Electrochemical Reduction of Flue Gas CO2 in a Dual Methanol/Water Electrolysis System for the Synthesis of Methyl Formate

Abstract

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of the nonaqueous solvent methanol allows for higher CO2 solubility and novel products through the incorporation of methanol as an intermediate. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with a faradaic efficiency for methyl formate as high as 75% measured in pH < 2. Furthermore, strategies to limit the concentration of formic acid and maintain the surface oxide of the catalyst have been shown to be effective at improving the steady-state durability of the CO2-to-methyl formate process. Tests with simulated flue gas as the feedstock have shown a high level of tolerance for the Pb-catalyzed electrolysis to SO2, NO, and dilute O2 contaminants. Finally, a comparative technoeconomic analysis will be discussed to highlight target performance metrics and the viability of alternate pathways for electrochemical conversion of CO2 to methyl formate.