Exsolution is a powerful tool that allows the improvement of the materials’ catalytic performance through the formation of highly catalytically active metallic nanoparticles of easily reducible 3d metals on the material’s surface. Exsolved nanoparticles are well anchored to the matrix, show superior coking and agglomeration resistance and outstanding catalytic activity. To fully utilize the benefits of exsolution, the meticulous control of both the reduction process parameters (temperature, time and oxygen partial pressure) and material’s composition (A-site deficiency, oxygen non-stoichiometry and the content of dopants) is necessary. In the context of exsolution, double perovskites are an especially promising group of materials because of their structure tuneability and doping flexibility. A prominent example of such a structure is the Sr₂Fe_1.5Mo_0.5O₆ system, which is already widely considered for application as an electrode material in solid oxide cells (SOC) technology and in the field of catalysis.

Therefore, in this study, we propose Cu and multicomponent (Cu, Co, Fe, Ni) doping of the conventional Sr₂Fe_1.5Mo_0.5O₆ double perovskite structure. The careful optimization of the synthesis and calcination process allows obtaining single-phase compositions of typical Fm-3m double perovskite symmetry. Special attention is paid to the optimization of the conditions of the exsolution process (temperature and time) and their influence on the stability of the double perovskite structure, the chemical composition of exsolved metallic nanoparticles and/or alloys, the population, size, and distribution of nanoparticles per unit area. It should allow for the assessment of the role of each individual dopant in the modification of the materials properties using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques. The reducibility of each composition is assessed both theoretically and experimentally, using temperature-programmed reduction (TPR). Additionally, a very detailed structural analysis allowing estimating the oxygen content and oxidation state of each element using iodometric titration, thermogravimetry and X-ray absorption spectroscopy (XAS) is conducted for both oxidized and reduced materials. Electrical data shows the presence of metallic-like type of conductivity at higher temperatures in air for all materials, while after reduction they behave like typical semiconductors. The presence of a chemical expansion mechanism responsible for elevated TEC values at higher temperatures is confirmed by dilatometric measurements. Meticulous analysis of various properties under oxidizing and reducing conditions together with careful optimization of the exsolution process provides a very solid foundation and gives hope for successful utilization of the presented materials in solid oxide cell- and catalysis-related applications.