No abstract

The search for new functional materials that combine high stability and efficiency with reasonable cost and ease of synthesis is critical for their use in renewable energy applications. Specifically in catalysis, nanoparticles, with their high surfaceto-volume ratio, can overcome the cost implications associated with otherwise having to use large amounts of noble metals. However, commercialized materials, i.e. catalytic nanoparticles deposited on oxide supports, often suffer from loss of activity due to coarsening and carbon deposition during operation. Exsolution has proven to be an interesting strategy to overcome such issues.Here the controlled emergence, or exsolution, of faceted iridium nanoparticles from a doped SrTiO3 perovskite is reported and their growth preliminary probed by in situ electron microscopy. Upon reduction of SrIr0.005Ti0.995O3 the generated nanoparticles show embedding into the oxide support, therefore preventing agglomeration and subsequent catalyst degradation. The advantages of this approach are the extremely low noble metal amount employed (~0.5% weight) and the catalytic activity reported during CO oxidation tests, where the performance of the exsolved SrIr0.005Ti0.995O3 is compared to the activity of a commercial catalyst with 1% loading (1% Ir/Al2O3). The high activity obtained with such low-doping shows the possibility for scaling up this new catalyst, reducing the high cost associated with iridium-based materials.Image analysis and calculations; XPS supplementary data; STEM-EDX maps of as-synthesised Ir0.5-STO (PDF)

The creation of nanomaterials requires simultaneous control of not only crystalline structure and composition but also crystal shape and size, or morphology, which can pose a significant synthetic challenge. Approaches to address this challenge include creating nanocrystals whose morphologies echo their underlying crystal structures, such as the growth of platelets of two-dimensional layered crystal structures, or conversely attempting to decouple the morphology from structure by converting a structure or composition after first creating crystals with a desired morphology. A particularly elegant example of this latter approach involves the topotactic conversion of a nanoparticle from one structure and composition to another, since the orientation relationship between the initial and final product allows the crystallinity and orientation to be maintained throughout the process. Here we report a mechanism for creating hollow nanostructures, illustrated via the decomposition of β-FeOOH nanorods to nanocapsules of α-FeO, γ-FeO, FeO, and FeO, depending on the reaction conditions, while retaining single-crystallinity and the outer nanorod morphology. Using in situ TEM, we demonstrate that the nanostructured morphology of the starting material allows kinetic trapping of metastable phases with a topotactic relationship to the final thermodynamically stable phase.

Herein we report an ultrasonic-and photobased synthetic approach for the production of size-selective SrTiO 3 nanomaterials that are surface-decorated with Pd nanoparticle cocatalysts for application as photocatalysts for organic dye degradation. Control over the final nanoparticle size was achieved through selection of both reagent concentrations and stoichiometries, allowing for the ability to generate structures with sizes between 50 and 155 nm. Pd nanoparticles were subsequently photochemically deposited onto the surface of the oxide materials to serve as cocatalysts for enhanced reactivity. The materials were fully characterized and then examined for their photocatalytic reactivity, where their overall catalytic properties were controlled by three factors: (i) composition, (ii) size, and (iii) particle surface charge. These studies demonstrate important information that correlates synthetic conditions to final material properties, providing approaches to generate materials with optimal reactivity. Such effects could likely be translated to additional systems for applications beyond photocatalysis, such as energy harvesting, plasmonics, sensing, etc.

In exsolution, nanoparticles form by emerging from oxide hosts by application of redox driving forces, leading to transformative advances in stability, activity, and efficiency over deposition techniques, and resulting in a wide range of new opportunities for catalytic, energy and net-zero-related technologies. However, the mechanism of exsolved nanoparticle nucleation and perovskite structural evolution, has, to date, remained unclear. Herein, we shed light on this elusive process by following in real time Ir nanoparticle emergence from a SrTiO3 host oxide lattice, using in situ high-resolution electron microscopy in combination with computational simulations and machine learning analytics. We show that nucleation occurs via atom clustering, in tandem with host evolution, revealing the participation of surface defects and host lattice restructuring in trapping Ir atoms to initiate nanoparticle formation and growth. These insights provide a theoretical platform and practical recommendations to further the development of highly functional and broadly applicable exsolvable materials.