In Situ Observation of Post‐CO Intermediates to Decode C─C Coupling Pathways in CO ₂ Electroreduction

Abstract Electrocatalytic carbon dioxide (CO 2 ) reduction reaction (CO 2 RR) has emerged as a promising strategy for sustainable energy conversion and carbon utilization. Despite intensive research efforts, the understanding of intermediates and pathways leading from CO 2 RR to multicarbon (C 2+ ) chemicals remains incomplete. The challenge is to gain insight into the activation of adsorbed CO and the subsequent pathways. Here, we design a specially tailored Cu nanowire array facing a hydrophobic interface as an electrode to highly enhance Raman signals in the in situ environment, allowing sensitive observation of the sequential change of various elusive intermediates during CO 2 RR, such as CO, CH 2 , CO coexisting with CH 2 , CH 2 CO, and CH 3 . Density functional theory calculations reveal that the C─C coupling during CO 2 RR originates from an asymmetric coupling between CH 2 and CO to form CH 2 CO, identified as the rate‐determining step in the formation of C 2+ products. These findings deepen the understanding of the C─C coupling processes, which are crucial for advancing catalyst development in electrochemical CO 2 upgrading.