Ultrathin two-dimensional metallenes for heterogeneous catalysis

Metallenes, the newest emerging two-dimensional metals of atom-ically thin layers, have aroused great interest for energy and catalytic applications due to their peculiar physicochemical and electronic properties. Particularly, the superhigh exposure of the under-coordinated metal atoms in metallenes endows them with enormous potentials for catalysis in terms of improving the atom utilization and intrinsic activity. In this review, we focus on the recent progress of metallenes for heterogeneous catalysis. It begins by briefly introducing the definition, classification, and some distinctive properties of metallenes. Then, the key protocols for the preparation of metallenes are summarized. Subsequently, we emphatically discuss the applications of metallenes in a variety of heterogeneous catalytic reactions, especially in electrocatalysis. Finally, from our point of view, we present the remaining challenges and propose the corresponding perspectives toward the future developments of metallenes for heterogeneous catalysis.