Theoretical design of dual-site metallo-covalent organic frameworks for efficient CO2 photoreduction into C2H4

Designing and modulating active sites in photocatalysts to achieve efficient CO2 conversion into high valueadded C2 products is crucial but challenging for CO2 resource utilization. A promising strategy is the construction of asymmetric dual-metal active sites, which generate asymmetric charge distribution and synergistic effect between adjacent metal centers, thereby promoting the key C-C coupling process required for C2 products formation. In particular, metallo-covalent organic frameworks (M-COFs) provide an ideal platform for strategic design of active sites, owing to their naturally large pores to integrate active metal sites into extended frameworks and the well-defined coordination environments of these metal atoms for understanding the structure- activity relationships. In this work, a series of homonuclear and heteronuclear dual-site M-COFs (M2/MM'-S- COFs) were constructed, and their CO2 reduction (CO2RR) performance and photocatalytic mechanism were systematically investigated using density functional theory (DFT). Among these, MgFe-S-COF and MgZn-S-COF were identified as the most promising catalysts for CO2-to-C2H4 conversion, exhibiting ultra-low energy barriers in C-C coupling process (0.04 and 0.03 eV, respectively). To explore the origin of this enhanced activity, MgFe-S-COF was selected as a representative system for in-depth mechanism analysis. The superior CO2RR performance of heteronuclear MgFe-S-COF, compared to its homonuclear counterparts (Mg2-S-COF and Fe2-S- COF), is attributed to the asymmetric charge distribution and a "donation-back donation-redonation" mechanism, which facilitates efficient C-C coupling. Furthermore, machine learning (ML) models predicted 69 structures with the potential for generating C2 products out of 136 M2/MM'-S-COF candidates. This work highlights the potential of dual-site M-COFs with charge-polarized active sites to address the challenges in C2 production, offering theoretical insights for future experimental synthesis.