Coordination Engineering of Single‐Atom Catalysts for the Oxygen Reduction Reaction: A Review

Future renewable energy supplies and a sustainable environment rely on many important catalytic processes. Single‐atom catalysts (SACs) are attractive because of their maximum atom utilization efficiency, tunable electronic structures, and outstanding catalytic performance. Of particular note, transition‐metal SACs exhibit excellent catalytic activity and selectivity for the oxygen reduction reaction (ORR)—an important half reaction in fuel cells and metal–air batteries as well as for portable hydrogen peroxide (H2O2) production. Although considerable efforts have been made on the synthesis of SACs for ORR, the regulation of the coordination environments of SACs and thus the electronic structures still pose a big challenge. In this review, strategies for manipulating the coordination environments of SACs are classified into three categories, including regulation of the center metal atoms, manipulation of the surrounding environment connecting to the center metal atom, and modification of the geometric configuration of the support. Finally, some issues regarding the future development of SACs for ORR are raised and possible solutions are proposed. The manipulation strategies for improving the intrinsic oxygen reduction reaction activity for single‐atom catalysts are summarized. Three aspects are discussed, including regulation of the center metal atoms, manipulation of the surrounding environment connecting to the center metal atom, and modification of the geometric configuration of the support.