Spray-flame-synthesized LaCo1–xFexO3±δ perovskites for electrocatalysis
This dissertation is based on experiments to research the potential of spray-flame-synthesized LaCo1̶ xFexO3 perovskite as non-precious-metal based electrocatalysts towards OER and EtOR. These complex oxide perovskites were successfully synthesized before by numerous synthesis techniques such as the Pechini sol-gel method, co-precipitation, and reactive grinding; and Co- and Fe-based perovskites were put forward as highly active OER catalyst in numerous studies. However, few research studies were oriented to develop methods to produce high-surface area, nanosized perovskite catalysts that could be used in large-scale production. Therefore, the rationale behind this research is to show that spray-flame synthesis can be the suitable technique to produce high-surface area perovskite nanoparticles as electrocatalysts in a continuous scalable process. A series of LaCo1–xFexO3 nanoparticles with different Fe contents were synthesized by spray-flame synthesis by varying process parameters and precursor solution compositions. With the aid of heat-treatment of the as-synthesized nanoparticles in O2, the physical properties of the as-synthesized nanoparticles were further modified. Comparative analyses on the bulk, surface, morphological, and magnetic properties of the perovskites were performed to determine the influence of Fe substitution on the OER catalytic activity. All experiments and analyses are a result of the collaborative research study of several research groups; namely, the synthesis and materials characterizations by the author in collaboration with the Interdisciplinary Center for Analytics on the Nanoscale (ICAN) and the Wende group in the University of Duisburg-Essen Electrocatalytic and operando electrochemistry investigations were performed in the Schuhmann and Muhler Groups at the Ruhruniversität Bochum. Based on this collaborative effort, spray-flame synthesis, nanoparticle characterization, and the investigation of the OER and EtOR catalytic activity of Fe-substituted LaCoO3 nanoparticles was combined with operando electrochemistry/ATR-FTIR measurements giving insight into the influence of Fe substitution on electrochemical properties of LaCoO3. The focus of this work is on optimizing spray-flame synthesis parameters and heat treatment processes for improving the stoichiometric perovskite phase content while decreasing carbon contamination. Overall, the synthesis and analyses methodology applied for the specific mate-rials system of LaCo1–xFexO3 perovskites in this dissertation, was intended to be made useful for a wide range of other spray-flame made perovskites and complex oxide nanoparticles for electrocatalytic and other catalytic applications.