Efficient Humidity‐to‐Hydrogen Photocatalysis: Engineering Polymer‐Catalyst Bonds in Hygroscopic Hydrogels with Sulfur‐Vacancy‐Rich Nanosheets

This study presents an efficient hydrogel-based photocatalytic system for green hydrogen production directly from atmospheric humidity. By constructing a triangular-pyramid Zn-O bonding structure between hygroscopic polyacrylamide (PAM) hydrogel and sulfur vacancy-rich ZnIn₂S₄ (Sv-ZIS) nanosheets, strong interactions between gel O atoms and Zn atoms near S vacancies lead to shorter, more stable bonds. This structure enhances charge separation, accelerates reactant and product transport, and reinforces the hydrogel's mechanical properties. The composite achieves an apparent quantum efficiency of 35.1% at 365 nm and a stable hydrogen evolution rate of 28.79 mmol/gcat/h at ∼30 °C and 50% RH under 100 mW cm^-2 irradiation - surpassing traditional water-based photocatalysis. It also performs well under low-intensity LED light, indicating potential for indoor use. Molecular dynamics and DFT simulations reveal that the pyramid structure promotes polymer chain extension, increases water binding sites, and that sulfur vacancies facilitate H* desorption and further strengthen Zn-O interactions. The synergistic effect of the polymer matrix and sulfur vacancies boosts both activity and durability, while maintaining hygroscopicity. The composite is prepared via a mild, scalable in-situ method, highlighting its potential for practical, sustainable hydrogen production from ambient moisture.