Quasi-homogenous dye-sensitized photocatalytic H^sub 2^ evolution catalyzed by in-situ grown cobalt-promoted MoS^sub x^ catalyst coupled with graphene quantum dots

The development of practical photocatalytic systems for large-scale and on-demand solar-to-hydrogen conversion requires that H2 evolution catalysts consist of earth-abundant materials and can be facilely obtained and modified. In this paper, we report a high-performance and quasi-homogenous dye-sensitized H2 evolution system by coupling graphene quantum dots (GQDs) with cobalt-promoted MoSx (Co-MoSx) catalyst. The Co-MoSx serving as H2 evolution catalyst can be facilely grown by a in-situ photochemical reduction method in the presence of an organic dye as the photosensitizer and simultaneously coupled with GQDs during photocatalytic reactions, forming GQDs/Co-MoSx catalyst. The resulted GQDs/Co-MoSx catalyst exhibits high activity for catalyzing H2 evolution under visible light due to the significant synergistic effects among GQDs, Co dopant, and MoSx. The doping of MoSx with Co ions results in an effective promotional effect on the H2 evolution activity of in-situ generated Co-MoSx catalyst, while the presence of GQDs can not only improve the dispersion of Co-MoSx catalyst by serving as a homogenous matrix but also lead to an efficient Förster resonance energy transfer (FRET) to sensitizing dye by acting as a quasi-homogenous energy donor for enhancing light utilization efficiency. In addition, the GQDs can also act as an electron transfer relay to facilitate the electron transfer from excited dye to Co-MoSx catalyst, thus retarding the back electron transfer and reducing energy loss. This work provides a new route to construct an efficient and quasi-homogenous dye-sensitized H2 evolution system by integrating inexpensive MoSx-based catalyst with transition metal modification and highly photoluminescent and soluble GQDs with outstanding optical properties.