Chemical and structural stability of SrTiO3-based materials under SOFC anode operating conditions

Kurzfassung

This work investigates the impact of the exposition to SOFC anode operating conditions on SrTiO3-based compounds, with A-site or B-site substitution: 10 at.% lanthanum or 20 at.% niobium, respectively. Structural and surface stability of the materials after the reaction was examined (post-mortem analysis) using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). These techniques have allowed us to obtain bulk and surface information of the samples which will have a crucial relevance in revealing possible modifications accomplished during system operation. These modifications could play an important role in the degradation of the cell. Structural analysis of materials before and after reduction did not show the formation of secondary phases, indicating a good stability of their crystalline structures for both samples under the conditions employed. In turn, surface study by means of XPS evidenced a surface enrichment in strontium oxide species for raw samples just after annealing. Nevertheless, exposure to the reducing environment caused an accumulation on the surface of the cations that occupy B positions in the perovskite structure oxides. At the same time, lanthanum segregation to the surface after the exposition to the reducing treatment was revealed as well. Achieved identification of the cationic diffusion processes that happened throughout cell operation will help us to understand and eventually minimize the degradation of the anode materials.