Abstract <p>The design of S-scheme heterostructures is a crucial approach to enhancing the separation and transport of photogenerated carriers in photocatalysts. Herein, a S-scheme SV-ZnIn₂S₄/Bi₄NbO₈Cl heterojunction photocatalyst was successfully prepared with enhanced internal electric field effect by using facile in situ growth strategy. Systematic research studies have shown that the S vacancies in ZnIn₂S₄ can enhance Fermi energy level, and increased Fermi energy level difference between ZnIn₂S₄ and Bi₄NbO₈Cl leads to the formation of a more robust interfacial electric field. The enhanced interfacial electric field accelerates the directional transport of photogenerated carriers in the S-scheme. Moreover, theoretical simulations verified the introduction of S vacancies and the construction of heterojunctions can significantly modulate the electronic structure of the catalyst surface. It significantly reduces the adsorption energy of H, from − 0.96&#xa0;eV (pristine ZnIn₂S₄) to − 0.28&#xa0;eV (SV-ZnIn₂S₄/Bi₄NbO₈Cl). The rapid proton desorption promotes the release of H₂ molecules. Thus, the optimized photocatalyst SV-ZnIn₂S₄/Bi₄NbO₈Cl exhibited a high hydrogen evolution rate of 1084.9&#xa0;μmol·g⁻¹&#xa0;h⁻¹, about 2.2 and 19.8 times that of the original ZnIn₂S₄ and Bi₄NbO₈Cl. This study reveals the mechanism of photocatalytic hydrogen evolution in SV-ZnIn₂S₄/Bi₄NbO₈Cl by modulating the internal electric field and H adsorption energy within the S-scheme heterojunction.</p> Graphical abstract <p></p>