Structural and electronic properties of NM-doped ceria (NM = Pt, Rh): a first-principles study

Abstract

The effects of noble metal (NM) dopants (NM = Pt, Rh) on the structural and electronic properties of ceria are studied using a density functional theory (DFT) method, with the inclusion of on-site Coulomb interaction (DFT+U). It is found that these NM dopants give rise to large perturbations of the atomic and electronic structures of ceria and induce metal-induced gap states at the Fermi level suitable for accommodating extra electrons, thereby lowering the reduction energy of ceria and making the NM-doped cerias more reducible than pure ceria. This mechanism for facilitating the reduction of ceria is different from that of Zr-doped ceria where the increased reducibility is largely due to the structural distortions and not to electronic modifications.

The origin of the enhanced oxygen storage capacity of Ce1−x(Pd/Pt)xO2

“…These results would suggest that the removal of an oxygen next to the dopant during formation of a charge-compensating vacancy costs energy. 19,20 This is at variance with previous X-ray photoelectron spectroscopy studies that indicate Pd and Pt to be present preferentially in the +2 oxidation state, and accompanied by spontaneously formed charge-compensating vacancies. 9,18 Despite the reported improvements in catalytic activity and OSC, the underlying reason for these has remained unclear.…”

“…Hermansson and co-workers have previously used the local density approximation (LDA)+U approach to model the doping of CeO 2 with Pd and Pt, 19,20 with the formation of the charge-compensating vacancy incorrectly considered as the reduction energy. The authors reported that the replacement of a Ce IV in both cases resulted in a very small relaxation around the dopants.…”

“…19,20 From method (ii), however, once the Pd/Pt is allowed to move off the perfect Ce lattice site, it undergoes a large lattice distortion away from the charge-compensating vacancy site to assume a square planar coordination between four lattice oxygens, Fig. 1(b).…”

“…In the work of Hermansson and co-workers, the Pd/Pt states in the band gap are proposed as the origin of the enhanced reducibility. 19,20 As their study does not find the lowest energy square planar configuration, and ignores the formation of a charge compensating vacancy, the author's calculated PEDOS for doped CeO 2 shows Pd/Pd defect states in the band gap, with some unoccupied defect states in the spin down (Beta spin). 19,20 Subsequent oxygen vacancy formation fills these unoccupied states, leaving the non-spin paired Pd/Pt states in the band gap.…”

“…19,20 As their study does not find the lowest energy square planar configuration, and ignores the formation of a charge compensating vacancy, the author's calculated PEDOS for doped CeO 2 shows Pd/Pd defect states in the band gap, with some unoccupied defect states in the spin down (Beta spin). 19,20 Subsequent oxygen vacancy formation fills these unoccupied states, leaving the non-spin paired Pd/Pt states in the band gap. 19,20 In our study, we have uncovered the ground state structure of Pd/Pt doped CeO 2 , which is in the square planar coordination with a charge compensating vacancy neighbouring the dopant.…”