Functional compartmentalization in asymmetric Co–Ni microenvironment for selective CO 2 ‐to‐ C 2 H 4 photoreduction

Abstract Photocatalytic CO 2 ‐to‐C 2 H 4 conversion faces a kinetic paradox in which enriching C 1 intermediates for C–C coupling inherently compromises their hydrogenation and product release due to strong surface binding. Here, we resolve this paradox through sulfur‐vacancy (Vs) engineering in CoNi 2 S 4 nanosheets, which creates a functionally compartmentalized Co–Ni microenvironment. Vs induces directional charge transfer from Ni to Co, generating adjacent electron‐deficient Ni(δ+) and electron‐rich Co(δ‐) sites. Ni(δ+) selectively stabilizes *CO while Co(δ‐) drives its hydrogenation to *CHO, enabling a spatially confined *CO–*CHO coupling pathway with a markedly lower thermodynamic barrier than direct *CO dimerization. Meanwhile, this microenvironment weakens C 2 H 4 adsorption relative to the pristine surface, alleviating product inhibition and promoting active‐site regeneration. The catalyst achieves a C 2 H 4 evolution rate of 57.24 μmol·g −1 ·h −1 with 75.81% selectivity, a 28‐fold enhancement over pristine CoNi 2 S 4 . This work establishes defect‐engineered geometric and electronic complementarity as a design paradigm for selective multicarbon photosynthesis.