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.