S-Scheme CdS/Co₃S₄ Double-Shelled Hollow Nanoboxes for Enhanced Photocatalytic Hydrogen Evolution

Developing S-scheme systems with high photocatalytic performance is crucial for long-term solar-to-hydrogen conversion. In this study, hollow cobalt tetrasulfide (Co₃S₄) nanoboxes (NBs), synthesized via sulfurization using zeolitic imidazolate framework (ZIF-67) as a template, are combined with cadmium sulfide (CdS) nanoparticles (NPs) to construct heterojunction photocatalysts under mild conditions. The optimized CdS/Co₃S₄ double-shelled nanoboxes (DSNBs) achieved a superior photocatalytic hydrogen production rate of 23.45 mmol h^-1 g^-1 under visible light, approximately 24 times greater than that of pure CdS NPs. The apparent quantum efficiency (AQE) of CdS/Co₃S₄ DSNBs is 18.5 %. The distinctive hollow structure enhances visible-light-harvesting by exposing active sites, enabling multiple light reflections, and allowing the thin shells to shorten the transport distance for charge carriers, effectively minimizing charge recombination. The improved photoactivity results from the synergistic effects of the aligned bandgap structures, strong visible-light absorption, and interfacial interactions driven by the inherent electric field (IEF). The findings offer insights into designing efficient S-scheme heterojunction catalysts for sustainable hydrogen evolution through photocatalytic water splitting.