In Situ Observation of Post-CO Intermediates to Decode C─C Coupling Pathways in CO₂ Electroreduction

Electrocatalytic carbon dioxide (CO₂) reduction reaction (CO₂RR) 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 CO₂RR to multicarbon (C₂₊) 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 CO₂RR, such as CO, CH₂, CO coexisting with CH₂, CH₂CO, and CH₃. Density functional theory calculations reveal that the C─C coupling during CO₂RR originates from an asymmetric coupling between CH₂ and CO to form CH₂CO, identified as the rate-determining step in the formation of C₂₊ products. These findings deepen the understanding of the C─C coupling processes, which are crucial for advancing catalyst development in electrochemical CO₂ upgrading.