Porous organic polymers with shiftable active Co(II) sites for photocatalytic reduction of CO2 to C2H4

Photoreduction of CO2 to multi-carbon products such as C2H4 is particularly attractive but extremely challenging due to kinetically sluggish C-C coupling and inefficient charge transfer. Herein, a flexible porous organic polymer (F-TotPp(Co)) with shiftable active Co(II) sites was constructed via the Sonogashira reaction of 5,10,15,20-tetra(4-bromophenyl)Co(II) porphyrin (Pp(Co)) and 2,4,6-tri(2-propyn-1-yloxy)-1,3,5-triazine (Tot). Under illumination, F-TotPp(Co) catalyst can photocatalytically reduce CO2 to C2H4 with an electron-based selectivity of 42.5 %, which has rarely been achieved in rigid R-TebPp(Co) and metal-free F-TotPp(2H) catalyst system. Electron paramagnetic resonance, in situ FT-IR, and density functional theory calculations show that the shiftable active Co(II) sites promote the C C coupling of *CO and *CHO, which is the rate-determining step for C2H4 formation. Photoelectrochemical studies including photoluminescence, electrochemical impedance spectroscopy, and time-resolved photoluminescence indicate that atomic Co2+ ions facilitate the separation and transfer of photogenerated electrons. Furthermore, cycling experiments, X-ray photoelectron spectroscopy, and X-ray absorption fine structure analysis confirm the excellent stability of F-TotPp(Co) during the CO2 reduction process. This work provides a new approach to construct efficient photocatalysts for the reduction of CO2 to multi-carbon products.