Equilibrium oxygen storage capacity of ultrathin CeO2-δ depends non-monotonically on large biaxial strain

Abstract

Elastic strain is being increasingly employed to enhance the catalytic properties of mixed ion–electron conducting oxides. However, its effect on oxygen storage capacity is not well established. Here, we fabricate ultrathin, coherently strained films of CeO2-δ between 5.6% biaxial compression and 2.1% tension. In situ ambient pressure X-ray photoelectron spectroscopy reveals up to a fourfold enhancement in equilibrium oxygen storage capacity under both compression and tension. This non-monotonic variation with strain departs from the conventional wisdom based on a chemical expansion dominated behaviour. Through depth profiling, film thickness variations and a coupled photoemission–thermodynamic analysis of space-charge effects, we show that the enhanced reducibility is not dominated by interfacial effects. On the basis of ab initio calculations of oxygen vacancy formation incorporating defect interactions and vibrational contributions, we suggest that the non-monotonicity arises from the tetragonal distortion under large biaxial strain. These results may guide the rational engineering of multilayer and core–shell oxide nanomaterials.

Oxygen exchange kinetics on systematically doped ceria: a pulsed isotope exchange study

“…Ce concentrations match almost exactly, so the charge of the surface layer is rather small. 71 For comparably high p(O 2 ) of 10 À4 bar at 450 C, the surface concentration of Ce 0…”

Major Advances and Challenges in Heterogeneous Catalysis for Environmental Applications: A Review

“…However, NO x is not the only contaminant that can be abated by ceria. It can use the stored oxygen on its surface to convert lethal carbon monoxide into less-harmful carbon dioxide [80].…”

Low oxygen partial pressure increases grain boundary ion conductivity in Gd-doped ceria thin films

“…Although the effects of doping, temperature and atmosphere are well explained by the space charge model, a mathematically exact grain boundary model is far from trivial. In addition to the electrostatic effect, also Gd accumulation, local lattice distortions and strain near grain boundaries may change the oxide ion mobility and Ce reduction enthalpy [3,27,57]. Such effects are, however, out of the scope of the present study, and shall just highlight that the mathematical description of the grain boundary space charge works excellently on a semi-quantitative level, but exact numbers should be taken with care.…”

“…(4) There is no structural distortion in the fluorite lattice next to the grain boundary, which may have an additional effect on the Ceria reduction enthalpy [27] and ion mobility.…”