Prediction of surface termination preference of out-of-plane ordered double-transition metal MXenes (o-MXenes) from first-principles calculations

Surface terminations greatly affect the MXene performance. On the basis of the first-principles thermodynamic calculations, the surface termination preference of 33 different out-of-plane ordered double-transition metal MXenes when prepared by etching the o-MAX phases with HF acid is revealed. By calculating the reaction enthalpy and reaction Gibbs free energy at finite temperature, it is concluded that when the outermost transition metal is a 3d-orbital transition metal, the surface termination is dominated by-F, and when the outermost transition metal belongs to 4d or 5d-orbital transition metal, the surface termination is mainly-O. And this preference law may be related to whether the outermost transition metal can donate enough electrons to surface groups.