Band-Aligned Trimetallic Ni-In-Zn Active Sites in a 2D/2D Type-II ZnIn ₂ S ₄ /g-C ₃ N ₄ Heterostructure for Vectorial Charge Transfer and Hydrogen Evolution

The pursuit of clean and sustainable hydrogen fuel has intensified research into cost-effective and visible-light-responsive photocatalysts. Herein, we report the construction of trimetallic Ni-In-Zn active sites with engineered band alignment in a 2D/2D heterostructure of Ni-doped ZnIn 2 S 4 /g-C 3 N 4 nanosheets (Ni-ZIS/CN) for efficient photocatalytic hydrogen evolution. The hydrothermally prepared Ni-ZIS/CN composite consists of ultrathin Ni-doped ZIS nanosheets grown on CN layers. Comprehensive characterization confirms successful Ni doping and strong interfacial coupling between Ni-ZIS and CN. Ni doping modulates the lattice structure, as well as the optical and electronic properties of ZIS while maintaining its hexagonal crystal structure, as evidenced by XRD and XPS. The incorporation of Ni introduces catalytically active sites with enhanced proton (H * ) affinity, narrows the band gap, and redistributes electron density around sulfur sites, thereby facilitating favorable proton adsorption and vectorial charge transfer via a 2D/2D type-II heterojunction. The synergistic interplay between Ni doping and the ultrathin heterojunction architecture produced a hydrogen evolution rate of 3.8 mmol h –1 g –1 for the optimized Ni-ZIS/CN photocatalyst, corresponding to an enhancement of 272-fold, 3.4-fold, and 2.7-fold compared to CN, ZIS, and Ni-ZIS, respectively, along with excellent reusability. Unlike previous studies focused on binary systems or precious metal co-catalysts, this work demonstrates that the synergistic integration of multimetallic active sites, a type-II heterojunction, and 2D/2D nanosheet interfacing provides an effective strategy for high-performance photocatalytic hydrogen production.