Vacancy Engineering of Ultrathin 2D Materials for Photocatalytic CO2 Reduction

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.