Novel Two-Dimensional MC2N4 (M = Cr, Mo, W) Monolayers for Overall Water Splitting with High Visible-Light Absorption

Abstract

Recently, the synthesis of 2D MoSi2N4 (Science; 2020;369; 670) proclaimed the dawn of a new family of 2D MA2Z4 materials. In this regard, through first-principles calculations, we proposed novel MC2N4 (M = Cr, Mo, W) monolayers with outstanding stability, which indicates a high possibility for experimental synthesis. The current study reveals that CrC2N4 (2.67 eV) is a direct bandgap semiconductor, whereas MoC2N4 (2.80 eV) and WC2N4 (2.84 eV) are indirect bandgap semiconductors, employing the HSE06 hybrid functional. All monolayers yield suitable band edge positions, making them ideal for photocatalytic water splitting and optoelectronics applications. Interestingly, the CrC2N4 monolayer has strong optical absorption in the visible spectrum. In contrast to MoC2N4 (WC2N4) monolayer, the Young's and layered moduli of the CrC2N4 monolayer are significantly high, 675 Nm−1 and 405 Nm−1, respectively. In contrast MC2N4 (M = Mo, W) monolayers exhibited a highly anisotropic nature compared to CrC2N4. Moreover, strain (+6% to −6%) has played an exciting role in modulating the bandgap and band alignment positions of the MC2N4 (M = Cr, Mo, W) monolayers. Interestingly, compressive strain is more beneficial for the CrC2N4 monolayer to perform photocatalytic water splitting under strong visible light. This work highlights the CrC2N4 monolayer as a novel 2D semiconductor with high stability and excellent photocatalytic properties.