Screening Surface Structure of MXenes by High-Throughput Computation and Vibrational Spectroscopic Confirmation

Functionalized MXenes hold promises in a variety of applications in which the dispensable functional groups are mixed. The functionalization is spontaneously realized through competitive adsorption of active species on the MX matrix during the acid etching process of MAX phases. Nevertheless, the knowledge of proportion and distribution of functional groups on MXenes, i.e., surface structures, is still limited. By high-throughput computation screening, ground-state stable structures of four kinds of typical MXenes—Ti2CTx, Ti3C2Tx, Nb2CTx, and Nb4C3Tx (T = O, F, and OH)—with mixed functional group compositions are figured out for the first time. The multicomponent functional group patterns definitely demonstrate an obvious feature of spatial mixing at a given component. However, the heterogeneous structure has a near linear dependence on the functional group components in terms of free energy. Most functionalized MXenes are dynamically stable except for Nb2CF2 and Nb2C(OH)2 due to their competing displacive counterparts. Last but not least, Raman spectra of the four kinds of MXenes confirm the predicted stable surface structures of MXenes. This study provides a clear fundamental basis for understanding the surface structures of MXenes.