Revisiting the Nature and Catalytic Role of the 530 cm ^–1 Raman Peak on Cu Catalysts during CO ₍₂₎ Electroreduction

Recently, an intense Raman peak at approximately 520–544 cm–1 (briefly named as *530 in this study) has been widely observed and discussed during in situ spectroscopic studies of electrochemical CO2 or CO reduction reaction (CO(2)RR). Several mechanisms were proposed to explain the nature of this peak, most notably attributing it to Cu–OHad or CuOx(OH)y, which was then utilized as a key spectroscopic indicator in various mechanistic discussions. Herein, by systematic isotopic-labeled spectroscopic studies, we show that the nature of the *530 peak may not be the previously proposed species, but more likely a surface species containing (C, O) in equilibrium with inert bridging-type adsorbed CO (*CObridge). Both the formation of *530 and *CObridge is shown to be associated with the spontaneous reconstruction of Cu. The *CObridge and *530 Raman modes share the same adsorption sites and can interconvert into each other via the variation of electrochemical potentials. Finally, the appearance of both peaks is shown to signalize a deteriorated C2+ products performance of CO2RR and CORR. These results update the current understandings of the role of *530 for CO(2)RR. It also highlights that the emerging-recognized electrocatalyst reconstruction phenomenon can be accompanied by the formation of diverse surface adsorbates, casting challenges, and necessitating rigorous spectroscopic studies for better mechanistic understanding.