Although transition-metal-based sulfides have been identified as efficient catalysts to replace expensive noble metal catalysts for photocatalytic H-2 evolution reaction (HER), their activities are still unsatisfied and could be further improved by controlling their microstructures and electronic structures. Herein, we present an effective strategy to confine highly active Mo-activated CoSx (Mo-CoSx) active sites within MCM-41 frameworks by sulfurization of Co-doped MCM-41 during the in situ photoreduction of [MoS4](2-) in Erythrosin B-triethanolamine (ErB-TEOA) system. It is found that Co-MCM-41 offers not only abundant coordinatively unsaturated Co sites to be activated by Mo and S but also large surface area to effectively disperse the in situ generated amorphous Mo-CoSx active sites. Under 520 nm irradiation, the most efficient Mo-CoSx/MCM-41-100 (Si/Co = 100) catalyst exhibits similar to 7, 3, and 4 times higher H-2 evolution activity than free MoSx, free Mo-CoSx, and CoSx/MCM-41-100, respectively, and an apparent quantum yield (AQY) of 12.3% for H-2 evolution. Furthermore, when Mo-CoSx/MCM-41-100 was sensitized with a more stable fluorescein (FL) dye, the photocatalytic system shows a sustainable H-2 evolution activity in a 20 h reaction, showing the good stability of Mo-CoSx/MCM-41-100 catalyst. This work provides a new insight into the design and development of highly active hybrid H-2 evolution catalysts based on transition metals for highly efficient and large-scale solar energy conversion to clean H-2 energy. (C) 2019 Elsevier Inc. All rights reserved.