Two-dimensional blue-phase CX (X = S, Se) monolayers with high carrier mobility and tunable photocatalytic water splitting capability

Two-dimensional blue-phase CX (X=S, Se) monolayers with large intrinsic dipoles, high carrier mobility, appropriate band edge alignments, and pronounced optical absorption simultaneously are theoretically predicted to be high efficient photocatalysts for water splitting. [Display omitted] Photocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the energy and environmental issues. Recently, two-dimensional (2D) materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance. In this work, blue-phase monolayer carbon monochalcogenides (CX, X = S, Se) are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory. After confirming the great dynamical, thermal, and mechanical stability of CX monolayers, we observe that they possess moderate band gaps (2.41 eV for CS and 2.46 eV for CSe) and high carrier mobility (3.23 × 104 cm2 V−1 s−1 for CS and 4.27 × 103 cm2 V−1 s−1 for CSe), comparable to those of many recently reported 2D photocatalysts. Moreover, these two monolayer materials are found to have large intrinsic dipole (0.43 D for CS and 0.51 D for CSe), thus the build-in internal electric field can be self-introduced, which can effectively drive the separation of photongenerated carriers. More importantly, the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting. Additionally, the effects of external strain on the electronic, optical and photocatalytic properties of CX monolayers are also evaluated. These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.