First-principles study on the electronic structure and catalytic properties of two-dimensional MX2N4 systems (M = Ti, Zr; X = Si, Ge)

•It is systematically investigated the thermal stability, dynamical stability, mechanical stability, electronic properties and HER performance for two-dimensional MX2N4 systems (M = Ti, Zr; X= Si, Ge).•TiSi2N4; ZrSi2N4; ZrGe2N4 exhibit excellent HER performance and meet the thermodynamic requirements of OER for photocatalytic.•It is predicted that ZrGe2N4 with 1% compression strain can be used for photocatalytic water-splitting reactions. Recently, the two-dimensional MA2Z4 family with a seven-atom layer structure (experimentally synthesized a MoSi2N4 monolayer), which has good stability and exhibits semiconductivity, providing a platform for photocatalytic hydrolysis studies of two-dimensional polyatomic layer materials. In this work, we systematically investigated the thermal stability, dynamical stability, mechanical stability, electronic properties, and HER performance of the MX2N4 systems (M = Ti, Zr; X = Si, Ge). All monolayers exhibit excellent hydrogen evolution reaction (HER) performance (The Gibbs free energy (ΔGH*) of TiSi2N4; ZrSi2N4; ZrGe2N4 are 0.11 eV; 0.05 eV; −0.03 eV, respectively) and meet the thermodynamic requirements of OER for photocatalytic. Furthermore, the effects of biaxial strain and pH value on ZrGe2N4 monolayer photocatalytic hydrolysis performance were studied. ZrGe2N4 monolayer with 1% compression strain has well HER performance (ΔGH∗=0.21eV) under light conditions (Ue = 0.04 eV, pH = 0), and the photocatalytic oxidation process of water can take place spontaneously under light conditions and pH ≥ 7. In addition, the ZrGe2N4 monolayer also has excellent absorption in the visible range (high absorption coefficients over 105 cm−1). Undoubtedly, the potential applications and properties of MX2N4 monolayers in the fields of electrocatalysis and photocatalysis are poised to expand significantly. These findings hold great promise and are expected to offer valuable insights for experimental research in these areas.