Electrochemical Reduction Of CO₂ At Pb Alloy Electrodes In Methanol

The CO₂ greenhouse effect has been identified as possibly serious environmental problem. In order to protect personnel in manned spacecraft, it is also required to control the concentration of CO₂. Electrochemical reduction of CO₂ appears to be more effective for the removal and conversion of CO₂. Based on previous studies of CO₂ reduction, this paper investigated the electrochemical reduction of CO₂ on Pb-Ag and Pb-Sb electrodes using methanol （0.1M KOH） as solvent. The effects of potential, temperature and pressure on the yield of CO and HCOOH were studied. Furthermore, the apparent kinetics of the electrochemical reduction of CO₂ was studied.When using Pb-Ag as a work electrode, less negative electrode potential appeared to be disadvantageous for HCOOH formation, and advantageous for CO formation at ambient pressure. For high pressure CO₂ system, the tendency was on the opposite. Experimental results showed that lower temperature appeared to be advantageous for CO and HCOOH formation. Higher pressure of CO₂ favored the formation of CO but not HCOOH on Pb-Ag electrode. On Pb-Sb electrode, less negative electrode potential appeared to be disadvantageous for CO formation but not for HCOOH formation. Lower temperature and higher pressure favored the formation of CO and HCOOH at ambient and high pressure.The influence of the overpotential on the partial current densities for CO and HCOOH formation was studied on Pb-Ag and Pb-Sb electrodes. The Tafel plots for CO and HCOOH formation showed that CO₂ reduction was not limited by its mass transfer in the investigated potential range. Finally, the kinetics of electrochemical reduction of CO₂ was studied primarily. The apparent kinetics for CO₂ reduction on Pb-Ag and Pb-Sb were described as follows:j_0.CO=119A₁P_CO2^0.299 1/（T-255）exp（-1970/T） （for Pb-Ag）,j_0.HCOOH=3596A₂P_CO2^0.1723 1/（T-204）exp（-738/T） （for Pb-Ag）,j_0.CO=69.4A₃P_CO2^0.1171 1/（T-254） exp（-1238/T） （for Pb-Sb）,j_0.HCOOH=0.0168A₄P_CO2^0.36 1/（T-236） exp（-695/T） （for Pb-Sb）.The results showed that electrochemical reduction of CO₂ is an efficient technology for air renewal.