Surface sites engineering on semiconductors to boost photocatalytic CO2 reduction

Solar-light-driven CO2 conversion is a promising approach to the production of renewable fuels, yet the efficiencies are severely confined by the strong inertness of CO2 molecules and intrinsic drawbacks of semiconductor photocatalysts, such as the rapid charge recombination and infertile reactive sites. Considerable research efforts have been thus made to develop effective strategies to conquer the above-mentioned issues. The probing of atomic-level reactive sites on the surface of photocatalysts furthers the understanding on surface structural property relationship and CO2 photoreduction mechanism, which can provide reference and guideline for preparation and design of efficient semiconductor photocatalysts. In this review, we attempt to provide a comprehensive summary and update of fundamental understanding on surface reactive sites engineering for enhancing the efficiency and selectivity of photocatalytic CO2 reduction. It focuses mainly on recent progress in the creation and regulation of facet-dependent sites, surface lattice sites, surface grafting sites and co-strategies, especially their essential roles in promoting the key processes occurring in the CO2 photoreduction, including photoexcitation, charge separation and migration, adsorption and activation of CO2, and desorption of products. The perspectives and challenges of surface sites design of photocatalysts for CO2 reduction are outlooked as a conclusion.