Electrochemical reduction of CO 2 at three-phase (gas ∣ liquid ∣ solid) and two-phase (liquid ∣ solid) interfaces on Ag electrodes

Abstract

In the long-term electrolysis of CO 2 with a metal electrode, it is very important to maintain the catalytic activity of the electrode. The Faradaic efficiency for the reduction of CO 2 on an Ag foil electrode is known to decrease rapidly several tens of minutes after the start of electrolysis, owing to the deposition of graphitic carbon, adsorbed organic intermediate or oxide/hydroxide acting as a catalytic poison. In order to settle this problem, the electrochemical reduction of CO 2 on a net Ag electrode was here performed at the three-phase (gas ∣ solid ∣ liquid) interface where CO 2 was supplied directly from the gas phase and a high concentration of CO 2 was sustainable in the course of electrolysis. The conversion of CO 2 (initial volume 219 cm 3) with this electrode (11.8 cm 2) was found to reach 60% at an electrolysis time of 5 h with the selective formation of CO. Furthermore, the addition of AgNO 3 to the electrolyte resulted in a 100% conversion of CO 2. This was brought about by in situ formation of the silver crystal face providing a favorable reaction site for the CO 2 reduction, and the Faradaic efficiency of H 2 was kept below 8% during the electrolysis.