Tetragonal-structured anisotropic 2D metal nitride monolayers and their halides with versatile promises in energy storage and conversion

Abstract

Here we propose a series of novel two-dimensional tetragonal-structured metal nitride (t-MN, M = Ti, Zr or Hf) monolayers mainly bonded with strong hybridization of N-p and M-d orbitals. These monolayers exhibit metallic properties which make them promising candidates as electrode materials for Li-ion batteries. The computations disclosed that t-TiN has a high theoretical Li-storage capacity of 432 mA h g⁻¹ and a low Li ion diffusion barrier of 0.25 eV. After halogenation, the t-MNX (X = Cl, Br and I) monolayers transform to semiconductors with high carrier mobility and direct band gaps ranging from 0.41 to 3.26 eV. Moreover, the 2D nature and strong light absorption endow them with wide applications to photocatalysis. The appropriate band edge position indicates that t-ZrNX and t-HfNX can be applied as 2D photohydrolytic catalysts. Finally, a top-down method followed by high-temperature treatment is proposed to prepare t-MN monolayers.