Hollow heterostructures for regulating charge transfer in solar-driven hydrogen production

The development of efficient photocatalysts for solar-driven hydrogen production critically depends on precise regulation of photogenerated charge carriers at semiconductor interfaces. In this context, hollow heterostructured photocatalysts (HHPs) have emerged as advanced nanoarchitectures that function as confined photoreactors for regulating interfacial charge-transfer processes. Their hollow architectures (HAs), featuring internal cavities, thin shells, and curvature-rich interfaces, promote photon confinement, shorten carrier diffusion pathways, and improve accessibility of catalytic sites, thereby strengthening interfacial electric fields, optimizing band alignment, and suppressing charge recombination. Simultaneously, Z-scheme and S-scheme heterojunctions have attracted considerable attention as effective charge-transfer configurations that maintain strong redox potential while enabling spatial separation of photogenerated carriers. Integrating these heterojunctions with HAs offers a powerful strategy to synergistically optimize light harvesting, interfacial charge separation, and surface reaction kinetics. This review provides a comprehensive overview of the roles of HAs in regulating interfacial charge-transfer pathways within Z- and S-scheme photocatalytic systems for solar-driven H 2 evolution. Representative material platforms, including oxide-, chalcogenide-, and framework-derived systems, are discussed alongside advances in synthetic strategies and structural engineering. In addition, advanced spectroscopic and electrochemical characterization techniques, combined with computational studies by density functional theory, are highlighted for elucidating interfacial energetics and carrier-transfer dynamics. Finally, emerging design principles and performance metrics are outlined to guide the rational development of efficient, stable, and scalable hollow photocatalysts for solar-to-hydrogen conversion.