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.
•A rapid degradation was observed at higher applied current density.•The adverse effects of the applied current were prevented by the GDC interlayer.•Degradation of the cells increased with increasing number of thermal cycles.•Performance degradation of the cells was attributed to Sr diffusion and cathode delamination.
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.
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.
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•LaNiO3 was successfully nanofabricated by chemically assisted electrodeposition.•Chemically assisted electrodeposition enabled LaNiO3 incorporation in a single step.•LaNiO3 showed a uniform morphology throughout the body of the cathode layer.•Nanofabricated LaNiO3 cathode showed a performance of 974 mWcm−2 at 750 °C.•Chemically assisted electrodeposition shows promise for SOFC electrode fabrication.
This paper summarizes various mechanisms involved in the degradation of Solid Oxide Fuel Cells (SOFCs) anode. Ni–YSZ is the most commonly used anode material in SOFCs, since it has various advantages ...such as high catalytic activity for H2, methane reforming, stability and high electronic conductivity. However, this material shows various types of degradations when used at high temperatures for prolonged time periods. The different types include Ni grain growth by sintering, carbon coking, sulfur poisoning and redox cycling. The in-detail mechanism of each type of degradation followed by different controlling mechanisms has been presented in greater detail. Modifications in the Ni–YSZ microstructure and optimization of operating conditions can effectively increase the life time of SOFCs and help in their commercialization.
•Effect of applied current load on the performance degradation of anode-supported SOFC is studied in detail.•Higher applied current density caused fast performance degradation during long-term ...operation.•Ohmic and polarization resistances of the SOFC significantly increased during operation at high applied current density.•Microstructural evolution of SOFC component materials was evaluated and quantified.
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.
State‐of‐the‐art cathodes for solid oxide fuel cells (SOFCs), such as (La,Sr)MnO3–(Y2O3)0.08(ZrO2)0.92 (LSM–YSZ), suffer from sluggish oxygen reduction reaction (ORR) kinetics at reduced ...temperatures, leading to a significant decline in their performance. Herein, we report a tailored SOFC cathode with high ORR activity at intermediate temperatures using a simple but effective approach based on “electrochemical” surface modification. The proposed process involves chemically assisted electrodeposition (CAED) of a metal hydroxide (LaCo(OH)x) on LSM–YSZ surfaces followed by in situ thermal conversion of LaCo(OH)x to perovskite‐type LaCoO3 (LCO) nanoparticles during the SOFC startup. This method facilitates easy loading of the LCO nanoparticles with a precisely controlled morphology without the need for repeated deposition/annealing processes. An anode‐supported SOFC with the LCO‐tailored LSM–YSZ electrode exhibits a remarkably increased power density, approximately 180 % at 700 °C, compared with an SOFC with the pristine electrode as well as excellent long‐term stability, which are attributed to the beneficial role of the CAED‐derived LCO nanoparticles in enlarging the active areas for ORR and promoting oxygen adsorption/diffusion. This work demonstrates that controlled surface tailoring of the cathode by CAED could be an effective approach for improving the performance of SOFCs at reduced temperatures.
Deposit for success: A tailored cathode for solid oxide fuel cells (SOFC) that has high oxygen reduction reaction activity at intermediate temperatures is fabricated by using a simple but effective approach based on “electrochemical” surface modification. An anode‐supported SOFC with (La,Sr)MnO3–(Y2O3)0.08(ZrO2)0.92 (LSM–YSZ) as electrode tailored using LaCoO3 exhibits a remarkably increased power density, approximately 180 % at 700 °C compared with a SOFC with the pristine electrode, as well as excellent long‐term stability.
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.
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•Life-time prediction model of SOFC anode is developed and experimentally validated.•Performance degradation of SOFC due to Ni grain growth is predicted.•Ni particles growth and TPB length reduction fits well with the prediction model.•Results of study discriminate degradation associated with Ni particles coarsening.
The present work aims to predict the degradation in the performance of a solid oxide fuel cell (SOFC) cathode owing to cation interdiffusion between the electrolyte and cathode and surface ...segregation. Cation migration in the (La0.60Sr0.40)0.95Co0.20Fe0.80O3–x (LSCF)–Gd0.10Ce0.90O1.95 (GDC) composite cathode is evaluated in relation to time up to 1000 h using scanning transmission electron microscopy (STEM)–energy-dispersive X-ray spectroscopy (EDXS). The resulting insulating phase formed within the GDC interlayer is quantified by means of the volume fraction using a two-dimensional (2D) image analysis technique. For the very first time, the amount of the insulating phase in the GDC interlayer is quantified, and the corresponding performance degradation of the LSCF cathode is predicted. Mathematical relationships are established for the estimation of degradation due to surface segregation of the cathode. The ohmic resistance between the cathode and the GDC interlayer/electrolyte interface and the polarization resistance of the cathode, characterized by electrochemical impedance spectroscopy (EIS), show an excellent match with the predicted results. The combined degradation analysis and modeling for the cathode lifetime prediction provide a systematic understanding of the time-dependent cation migration and segregation behavior.
In this work, thin-film based 4-layered (NiO-YSZ, NiO-ScCeSZ, ScCeSZ, and GDC) anode-supported solid oxide fuel cell (SOFC) with a large-area (12cm × 12 cm) is fabricated by sequential co-lamination ...and GDC cofiring process to improve the cell durability. This results in a highly dense electrolyte (5–6 μm) and buffer layer (2–3 μm) on the porous anode support. The single cell shows a high-power output of 41.5W at 50A and a maximum power density of 1.6 Wcm−2 at 700 °C. After the current load cycling of 21 times from 25 to 50 A, the large-area cell shows a very small degradation of 0.018V, which is attributed to strong interfacial connectivity between the ScCeSZ electrolyte and GDC buffer layer. Subsequently, the long-term test is carried out for 1000 h at 700 °C under a constant current density of 250 mA/cm2. The cell with a 4-layered structure exhibits the lowest degradation rate of 0.2% kh−1 at 25A current, which satisfies the stringent benchmark of longevity for the commercialization of technology.
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•Large-area SOFC was fabricated by sequential co-lamination and cofiring process.•The large-area SOFC showed a maximum power dentisty of 1.6 W cm-2 at 700 °C.•The cell exhibited exceptional durability with a degradation rate of 0.2% kh−1.•A very thin (2–3 μm) and highly dense GDC buffer layer is fabricated.
Herein, a practical, facile, and ultra-fast technique to fabricate a large-area multi-layered solid oxide fuel cell (SOFC) is reported. In this technique, a total 25 tape-casted green films of ...anode-support layer, anode functional layer (AFL), electrolyte layer, and buffer layer were sequentially co-laminated and co-sintered at 1250 °C using microwave energy (2.45 GHz) in a record short time of 90 min. This process is 16 times faster than the conventional sintering process. The microwave-assisted sintering method enhanced the densification of the electrolyte and buffer layer by directly transferring the heat into the cell material. Despite the incredibly rapid processing time, the microwave-assisted sintered cell showed improved interfacial connectivity of the electrolyte and buffer layer in comparison to the conventionally sintered cell. The large-area (6 cm × 6 cm) SOFC fabricated through this route showed a maximum power density of 1.05 Wcm-2 at 750 °C. Moreover, the cell showed exceptional long-term stability tested under a constant current of 10 A for 500 h at 750 °C. The approach seems appealing in terms of its rapidity, simplicity, economic viability, and applicability in multi-layer energy devices.
