Promoted CO2 photoreduction toward HCOOH generation through a nucleophilic effect in Co/Mg synergistic catalysis†

The photoreduction of carbon dioxide (CO₂) into valuable energy is one of the most promising strategies to overcome the current global climate crisis. The synergistic catalysis of bimetallic metal–organic frameworks (MOFs) has shown considerable potential for the photocatalytic reduction of CO₂. However, how to design an efficient catalytic active center is still a thorny problem. Herein, a bimetallic MOF, CoMg-TCPP, was successfully prepared via a post-synthetic exchange method. Under visible light, CoMg-TCPP can be an efficient catalyst for CO₂ reduction with yields of gas product (CO) and liquid product (HCOOH) of up to 14.34 mmol g⁻¹ h⁻¹ and 0.94 mmol g⁻¹ h⁻¹, respectively. Notably, the synergistic effect between the bimetals in CoMg-TCPP generated formic acid with an yield more than twice that generated by the monometallic counterpart Co-TCPP. Theoretical calculations show that the introduction of the second metal regulates the electronic structure of intermediates, which reduces the formation energy barrier of Co–O–COH intermediates and significantly promotes the formation of Co–HCOOH, thus obtaining efficient HCOOH generation performance. Moreover, the addition of Mg to Co-TCPP enhances the nucleophilicity of the Co center and makes it more inclined to interact with O–COH groups. This work provides further insights into the mechanisms of CO₂ photocatalytic reduction based on a bimetal–organic framework.