Pressure dependence of electrochemical CO2 reduction to ethanol in flow cell

Abstract

The electroreduction of carbon dioxide (CO2RR) to ethanol is an ideal approach for using released CO2 and producing fuel. The impact of CO2 partial pressure (PCO2) on ethanol synthesis was significant but was not well understood. The present study investigates the pressure dependence of ethanol formation from 0.25 bar to 15 bar in a high-pressure flow cell. It displayed a volcano type. The PCO2 associated with the peak Faradaic efficiency (FE) of ethanol increased as the current density increased. The pressure peak values were 0.5 bar, 0.75 bar at 100, 200, and 300 mA cm−2, respectively. Ethanol formation kinetics was affected by adsorbate-adsorbate interactions and the physical blocking of active sites on catalysts with excess CO2. Besides, ethanol synthesis using the configured flue gas, i.e., low-concentration CO2 (VCO2 = 5–30%), was realized via system pressurization from 5 to 20 bar at 200 mA cm−2. By optimizing the combination of CO2 concentration and total pressure (Ptot), the fuel efficiency (FE) of ethanol was maximized to 26.5%. This study uncovers the ideal CO2 partial pressure for ethanol synthesis under industrial current densities, hence presenting potential industrial applications for utilizing flue gas directly in ethanol production.