Graphene Quantum Dots as Electron Acceptor Tailoring S-Scheme Heterojunction Bi 2 MoO 6 @Cu 2 O for Highly Efficient Photocatalytic H 2 Evolution

Hydrogen (H2) energy is a clean, renewable energy carrier with a high energy density and zero carbon emissions. Photocatalytic water splitting offers a promising route to H2 production by utilizing abundant solar energy; yet, it is often limited by sluggish charge carrier kinetics and low quantum efficiency. Herein, we incorporate graphene quantum dots (GQDs) as cocatalysts into the S-scheme heterojunction inorganic semiconductor Bi2MoO6@Cu2O (BMO@Cu2O) to boost photocatalytic H2 evolution. Under simulated sunlight, the GQDs/BMO@Cu2O composite achieves an exceptional H2 production rate of 16.1 mmol·g-1·h-1 and an apparent quantum yield of 33.6% at 420 nm. The built-in electric field (IEF) between BMO and Cu2O promotes S-scheme charge transfer, enhancing carrier separation. GQDs function as electron acceptors and active sites, where their delocalized π-electron cloud in the sp2-hybridized carbon skeleton shortens charge migration paths and lowers the energy barrier for surface H2 evolution. In situ X-ray photoelectron spectroscopy, Kelvin probe force microscopy, and density functional theory calculations collectively confirm the IEF and S-scheme electron transfer. This work presents a strategic design of GQDs-mediated heterojunctions with efficient charge separation and strong redox capacity, advancing solar-driven H2 production technology.