Structural and electronic properties of MXene fakes: from edge e ects to bandgap evolution

Abstract

The structural and electronic properties of MXenes were investigated by means of a nite-systemapproach using all-electron Density Functional Theory-based calculations. Pristine (M2C)n akes and theirO-terminated counterparts (M2CO2)n (M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W; 12 ≤ n ≤ 216) werecomputationally modelled. Surface-like behaviour is lost for n ≤ 90, corresponding to ca. 3 nm wideakes, where nite-size e ects become increasingly relevant. While the ake structure at the core is verysimilar to that found in extended periodic models, the edges are often deformed due to structuraldefects, which impact their electronic properties. Pristine M2C akes are metallic, while the O-terminatedM2CO2 counterparts present bandgaps exceeding 1 eV for metals of Groups III and IV when neglectinglow-populated gap states near the Fermi level. The alignment of the valence and conduction bands forthese systems evolves favourably to nearly include the water splitting half-reactions within the bandgapfor the largest akes. Overall, our results show that Sc, Y, Zr, and Hf O-functionalised MXenes are the bestsuited for photocatalytic water splitting, obtaining energy gaps within the visible spectrum for severalflake sizes, and band alignments closer to water oxidation and hydrogen reduction reactions.