Defective ultrathin two-dimensional materials for photo-/electrocatalytic CO2 reduction: Fundamentals and perspectives

Abstract

Photo-/electrocatalytic reduction of carbon dioxide (CO₂) to carbon-based fuel molecules driven by renewable energy is an attractive strategy for resource regeneration and energy storage, especially for achieving carbon peak and carbon-neutral goals. However, the high thermodynamic stability and chemical inertness of CO₂ molecules make the conversion efficiency and selectivity of reduction products very low, which further hinders its application. In addition, different CO₂ reduction products have similar reduction potential and usually face severe hydrogen evolution competition under aqueous system conditions, which makes the selectivity of specific reduction products unable to be effectively controlled. To overcome these bottlenecks, researchers have been working for many years to develop efficient photo/electrocatalysts to enhance the activity and product selectivity of CO₂ reduction. Thanks to the ultrathin thickness and large specific surface area, ultrathin two-dimensional materials possess highly active sites with high density and high uniformity, which can effectively regulate the key thermodynamic and kinetic factors of CO₂ photo-/electroreduction reactions. As a typical two-dimensional material, the defective ultrathin two-dimensional materials can provide a large number of electron-rich catalytic sites to efficiently adsorb and highly activate CO₂ molecules, which can effectively reduce the reaction barrier, thus accelerating CO₂ reduction and enhancing product selectivity. Moreover, the local atomic and electronic structure of the defects can effectively stabilize the intermediate of CO₂ reduction reactions, thus further optimizing the kinetics of CO₂ reduction reactions. Furthermore, the surface defects are beneficial to the mass and electron transfer in the catalytic process, thus further improving the catalytic activity of the catalysts. In this review, we overview the latest research progress in CO₂ photo-/electrocatalytic reduction using defective ultrathin two-dimensional materials, including the controllable synthesis and fine structure characterization of defective ultrathin two-dimensional materials; the modulation effect of defect structure on the local atomic and electronic structure; the advantages of defective ultrathin two-dimensional materials for CO₂ reduction. We also discuss the challenges and opportunities of defective ultrathin two-dimensional materials for future development of CO₂ photo-/electrocatalytic reduction. It is expected that this review will provide a guide for designing highly efficient CO₂ reduction systems.