Identifying Optimal Alkaline Earth Metal to Passivate Oxygen Vacancies and Enhance Carrier Lifetimes in Transition Metal Oxides

Charge compensation at oxygen vacancies via elemental doping is an effective strategy for suppressing rapid carrier recombination. However, a systematic criterion for element selection toward efficient oxygen vacancy (Ov) passivation is still lacking. Herein, we perform ab initio quantum dynamics simulations on rutile TiO2 as a model system and elucidate the charge compensation mechanism of Ov passivation by alkaline earth metal doping (Be, Mg, Ca, and Sr). The simulations allow us to demonstrate and rationalize the influence of ionic radius on the passivation mechanism. Analysis of carrier recombination dynamics reveals that dopants with smaller atomic radii (e.g., Be) readily dissociate from Ov sites. This dissociation markedly reduces the electron−phonon coupling, consequently extending the carrier lifetime to 400 times that of the unpassivated system and 3 times that of pristine TiO2. Importantly, we extend and validate the demonstrated Ov passivation strategy to other materials, including anatase TiO2, ZrO2, and BiVO4, confirming its universal applicability. The work establishes an element selection criterion for defect passivation based on the charge compensation strategy and provides a material design principle for overcoming the bottleneck in the charge separation efficiency in oxide photocatalysis.