Electrochemical CO2 Reduction to Methyl Formate/Formic Acid in a Dual Non-Aqueous/Aqueous Flow Cell Electrolyzer

Abstract

Electrochemical conversion of CO2 has been very promising in neutralizing existing carbon in the atmosphere as well as creating a pathway to produce various fuels and chemicals. The use of a CO2 flow electrolyzer makes it possible to achieve high faradaic efficiencies at high current densities from pure CO2 or dilute flue gas feeds. CO2 solubility in methanol is higher than in aqueous solutions and with acidic methanol as a solvent, it is possible to generate a unique product, methyl formate. This work describes the use of mixed propylene carbonate/methanol solutions as a solvent for CO2 reduction using a gas diffusion electrode and an aqueous anolyte and optimization of a high mass flux CO2 electrolyzer to produce methyl formate using a Pb-catalyst at higher current densities. pH-dependent product distribution is also described. The partial current densities varied depending on the cell design; cells where charge passes through more solvent result in lower current density because methanol has a higher solution resistance than aqueous solutions. The methanolic catholyte is paired with an aqueous anolyte to promote a sustainable water oxidation half-reaction.