Rational Design of Two‐Dimensional Octuple‐Atomic‐Layer M ₂ A ₂ Z ₄ for Photocatalytic Water Splitting Based on First‐Principles Calculations

Two-dimensional (2D) materials have emerged as promising candidates as photocatalytic materials due to their large surface areas and tunable electronic properties. In this work, we systematically design and screen a series of octuple-atomic-layer M₂A₂Z₄ monolayers (M = Al, Ga, In; A = Si, Ge, Sn; Z = N, P, As) using first-principles calculations. One hundred and eight structures are constructed by the intercalation approach, followed by a comprehensive evaluation of their thermodynamic and dynamic stability, band gaps, and band edge alignments to assess their potential for photocatalytic overall water splitting. Eight candidates meet the criteria for overall water splitting, among which Al₂Si₂N₄ and Al₂Ge₂N₄ exhibit suitable band edge positions, pronounced visible-light absorption, high electron mobility, and high solar-to-hydrogen (STH) efficiencies for photocatalysis under both acidic and neutral environments (pH = 0 and 7). Importantly, the introduction of N vacancies on the surfaces of Al₂Si₂N₄ and Al₂Ge₂N₄ significantly enhances their catalytic activity for both hydrogen reduction and water oxidation reactions, further supporting their potential as photocatalysts for overall water splitting. Both materials also display robust structural stability in aqueous environments. Our study provides theoretical insights for the rational design of efficient and stable 2D photocatalysts for overall water splitting.