Chiral (BiO)₂CO₃ catalysts with spin-selective charge transport enhance photocatalytic oxygen evolution

Photocatalytic water splitting for hydrogen production is limited by the sluggish kinetics of the oxygen evolution reaction (OER) and rapid recombination of photogenerated charge carriers. Because the OER requires the formation of triplet O₂ from singlet-state reactants, the spin states of reaction intermediates critically influence the reaction pathways. Spin mismatch introduces substantial kinetic barriers and can promote a competing two-electron pathway that produces H₂O₂, thereby lowering the overall efficiency. The chirality-induced spin selectivity (CISS) effect enables spin polarization without external magnetic fields, providing a promising strategy to regulate multi-electron catalytic processes. Here, we report the first synthesis of intrinsically chiral bismuth subcarbonate ((BiO)₂CO₃, BOC) photocatalysts using sucrose as a bifunctional chiral directing agent. The resulting materials exhibit hierarchical chirality spanning lattice distortion, mesoscopic organization, and macroscopic helical nano-architectures. Magnetic conductive atomic force microscopy demonstrates that spin polarization increases monotonically with the optical chirality factor (g), reaching 68.3% in the most strongly chiral sample. Correspondingly, increasing chirality leads to progressively enhanced photocurrent density, accelerated OER kinetics, improved charge utilization efficiency, and significantly suppressed H₂O₂ formation. Electrochemically active surface area analysis reveals that samples with stronger chirality possess fewer exposed active sites but higher intrinsic activity per site, indicating that performance enhancement originates from improved single-site reactivity rather than increased site density. These results establish a direct correlation among chiral structure, spin polarization, and catalytic activity, providing a new design principle for spin-regulated high-performance photocatalysts.