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.