• • Achieves ultrahigh Cu loadings of 7.4 wt% as isolated single atoms and 12.4 wt% as single-atom/subnanometer-cluster hybrids, overcoming the typical <1.5 wt% loading ceiling of oxide-supported SACs; this enables higher areal density of active sites, directly boosting per-gram activity and reducing catalyst cost per unit H2 produced.
• • The optimized hybrid catalyst delivers a photocatalytic H2 evolution rate of 28.8 mmol g−1 h−1 under simulated sunlight, surpassing conventional low-loading Cu/TiO2 systems under comparable conditions; this represents a >10-fold improvement over typical Cu SACs, making solar H2 production economically more viable.
• • The hollow flower-sphere TiO2 nanoreactor, derived from sodium titanate, provides broad accessibility of ion-exchange sites and structural confinement, enabling high Cu uptake prior to oxide formation; this addresses the diffusion limitations and site inaccessibility that plague conventional impregnation methods.
• • The strategy is extendable to other transition metals (Fe, Co, Ni), establishing a general structural design principle for high-density, speciation-controlled metal sites on oxide supports; this offers a scalable route for manufacturing high-performance photocatalysts and electrocatalysts.