Selective H2O2 Photosynthesis in Ferroelectric Photocatalyst: Rare-Earth 4F-State-mediated Charge-Spin Regulation.

Solar-driven photocatalytic H2O2 synthesis is critically hampered by bulk charge recombination and spin-forbidden surface kinetics. This study proposes a rare-earth 4f-state-mediated strategy that simultaneously reconstructs the band structure and induces spin polarization. Using Aurivillius-phase Bi3TiNbO9 as a ferroelectric model system, we show that low-concentration Ce doping engenders three synergistic effects via a full-pathway charge-dynamics regulation: (i) Ce-induced lattice distortion enhances ferroelectric polarization, reinforcing the polarization electric field for directional charge separation; (ii) band-edge reconstruction reduces both carrier effective masses and exciton binding energy, accelerating exciton dissociation and carrier transport; and (iii) the unpaired 4f1 electron of Ce3+ induces spin polarization, effectively lowering the spin-related kinetic barriers for H2O2 generation. Consequently, Ce-doped Bi3TiNbO9 delivers an H2O2 production rate of 1151.7 µmol g-1 h-1 in pure water, a 6.9-fold enhancement over pristine Bi3TiNbO9. Critically, applying a 300 mT external magnetic field further boosts the rate to 1831.2 µmol g-1 h-1, providing direct evidence for spin-polarization-controlled photocatalysis. H2O2 is selectively generated through synergistic 2e- oxygen reduction reaction (ORR) and water oxidation reaction (WOR) pathways, while the competing side reactions are effectively suppressed. This work demonstrates an integrated 4f-mediated charge-spin regulation strategy that couples charge separation with spin-dependent surface reaction kinetics for efficient H2O2 photosynthesis.