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The unique properties of 2D materials have motivated the discovery of new atomically thin materials that push the boundaries of synthetic design and device performance. In a review published in the Journal of Materials Chemistry C, researchers in the Scott Warren group explore the unique properties of a new class of 2D materials, which are the atomically thin form of layered electrides, consisting of alternating layers of atoms and electrons. The group members call these ultrathin electrides, “electrenes.”

Electrides are ionic crystals that, in place of traditional anions like Cl−, have just an electron, e−, that serves as the anion. They are the solid-state analogue of solvated electrons. Some electrides crystallize in a layered structure and in these layered electrides, electrons reside in the interlayer gap and partially delocalize to form a 2D electron gas. Because of the 2D electron gas, these materials offer exciting properties such as high electrical conductivities, ultra-low work functions, highly anisotropic optical response, and rich surface chemistries. Recently, the Warren Group demonstrated that this exotic type of ionic solid can be made as a 2D material. We refer to these 2D materials as “electrenes” in accord with the nomenclature of 2D materials. The realization of this radically different type of 2D material opens opportunities to experiment with nearly-free electrons in a host of applications.

In the review, the Warren Group members provide historical context for the development and understanding of electrenes, describe the structures of layered electrides and their asymmetric bonding that resembles that of van der Waals crystals, and also discuss their physical properties—mechanical, electronic, optical, and chemical, They also compare the bulk layered electrides with the 2D material when experimental or theoretical data is available. The work concludes with a discussion on synthetic strategies for making electrides as 2D materials and the emerging applications for electrenes.