Copper(II) Frameworks with Varied Active Site Distribution for Modulating Selectivity of Carbon Dioxide Electroreduction.

Abstract

Metal-organic frameworks (MOFs) can be utilized as electrocatalysts for CO2 reduction reaction (CO2RR) due to their well dispersed metal centers. However, the influence of metal node distribution on electrochemical CO2RR was rarely explored. Here, three Cu-MOFs with different copper(II) site distribution were employed for CO2 electroreduction. The Cu-MOFs [Cu(L)SO4]·H2O (Cu1), [Cu(L)2(H2O)2](CH3COO)2·H2O (Cu2), and [Cu(L)2(H2O)2](ClO4)2 (Cu3) were achieved by using the same ligand 1,3,5-tris(1-imidazolyl)benzene (L) but different Cu(II) salts. The results show that the Faraday efficiency of CO (FECO) for Cu1 is 4 times that of the FEH2, while the FECO of Cu2 is twice that of the FEH2. As for Cu3, there is not much difference between FECO and FEH2. Such difference may arise from the distinct electrochemical active surface area and charge transfer kinetics caused by different copper site distribution. Furthermore, the different framework structures also affect the activity of the copper sites, which was supported by the theoretically calculated Gibbs free energy and electron density, contributing to the selectivity of CO2RR. This study provides a strategy for modulating the selectivity of CO2RR by tuning the distribution of the active centers in MOFs.