Enhanced Water Splitting for Hydrogen Production via Z-Scheme Heterostructures of Mo@CTF-0, HfS2, and HfSSe Monolayers

Abstract

Two-dimensional covalent triazine frameworks (CTFs) are promising candidates for photocatalytic hydrogen evolution, yet their intrinsically wide band gaps limit solar energy harvesting. Herein, we employ Mo doping to narrow the band gap of a CTF-0 monolayer to an optimal 1.60 eV, thereby constructing three novel Z-scheme heterostructures: Mo@CTF-0/HfS2, Mo@CTF-0/α-HfSSe, and Mo@CTF-0/β-HfSSe. First-principles calculations confirm their thermodynamic stability and favorable band edge alignments for overall water splitting. Notably, nonadiabatic molecular dynamics (NAMD) simulations reveal the ultrafast interlayer charge transfer and suppressed carrier recombination, providing direct insights into the superior charge separation efficiency of these heterostructures. Among them, Mo@CTF-0/α-HfSSe exhibits the most efficient charge carrier dynamics, correlating with its highest predicted solar-to-hydrogen efficiency of 20.36%. Additionally, Gibbs free energy analyses confirm that both hydrogen evolution and oxygen evolution reactions proceed spontaneously across a broad pH range. This work not only demonstrates the potential of Mo@CTF-0-based heterostructures as high-performance Z-scheme photocatalysts, but also highlights the critical role of NAMD simulations in uncovering charge-transfer-driven mechanisms in low-dimensional photocatalytic systems.