Circularly Polarized Light Amplifies Spin Polarization for Efficient Photoredox Chemistry in a Chiral Magnetic Catalyst

ABSTRACT Photocatalysis offers a promising route to sustainable energy, yet the role of carrier spin in charge transport and interfacial redox chemistry remains poorly understood. Chiral and magnetic catalysts selectively transmit spin‐compatible carriers, whereas non‐polarized light generates mixed‐spin populations, limiting carrier utilization. Herein, we demonstrate that circularly polarized light (CPL) reversibly modulates spin‐dependent carrier transport in Ni‐cocatalyst‐decorated, cysteine‐modified CdS nanorods, thereby promoting spin‐sensitive carrier utilization during aqueous methanol reforming. Optimized D(−)‐CdS/Ni exhibits a 71.1% higher hydrogen evolution rate under left‐handed CPL (LCP) than under right‐handed CPL (RCP) at identical light intensity and spectrum, achieving an apparent quantum efficiency of 74.4% at 420 nm while promoting methanol oxidation toward formic acid. CPL‐coupled magnetic conductive atomic force microscopy reveals that LCP increases the apparent spin polarization from 70.9% in the dark to 89.1%, whereas RCP suppresses it to 12.8%. Spin‐polarized calculations identify nonequivalent electronic channels, while spectroscopic and kinetic measurements support enhanced carrier extraction and reduced recombination under LCP. Together, these findings establish photon handedness as a reversible optical variable for modulating spin‐selective transport and photoredox chemistry, offering a strategy to complement material‐encoded spin filtering with dynamic optical control of carrier utilization.