Prediction of T‐ and H‐Phase Two‐Dimensional Transition‐Metal Carbides/Nitrides and Their Semiconducting–Metallic Phase Transition

The discovery of various two-dimensional (2D) nanomaterials with different phases is fundamentally and technologically intriguing, leading to diverse physical and chemical properties for expanded applications. Herein, we performed systematic first-principles calculations to explore a series of single-layer MXenes (M2 X: M=Sc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta; X=C, N). The new H-phase MXenes are firstly predicted, which are compared with the usually synthesized MXenes named as T-phase MXenes on their structure and electronic properties. Semiconducting-metallic transitions could be realized by T-/H- phase transition for Sc2 CO2 , Sc2 CO2 H2 , and Ti2 CO2 . Besides, the differences between MXenes and MoS2 on energy storage are discussed. Our work will provide valuable directions for the discovery of new MXene phases and give a systematic understanding of 2D MXenes.