Exceptionally Durable CO ₂ Photoreduction Mediated by Defect‐Engineered CaIn ₂ S ₄ Nanoflowers

ABSTRACT Solar‐driven CO 2 reduction faces major limitations due to insufficient photoabsorption, delayed electron‐hole separation, and a significant CO 2 activation barrier. Defect engineering was used to optimize these vital processes. As a prototype, typical nontoxic ternary sulfide CaIn 2 S 4 (CIS) nanoflowers were designed, and abundant sulfur vacancies were deliberately created on their surfaces. The charge delocalization around the sulfur vacancies contributes to CO 2 conversion into the *COOH intermediate, which was confirmed by in situ Fourier‐transform infrared spectroscopy. Ultrafast transient absorption spectroscopy manifests the sulfur vacancy that allows for a ∼1.3‐fold increase in average recovery lifetime, confirmed by photoelectrochemical analysis and DFT calculations, which ensure promoted carrier separation rates. Consequently, the CISv demonstrates a CO rate of 10.95 μmol g −1 h −1 , which is about 6.5 times greater than the pristine CIS nanoflowers, and its photocatalytic activity remains almost unchanged after 120 h of photocatalysis. Our findings will stimulate further research on vacancy‐containing catalyst design for CO 2 reduction to hydrocarbons.