Gradient Hydrogen Migration Modulated with Self-Adapting S Vacancy in Copper-Doped ZnIn₂S₄ Nanosheet for Photocatalytic Hydrogen Evolution

It is a challenge to regulate charge flow synergistically at the atomic level to modulate gradient hydrogen migration (H migration) for boosting photocatalytic hydrogen evolution. Herein, a self-adapting S vacancy (Vs) induced with atomic Cu introduction into ZnIn₂S₄ nanosheets was fabricated elaborately, which can tune charge separation and construct a gradient channel for H migration. Detailed experimental results and theoretical simulations uncover the behavior mechanism of Vs generation with Cu introduction after substituting a Zn atom tendentiously. Cu-S bond shrinkage and Zn-S bond distortion are presented around Vs areas. Besides, Vs induced by Cu introduction lowers the internal electric field to restrain electron transmission between layers, which are enriched on the Vs area because of the lower surface electrostatic potential. Atomic Cu and Vs show a synergistic effect for regulating regional charge separation due to the Cu dopant being a hole trap and Vs being an electron trap. The channels for H migration with gradient ΔG_H⁰ are constructed by different S atom sites, which are modulated by Vs. Gradient H migration driven by a photothermal effect occurs on an identical surface without striding across a heterogeneous interface, which is a valid pathway with lower resistance for boosting H₂ release. Ultimately, 5 mol % Cu confined in ZnIn₂S₄ nanosheets achieves an optimum photocatalytic hydrogen evolution activity of 9.8647 mmol g^-1 h^-1, which is 14.8 times higher than 0.6640 mmol g^-1 h^-1 for ZnIn₂S₄, and apparent quantum efficiency reaches 37.11% at 420 nm. This work demonstrates the behavior mechanism of atomic substitution and provides cognition for hydrogen evolution mechanism deeply.