First-principles study of Ga ₂Ge ₂S ₃Se ₃ monolayer: a promising photocatalyst for water splitting†

Abstract

Recently, the quaternary Janus monolayers with the formula A ₂B ₂X ₃Y ₃ have been shown to be promising candidates for optoelectronic applications, especially in the photocatalytic water splitting reaction. Therefore, first-principles calculations were employed to investigate the photocatalytic properties of Ga ₂Ge ₂X ₃Y ₃ (X and Y represent S, Se or Te atoms) monolayers. The Ga ₂Ge ₂S ₃Se ₃ and Ga ₂Ge ₂Se ₃Te ₃ monolayers exhibit dynamic and thermal stability, supported by high cohesive energies (3.78–4.20 eV) and positive phonon dispersion. With a moderate Young's modulus (50.02–65.31 N m ⁻¹) and high Poisson's ratio (0.39–0.41), these monolayers offer a balance of stiffness and flexibility, making them suitable for flexible electronic applications. Especially, the difference in work function of 0.27 eV induces an intrinsic electric field in the Ga ₂Ge ₂S ₃Se ₃ monolayer, making the electronic structure of this material be suitable for the photocatalytic water splitting process. With light irradiation, the oxygen evolution reaction (OER) happened simultaneously, producing electrons and H ⁺ protons for the hydrogen evolution reaction (HER) to happen at a low potential barrier. Moreover, the Ga ₂Ge ₂S ₃Se ₃ monolayer has a high absorption rate α( ω) of 10 ⁵–10 ⁶ cm ⁻¹ and a high electron mobility of 430.82–461.50 cm ² V ⁻¹ s ⁻¹. These characteristics result in a good solar-to-hydrogen of the Ga ₂Ge ₂S ₃Se ₃ monolayer (14.80%) which is promising for use in photon-driven water splitting.

Abstract

The Ga ₂Ge ₂S ₃Se ₃ monolayer: a promising 2D photocatalyst with high solar-to-hydrogen efficiency, efficient charge separation, and electron mobility.