Effect of the Reaction Environment on Electrochemical CO₂ Reduction Using Copper-Electrodeposited Carbon Paper

Electrochemical CO2 reduction (CO2R) using copper (Cu) as a catalyst has attracted attention for the production of ethylene from nonfossil fuels. Herein, the effect of the reaction environment formed in three-dimensional carbon structures on the product selectivity of CO2R is discussed. When Cu was deposited only on the carbon paper (CP) surface (Cu/CPSurface), ethylene was formed at potentials <−1.0 V vs RHE, and the Faradaic efficiency of ethylene was 25.7 ± 7.2% at −1.2 V. By contrast, the competing hydrogen evolution reaction was dominant when Cu was deposited throughout CP in the thickness direction of CP (Cu/CPFull). Model calculations suggested that CO2 was depleted in most parts of Cu/CPFull due to the increase in pH and the concomitant decrease in the CO2 concentration by carbonate equilibria, whereas the limited thickness of the electrodeposited Cu layer in Cu/CPSurface enabled the formation of a suitable reaction environment for ethylene production.