DFT Study of the Stability and Reducibility of Hf-Doped Ceria Nanoparticles

The structure, stability, and reducibility of ceria (CeO2) nanostructures doped by hafnium are studied computationally using density functional theory. For that, ∼2.4 nm large Ce140O280 nanoparticle and CeO2(111) surface slab models with varying amounts of Hf dopants and the presence of oxygen vacancies are calculated. Doping Hf4+ ions preferentially substitute inner Ce4+ ions avoiding lower-coordinated surface positions. The overall stability of the Hf-doped nanostructures is determined by the stability of the positions occupied by individual Hf4+ ions. The presence of Hf4+ ions dramatically decreases the already quite low oxygen vacancy formation energies of ceria. Such strongly increased reducibility of Hf-doped ceria nanomaterials should have important implications for chemical reactivity.