Multilevel Theoretical Screening of Novel Two-Dimensional MA₂Z₄ Family for Hydrogen Evolution

The synthesis of 2D MoSi₂N₄ marked the birth of a new family of 2D MA₂Z₄ materials, whose potential applications are expected to sweep the field of nanoscale devices and catalysis in the future. In this work, we propose a multilevel screening workflow to systematically explore the mechanic stabilities, electronic properties, and hydrogen evolution performances of the 2D MA₂Z₄ family, among which seven stable, metallic, and highly active 2D MA₂Z₄ monolayers (2H-α-VGe₂N₄, 2H-α-NbGe₂N₄, 2H-α-TaGe₂N₄, 2H-α-NbSi₂N₄, 2H-β-VGe₂N₄, 2H-β-NbGe₂N₄, and 2H-β-TiGe₂P₄) are predicted as promising hydrogen evolution reaction (HER) catalysts with near-zero hydrogen adsorption free energy (ΔG_H). The lowest unoccupied state energy (E_LUS) of the MA₂Z₄ basal plane is identified as a concise descriptor to influence the electron filling and eventually determine its ΔG_H. The criteria of -6.0 < E_LUS < -5.6 eV is confirmed as the HER active window to explore novel HER catalysts. In particular, group-VI-terminated MA₂Z₄ basal planes have a higher E_LUS (> -5.6 eV), which leads to weak H adsorption and poor HER activities accordingly.