Universal Formation, Dynamics, and Reactivities of *CObridge Accompanying Spontaneous Reconstruction of Cu during Electrochemical CO2 or CO Reduction

This study demonstrates a unifying understanding of spontaneous Cu reconstruction during electrochemical CO 2 and CO reduction reactions (CO (2) RR) and its influence on the surface-adsorbed CO (*CO), the most important reaction intermediate of CO (2) RR. Specifically, by employing various in situ/operando Raman and infrared spectroscopy techniques, we reveal a universal gradual formation of bridge-type adsorbed CO (*CO bridge ) accompanying the reconstruction in addition to CO adsorbed on the atop site (*CO atop ). This phenomenon is observed across diverse Cu catalysts and electrolyzer configurations. Especially, it also occurs during CV measurements of Cu, causing interference for spectroscopic characterization of *CO for mechanistic studies. The formation of *CO bridge on reconstructed Cu is revealed to involve two steps: first, CO adsorption to form *CO atop followed by its surface conversion to *CO bridge, while kinetic studies show that *CO bridge is inactive and detrimental to catalytic conversion. Finally, to provide reference results valuable for future studies, we benchmark the line shape and potential-dependent population of *CO for widely utilized Cu catalysts, proposing protocols necessary for accurate measurements. Collectively, these results explain why spontaneous Cu reconstruction would result in lower activities of CO (2) RR, the surface dynamics and activities of *CO bridge, as well as how to accurately characterize *CO for future mechanistic studies. These insights not only advance the fundamental understanding of Cu-based electrocatalysts but also provide a framework for studying the dynamic reconstruction of electrocatalysts for other reactions.