Fluorinated Covalent Organic Frameworks Coupled with Molecular Cobalt Cocatalysts for Efficient Photocatalytic CO2 Reduction

The combination of covalent organic framework (COF) photosensitizers with molecular cocatalysts is a promising avenue for photocatalytic carbon dioxide (CO2) reduction. Here, a series of isostructural COFs was synthesized using linkers of different lengths, with or without partial fluorination. These COFs were investigated for photocatalytic CO2 reduction under visible-light irradiation when combined with cobalt(II) bipyridine complexes as a cocatalyst. Fluorination was found to enhance both CO2 affinity and catalytic activity, and a partially fluorinated COF, FBP-COF, achieved the highest CO2-to-CO conversion efficiency, showing a carbon monoxide (CO) generation rate of 2.08 mmol h-1 g-1 and a 90% CO selectivity. FBP-COF also showed good stability under sacrificial conditions, generating CO for 50 h with a turnover number of 91.5. This activity is much higher than a homogeneous system using ruthenium bipyridine complexes as the photosensitizer combined with the same cobalt bipyridine complexes.