Development of Electrodes for Symmetrical SOFC Based on LSGM-Electrolytes: Performance Under Different Fuels

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Solid oxide fuel cells (SOFCs) are highly versatile energy conversion devices that offer fuel flexibility, they can feed natural gas (CH4), ammonia (NH3), hydrogen (H2), methanol, biogas, synthesis gas, etc. Among these, ammonia and hydrogen, as carbon-free fuels, are two of the significant clean feed gases for the SOFC systems. Methanol and natural gas can also be employed to generate power through SOFCs, yielding significantly lower emissions compared to conventional combustion processes. This fuel adaptability is one of the key advantages of SOFCs, enhancing their potential for sustainable energy applications.In terms of SOFCs geometry, symmetrical cells, which use identical electrodes on both sides of the electrolyte, represent a promising approach to simplifying cell design. This configuration reduces the number of interphases and solves problems such as carbon deposition or sulfur poisoning by electrode regeneration. They can operate in reversible mode by changing the operating atmosphere or potentials of the electrodes. Compared to traditional asymmetric designs, symmetrical SOFCs provide multiple benefits, including simplified fabrication, improved thermo mechanical compatibility between cell components, greater operational stability, and resistance to sulfur poisoning and carbon deposition.In addition, symmetric planar cells are generally the preferable structural design choice, because they can provide high power density and the processing methods are easily scalable. Among the various SOFC manufacturing methods, tape casting is an established technique for manufacturing large ceramic sheets with controlled thickness. This technique simplifies the process and reduces cost by casting the components as a single multilayer sheet that can be sintered in a single step. The major challenge is the sintering of the multilayer tape in a single step, keeping the different desired microstructures while avoiding shrinkage, chemical reactions and interdiffusion between the cell components, which could compromise the microstructural integrity of the final cell.In this work, we have applied tape casting technique to fabricate multilayer ceramics for symmetrical SOFC with the aim of simplifying and reducing the processing steps. The symmetric cells were composed of La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as the electrolyte, of La0.4Ce0.6O2-δ (LDC) as a buffer layer, and Sr(Ti,Fe,M)O3 (where M = Ni and Co) as the electrode material. These cells were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy to evaluate their composition, structural, and microstructural properties.The fuel cell microstructure and chemical composition of the SFTN cell, studied by SEM and EDS, are presented in Figure 1a. The results indicate that the electrolyte/buffer assembly exhibits a dense microstructure, free of cracks or delamination at the interfaces. Additionally, EDS line scans confirmed the absence of significant elemental interdiffusion between the electrode and the electrolyte, preserving the integrity of the interfaces. The STFN electrodes, in contrast, exhibited a porous microstructure, which is essential for efficient gas transport and electrochemical performance.The performance and stability of the STFM electrode were studied under different operating conditions, testing its tolerance to various gaseous environments. The symmetrical cells were characterized using power density measurements and electrochemical impedance spectroscopy (EIS) under H2, CH4, and NH3 atmospheres at temperatures ranging from 600 to 800 °C.When the STFN cell was tested with wet hydrogen (H2 containing 3% H2O), the maximum power density achieved was 69 mW.cm⁻² at 750 °C. When a gas mixture consisting of 54% H2, 43% CH4, and 3% H2O was used as fuel, the power density decreased to 52 mW.cm⁻². In a pure CH4 environment, the cell exhibited an immediate current drop, which was initially attributed to potential carbon deposition on the anode surface. However, Raman analysis revealed no detectable carbon deposition, suggesting that the performance drop may be related to other factors, such as electrode microstructural changes or incomplete methane reforming. Although the performance is lower than that obtained with H2 as fuel, it follows the same trend.When the cell was tested with dry NH3, exhibited a trend similar to that observed with wet hydrogen. Figure 1b presents the chronoamperometry measurements performed at 750 °C under a constant voltage of 0.6 V for both fuels. With dry NH3, small microstructural changes were observed on the STFN electrode. However, its performance is consistent with the decrease of H2 concentration due to the partial cracking of NH3, making the symmetrical STFN cell a promising candidate for NH3 or CH4 direct-fueled SOFC.In conclusion, this study demonstrates that tape casting is an effective technique for fabricating symmetrical SOFCs with well-controlled microstructures and robust electrochemical performance. The symmetrical configuration not only simplifies the manufacturing process but also enhances cell stability and fuel flexibility, making it an attractive alternative to conventional SOFC designs. Figure 1