Catalysts play a crucial role in advancing energy conversion and storage systems, particularly in chemical and electrochemical reactions. A recent advance in this field has been the synthesis of self-assembled metal nanoparticles through a process known as “exsolution.” In exsolution, metal nanoparticles grow in situ, anchored to a host oxide, with perovskite oxides commonly serving as the parent oxide. Perovskites are important because they provide electron and ion conductivity, essential in energy-related applications such as fuel cells and electrolysis cells for power generation and hydrogen production.[1] Previous studies have revealed how external stressors can be used to tune the perovskite defects,[2] particularly oxygen vacancies at the surface, which will be key in determining the transport properties and the kinetics of exsolution.[1,2] A previous work from our group [2] showed that the density of exsolved Fe^0 nanoparticles from La0.6Sr0.4FeO3 (LSF) oxide matched the concentration of oxygen vacancies, revealing that oxygen vacancies are preferential nucleation sites for exsolution. Another study by Wang et al. from our group [3] showed how the Fe^0 exsolution also changed the bulk structural properties, creating Fe-deficient percolating channels that assisted the increase in electronic conductivity. However, the role of surface chemistry in exsolution kinetics and nanoparticle formation is not yet fully understood.[1]

In this work, we explored how the surface chemistry of La0.5Sr0.5Ti0.94Ni0.06O3 (LSTN) affects the exsolution kinetics of metallic nickel (Ni) nanoparticles. To investigate this, we modified the surface using various metal oxides through pulsed laser deposition. Previous work by Nicollet et al. [4] demonstrated that the acidity of binary oxides can influence oxygen surface kinetics in mixed conducting oxides. Building on this insight, we selected three metal oxides (MgO, ZnO, and SnO2) with varying acidity levels, as suggested by Nicollet et al. We hypothesize that the acidity of the metal oxide influences the exsolved nanoparticles’ surface area, particle size, and kinetics of Ni nanoparticles by affecting the formation of oxygen vacancies. The “surface decorations” adjust the concentration of oxygen vacancies, hence influencing the exsolution sites and properties of the nanoparticles. We assessed how adding different monolayers of binary oxides to LSTN thin films impacts the thermal exsolution of nanoparticles by using ambient-pressure spectroscopic techniques such as X-ray photoelectron spectroscopy and X-ray absorption spectroscopy.[1] Establishing correlations between surface chemistry, particularly acidity, and nanoparticle properties is crucial for controlling exsolution surfaces tailored for specific electrochemical reactions, such as hydrogen production through water splitting or carbon dioxide reduction.