Multi-scale Modeling and Experimental Investigation of Oxidation Behavior in Platinum Nanoparticles

Understanding the oxidation behavior of Pt nanoparticles (NPs) is crucial for developing durable and efficient catalysts. In this study, we investigate the oxidation of a realistic Pt NP, retrieved from scanning transmission electron microscopy (STEM) images. We use a multistep approach combining ReaxFF and MACE-MP-0 forcefields with Density Functional Theory (DFT) calculations. Our Monte Carlo simulations reveal high oxidation of the nanoparticle, with oxygen penetrating deep into the core. We explore the plausibility of these configurations by carrying out XRD, TEM and EXAFS measurements on samples of various average particle sizes. Progressing in our workflow, we find that 100 ns of thermostated dynamics at 350 K using the ReaxFF forcefield leads to the formation of detached Pt$_6$O$_8$ species. To explore the validity of this small platinum-oxide cluster, we first optimize the geometries using the recent MACE-MP-0 forcefield resulting in structures without the species. We then compare both forcefields to DFT calculations showing closer agreement for MACE-MP-0 compared to ReaxFF. Finally, we discuss the electronic structure of our oxidized nanoparticles spanning a whole range of oxygen coverages, finding substantial changes in the Pt-5$d$ and O-2$p$ projected density of states of the platinum structure as the coverage increases. Our findings emphasize the importance of accurately describing the potential energy surface and explicitly modeling oxygen coverage to predict catalytically relevant properties at high potentials. This study aims to provide a foundation for understanding the complex interplay between nanoparticle structure, oxidation state, and catalytic performance, aiming to guide the rational design of advanced catalytic materials.