This study investigates the enhancement of photocatalytic hydrogen evolution (PHE) using single-atomic Mo-doped ZnIn₂S₄ (Mo-ZIS) nanosheets. The authors report a one-step hydrothermal method to prepare Mo-ZIS nanosheets, which exhibit significantly improved PHE performance. The substitution of In atoms with Mo atoms in ZIS nanosheets leads to spatial charge redistribution, enhancing the separation of photogenerated charge carriers and optimizing the Gibbs free energy of H⁺ adsorption on S atoms at the basal planes. As a result, Mo-ZIS shows an impressive PHE rate of 6.71 mmol·g⁻¹·h⁻¹, over 10 times higher than pristine ZIS, with an apparent quantum efficiency (AQE) of 38.8% at 420 nm. The study provides insights into the coordination configuration and electronic modulation resulting from single-atom decoration, offering a promising approach for developing advanced photocatalysts via non-precious metal atomic modification.This study investigates the enhancement of photocatalytic hydrogen evolution (PHE) using single-atomic Mo-doped ZnIn₂S₄ (Mo-ZIS) nanosheets. The authors report a one-step hydrothermal method to prepare Mo-ZIS nanosheets, which exhibit significantly improved PHE performance. The substitution of In atoms with Mo atoms in ZIS nanosheets leads to spatial charge redistribution, enhancing the separation of photogenerated charge carriers and optimizing the Gibbs free energy of H⁺ adsorption on S atoms at the basal planes. As a result, Mo-ZIS shows an impressive PHE rate of 6.71 mmol·g⁻¹·h⁻¹, over 10 times higher than pristine ZIS, with an apparent quantum efficiency (AQE) of 38.8% at 420 nm. The study provides insights into the coordination configuration and electronic modulation resulting from single-atom decoration, offering a promising approach for developing advanced photocatalysts via non-precious metal atomic modification.