In Situ Observation of Post‐CO Intermediates to Decode C─C Coupling Pathways in CO_2 Electroreduction

Electrocatalytic carbon dioxide (CO_2) reduction reaction (CO_2RR) 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_2RR 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_2RR, such as CO, CH_2, CO coexisting with CH_2, CH_2CO, and CH_3. Density functional theory calculations reveal that the C─C coupling during CO_2RR originates from an asymmetric coupling between CH_2 and CO to form CH_2CO, 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.