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.