EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

New functional materials combining stability, resistance to degradation, and efficiency with reasonable cost and ease of synthesis are crucial for their use in renewable energy applications. In catalysis, active metal nanoparticles dispersed on oxide surfaces are of fundamental interest to overcome the use of bulk noble metals. However, these bear the substantial limitations of the conventionally employed “top-down” deposition techniques, resulting in loss of activity and performance during operation.
Exsolution, i.e. metal atoms that, in a reducing environment, segregate to the surface from sites within a host oxide lattice to generate anchored nanoparticles, has proven a successful strategy to overcome such issues. However, many questions remain regarding their growth mechanism and the host crystal structure evolution during the reduction process. Here, the SrTiO3 perovskite has been doped with iridium (∼0.5 wt. %) at the B-site and subjected to reducing conditions required for exsolution. Ex situ characterization with a range of techniques including XRD, XPS, HR-TEM, and STEM–EDX showed that iridium metal nanoparticles are grown on the SrTiO3 surface with the unique characteristic of “socketing” to the host lattice. In situ TEM/EELS studies allowed to monitor in real time nanoparticle exsolution, enabling us to gain general understanding on the mechanistic steps involved, and to investigate variations in composition, chemistry, and structure of the nanoparticles and the host during reduction. Insights in the crystallographic behaviour of both the host lattice and the exsolved nanoparticles at the atomic scale were obtained, and the materials composition at the unique anchoring interface was studied through high-resolution chemical characterization. This approach allowed us to explore the evolution and transformation of the exsolved NPs to understand the structure of the NPs and the support substrate, which is of fundamental importance in order to tailor materials design for even better reactivity.