Prolonged Stability of Pb-Catalyzed CO2 Electroreduction to Methyl Formate in Acidic Methanol

Abstract

Electrochemical CO2 reduction from renewable energy is a promising route to mitigate greenhouse gas emissions from waste sources while generating value-added products. CO2 electroreduction in methanol is particularly interesting due to the increased CO2 solubility compared to water and the propensity to form methyl formate, a product absent in aqueous electrolysis. Four factors have been identified as critical to achieving prolonged high selectivity for methyl formate production on a Pb cathode in methanol: high pH near the electrode, low bulk pH, low water content, and regeneration of Pb2+ sites. Increasing concentration of the formic acid product was observed to induce a selectivity shift toward hydrogen, which was mitigated by the in situ conversion of the formic acid to methyl formate via an esterification reaction. Furthermore, co-electrolysis of CO2 with dilute molecular oxygen (4% O2) led to Pb catalyst repair through in situ surface oxidation. Using CO2 and dilute O2 along with single-pass catholyte flow to maintain a low formic acid concentration, sustained high selectivity for methyl formate was attained at ∼60% faradaic efficiency at −20 mA cm–2 for over 72 h.