Spin‐Selective Hydrogen Utilization Enables Efficient Electrochemical CO 2 ‐to‐CH 4 Conversion in Ag‐Modified Chiral Cu Catalysts for Unassisted Solar Fuel Production

ABSTRACT Although electrochemical CO 2 ‐to‐CH 4 conversion offers a viable pathway to sustainable fuel synthesis, its efficiency is limited by the difficulty of balancing the availability of reactive hydrogen species for multistep CO 2 hydrogenation against the suppression of the competing hydrogen evolution reaction (HER). Here, we establish a spin‐selective catalytic strategy using Ag‐modified chiral Cu electrocatalysts to overcome this intrinsic trade‐off. Structural chirality in the Cu framework induces chirality‐induced spin selectivity, which disfavors spin‐singlet H 2 formation, thereby mitigating the HER and favoring productive hydrogen utilization toward CO 2 hydrogenation. Ag modification facilitates the supply of *CO intermediates on adjacent Cu sites. Thus, the chiral Ag/Cu catalyst selectively drives CO 2 reduction toward CH 4 , delivering a CH 4 Faradaic efficiency (FE) of 67.0% at −0.7 V versus the reversible hydrogen electrode while suppressing the HER. When coupled with perovskite‐based photoelectrochemical electrodes, the chiral catalyst enables unassisted solar‐driven CO 2 ‐to‐CH 4 conversion with an FE CH4 of 54.1% and a solar‐to‐fuel efficiency of 5.86%. These results suggest spin‐selective hydrogen utilization as an effective approach to selective hydrocarbon synthesis and bias‐free solar CO 2 ‐to‐fuel conversion.