Electrochemical reduction of carbon dioxide with lead cathode and zinc anode in dry acetonitrile solution

Abstract

The electrochemical reduction of carbon dioxide (CO₂) is investigated in acetonitrile with tetrabutylammonium perchlorate as an electrolyte using a lead cathode and a sacrificial zinc anode, and the product under such a setup is insoluble zinc oxalate at potentials between −2.2 and −2.8 V vs. Ag rod electrode. Preelectrolysis is an effective method to remove the water in the electrolyte, which makes a distinct reduction peak of CO₂ appear at −2.6 V vs. Ag on cyclic voltammogram. Even trace amounts of water in the electrolyte can interfere with the faradaic efficiency of reduction of CO₂ to oxalate, and the product could be β-ZnC₂O₄ (in anhydrous solution) or ZnC₂O₄ · 2H₂O (if water exists). The faradaic efficiency for oxalate production also depends on the cathode potential and the temperature, and the maximum is 96.8 % at −2.6 V vs. Ag and 5 °C. This is the highest value of CO₂ electrochemical reduction found in the literature under ambient pressure.