Synthesis of phase pure high entropy perovskites with unique electrocatalytic and oxygen transport properties

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This project focuses on the synthesis of phase-pure, chromium-free, high-entropy perovskites that are expected to exhibit exceptional properties, such as enhanced temperature and chemical stability and improved catalytic and oxygen transport performances. Therefore, the hypothesis that compounds with high configurational entropy are phase pure at high temperatures and that rapid cooling leads to phase purity at room temperature is being tested. For this reason, nebulized spray pyrolysis is chosen as the synthesis method that enables rapid cooling so that the metastable phase stabilized at high temperatures by entropic effects is also retained at room temperature. In addition to cooling, overall synthesis using nebulized spray pyrolysis is also more time efficient than other synthesis methods. After the chromium-free high-entropy perovskite powders have been synthesized, they are next analysed structurally using X-ray diffraction and scanning electron microscopy. The process parameters and elemental compositions can thus be optimized via iteration loops until phase purity of the product is achieved, for which additionally crystal structure, morphology and particle size are determined. Chromium should be omitted from the composition due to potential environmental and safety issues. If the synthesis of the perovskite powders with an equimolar composition of cations is successful, the nickel proportion of the composition should be varied. This could result in an exsolution of nickel, which would have positive effects on the catalytic properties of the powder. In order to classify the resulting particles structurally, transmission electron microscopy and electron energy-loss spectroscopy are used in addition to the methods already mentioned, which provides more precise information on particle size and structure. The powders are then processed into membranes by pressing and sintering. Iteration loops in which the parameters are adjusted, in combination with structural analysis, should enable the phase purity to be maintained despite the high temperatures required for sintering. The electrical conductivity and oxygen permeation of the membranes are investigated. In addition, the electrocatalytic properties of the powders and the membranes are analyzed. Electrocatalytic oxygen-transporting membranes are thus obtained, which can be used in various heterogeneous catalytic processes.