Blocking Sr-Segregation in Perovskite Cathodes for Solid Oxide Cells by Mn Codoping

Abstract

State-of-the-art electrodes for the oxygen reduction/oxidation reaction typically present durability issues due to the appearance of (surface) precipitates during operation at high temperature. In this work, we employ a combinatorial approach to study the effect of B-site co-doping on the thermal degradation of the La<inf>0.8</inf>Sr<inf>0.2</inf>Mn<inf>x</inf>Co<inf>y</inf>Fe<inf>1-x-y</inf>O<inf>3±δ</inf> family. A continuous library of materials was fabricated in a single process by means of combinatorial pulsed-laser deposition, followed by an annealing at 800 °C for a period of 100 h. The library was then characterized by advanced techniques, involving surface microstructural and chemical analysis and cation profiling throughout the range of compositions. Remarkable stability of Mn-doped materials (and of the parent La<inf>0.8</inf>Sr<inf>0.2</inf>MnO<inf>3-δ</inf> compound) was observed regarding the appearance of segregated surface strontium species, particularly sulfates. This result was correlated with a drastic reduction of the degradation of the Mn-containing La<inf>0.8</inf>Sr<inf>0.2</inf>Mn<inf>x</inf>Co<inf>y</inf>Fe<inf>1-x-y</inf>O<inf>3 ± δ</inf> films during midterm electrochemical performance studies. Complementary density functional theory calculations reveal a direct correlation between cation reducibility (i.e., the O 2p band center position) and surface Sr enrichment. These results indicate that the addition of Mn to La<inf>0.8</inf>Sr<inf>0.2</inf>Mn<inf>x</inf>Co<inf>y</inf>Fe<inf>1-x-y</inf>O<inf>3</inf> electrodes plays a substantial role in the stabilization of strontium segregation phenomena and suggest a general strategy for enhancing perovskite stability based on co-doping and band engineering.