Producing H2 using solar-driven photocatalysts is a potential way to sustainably create energy and replace fossil fuels. Semiconducting CdS quantum dots, given their fitting bandgap, solution processability and tunable optical and electronic properties, are excellent photocatalytic candidates. To stabilize them under practical conditions, a passivating shell of another semiconductor, such as ZnS, is often used. However, the wider bandgap of this shell confines the charge carriers within the core, making available only a small amount of photogenerated electrons and holes. These so-called type-I core–shell quantum dots are thus essentially inert as photocatalysts. Ou Chen and colleagues show that studding metallic Au domains on CdS-ZnS core–shell quantum dots activates them as catalysts, enhancing their photocatalytic H2 evolution rate by more than 400 times compared with bare CdS-ZnS particles. This effect owes to an interfacial Au2S layer that weakens the quantum confinement and frees the confined charges to the surface.