Sub-Band Assisted Z-Scheme for Effective Non-Sacrificial H₂O₂ Photosynthesis

Photosynthesis of H₂O₂ from earth-abundant O₂ and H₂O molecules offers an eco-friendly route for solar-to-chemical conversion. The persistent challenge is to tune the photo-/thermo- dynamics of a photocatalyst toward efficient electron-hole separation while maintaining an effective driving force for charge transfer. Such a case is achieved here by way of a synergetic strategy of sub-band-assisted Z-Scheme for effective H₂O₂ photosynthesis via direct O₂ reduction and H₂O oxidation without a sacrificial agent. The optimized SnS₂/g-C₃N₄ heterojunction shows a high reactivity of 623.0 µmol g^-1 h^-1 for H₂O₂ production under visible-light irradiation (λ > 400 nm) in pure water, ≈6 times higher than pristine g-C₃N₄ (100.5 µmol g^-1 h^-1). Photodynamic characterizations and theoretical calculations reveal that the enhanced photoactivity is due to a markedly promoted lifetime of trapped active electrons (204.9 ps in the sub-band and >2.0 ns in a shallow band) and highly improved O₂ activation, as a result of the formation of a suitable sub-band and catalytic sites along with a low Gibbs-free energy for charge transfer. Moreover, the Z-Scheme heterojunction creates and sustains a large driving force for O₂ and H₂O conversion to high value-added H₂O₂.