Exfoliation Energy as a Descriptor of MXenes Synthesizability and Surface Chemical Activity

Abstract

MXenes are two-dimensional nanomaterials isolated from MAX phases by the selective extraction of the A component —a p-block element. The MAX phase exfoliation energy, Eexf, is regarded as a chemical descriptor of the MXene synthesizability. Here we show, by density functional theory estimations of the Eexf values for 486 different MAX phases, that Eexf decreases i) when MAX is a nitride, ii) when going along a d series of the metal M component, iii) when going down a group of the p-block A element, as well as iv) when having thicker MXene phases. Furthermore, Eexf is found to bias, even to govern, the surface chemical activity, as evaluated here on the CO2 adsorption strength, so that more unstable MXenes, displaying larger Eexf values, display a stronger attachment of species upon.

Concepts, models, and methods in computational heterogeneous catalysis illustrated throughCO2conversion

“…On the other hand, the MXenes basal (0001) planes are equivalent to TMCs and TMNs polar (111) surfaces, which normally display surface energies much higher than those of the (001) non‐polar surfaces and, consequently, are rarely exposed 259,260 . Indeed, the high surface energy, seized, for instance, by the exfoliation energy, is linked to a high chemical activity, 261 indicating that MXenes may be active enough to catalyze bond breaking on highly stable molecules. This has indeed been predicted for N 2 dissociation and ammonia synthesis 262,263 …”