Rational Development of IT-SOFC Electrodes Based on the Nanofunctionalization of La_0.6Sr_0.4Ga_0.3Fe_0.7O₃ with Oxides. PART 1: Cathodes by Means of Iron Oxide

Solid oxide fuel cells (SOFCs) are electrochemical devices capable of converting and storing energy in a sustainable and efficient way. The decrease in the operating temperature could be of great help in diffusion. The use of nanocomposites is a smooth way to design materials with many advanced functionalities that could not be reached at the same time with only a single component. Our aim is in developing LSGF-based nanocomposites by depositing oxide nanoparticles in order to improve the electrocatalytic performances. In the first part, we focused on the cathode, and iron oxide was deposited by wet impregnation. The composite powders have been extensively characterized by means of XRD, XPS, N2 asdorption, SEM, EDX, TPR, and O2-TPD, and the results were compared with those obtained for LSGF. The supporting perovskite stabilizes Fe(II), and a deep interaction between the deposited oxides and the perovskite surface is evident. Fe was observed to diffuse inside perovskite during thermal treatment, and this phenomenon greatly affects the oxygen vacancies, mobility, and exchange capability. Focusing on the IT-SOFCs, symmetric cells of the type FeOx + LSGF/CGO/LSGF + FeOx have been prepared starting from the nanocomposite powder. The effect of the SOFCs’ preparation conditions (temperature and atmosphere) on the electrode and on the cell has been assessed and compared, also through in situ high-temperature XRD, simulating, on the electrode powder, the same treatment necessary to prepare the cell. The use of nanocomposites powders as a starting point for electrodes allows us to significantly modify the electrochemical performance. A thin, Sr/Fe-rich foil forms on the surface of the electrode during SOFC thermal treatment and greatly improves the electrochemical behavior of the FeOx + LSGF cathode. The electrochemical results are encouraging for future applications in SOFCs because the nanocomposite has an ASR of 2.1 Ω·cm2 at 620 °C, only one-third of that of the LSGFs under the same conditions.