This study investigates the carbon deposition on copper (Cu) electrodes during electrochemical CO₂ reduction, a critical issue that often leads to deactivation of Cu-based catalysts. The research reveals that *C*, an intermediate for methane formation, can desorb from the electrode surface to form carbon species, which block active sites and cause rapid deactivation. The formation of methane is strongly correlated with carbon deposition, and reaction conditions favoring methane production result in more carbon deposition. The study demonstrates that increasing the roughness of the electrode and adjusting the pH of the electrolyte can mitigate carbon deposition. These findings provide new insights into the stability of Cu-based catalysts for CO₂ reduction and offer strategies to design more stable catalysts. The work highlights the importance of understanding the mechanisms of carbon deposition and its impact on catalytic performance, which is crucial for advancing the development of efficient and stable CO₂ electrolysis technologies.This study investigates the carbon deposition on copper (Cu) electrodes during electrochemical CO₂ reduction, a critical issue that often leads to deactivation of Cu-based catalysts. The research reveals that *C*, an intermediate for methane formation, can desorb from the electrode surface to form carbon species, which block active sites and cause rapid deactivation. The formation of methane is strongly correlated with carbon deposition, and reaction conditions favoring methane production result in more carbon deposition. The study demonstrates that increasing the roughness of the electrode and adjusting the pH of the electrolyte can mitigate carbon deposition. These findings provide new insights into the stability of Cu-based catalysts for CO₂ reduction and offer strategies to design more stable catalysts. The work highlights the importance of understanding the mechanisms of carbon deposition and its impact on catalytic performance, which is crucial for advancing the development of efficient and stable CO₂ electrolysis technologies.