Design and Characterization of Fuel Electrodes for Ammonia-fed Solid Oxide Fuel Cells: Advanced and Innovative Materials by Exsolution

Solid Oxide Fuel Cells (SOFCs) are high-temperature electrochemical devices (operating between 600–1000°C) that efficiently convert chemical energy from fuel into electricity. Hydrogen is the conventional fuel in commercial SOFCs; however, challenges associated with its production, transportation, and storage hinder widespread adoption of this technology to meet growing energy demands. As a result, the use of more readily available fuels like ammonia could facilitate the commercialization of SOFC technology. While Ni/YSZ remains the state-of-the-art electrocatalyst for these applications, it faces performance degradation due to the sintering and oxidation of nickel particles, which affects long-term stability. To address these issues, a novel preparation method called exsolution has emerged over the last 15 years. This approach has been widely studied for synthesizing oxide-supported nanoparticles, focusing on better understanding the mechanisms behind the process to align theoretical designs with actual catalyst performance. The aim of this work is to compare current state-of-the-art materials and identify more active, stable, and alternative electrocatalysts prepared via exsolution for ammonia-fuelled SOFCs. In this study, the exsolution method was explored for the preparation of supported nanoparticle systems with perovskite structure and featured by high catalytic level and enhanced durability. Several materials were synthesized by the citrate route and characterized by X-Ray Diffraction (XRD, using conventional source and synchrotron radiation), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS). The catalytic activity of the materials was studied by a Gas Chromatographer (GC) and the electrochemical properties by Impedance Electrochemical Spectroscopy (EIS). Further insights into the exsolution mechanism were gained from in situ X-Ray diffraction and X-Ray absorption experiments through synchrotron radiation for the Ni and Cu doped La0.45Sr0.45Ti0.90M0.10O3 samples. Similarly, the catalysts described by La0.45Sr0.45Ti0.95-xNi0.05MxO3 with M = 0.05 = Ni, Fe, Co were prepared to examinate several properties of the exsolution such as the catalytic activity, durability and the regeneration. These catalysts were tested for the Dry Reforming of the Methane (DRM) to explore their performances for this reaction that has a great interest in the fuel conversion and pollutant abatement research fields. Same catalysts were also explored for the ammonia conversion reaction and NiFe exsolved NPs reveals to be the most active for this application. Therefore, several electrocatalysts with increasing content of Fe to replace the Ti in the perovskite structure were prepared and described by: (La0.50Sr0.50)1-αTi0.95-xNi0.05FexO3-δ with α = 0.10 or 0.20 and x = 0.05, 0.35, 0.60. These materials were studied both in ammonia conversion reaction and measuring their electrochemical properties. The inclusion of Fe cations in the perovskitic matrix as well as in form of metal in NiFe alloy leads to a reduction of the operating temperature and an enhancement of the NPs stability towards sintering effects.