Tailoring Coordination Microenvironment of Cu(I) in Metal-Organic Frameworks for Enhancing Electroreduction of CO2 to CH4

The coordination microenvironment of metal active sites in metal-organic frameworks (MOFs) plays a crucial role in its performance for electrochemical CO2 reduction reaction (CO2RR). However, it remains a challenge to clarify the structure-performance relationship for CO2RR catalyzed by MOFs. Herein, a series of MOFs with different coordination microenvironments of Cu(I) sites (Cu-Cl, Cu-Br, and Cu-I) to evaluate their performances for CO2RR is synthesized. With the increasing radius of halogen atom, the CO2 adsorption capacity increases and d-band center of Cu positively shifts to the Fermi level, leading to enhance the selectivity of CO2 to CH4 conversion. Cu-I gives the highest total Faradaic efficiency (FE) of 83.2%, with a FE of CH4 up to 57.2% and CH4 partial current density of 60.7 mA cm(-2) at -1.08 V versus reversible hydrogen electrode. Theoretical calculations reveal that the shifted d-band center of Cu site contributes to reduced formation energies of *CH2O and *CH3O intermediates, which is the potential-determining step of CO2RR and thus facilitates the electrocatalytic CO2 reduction to CH4. This study opens a new avenue for studying the relationship between the coordination microenvironment of active site and electroreduction reaction performance of MOFs.