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

COx (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 COx-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 over-come these obstacles in COx 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 cur-rent challenges and future directions for SACs in COx and O2 chemistry. (c) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.