Enhanced water splitting for hydrogen production via Z-scheme heterostructures of Mo@CTF-0, HfS2, and HfSSe monolayers

Abstract

Two-dimensional (2D) covalent organic frameworks (CTFs) show great potential for the photocatalytic hydrogen evolution reaction (HER), but their broad band gaps often hinder their solar-to-hydrogen (STH) efficiency. In this work, we overcame this limitation by doping transition metal atoms into a 2D CTF-0 monolayer, narrowing its band gap to an optimal value of 1.60 eV (considering Mo@CTF-0). Leveraging this tuned foundation, we designed innovative heterostructures—Mo@CTF-0/HfS₂, Mo@CTF-0/α-HfSSe, and Mo@CTF-0/β-HfSSe—to boost their STH performance. Through detailed analysis of their electronic structure, optical properties, and thermodynamic stability, we demonstrated their suitability for Z-scheme water splitting. Non-adiabatic molecular dynamics simulations further revealed the dynamics of charge transfer and interlayer recombination, shedding light on their photocatalytic efficiency. Remarkably, these systems achieved a maximum STH efficiency of 20.36%. Gibbs free energy analysis confirmed that the HER and oxygen evolution reaction proceeded spontaneously across a practical pH range. Among the candidates, the Mo@CTF-0/α-HfSSe heterostructure stood out, offering superior protection for photogenerated carriers and positioning itself as a top contender for next-generation photocatalytic hydrogen production.