Charge Compensation and Ce³⁺Formation in Trivalent Doping of the CeO₂(110) Surface: The Key Role of Dopant Ionic Radius

Abstract

In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is doped with a series of trivalent dopants, namely, Al3+, Sc3+, Y3+, and In3+. Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized MCe / + OO • (M = the 3+ dopant), O− hole state, confirming the description found with DFT + U. We use DFT + U to investigate the energetics of dopant compensation through formation of the 2MCe ′ +VO ·· defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al3+, which has the smallest ionic radius, and Sc3+ and In3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the other hand, the Y3+ dopant, with an ionic radius close to that of Ce4+, shows a positive anion vacancy formation energy, as does La3+, which is larger than Ce4+ (J. Phys.: Condens. Matter201020135004). When considering the resulting electronic structure, in Al3+ doping, oxygen hole compensation is found. However, Sc3+, In3+, and Y3+ show the formation of a reduced Ce3+ cation and an uncompensated oxygen hole, similar to La3+. These results suggest that the ionic radius of trivalent dopants strongly influences the final defect formed when doping ceria with 3+ cations. In light of these findings, experimental investigations of these systems will be welcome.

Mechanistic Studies of Water Electrolysis and Hydrogen Electro-Oxidation on High Temperature Ceria-Based Solid Oxide Electrochemical Cells

“…The value of the U is set to 5 eV, as used in previous calculations. 39,40 A CeO 2 (111)-p(4×4) slab with three CeO 2 layer thickness separated by 15 Å vacuum was used to model the ceria surfaces with different coverage of oxygen vacancy and hydroxyl, and only Γ-points were used to sample the surface Brillouin zone. All atoms in the super cell were relaxed until the residual force on each atom was less than 0.01 eV Å −1 .…”

Descriptor Analysis in Methanol Conversion on Doped CeO2(111): Guidelines for Selectivity Tuning

“…[40][41][42][43][44][45][46][47][48][49] Another trivalent dopant, Ga, enhances the activity of alkyne semi-hydrogenation, 50 69 This U eff was set to 4.5 eV, as it was been previously proven to provide satisfactory results. 55,[70][71][72] Projector-augmented wave (PAW) pseudopotentials 73 were used to describe the core electrons with a plane-wave cutoff energy of 500 eV for the valence electrons (i.e., 5s, 5p, 4f, 6s for Ce atoms, 2s, 2p for O and C atoms, 4s, 4p, 5s, 4d for Zr atoms, 5s, 5p, 6s, 5d for Hf atoms, and 6s, 6p, 5f, 7s for Th atoms).…”

Low Valence Cation Doping of Bulk Cr2O3: Charge Compensation and Oxygen Vacancy Formation

“…[46][47][48] The introduction of holes through incorporating a LV dopant will lead to spontaneous formation of oxygen vacancies to compensate the lower oxidation state of the dopant compared to the host. [49][50][51][52] The resulting absence of oxygen in the lattice after the release of oxygen can be experimentally observed, as the vacancy cannot be annealed in the presence of oxygen. Given that this vacancy will therefore always be present, it will induce structural distortions, which can lead to potentially more favorable oxygen vacancy formation and mobility.…”