Single-atom catalysts for CO oxidation, CO₂ reduction, and O₂ electrochemistry

CO_x (x = 1, 2) and O₂ chemistry play key roles in tackling global severe environmental challenges and energy issues. To date, the efficient selective electrocatalytic transformations of CO_x-carbon chemicals, and O₂-hydrogenated products are still huge challenges. Single-atom catalysts (SACs) as atomic-scale novel catalysts in which only isolated metal atoms are dispersed on supports shed new insights in overcome these obstacles in CO_x and O₂ chemistry, including CO oxidation, CO₂ reduction reaction (CO₂RR), oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). In this review, the unique features and advanced synthesis strategies of SACs from a viewpoint of fundamental synthesis design are first highlighted to guide future strategy design for controllable SAC synthesis. Then, the to-date reported CO₂RR, CO oxidation, OER, and ORR mechanism are included and summarized. More importantly, the design principles and design strategies of improving the intrinsic activity, selectivity, and stability are extensively discussed and the engineering strategy is classified as neighbor coordination engineering, metal-atom engineering, and substrate engineering. Via the comprehensive review and summary of state-of-the-art SACs, the synthesis – structure – property – mechanism – design principle relation can be revealed to shed lights into the structural construction of SACs. Finally, we present an outlook on current challenges and future directions for SACs in CO_x and O₂ chemistry.