Fast\nCarrier Recombination, Nanoconfinement, and Defects\nBoost Solar-Driven Hydrogen Evolution Reactions at Z‑Scheme\nHeterojunctions

The\nvertical heterostructure between phase-different two-dimensional\n(2D) transition metal dichalcogenides (TMDs) and metal monochalcogenides\nexhibits a promising photocatalytic performance. We combine several\ncomputational methods to explore catalytic processes for solar-driven\nhydrogen evolution reactions (HERs) on thermodynamically stable Mo<i>X</i><sub>2</sub>/SnS (<i>X</i> = S, Se, and Te).\nExcept for MoTe<sub>2</sub>/SnS, these heterostructures have prominent\nstaggered band alignment, significantly reducing the band gap and\nenhancing optical response to visible light irradiation. The time-domain\nKohn–Sham (TD-KS) theory and nonadiabatic molecular dynamics\n(NAMD) depict fast interlayer electron–hole recombination between\nband edge states, revealing prominent Z-scheme heterojunction formation.\nThe band-to-band relaxation eventually leads to long carrier lifetimes\nand high redox potential for photogenerated electrons in the SnS layer,\nenhancing HER catalytic performance. Moreover, the inner layer of\nSnS that noncovalently interacts with MoS<sub>2</sub> emerges as a\nsuperior photocatalytic surface compared to the traditionally investigated\nouter one. Nanoconfinement influences the hydrogen bond formation\nbetween the reactant H atom and <i>X</i> of Mo<i>X</i><sub>2</sub> (<i>X</i> = S and Se), boosting the catalytic\nprocess at the interlayer space. The defect engineering, especially\nthe facile formation of Sn vacancy sites within the nanoconfined SnS\nlayer emerge as the most thermodynamically favourable sites for enhancing\nthe HER activity in the SnS layer. These vacancies introduce a unique\nlocal electronic environment that promotes the adsorption and activation\nof reaction intermediates. The significant dynamic fluctuations of\nthe transient S–H bond at these sites further depict the optimal\nbinding of the reactant, ensuring the best catalytic activity of Sn\nvacancies in the inner layer. The <i>in silico</i> study\nprovides a detailed atomistic understanding of the hydrogen evolution\nprocess on metal chalcogenide heterostructures, suggesting their strategic\ndesign principles to boost photocatalytic activities.