<p>The utilization of ZnIn₂S₄ in photocatalytic hydrogen&#xa0;applications has garnered immense interest due to its promising features encompassing non-toxic nature, suitable band gap, and robust stability. However, the performance of ZnIn₂S₄ remains constrained by its limited absorption range and swift charge recombination. In this context, doping with rare earth metals has emerged as a potential strategy to enhance photocatalytic efficiency, yet this approach remains understudied. Herein, we report the synthesis of Er-doped ZnIn₂S₄ nanostructures utilizing a hydrothermal method, followed by structural characterization and HER evaluations. The XRD analysis confirms the primarily hexagonal crystal structure of ZnIn₂S₄. Notably, an optimal Er concentration of 70% exhibits enhanced hydrogen production efficiency. This improvement is attributed to the efficient charge transfer facilitated by Er doping, as evidenced by the photocurrent and Nyquist plots of ZnIn₂S₄. Moreover, the introduction of new energy levels by Er in the band gap enhances the light harvesting capability of ZnIn₂S₄. Furthermore, SEM studies reveal that Er doping influences the crystal growth rate of the material.</p> Graphical Abstract <p>The Er doped ZnIn₂S₄ photocatalyst were prepared through hydrothermal methods. The Er ions doping reduce the band gap of ZnIn₂S₄ by introducing the new energy levels in the band gap. The reduction of band gap enhances the absorption efficiency and also enhance the number of photogenerated charge carries, which results in enhanced the hydrogen evolution performance.</p> <p></p>