Effects of Crystal Lattice Deformation on Catalytic Activities

Deformations of hierarchical structures at the atomic scale, especially long-range ones, can significantly enhance their functional behavior, such as catalytic activity. Metastable states or grain boundaries during the synthesis and processing of nanomaterials can introduce and control deformations (strains) in crystal lattices. We will design the deformations in the crystal lattice to enhance the catalytic functionality of catalysts, such as TiO₂ and platinum-group-based metals, by controlling their synthesis processes of phase transformation and particle aggregation. For example, TiO₂ polymorphs have distinct properties that have been widely employed in various applications. It is well known that these polymorphs can transform into more stable phases, such as from anatase to rutile and from TiO₂-B to anatase. Here, based on results from semi-in-situ transmission electron microscopy, density functional theory, and X-ray photoemission experiments, we discover a physical picture of transitional structures, in which continuous variations in atomic positions form along these two phase-transformation pathways. These gradient structures give rise to continuous band bending, which promotes electron-hole separation and inhibits their recombination across the bulk of the particles, leading to a large functionally active volume fraction and resulting in high photoactivity. We also seek to control deformations in supporting materials and their effect on catalytic materials to uniquely tailor functionalities. These findings suggest that extended gradient structures (lattice deformations) can be designed to advance new functions not achievable using abrupt interfaces.