Electrochemical conversion of CO₂ using metal-organic framework catalysts

Metal-organic frameworks (MOFs) have been an excellent platform for carbon dioxide reduction reactions (CO₂RR). In this work, the feasibility of electrochemical reduction of CO₂ to obtain C₂-deep value-added products was investigated by the preparation of Mg-containing MOF-74 samples combined with transition metal cations (Ni²⁺, Co²⁺ and Zn²⁺). The prepared MOFs were used as electrocatalysts in CO₂RR. Chronoamperometric analysis coupled to ATR-FTIR spectroscopy was employed to characterize the CO₂ reduction products and subsequently via ¹H NMR. Although an isostructural crystalline structure was observed in all synthesized MOFs, the pore diameter distribution was significantly affected due to the Mg coordination along with each transition metal nuclei with the organic ligand to form the MOF-74. Our results showed that Mg-containing MOF-74 electrocatalysts combined with Ni, Co and Zn ions successfully reduced CO₂ to C₂-deep products, while the monometallic Mg-MOF-74 showed only CO₂ mineralization. An ester acetate, isopropyl alcohol, and formic acid were produced by Mg/Ni-MOF-74; isopropyl alcohol was provided by Mg/Co-MOF-74, and ethanol was generated by Mg/Zn-MOF-74. We observed that the change of the transition cation was a key factor in the selectivity of the obtained products, while the degree of Mg ions effectively incorporated into the MOF structure tuned the porosity and the electrocatalytic activity. Among them, Mg/Zn-MFOF-74 showed the highest Mg content loaded after synthesis and thus the most favorable electrocatalytic behavior towards CO₂ reduction.