Thermodynamic Evolution of Cerium Oxide Nanoparticle Mor-phology using Carbon Dioxide.

Many nanoparticles show enhanced catalytic activity on particular surfaces. Hence, a key challenge is to identify strategies to control the expression of such surfaces and to avoid their disappearance over time. Here, we use density functional theory to explore the adsorption of carbon dioxide on the surfaces of Cerium oxide (CeO₂), and its relationship with the resulting nanoparticle morphology under conditions of pressure and temperature. CeO₂ is an important solid electrolyte in fuel cells, a catalyst, and enzyme mimetic agent in biomedicine, and has been shown to interact strongly with CO₂. We demonstrate that the adsorption of CO₂ as a carbonate ion is energetically favorable on the {111}, {110} and {100} surfaces of CeO₂, and that the strength of this interaction is morphology and surface stoichiometry dependent. By predicting the surface stability as a function of temperature and pressure, we built surface phase diagrams and predict the surface dependent desorption temperatures of CO₂. These temperatures of desorption follow the order {100} > {110} > {111} and are higher for surfaces containing oxygen vacancies compared to stoichiometric surfaces, indicating that surface oxidation processes can reduce the stability of surface carbonate groups. Finally, we propose a thermodynamic strategy to predict the evolution of nanoparticle morphology in the presence of CO₂ as the external conditions of temperature and pressure change. We show that there is a thermodynamic driving force dependent on CO₂ adsorption that should be considered when selecting nanoparticle morphologies in catalytic applications.