue power production (i.e., power generated starting from natural gas while capturing CO2), the SOFC cathode is supplied with mixtures of CO2 and O2, up to 79% CO2 molar fraction, while the anode is supplied with a reformate feed, containing H2, CH4, CO, CO2, and water vapour. Aim of this work is to experimentally evaluate the performance and the durability of industrial 5x5 cm2 Ni-YSZ anode-supported SOFCs under the SOS-CO2 cycle conditions, focusing on the effects of the CO2-rich cathodic atmosphere. The cells mounted a LSCF-based (La0.6Sr0.4Co0.2Fe0.8O3) single phase cathode, coated by a current collection layer of LSC (La0.6Sr0.4CoO3). Laboratory tests were performed at 700°C, acquiring polarization (I/V) curves and EIS spectra by means of a Horiba – FuelCon C50 Evaluator test station. Initial investigations with 7% humidified H2 and 21/79 O2/CO2 cathodic mixture revealed 25% power loss compared to the base case with cathodic air. The test showed not only that the loss of performance was stable in time, but also that the power reduction was reversible since the initial performance in air was recovered. The EIS spectra showed an increase of the polarization resistance and of the ohmic resistance upon feeding CO2. This latter observation suggested a reduction of the electronic conductivity of the cathode, compatible with the formation of Sr carbonates on the perovskite surface [2–4]. To assess the performance of the SOFC under the operating conditions of the SOS-CO2 cycle, the anode was supplied with reformate. Compared to the base case with humidified hydrogen and air, the current density at 0.7 V decreased by 37% (490 mA/cm2). When supplying the 21/79 O2/CO2 mixture at the cathode, the current density stabilized at 420 mA/cm2 (Figure 1). Durability tests (over 300 h) at 700°C with reformate and 21/79 O2/CO2 mixture highlighted a moderate decrease of the current density at 0.7 V. After these tests, the cathode was characterized post-mortem with XRD, SEM and Raman to analyse the consequences of the prolonged exposure to CO2. To further quantify the effect of CO2 on the cathode, symmetric button cells were also characterized with EIS, measuring ohmic and polarization resistances. The results suggested that the adsorption of CO2 is reversible and indicated a better suitability of LSCF- compared to LSC-based cathodes for operations with CO2-rich mixtures. Experiments performed between 550 and 700°C at varying CO2 and O2 partial pressures allowed to describe the kinetics of the oxygen reduction reaction and extract its activation energy. Overall, the results provided key elements for the integration of SOFCs in the SOS-CO2 blue power technology.

Electrochemical Performance of Direct Ammonia Solid Oxide Fuel Cell

Recently, as regulations on greenhouse gas emissions have been strengthened in various industries such as automobiles and ships, many studies on alternative energy are being conducted. Hydrogen is a good energy carrier and an environmentally benign fuel because the reaction product is only water or water vapor when it is burned or is used for fuel cells. However, hydrogen suffer from its low specific volume, so the storage issue is still remained unsolved.Ammonia (NH3) has a higher energy density (12.7 MJ/L) than liquid hydrogen (8.5 MJ/L). Liquid hydrogen has to be stored at cryogenic conditions of –253°C, whereas ammonia can be stored at a much less energy-intensive –33°C. In addition, ammonia is much less flammable than hydrogen although it is hazardous to handle.In this study, anode-supported SOFCs consisting of LSCF-GDC cathode, YSZ electrolyte, and Ni/YSZ cermet anode was fabricated and their electrochemical performances (Impedance spectra, J-V curve and cell voltage degradation with operation time) were investigated at 600, 650, and 700°C under ammonia and hydrogen. Regardless of the operating temperature, the power densities of ammonia-fueled SOFCs were almost similar to those of hydrogen-fueled SOFCs. This suggested that the ammonia cracking reaction effectively occurred in the Ni-YSZ anode support. However, the cell voltage at 0.2 A/cm2 was slightly decreased as a function of operating time, which means that the nickel was degraded under ammonia atmosphere. The change of an anode’s microstructure before and after the degradation test will be discussed. In addition, Ni-YSZ catalysts for ammonia cracking were fabricated and their catalytic activity was measured in terms of operating temperature and space velocity using in-line gas chromatography. The phase evolution and microstructure of catalysts were characterized by XRD, SEM and TEM.

Durability Study of Anode-Supported SOFC with Large-Area Fabricated By 4-Layer Sequential Co-Lamination and GDC Co-Firing Process

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 electrolyte-cathode to limit the cation exchange across the interface. However, state of art buffer layer coated by screen printing does not fully prevent cation migration which results in the formation of insulating phases such as SrZrO3. Herein, a reliable four-layered (NiO-YSZ, NiO-CeScSZ, CeScSZ, and GDC) thin film-based anode supported SOFCs with a large-area (12cm×12cm) 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 (5-6µm) and buffer layer (2-3 µm) accomplished on the porous anode support without any structural defects. The single cell (144cm2) showed a power output of 38W at total current 50A (700°C). The Post-tested cell had exceptional micro-structural characteristics, excellent interfacial adhesion and retained its structural integrity during static and dynamic operation. Also, the formation of insulating phases and decomposition of cathode was effectively prevented, resulting in a remarkable improvement in durability. The cell with four-layered structure exhibits an extreme low-degradation rate of 0.2% kh-1 under 25A current and 21 dynamic load cycling conditions, which satisfies the strict benchmark of durability for commercialization of technology. Key word: Durability, interfacial connectivity, insulating phase, sequential co-lamination Figure 1

A new method for manufacturing anode supported solid oxide fuel cells with AFL

In this study, two new methods are proposed for manufacturing anode-supported tubular SOFCs (solid oxide fuel cells) with AFL (anode functional layer). The anode supports are manufactured via thermoplastic extrusion. PEG is used as a secondary binder in the anode tubes and it is selectively removed by water debinding and sweat debinding methods and an AFL layer is obtained with different microstructure and porosity. The Sweat debinding method is suggested as a new method for forming an alternative layer with a different microstructure than the main body of the anode support. Full cells are produced from the altered anode supports. The peak power densities of the cells are measured as 0.38 W/cm2 for Sweat Debound cells, while it is 0.29 W/cm2 for the Water Debound cells.

Direct-methane anode-supported solid oxide fuel cells fabricated by aqueous gel-casting

Direct methane Solid Oxide Fuel Cells (SOFCs) operated under catalytic partial oxidation (CPOX) conditions are investigated, focusing on the processing of the anode support and the anode deactivation caused by carbon deposition. Anode-supported SOFCs based on gadolinium-doped ceria (GDC) electrolyte, and NiO-GDC anode support were fabricated by the gel-casting method. Suitable aqueous slurries formulations of NiO–GDC were prepared, starting NiO-GDC nanocomposite powders, agarose as gelling agent and rice starch as pore former. Electrochemical and mechanical tests evidenced that the support of 550 ± 50 µm thickness and 10 wt% pore former is a good candidate for direct-methane SOFCs. The cells operating under stoichiometric conditions of CPOX reached a performance of 0.64 W·cm−2 at 650 ºC, a very close value to that measured under humidified hydrogen (0.71 W·cm−2). The best electrochemical stability of the cell is achieved at a CH4/O2 ratio of 2.5, showing no evidence of carbon deposition and reducing nickel re-oxidation significantly.

An Anode-Supported Solid Oxide Fuel Cell (SOFC) Half-Cell Fabricated by Hybrid 3D Inkjet Printing and Laser Treatment

A NiO-10YSZ/10YSZ half-cell for anode-supported solid oxide fuel cells (SOFCs) was fabricated using 3D inkjet printing and layer-by-layer laser treatment of printing compositions followed by thermal sintering by a co-firing method. The optimal granulometric composition and rheological characteristics of the printing compositions to fabricate the NiO-10YSZ (60:40 wt.%) anode support, NiO-10YSZ (40:60 wt.%) anode functional layer (AFL), and 10YSZ electrolyte were determined. Effects of the pore former and laser post-treatment on the morphology of the as-prepared anodes for the manufacture of SOFC anode supports were studied, and the optimum laser exposure for hybrid 3D printing was determined. A mechanism of influence of the exposure of laser post-treatment on the morphology of the NiO-10YSZ anode supports has been proposed. The mass content of 10YSZ and the number of layers were shown to affect the surface microstructure and the thickness of the thin-film electrolytes deposited on the surface of the anode supports. The hybrid inkjet 3D printing offers great opportunities as it allows a one-pot procedure to fabricate a NiO-10YSZ/10YSZ SOFC half-cell for SOFC anode supports.

Solid Oxide Fuel Cells with Magnetron Sputtered Single-Layer SDC and Multilayer SDC/YSZ/SDC Electrolytes.

Samarium-doped ceria (SDC) is considered as an alternative electrolyte material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because its conductivity is higher than that of commonly used yttria-stabilized zirconia (YSZ). The paper compares the properties of anode-supported SOFCs with magnetron sputtered single-layer SDC and multilayer SDC/YSZ/SDC thin-film electrolyte, with the YSZ blocking layer 0.5, 1, and 1.5 μm thick. The thickness of the upper and lower SDC layers of the multilayer electrolyte are constant and amount to 3 and 1 μm, respectively. The thickness of single-layer SDC electrolyte is 5.5 μm. The SOFC performance is studied by measuring current-voltage characteristics and impedance spectra in the range of 500-800 °C. X-ray diffraction and scanning electron microscopy are used to investigate the structure of the deposited electrolyte and other fuel cell layers. SOFCs with the single-layer SDC electrolyte show the best performance at 650 °C. At this temperature, open circuit voltage and maximum power density are 0.8 V and 651 mW/cm2, respectively. The formation of the SDC electrolyte with the YSZ blocking layer improves the open circuit voltage up to 1.1 V and increases the maximum power density at the temperatures over 600 °C. It is shown that the optimal thickness of the YSZ blocking layer is 1 µm. The fuel cell with the multilayer SDC/YSZ/SDC electrolyte, with the layer thicknesses of 3/1/1 µm, has the maximum power density of 2263 and 1132 mW/cm2 at 800 and 650 °C, respectively.