Two-dimensional MX2Y4 systems: ultrahigh carrier transport and excellent hydrogen evolution reaction performances

Abstract

Very recently, two-dimensional MoSi₂N₄ has been synthetized (Y.-L. Hong, Z. Liu, L. Wang, T. Zhou, W. Ma, C. Xu, S. Feng, L. Chen, M.-L. Chen and D.-M. Sun, Chemical vapor deposition of layered two-dimensional MoSi₂N₄ materials, Science, 2020, 369, 670–674.). In this work, we systematically explore the mechanical, electronic, and catalytic properties of the MX₂Y₄ (M = Cr, Hf, Mo, Ti, W, Zr; X = Si, Ge; Y = N, P, As) monolayers by first-principles calculations. These observed monolayers exhibit an isotropic Young's moduli of 165–514 N m⁻¹ and a Poisson's ratio of 0.26–0.33. The calculated band structures indicate that their bandgaps are in the range of 0.49–2.05 eV at the HSE06 level. In particular, a high electron mobility of about 1.04 × 10⁴ cm² V⁻¹ s⁻¹ is observed in TiSi₂N₄ monolayers, which shows potential for high-speed electronic devices. MX₂Y₄ monolayers also reveal decent performances in the hydrogen evolution reaction. More importantly, the Gibbs free energy change of the TiSi₂N₄ (ZrSi₂N₄) monolayer is as small as 0.078 eV (−0.035 eV), even being comparable with that of Pt (−0.09 eV). This investigation suggests that the MoSi₂N₄ family monolayers have potential advanced applications such as photocatalytic, electrocatalytic, and photovoltaic devices.