Defect Chemistry in 2D Atomic Layers for Energy Photocatalysis

Conspectus Photocatalysis is a promising technology to simultaneously relieve the worldwide energy crisis and environmental pollution issues, providing an effective avenue for carbon neutrality. Numerous efforts have been dedicated to the reasonable design of photocatalytic materials to improve the photocatalytic efficiency. Among these, building two-dimensional (2D) atomic layers with suitable energy band structure offers an alternative configuration to optimize bulk charge separation and surface reactions at the same time. The limited thickness of the 2D atomic layer favors the rapid bulk charge migration to the surface, reducing the recombination of electron-hole pairs and boosting the bulk charge separation efficiency. Moreover, the 2D atomic layer configuration makes the surface atomic structure easily regulated, for example, engineering defects. In 2D atomic layers, even infinitesimal amounts of defects can unlock the great potential that exists for tailoring the carrier concentration, electronic states, spin nature, and so on. The specific defects can introduce defect energy levels into the band gap and extend the light absorption. The carrier dynamic can be regulated by the defects and optimize the charge separation efficiency. Moreover, these defect configurations provide specific reactive sites to bind with different molecules, tuning the intermediate formation and facilitating reaction progression. In this Account, we present the group’s recent research progress in search of defective 2D atomic layers for energy photocatalysis. We start with the classification of defects in the 2D atomic layers, such as anion vacancies, cation vacancies, vacancy associates, single atom doping, pits, amorphization, grain boundaries, and single-metal-atom chains. Then, different defect controlling formation strategies are introduced to engineer various defects in 2D atomic layers with an emphasis on formation principle, such as thickness controlling, curve controlling strategy, template directed strategy, etching strategy, and matrix induction. Additionally, the critical roles of defects for enhanced photocatalytic performance from different aspects are highlighted, including electronic structure tailoring, charge trapping, interface interaction strengthening, reactant adsorption and activation, molecular intermediate interaction force tuning, and reaction energy barriers and paths, to acquire the fundamental insight of the photocatalytic mechanism and elucidate the relationship between the defective local allocation and photocatalytic behavior. Finally, diversified energy-related photocatalytic applications over defective 2D atomic layers are discussed, such as water splitting, N₂ reduction, and CO₂ reduction. We hope that this Account can facilitate the development of defect chemistry in 2D atomic layers and realize high-efficiency photocatalysis.