Design and Tuning of Photocatalytic Properties in MoC₂N₄/WC₂N₄ van der Waals Heterostructure: A DFT Investigation

Humanity is currently confronted with significant challenges including energy shortages and limited access to clean energy sources. Photocatalytic water splitting for hydrogen production, utilizing two-dimensional van der Waals heterostructures, offers a promising solution to these pressing issues. In this study, we constructed a type-II van der Waals heterostructure of MoC 2 N 4 /WC 2 N 4, with a lattice mismatch of 0.76%, composed of monolayers of MoC 2 N 4 and WC 2 N 4 . After conducting a thorough thermodynamic stability screening, we identified the most stable stacking configuration. Subsequent calculations of the optical and electronic properties demonstrate that this heterostructure is a highly promising candidate for the overall water splitting photocatalysis. Its stability was further confirmed through phonon dispersion spectroscopy and ab initio molecular dynamics (AIMD) simulations. Then, the electronic properties of the MoC 2 N 4 /WC 2 N 4 heterostructure were calculated using HSE functional. The results show that it is a type-II van der Waals heterostructure with appropriate band edge positions. The photogenerated electrons and holes in the heterostructure are efficiently separated, which significantly enhances photocatalytic activity. Furthermore, the carrier mobility and optical absorption efficiency of the heterostructure are significantly improved compared to those of the monolayer materials. Additionally, we computed the band structure, optical absorption spectra, and hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances under biaxial strain ranging from −5 to +5%. Our findings indicate that biaxial strain substantially influences the band structure and optical absorption efficiency. In particular, under 1% tensile biaxial strain, the heterostructure exhibits enhanced catalytic activity, making it a promising candidate for water splitting photocatalysis.