Noble Metal-Free 2D/3D S-Scheme Heterojunction Enabling Effective Charge Transfer for Photocatalytic Hydrogen Evolution

In this work, O-incorporated MoS2 nanosheets (OMS) and pristine ZnIn2S4 (ZIS) nanoflowers are synthesized by solvothermal and hydrothermal methods, respectively. The heterostructure of optimized 9% OMS@ZIS is prepared using a simple chemical reduction method. The prepared 1T phase of OMS is well characterized by XRD, EPR spectroscopy, and Raman spectroscopy. XRD, Raman, FE-SEM, HR-TEM, and XPS characterizations clearly demonstrate the successful formation of a heterostructure between OMS and ZIS. The photocatalytic hydrogen evolution experiment is run under a solar simulator, using 0.45 M Na2S/1.00 M Na2SO3 as a hole scavenger, and produces 3429 μmol/g hydrogen with 9% OMS@ZIS as the catalyst, which is 21-fold and 72-fold higher than with pristine ZIS (160 μmol/g) and OMS (47 μmol/g). The type II band alignment and S-scheme mechanism for photocatalytic hydrogen evolution are well explained by cyclic voltammetry and DFT studies. The optimized OMS@ZIS catalyst retains 87.94% of its hydrogen evolution efficiency through the fourth cycle, with no significant structural changes observed, as confirmed by XRD analysis. This work highlights the significant role of the isoelectronic effect in OMS nanosheets as an efficient, metal-free cocatalyst for pristine ZIS, with a systematic discussion of charge transfer between them, and offers a promising approach to designing cost-effective photocatalysts for solar light-driven hydrogen evolution.