Anode-supported Cells Research Articles

Investigation of the Electrode-Electrolyte Interfaces in Solid Oxide Cells

The interfaces between electrodes and electrolyte are critical locations in a solid oxide cell (SOC). These interfaces originate from the chemical interaction of two different materials during processing, and are therefore very sensitive to the chemical nature of the materials, as well as the thermal history of the cell. On the air side, perovskite air electrodes tend to form insulating zirconates when sintered on stabilized zirconia, the most common electrolyte material. On the fuel side, using an ionic conductor with a different chemical composition as zirconia can lead to pronounced interdiffusion and the formation of new phases.Interlayers of doped ceria are frequently used in order to suppress these undesired chemical reactions between electrodes and stabilized zirconia electrolytes. Prior investigations have focused extensively on the chemical composition of the interface and its consequences for cell performance. The focus of this contribution is the microstructure of the interface, as well as the microstructural development during processing.On the fuel side, the interdiffusion of ceria and zirconia is known to lead to an intermixed phase with decreased conductivity. However, the reduced cell performance of anode-supported cells with Ni-GDC electrodes cannot be explained by an increase in the electrolyte resistance alone. We show that the formation of porosity due to a difference in the diffusion coefficients of ceria and zirconia leads to an increase in the fuel electrode polarization, and investigate possible countermeasures. It is shown that specifically the presence of NiO leads to the formation of porosity at the interface.On the air side, we investigate the role of a dense interdiffusion layer between ceria and zirconia on the air electrode polarization. We confirm that only a dense interdiffusion layer is necessary by using Pr-doped ceria as a barrier layer, which delaminates after sintering and leaves behind a submicron barrier layer. Finally, we investigate the hypothesis that the densification of the barrier layer during air electrode sintering is essential for electrode adhesion and performance.

Status of SOC Development at Chaozhou Three-Circle

Chaozhou Three-Circle (Group) Co., Ltd. (CCTC) is a leading company in developing and manufacturing of electronic and ceramic components. Since more than 19 years ago, CCTC has been focusing on SOFC R&D and manufacturing, covering the complete value chain from powder to power. Based on anode-supported cell technology (ASC in fuel cell mode), the latest C2-stack in planar design using metallic interconnect exhibits a high efficiency of more than 69% (DC, LHV) at 1.5 kW. Long-term stack tests using pipeline natural gas have been conducted for 20,000 hours, with low degradation rates of below 0.4%/kh. In 2022, several 35 kW SOFC CHP systems were demonstrated with C2 stacks, which showed stable performance over 3,000 hours of operation. According to the verification test by Societe Generale de Surveillance S.A., the net AC efficiency of the system reached 64.1%, and the total efficiency was up to 91.2% after 1,000 hours of continuous operation. In parallel to the continuous progressing in SOFC, optimization in cells and stack designs dedicated for SOEC applications were also conducted in recent years. The status of both SOFC and SOEC development at CCTC will be presented.

Performance of solid-oxide fuel cells fed with pure hydrogen and methanol steam reforming products – experimental study

A solid-oxide fuel cell (SOFC) can be fed by fuels other than pure hydrogen, making it suitable for methanol-based economy power cycles. In the reported article, we carried out for the first-time experiments on different types of SOFCs fueled with methanol steam reforming (MSR) products to evaluate and compare the SOFC performance with pure hydrogen. Through this novel comparison, the study provides new insights into the potential of using methanol as a fuel source for SOFCs. Experimental investigation was conducted to evaluate a button SOFC performance operating with MSR products and pure hydrogen under 700, 750, 800, and 850 °C. Two types of SOFC were tested: 1) NiO-YSZ anode-supported cell and 2) the Next-Cell-HP Hionic™ electrolyte-supported cell. The results indicate that the fuel cell fed with MSR products exhibits slight reduction (less than 5%) in power density compared to pure hydrogen. The results were compared with the theoretical values using zero-dimensional simulations. It was found that the change in effective diffusivity causes the main disparity in the SOFC performance when fed with MSR products and hydrogen. Based on the obtained results, we suggest that the SOFC has the potential to be successfully integrated into methanol-based power generating cycles with thermochemical recovery of a waste heat.

Carbon Deposition Mechanisms on Ni-Based Anode for SOFC: A Comparison Between Non-Discharge and Discharge Modes

Carbon deposition mechanisms were studied in Ni-based electrode in non-discharge and discharge modes. A Ni/XSZ pellet(dopant X=Y, Sc) and an anode support cell were used in a thermobalance experiment showed that operating temperature changed carbon tolerance in electrode. The Ni/ScSZ was superior to the Ni/YSZ in carbon deposition at 1173K. Meanwhile, the trend was opposite at 973K. Especially, notable difference was found at S/C(Steam-to-Carbon) ratio = 0.15. Carbon was feromed in Ni/YSZ, wherease carbon deposition was progressed in Ni/ScSZ at S/C=0.15 at 973K. It was shown that electrolyte dopant was a key to enhance carbon tolerance in the electrode. Anode support cell achieved high I-V performance when using H2, whereas that was decreased in CH4/H2O/Ar. Less carbon was found in the Ni/XSZ cermet after discharge mode.

Status of SOC Development at Chaozhou Three-Circle

Chaozhou Three-Circle (Group) Co., Ltd. (CCTC) is a leading company in development and manufacturing of electronic and ceramic components. CCTC has been focusing on SOFC R&D and manufacturing since 2004, covering the complete value chain from powder to power. Based on anode-supported cell technology (ASC in fuel cell mode), the C2-stack in planar design using metallic interconnect exhibits a high efficiency of more than 69% (DC, LHV) at 1.5 kW. Long-term stack tests using pipeline natural gas have been conducted for 20,000 hours, with low degradation rates of below 0.4%/kh.

Direct Deposition of Dense YSZ/Ni-YSZ Thin-Film Bilayers on Porous Anode-Supported Cells with High Performance and Stability

We present an approach for integrating a thin-film bilayer combination comprising a Ni(O)-YSZ nanocomposite layer and a YSZ thin-film electrolyte prepared using pulsed laser deposition into the architecture of porous Ni-YSZ-supported cells. Achieving a minimum bilayer thickness threshold of ~1.5 µm is found to be critical to achieve a high open circuit voltage value, as well as a significant decrease in the ohmic resistance to ~0.06 Ωcm2 at 750 °C and increase in maximum power density to 1.83 W/cm2. Short-term durability tests up to 45 h at a constant potential of 0.8 V showed stable operation with current densities reaching ~1.7 A/cm2. Cells utilizing thin-film bilayers can overcome issues associated degradation in conventionally sintered cells, in terms of maintaining excellent contact with the anode support and significantly suppressing Ni diffusion into the YSZ electrolyte.

Electrochemical performances of LiNiCoMn bifunctional electrode for low temperature solid oxide fuel cells

Lithium transition metal oxides LiNi0.83Co0.11Mn0.06O2 (NCM-83) and LiNi0.8Co0.1Mn0.1O2 (NCM-811) are prepared and acted as cathodes and bifunctional electrodes for low temperature solid oxide fuel cells with H2 and CH4 fuels. The Ni anode-supported cell with NCM-83 cathode exhibits maximum power density (Pmax) of 0.72 W cm−2 with H2 fuel at 600 °C. The symmetric cell with NCM-83 electrodes shows high Pmax of 0.465 W cm−2 with H2 fuel and 0.354 W cm−2 with CH4 fuel at 600 °C. And the Pmax of the cell with NCM-811 as anode and NCM-83 as cathode is 0.204W cm−2 with H2 fuel at 600 °C. The oxygen vacancies in NCM materials are conducive to the rapid oxygen ion conduction of the cathode, and in the anodic reduction atmosphere, the NCM materials will generate Ni/Co active particles in situ, proving the NCM materials can be advanced bifunctional electrode materials for hydrogen oxidation reaction and oxygen reduction reaction at low temperature.

Study of the efficiency of composite LaNi0.6Fe0.4O3-based cathodes in intermediate-temperature anode-supported SOFCs

The paper focuses on the performance comparison of LaNi0.6Fe0.4O3-δ (LNF) composite cathodes comprising Ce0.8Sm0.2O1.9 (SDC) and Bi1.5Y0.5O3 (YDB) electrolytes and La0.6Sr0.4Fe0.8Co0.2O3-δ (LSFC)-SDC cathodes in anode-supported SOFCs with YSZ/GDC electrolyte films obtained by magnetron sputtering. Cathodes with LNF-SDC and LNF-YDB functional layers and the LNF-YDB-CuO oxide collector show a sufficient thermo-mechanical compatibility with the electrolyte. The performance of the anode-supported SOFC with the LNF-YDB/LNF-YDB-CuO cathode, reaches 650 and 1050 mW/cm2 at 700 and 800 °C, respectively, which is significantly higher than that obtained in other works for anode-supported cells with LNF cathodes. The initial total polarization resistance of the NiO-YSZ/YSZ/GDC/LNF-YDB/LNF-YDB-CuO cell, is 0.53 Ω cm2, which is lower than the initial resistance of the similar anode-supported cell with the LNF-SDC/LNF-YDB-CuO cathode (1.35 Ω cm2) and LSFC-SDC cathode with LNF-YDB-CuO (1.71 Ω cm2) and La0.6Sr0.4CoO3 (1.17 Ω cm2) collectors. The most probable reason for the LNF-YDB electrode aging is the growth of Bi-containing particles. Experimental results show that LNF-based composite cathodes are competitive with cobalt-containing cathodes and can be promising for anode-supported SOFCs with decreased operating temperature, that allows extending the material choice for both functional and collector cathode layers.

Detailed Study of Sulfur Poisoning and Recovery of Ni-YSZ-Based Anodes Operating up to 1.8 W cm-2 in a Biogas Fuel

Ni-YSZ (nickel-yttrium-stabilized zirconia) is a common anode for solid oxide fuel cells (SOFCs) because of its excellent catalytic performance and electronic conductivity. It shows that the nickel anode-supported cell exhibits good cell performance in a biogas fuel of 36CH4-36CO2-20H2O-4H2-4CO. Unfortunately, natural biogas fuels often contain sulfur, so using nickel anodes is not always straightforward. This paper investigates the sulfur poisoning and the recovery of BaCe0.7Zr0.1Y0.1Yb0.1O3-δ- (BCZYYb-) (Ce, Y, and Yb codoped barium zirconate) impregnated nickel anode-supported cells operating up to 1.8 W cm-2 in the biogas. The in situ gas analysis reveals that the suppression of the reforming reactions might cause sulfur poisoning in a 4 ppm (v) H2S (hydrogen sulfide) in open circuit conditions, whereas the current degradation in working conditions could be attributed to the deactivation of reforming reactions and catalyst activity. The incidence of water-gas shift reactions is associated with the degradation rate of these two reactions. After removing the H2S, the recovery is accelerated by a steam hydrogen fuel, indicating that steam facilitates the efficient release of sulfur from nickel sites.

Elucidating the performance benefits enabled by YSZ/Ni-YSZ bilayer thin films in a porous anode-supported cell architecture.

Increasing the performance and improving the stability of solid oxide cells are critical requirements for advancing this technology toward commercial applications. In this study, a systematic comparison of anode-supported cells utilizing thin films with those utilizing conventional screen-printed yttria-stabilized zirconia (YSZ) is performed. High-resolution secondary ion mass spectrometry (SIMS) imaging is used to visualize, for the first time, the extent of Ni diffusion into screen-printed microcrystalline YSZ electrolytes of approximately 2-3 μm thickness, due to the high temperature (typically >1300 °C) used in the conventional sintering process. As an alternative approach, dense YSZ thin films and Ni(O)-YSZ nanocomposite layers are prepared using pulsed laser deposition (PLD) at a relatively low temperature of 750 °C. YSZ thin films exhibit densely packed nanocrystalline grains and a remarkable suppression of Ni diffusion, which are further associated with some reduction in the ohmic resistance of the cell, especially in the low temperature regime. Moreover, the use of a Ni-YSZ nanocomposite layer resulted in improved contact at the YSZ/anode interface as well as a higher density of triple phase boundaries due to the nanoscale Ni and YSZ grains being homogeneously distributed throughout the structure. The cells utilizing the YSZ/Ni-YSZ bilayer thin films show excellent performance in fuel cell operation and good durability in short-term operation up to 65 hours. These results provide insights into ways to improve the electrochemical performance of SOCs by utilizing innovative thin film structures in conjunction with commercially viable porous anode-supported cells.

Performance Analysis of Anode-Supported Solid Oxide Fuel Cells: A Machine Learning Approach.

Prior to the long-term utilization of solid oxide fuel cell (SOFC), one of the most remarkable electrochemical energy conversion devices, a variety of difficult experimental validation procedures is required, so it would be time-consuming and steep to predict the applicability of these devices in the future. For numerous years, extensive efforts have been made to develop mathematical models to predict the effects of various characteristics of solid oxide fuel cells (SOFCs) components on their performance (e.g., voltage). Taking advantage of the machine learning (ML) method, however, some issues caused by assumptions and calculation costs in mathematical modeling could be alleviated. This paper presents a machine learning approach to predict the anode-supported SOFCs performance as one of the most promising types of SOFCs based on architectural and operational variables. Accordingly, a dataset was collected from a study about the effects of cell parameters on the output voltage of a Ni-YSZ anode-supported cell. Convolutional machine learning models and multilayer perceptron neural networks were implemented to predict the current-voltage dependency. The resulting neural network model could properly predict, with more than 0.998 R2 score, a mean squared error of 9.6 × 10-5, and mean absolute error of 6 × 10-3 (V). Conventional models such as the Gaussian process as one of the most powerful models exhibits a prediction accuracy of 0.996 R2 score, 10-4 mean squared, and 6 × 10-3 (V) absolute error. The results showed that the built neural network could predict the effect of cell parameters on current-voltage dependency more accurately than previous mathematical and artificial neural network models. It is noteworthy that this procedure used in this study is general and can be easily applied to other materials datasets.

Investigation of the Stability of SOC Stacks By Thermo Cycles

In recent years different research institutes and companies have developed anode supported cells (ASCs) with an LSC ((La,Sr)CoO3δ) oxygen electrode for solid oxide cells (SOCs), which showed an improved performance in comparison to ASCs with an LSCF electrode. Until now, the SOC-stacks by Forschungszentrum Jülich GmbH (FZJ) used ASCs with LSCF on the oxygen side. To minimize undesired effects which might occur due to the inter-diffusion of the constituting cations between adjacent layers, the contact layer on the oxygen side was made of the same LSCF composition.One mayor concern accompanying the use of LSC layers in ASCs and stacks is the thermal expansion coefficient (TEC) of the LSC material, which is almost a factor two higher than the TECs of the other materials of the cells and in the stacks (La0.6Sr0.4CoO3: 20.5·10-6 K-1 [1], La0.6Sr0.4Co0.2Fe0.8O3: 17.5·10-6 K1 [1], 8mol% Y2O3 stabilized ZrO2 (8YSZ): 9.3·10-6 K-1 [2], 30vol% Ni – YSZ cermet: 11.6·10-6 K-1 [3], CroFer 22 APU: 11.6·10-6 K-1 [4]). This large difference may lead to cracking in the layers or in the worst case to delamination between the layers. To meet this concern and demonstrate the stability and robustness of ASCs with LSC on the oxygen side of SOC-stacks performance tests were done with three F-10 stacks by FZJ, each consisting of four repetitive units (RU). The first stack (stack#1) used ASCs with LSCF as electrode and contact layer on the oxygen side and was taken as reference. Then, replacing LSCF by LSC was performed step wise. First only the cells with LSCF were replaced by cells with LSC, leaving all other components of the stack the same, including the LSCF contact layer on the oxygen side (stack#2). In the second step also the contact layer on the oxygen side was manufactured from the same LSC composition (stack#3). Thereby, commercially available cells were used resulting in additional differences between stack#1 (30 µm oxygen electrode, 5 µm oxygen barrier, 10 µm electrolyte, 7 µm fuel electrode and 300 µm fuel electrode support layer) and stack#2 as well as stack#3 (30 µm oxygen electrode, 2 µm oxygen barrier, 3 µm electrolyte, 10 µm fuel electrode and 400 µm fuel electrode support layer). Each stack was characterized in fuel cell mode and investigated by thermo cycles.The performance enhancement of stack#2 due to the introduction of LSC electrodes can be reported. At an operating temperature of 700 °C with 20% humidified hydrogen as fuel, current densities well over 1.2 A/cm² could be obtained at a cell voltage of 700 mV. This is a substantial increase in performance compared to the reference stack, stack#1, with LSCF electrodes on the oxygen side for which only 0.7 A/cm² at 700 mV could be reached. An initial analysis of impedance spectra recorded showed that this improvement could be attributed a lower ohmic resistance, mainly due to the thinner electrolyte layer, and a lower polarization contribution of the ASCs with LSC electrode.After this initial characterization all three stacks were subjected to thermo cycles from the operating temperature of 700 °C down to 200 °C and backwards. After 21 initial thermo cycles both, stack#2 and stack#3 were subjected to even more severe thermo cycles down to below 100 °C and back to 700 °C. From OCV, IV and EIS measurements during each cycle the stability of all three stacks could be shown for up to 50 thermo cycles with voltage losses from 0.2 to 0.5 mV/cycle despite the introduction of LSC layers in two of these stacks.Compared to ASCs with LSCF electrodes on the oxygen side an enhancement in performance was achieved by using ASCs with LSC electrodes and LSC contact layers on the oxygen side in the FZJ F10-design. Also, the stability of performance was demonstrated for up to 50 thermo cycles despite the higher TEC of LSC compared to the other stack materials.

BaCO3 Nanoparticles-Modified Composite Cathode with Improved Electrochemical Oxygen Reduction Kinetics for High-Performing Ceramic Fuel Cells

The effects of the electrochemical oxygen reduction reaction (ORR) on the surface of single-phase perovskite cathodes are well understood, but its potential for use in a complex system consisting of different material types is unexplored. Herein, we report how BaCO3 nanoparticles-modified La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.2Ce0.8O2-δ (LSCF–GDC)-composite cathodes improved the electrochemical oxygen reduction kinetics for high-performing ceramic fuel cells. Both X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies reveal that BaCO3 is stable, and that it does not show any solid-state reaction with LSCF–GDC at SOFCs’ required operating temperature. The electrochemical conductivity relaxation (ECR) study reveals that during the infiltration of BaCO3 nanoparticles into LSCF–GDC, the surface exchange kinetics (Kchem) are enhanced up to a factor of 26.73. The maximum power density of the NiO-YSZ anode-support cell is increased from 1.08 to 1.48 W/cm2 via surface modification at 750 °C. The modified cathode also shows an ultralow polarization resistance (Rp) of 0.027 Ω.cm2, which is ~4.4 times lower than that of the bare cathode (~0.12 Ω.cm2) at 750 °C. Such enhancement can be attributed to the accelerated oxygen surface exchange process, possibly through promoting the dissociation of oxygen molecules via the infiltration of BaCO3 nanoparticles. The density functional theory (DFT) illustrates the interaction mechanism between oxygen molecules and the BaCO3 surface.

Stability of infiltrated cathodes using Pr2NiO4+delta precursor for low-temperature fuel cell applications

The electrochemical performance and stability of infiltrated praseodymium nickelate (PNO) as the cathode for solid oxide fuel cell (SOFC) applications was studied. PNO cathode (Pr2NiO4+δ) was infiltrated into gadolinium-doped ceria (GDC) scaffolds and tested in two different anode-supported cells with tubular geometry: i) tubular cell A with Ni-YSZ support, Ni-YSZ anode functional layer (AFL), and thin (∼7 μm) electrolyte and; ii) microtubular cell B with Ni-YSZ support, without AFL and thick (34 μm) electrolyte. Both cells were stable during 91 h and 260 h of stability testing at 650 °C and experienced a reduction in total polarization resistances. Post-mortem X-ray diffraction (XRD) analysis confirmed PNO's partial transformation into the Pr4Ni3O10 phase with higher electrical conductivity and thermal stability. Improvement in the oxygen reduction reaction was confirmed using DRT analysis. This finding confirms that PNO infiltrated into GDC scaffold can be considered a promising cathode for SOFC applications.

High-stable power generation from low concentration ethanol by catalyst layer modified solid oxide fuel cells

Power generation from ethanol by solid oxide fuel cells (SOFCs) can be a clean and green way to utilize renewable fuel. In this study, the performance of the reduced La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) with anchored Co-Fe nanoparticles is investigated as the electrode in low concentration ethanol for the first time. The cell with the LSCFN as the symmetrical electrodes demonstrates considerable peak power density (0.32 W cm−2) and excellent durability (160 h) at 800 ℃. Moreover, the reduced LSCFN is further applied as a catalyst layer to prevent the Ni‐YSZ anode-supported cell from coking in ethanol fuel. Interestingly, both cells modified with or without this LSCFN layer demonstrate similar output performance in H2. While in ethanol, the catalyst layer modified cell exhibits better coking resistance and stability than the conventional cell, showing 0.97 W cm−2 at 800 ℃, as well as excellent durability for 210 h. The results suggest that combining the Ni-YSZ anode-supported cells with the excellent carbon tolerance of the LSCFN can clean and stable directly generate power from ethanol.

Deconvolution of deterioration of anode-supported cells by chromium poisoning from alumina-forming austenitic stainless steels for balance of plant applications in solid oxide fuel cells

Al2O3-forming austenitic (AFA) stainless steels are potential replacements for the existing balance of plant (BoP) components in solid oxide fuel cells (SOFCs). In this study, chromium (Cr) poisoning of anode supported cells (ASCs) coupled with various alloys was analyzed by the distribution of relaxation times (DRT). The performance deterioration of ASCs was mainly attributed to the increased polarization resistances of chemisorption of oxygen on the cathode and the oxygen diffusion and reaction in the cathode. The superior performance of ASC coupled with AFA alloys was due to the formed continuous alumina layer which can vastly decrease the evaporated gaseous Cr species, thus alleviating the Cr poisoning on the cathode region.

(Invited) Operando Measurement of Redox-Originated Stress in Anode Supported SOFC

Mechanical failures of an anode supported SOFC implies crack formation in the electrolyte, delamination of the electrode/electrolyte interfaces, and contact loss caused by cell deformation. To find the risk of those failures, it is essential to know the complicated behavior of stress state which is affected not only by thermal expansion mismatch but also by chemical change of the components. Structural analyses have been made by various groups by using mechanical property data accumulated in these decades. However, effects of chemical strain are not always taken into consideration, and even when it is properly included in the calculation, actually observed behavior does not always follow the expectation. It is thus important to make in-situ or operando measurement of the stress in cell components. Several in-situ measurement methods were tested, and cosα method of X-ray diffraction was chosen as the best suited method for the operando application [1]. With cosα method, focused X-ray beam irradiates the sample surface with a certain angle to the normal, and the Debye ring is monitored with a co-axially aligned imaging plate. The stress of the sample is estimated from the deformation of the Debye ring from the stress-free state. A specially designed one- or two-chamber cell holder was developed to be used with a portable X-ray stress analyzer (μ-X360s, Pulstec Industrial. Co. Ltd.). Anode-supported cells purchased from multiple sources were analyzed. Measurements were made focusing on the initial reduction of the nickel oxide support, re-oxidation at operation temperatures, and re-oxidation at medium temperature ranges. In the initial reduction at 700˚C, highly compressive stress of about -300 MPa appeared on the electrolyte. It, however, was gradually mitigated down to around -100 MPa in 3 hours. This behavior was explained with the reduction contraction of NiO to Ni and subsequent softening of the support layer. Similarly, as is expected, reoxidation at 700˚C caused the shift of the residual stress to the tensile direction. The transient behavior, however, was different with the cells from different manufacturers. This could be due to the difference of the microstructure of the anode support layer which causes different bending behavior. Another interesting behavior was on the reoxidation of the support at intermediate temperature range. As reported elsewhere [2,3], nickel metal shows oxidation “contraction” when it is oxidized at temperatures around 400˚C to 500˚C, which is accompanied by enhancement of creep deformation rate. The mechanism is interpreted as the formation of slightly oxidized layer which promotes mass transport at the particle surfaces and grain boundaries. It is coupled with the driving force of oxidation that makes the nickel ions move from the inside to the outside. Consequently, neck growth takes place and the separation of the particles are reduced. The same mechanism can work with Ni-YSZ cermet anode and can cause compressive stress on the electrolyte. With this expectation, the reduced cell without cathode was re-oxidized at 400˚C. Actually, increase in the compressive stress was found on the electrolyte. The magnitude of the stress, however, was unexpectedly large as -600 MPa. It is even larger than that on the initial reduction, and the stress mitigation did not work despite the enhanced creep rate. This is probably because the driving force for the contraction is the oxidation that continues to exist before all nickel is re-oxidized. In an actual cell, this large compressive stress may cause buckling delamination of the electrolyte. Reoxidation during shutdown operation must be carefully avoided. As was found in several experiments, unexpected stress state may appear in an actual SOFC operation, which emphasizes the importance of operando analyses.AcknowledgementThis study was supported by the New Energy and Industrial Technology Development Organization (NEDO) .Acknowledgement[1] K. Oshima et al.,ECS Trans. 103(1), 1251-1260 (2021)[2] K. Yashiro et al., 12th European SOFC&SOE Forum, Lucerne, Switzerland, 05-08 July (2016)[3] Y. Morishita et al. , ECS Trans., 91(1) 1979 (2019).

Microwave sintering of high-performance BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolytes for intermediate-temperature solid oxide fuel cells

As a promising electrolyte material for solid oxide fuel cells (SOFCs), BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) often surfers from its high sintering temperature, which causes Ba evaporation and sluggish grain growth, thus reducing the electrical conductivity. In this work, densified BZCYYb electrolytes were fabricated at temperatures as low as 1400 °C using the microwave sintering technique. Comparing with the conventional sintered ones, a temperature decrease of 150 °C is achieved. The Ba evaporation is effectively suppressed, and large grain sizes of ∼4 μm are obtained. The total conductivity for microwave sintered symmetric cell measured in wet air at 700 °C is 3.8 × 10−2 S cm−1, benefiting from both enhanced bulk conductivities by 1–2 times and grain boundary conductivities by 50 times. With the microwave sintered BZCYYb as electrolyte, an anode-supported cell reaches a maximum power density of 0.64 W cm−2 at 700 °C.

Study on the cell configurations and mechanical strength of planar-type solid oxide fuel cells

For solid oxide fuel cells, the following cell configurations have been developed: electrolyte-supported cell (ESC), anode-supported cell (ASC), and metal-supported cell (MSC). In this study, to compare the mechanical load tolerance corresponding to each of the abovementioned cell configurations, the curvature and residual stress were calculated using the Euler–Bernoulli beam theory. The results indicated that when the cells were flattened under the application of an external bending moment, the stress gradient in each layer of the cell disappeared, and the maximum stress in the cell was shown to decrease. Eventually, the failure probability of the cell substrate was demonstrated to take the smallest value. The allowable bending moments for the cell substrates were as follows: −0.17 to 0.08 Nm for ESC, −0.18 to 0.11 Nm for ASC, and −0.29 to 0.40 Nm for MSC at room temperature. Thus, MSC was found to possess the highest bending moment tolerance.

Damage Modeling of Solid Oxide Fuel Cells Accounting for Redox Effects

This work applies a multiscale mechanistic damage model developed for brittle ceramics and implemented in commercial finite element (FE) packages via user subroutines to study progressive damage in solid oxide fuel cells (SOFC) subjected to thermomechanical loading under normal operating and shutdown conditions including redox effects. The damage model captures the micromechanics of stiffness reduction due to material porosity change and microcracking and integrates the as-obtained stiffness reduction law into a continuum damage mechanics (CDM) formulation for the evolution of microcracks up to fracture. The volumetric “swelling” that occurs during redox is treated in constitutive modeling similarly to thermal expansion, but swelling strains are irreversible. This damage model was first validated through predictions of strength and stress-strain response for the SOFC electrode materials. Next, it has been applied to predict the potential for degradation in a generic planar SOFC stack with large active area cells. Multicell stack models were simulated in both co-flow and counter-flow configurations. In addition, a constant temperature redox cycle was also simulated to capture overall cell electrode damage due to volumetric swelling of the nickel (Ni)-based anode in the anode-supported cells.