Facilitated vacancy formation at Zr-doped ceria(1 1 1) surfaces

The effects of Zr doping on the atomic and electronic properties of the ceria(1 1 1) surface are studied using first-principles density functional theory with the inclusion of on-site Coulomb interaction. The atomic structures, electronic structure, and the vacancy formation energies of the Zr-doped and undoped ceria(1 1 1) surfaces are compared. It is found that (i) Zr doping induces a severe distortion of the unreduced surface structure; (ii) at the reduced Zr-doped ceria(1 1 1) surface, the oxygen anions around the oxygen vacancy show much larger displacements than those on the pure CeO2(1 1 1) surface; (iii) an oxygen vacancy is more easily formed around the Zr dopant, and the reduction energy is lowered by about 0.5 eV; (iv) the excess electrons left by the removed oxygen atom localize on the two Ce cations neighboring the vacancy and thus brings about the reduction of the two Ce4+ ions; and (v) the atomic structure modification induced by the Zr doping plays a vital role in facilitating the reduction of the ceria-zirconia solid solution as compared to the pure ceria.