Selective CO ₂ ‐to‐CH ₄ Photocatalytic Reduction via Spin‐Modulation in a Metal─Carbon‐Bonded MOF

The spin modulation of the electronic structure of photocatalysts offers a promising strategy to address selectivity challenges in photocatalysis. Herein, we present a novel ruthenium–carbon‐bonded MOF (RuCMOF) and construct a heterojunction with Cu 2 O nanoparticles for photocatalytic CO 2 reduction using water vapor. The optimized RuC‐MOF/10%Cu 2 O heterojunction achieves a remarkable CH 4 production rate of 663.6 µmol g −1 h −1 with 96.7% selectivity under visible light irradiation. The apparent quantum yield reaches 4.6% at 400 nm. Experimental and theoretical studies reveal that the atomically dispersed ruthenium–alkynyl units of RuC‐MOF and the heterostructure enable efficient photo‐excited carrier separation/transfer. Moreover, the Cu 2 O incorporation triggers a low‐spin to high‐spin transition in the Ru active centers of RuC‐MOF, suppressing charge recombination through spin‐selective electron transfer. Furthermore, the spin‐state modulation also weakens *CO adsorption, lowers the energy barrier for *CHO formation and accelerates the rate‐determining step. This work provides a new way for designing high‐performance metal─carbon‐bonded MOF photocatalysts through spin polarization engineering.