Modulating the Coordination Environment of Cu Sites for Highly Selective CO₂ Electroreduction to Ethylene

Carbon dioxide (CO₂) can be reduced to a variety of value-added products by the electrochemical reduction of CO₂ (ERC). Modulating the coordination environment of the Cu sites can effectively optimize the selectivity and activity of the reduction process. In this work, we report a facile strategy to regulate the coordination environment of Cu sites for improving the Faradaic efficiency (FE) of ethylene. Room-temperature Ar plasma with different powers and treating times was employed to partially remove the 2,5-dihydroxyterephthalic moieties from the structure of Cu-MOF-74, thus resulting in more unsaturated coordinated Cu sites and lower oxidation state. The structure distortion and electron configuration change of Cu-MOF-74-P was observed from electron paramagnetic resonance (EPR). Meanwhile, the proportion of Cu⁺ in Cu-MOF-74-P has increased significantly. By combination of XAFS and in situ DRIFTS, it was shown that the coordination number of Cu-MOF-74-P has decreased from 2.7 to 1.6, thus facilitating the formation of more *CO intermediates on the surface during the reduction process. This modification strategy successfully increased the Faradaic efficiency of C₂H₄ in the product up to 48%, which was 3.2 times of its original performance. This work provides some guidance for the design of catalysts with tailored selectivity during CO₂ electroreduction.