Influence of dilute feed and pH on electrochemical reduction of CO2 to CO on Ag in a continuous flow electrolyzer

Electrochemical conversion of CO2 to useful chemical intermediates may be a promising strategy to help reduce CO2 emissions, while utilizing otherwise wasted excess renewable energy. Here we explore the effect of diluted CO2 streams (10-100% by volume using N-2 as diluting inert gas) on the product selectivity and on the CO/CO2 conversion ratio for the electrochemical reduction of CO2 into CO, specifically using a gas diffusion electrode loaded with Ag catalyst in a continuous flow electrolyzer. When using diluted CO2 feeds for the electrolyzer, we still observed high Faradaic efficiencies for CO (>80%), high conversion ratios (up to 32% per pass), and partial current densities for CO of 29 mA/cm(2) when operating the cell at 3.0 V. Most notably, we observed that the decrease in partial current density for CO was less than 45% when switching from a 100% CO2 feed to a 10% CO2 feed. Also, we studied the effect of pH and the interplay between pH and the diluted CO2 feed. We observed higher levels of CO formation as well as a higher Faradaic efficiency for CO when using an alkaline electrolyte, compared to when using a neutral or acidic electrolyte. However, the effect of CO2 concentration in the feed is more significant than the effect of pH on electrochemical reduction of CO2 to CO. (C) 2015 Elsevier Ltd. All rights reserved.