How Synthesis Conditions Define the Quality of the Perovskite Oxide Electrocatalysts

Rationalizing synthesis conditions in perovskite oxides is difficult due to the complex interplay of several factors such as precursor size and composition, presence of doping elements and formation of metastable intermediate phases. In our study, we track morphological and chemical state of La0.8Sr0.2CoO3-δ particles on the meso- and nano-scale as a function of time and temperature using transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM). We explore the entire transformation of the electrocatalyst particles, from the precursor state to the formation of nanoparticles and eventual growth into mesoscale agglomerates. Our experiments show how the initial compositional non-uniformity first translates into intermediate phases and then results in the formation of the perovskite phase. Importantly, we notice that the segregation of Sr shows up already at 800°C and is temperature-dependent. Our results indicate that the range of possible temperature/time used in the solid-state synthesis is much narrower than previously assumed when a higher quality of the oxide material is required.