Vacancy Engineering of Ultrathin 2D Materials for Photocatalytic CO₂ Reduction

Abstract Photocatalytic carbon dioxide (CO₂) reduction is a sustainable and green strategy for the conversion of CO₂ into hydrocarbon solar fuels, whereas its large‐scale application is severely restricted by lack of highly effective photocatalysts. Ultrathin 2D materials with tunable electronic structure display great potential towards photocatalytic CO₂ reduction. However, the photocatalytic performance still remains unsatisfied due to high activation energy of CO₂ molecules on catalytic sites. To this end, surface vacancy engineering can endow coordinately unsaturated sites as actively catalytic sites for CO₂ molecules chemisorption and activation. In this review, we focus on vacancy‐engineered ultrathin materials for CO₂ photoreduction. Different vacancies with classified anion vacancies, cation vacancies, vacancy pairs, voids, and their corresponding role in CO₂ photoreduction are proposed. The different strategies based on vacancy engineering, including direct modulation of vacancy concentrations, refining vacancy states by heteroatom, and vacancy‐engineered heterostructure, are presented. Finally, the future developments and their associated challenges concerning defective ultrathin 2D materials are discussed.