This project aims at systematically acquiring knowledge on Co-oxide based multinay oxide thin film systems, which depending on composition can form spinel (AB2O4) or perovskite (ABO3) structures, by combinatorial deposition of thin film material libraries and their high-quality high-throughput characterization. The project aims to identify a) trend-lines: how does composition and structure change functional properties, and b) which composition/structure combinations show the best catalytic properties. To reach these goals, A- and B-site compositions will be systematically explored using additional elements such as Fe, V, Mn, Al, and Mo.
In the first funding period of the CRC, FexCo3-xO4 spinel and La-Co-O perovskite thin-film systems were investigated with respect to structural and functional properties and were screened for trends of catalytic activity related to composition and structure. In the next phase this screening will be extended by increasing the compositional complexity, by adding additional elements and analyse their influence on electric resistance, microstructure, phases, and morphology which are the key properties for application of thin film oxides as electrocatalysts for the OER. In addition to the extension of the CCS (Continuous Composition Spread) synthesis, different post treatment methods will be applied to the films, to also investigate their influence on the thin film properties. For identification of active sites in the best performing compositions, thin polycrystalline films with large grains (micrometer instead of nanometer range) will be grown using a unique step heater. The crystallographic orientation of the large grains will be analysed by electron back-scatter diffraction (EBSD) and will then, together with partners in the CRC, be systematically investigated with scanning droplet cell (SDC) and scanning electrochemical cell microscopy (SECCM) for catalytic activity to determine active sites. In this way a high number of well-defined and well-comparable samples will enable the generation of composition-processing-(micro- and crystal)structure-property correlation maps visualized in functional phase diagrams as a data basis to enable a mechanistic understanding of surface catalytic properties.
(Figure: Combined EBSD and SECCM measurements for generation of catalytic activity maps of microscale-grained films. Schematic illustration of combining EBSD and SECCM measurements to correlate crystallographic data with catalytic activity to identify most active crystallographic orientations in catalytic activity maps).