Enhanced production of dimethyl carbonate from the alternating polarity electrolysis of methanol and carbon dioxide

Abstract

The alternating polarity methodology in electrochemical synthesis is a procedure where an electrode's polarity is inverted at regular intervals. This technique offers enhanced selectivity, mass transport and can be used to overcome issues with electrode passivation. In this study the application of an alternating polarity protocol to the redox-neutral electrochemical synthesis of dimethyl carbonate (DMC) from gaseous carbon dioxide (CO₂) and methanol was explored using glassy carbon electrodes and catalysed by palladium bromide. Screening different polarity inversion intervals revealed that the DMC yield could be increased up to 482 μmol after 4 h using a 500-second polarity inversion, compared to non-inverting (static) experiments which gave DMC yields of 270 μmol after 4 h. As the reaction proceeded, DMC productivity (as measure of reaction efficiency – i.e. how much DMC is being produced per time unit, for instance μmol h⁻¹) was enhanced under the 500 s alternating polarity methodology, nearly doubling after 4 hours compared to the first 30 minutes. On the contrary, productivity was diminished over time in the case of static electrodes. Analysis revealed that under these reaction conditions, methyl formate and formaldehyde were also being formed in competition to DMC. This is attributed to the concurrent oxidation and reduction of methanol and has been confirmed in the absence of CO₂ and Pd. Notably, the presence of CO₂ under alternating polarity led to increased selectivity for DMC.