Investigation and Mitigation of Carbon Deposition over Copper Catalyst during Electrochemical CO₂ Reduction

Copper (Cu) is considered to be the most effective catalyst for electrochemical conversion of carbon dioxide (CO₂) into value-added hydrocarbons, but its stability still faces considerable challenge. Here, we report the poisoning effect of carbon deposition during CO₂ reduction on the active sites of Cu electrode-a critical deactivation factor that is often overlooked. We find that, *C, an intermediate toward methane formation, could desorb on the electrode surface to form carbon species. We reveal a strong correlation between the formation of methane and the carbon deposition, and the reaction conditions favoring methane production result in more carbon deposition. The deposited carbon blocks the active sites and consequently causes rapid deterioration of the catalytic performance. We further demonstrate that the carbon deposition can be mitigated by increasing the roughness of the electrode and increasing the pH of the electrolyte. This work offers a new guidance for designing more stable catalysts for CO₂ reduction.