Direct Atomic-Scale Investigation of the Coarsening Mechanisms of Exsolved Catalytic Nanoparticles

Exsolution-active catalysts allow for the formation of highly active metallic nanoparticles, yet their long-term thermal stability remains a challenge. In this work, the dynamics of exsolved Ni nanoparticles are probed in situ with atomically resolved secondary electron imaging in an environmental STEM. STEM pre-characterization shows embedded NiOx nanostructures within the parent oxide. Subsequent in situ exsolution demonstrates that two populations of exsolved particles form with distinct metal-support interactions and coarsening behaviors. Nanoparticle migration which fits random-walk kinetics is observed, and particle behavior is shown to be analogous to a classical wetting model. Additionally, DFT calculations indicate that particle motion is facilitated by the support oxide. Ostwald ripening processes are visualized simultaneously to migration, including particle redissolution and particle ripening.