DFT + U Study of Strain-Engineered CO₂ Reduction on a CeO_{2- x}(111) Facet

Ceria is a promising material for cathodes in high-temperature CO₂ electrolysis cells because ceria can become a mixed electronic and ionic conductor through doping, which enables a high surface area for electrocatalysis. Here, we systemically investigate the effect of strain to enhance the activity for electrocatalytic CO₂RR on CeO₂(111) using density functional theory corrected for on-site Coulomb interactions (DFT + U). We find that tensile strain decreases the oxygen vacancy formation energy due to a downshift of the Ce 4f orbital energy, in agreement with the larger size of the Ce³⁺ ion than the Ce⁴⁺ ion. The corresponding upshift in the Ce f-band center with compressive strain destabilizes the formation energy of the critical surface oxygen vacancies and reduces the energetic span of the reduction reaction, leading to a 4 orders of magnitude higher turnover frequency at 800 K for 4% compressive strain. These findings shed new light on possible pathways to enhance the catalytic activity for CO₂RR on CeO₂(111) and related catalytic systems by strain engineering.