Wei Zhang

The electrochemical reduction of CO₂ to hydrocarbons involves a multistep proton‐coupled electron transfer (PCET) reaction. Second coordination sphere engineering is reported to be effective in the PCET process; however, little is known about the actual catalytic active sites under realistic operating conditions. We have designed a defect‐containing metal–organic framework, HKUST‐1, through a facile “atomized trimesic acid” strategy, in which Cu atoms are modified by unsaturated carboxylate ligands, producing coordinatively unsaturated Cu paddle wheel (CU−CPW) clusters. We investigate the dynamic behavior of the CU−CPW during electrochemical reconstruction through the comprehensive analysis of in situ characterization results. It is demonstrated that Cu₂(HCOO)₃ is maintained after electrochemical reconstruction and that is behaves as an active site. Mechanistic studies reveal that CU−CPW accelerates the proton‐coupled multi‐electron transfer (PCMET) reaction, resulting in a deep CO₂ reduction reaction.

The electrochemical reduction of CO₂ to hydrocarbons involves a multistep proton‐coupled electron transfer (PCET) reaction. Second coordination sphere engineering is reported to be effective in the PCET process; however, little is known about the actual catalytic active sites under realistic operating conditions. We have designed a defect‐containing metal–organic framework, HKUST‐1, through a facile “atomized trimesic acid” strategy, in which Cu atoms are modified by unsaturated carboxylate ligands, producing coordinatively unsaturated Cu paddle wheel (CU−CPW) clusters. We investigate the dynamic behavior of the CU−CPW during electrochemical reconstruction through the comprehensive analysis of in situ characterization results. It is demonstrated that Cu₂(HCOO)₃ is maintained after electrochemical reconstruction and that is behaves as an active site. Mechanistic studies reveal that CU−CPW accelerates the proton‐coupled multi‐electron transfer (PCMET) reaction, resulting in a deep CO₂ reduction reaction.

Oxygen-bearing copper (OBC) has been widely studied for enabling the C–C coupling of the electrocatalytic CO₂ reduction reaction (CO₂RR) since this is a distinctive hallmark of strongly correlated OBC systems and may benefit many other Cu-based catalytic processes. Unresolved problems, however, include the instability of and limited knowledge regarding OBC under realistic operating conditions, raising doubts about its role in CO₂RR. Here, an atypical and stable OBC catalyst with a hierarchical pore and nanograin-boundary structure was constructed and was found to exhibit efficient CO₂RR for the production of ethylene with a Faradaic efficiency of 45% at a partial current density of 44.7 mA cm^–2 in neutral media, and the ethylene partial current density is nearly 26 and 116 times that of oxygen-free copper (OFC) and commercial Cu foam, respectively. More importantly, the structure–activity relationship in CO₂RR was explored through a comprehensive analysis of experimental data and computational techniques, thus increasing the fundamental understanding of CO₂RR. A systematic characterization analysis suggests that atypical OBC (Cu₄O) was formed and that it is stable even at −1.00 V [(vs the reversible hydrogen electrode (RHE)]. Density functional theory calculations show that the atypical OBC enables control over CO adsorption and dimerization, making it possible to implement a preference for the electrosynthesis of ethylene (C₂) products. These results provide insight into the synthesis and structural characteristics of OBC as well as its interplay with ethylene selectivity.