Artificial photosynthetic system for diluted CO₂ reduction in gas-solid phase

Rational design of robust photocatalytic systems to direct capture and in-situ convert diluted CO₂ from flue gas is a promising but challenging way to achieve carbon neutrality. Here, we report a new type of host-guest photocatalysts by integrating CO₂-enriching ionic liquids and photoactive metal-organic frameworks PCN-250-Fe₂M (M = Fe, Co, Ni, Zn, Mn) for artificial photosynthetic diluted CO₂ reduction in gas-solid phase. As a result, [Emim]BF₄(39.3 wt%)@PCN-250-Fe₂Co exhibits a record high CO₂-to-CO reduction rate of 313.34 μmol g^-1 h^-1 under pure CO₂ atmosphere and 153.42 μmol g^-1 h^-1 under diluted CO₂ (15%) with about 100% selectivity. In scaled-up experiments with 1.0 g catalyst and natural sunlight irradiation, the concentration of pure and diluted CO₂ (15%) could be significantly decreased to below 85% and 10%, respectively, indicating its industrial application potential. Further experiments and theoretical calculations reveal that ionic liquids not only benefit CO₂ enrichment, but also form synergistic effect with Co²⁺ sites in PCN-250-Fe₂Co, resulting in a significant reduction in Gibbs energy barrier during the rate-determining step of CO₂-to-CO conversion.