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Abstract:
Two-dimensional Janus materials, recognized for their asymmetric structure and intrinsic electric dipole, exhibit unique properties such as enhanced surface exposure and efficient charge separation, making them highly suitable for energy-related applications. In this study, we investigated two novel Janus structures, MgZnS and MgZnSe, through first-principles calculations, confirming their structural stability via phonon dispersion and ab initio molecular dynamics simulations. Both materials exhibit indirect band gaps, with MgZnS showing values of 0.74 eV and 1.20 eV, and MgZnSe 0.94 eV and 1.40 eV, as obtained using the PBE and HSE06 approximations, respectively. Optical analysis revealed strong absorption in the visible and ultraviolet regions, with MgZnS achieving a maximum absorption coefficient of 4.3 x 105 cm-1, and both materials covering a broad visible spectrum. The conduction band minima (-2.77 eV for MgZnS and-2.76 eV for MgZnSe) and valence band maxima (-5.9 eV for MgZnS and-5.88 eV for MgZnSe) align well with water's redox potentials in acidic and neutral environments, facilitating effective charge separation for photocatalytic reactions. Furthermore, their Gibbs free energy values for hydrogen evolution are negative and near zero (-0.037 eV for MgZnS and-0.32 eV for MgZnSe), indicating thermodynamic feasibility and spontaneity at pH = 7. The solar-to-hydrogen (STH) conversion efficiencies are particularly noteworthy, reaching 27.35 % for MgZnS and 25.79 % for MgZnSe at pH values exceeding 6.3, surpassing many conventional photocatalytic materials. These exceptional properties, combined with strong absorption, favorable band alignment, and the intrinsic dipole of the Janus structures, position MgZnS and MgZnSe as highly promising candidates for water photodissociation and green hydrogen production.
