Composition-Dependent Morphology of Stoichiometric and Oxygen Deficient PuO₂ Nanoparticles in the Presence of H₂O and CO₂: A Density-Functional Theory Study

Among the most pressing challenges faced by the UK nuclear industry is how to safely handle its large stockpile of plutonium dioxide. In particular, understanding how the exposed surfaces interact with the environment is critical to establishing the chemical reactivity and determining suitable processing and storage conditions. In this work, we apply an ab initio modelling approach to predict the morphology and surface speciation of stoichiometric and oxygen deficient PuO₂ nanoparticles as a function of temperature and in the presence of individually- and co-adsorbed H₂O and CO₂. We find that co-adsorption of the two species has a significant impact on the surface composition, resulting in the equilibrium particle morphology being strongly dependent on the storage conditions. This work provides valuable insight into the behaviour of nanoparticulate PuO₂in the presence of ubiquitous small molecules and marks an important step toward more realistic models extendable to other adsorbates and actinide oxides.