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.