Electrolytic Conversion of Bicarbonate into CO in a Flow Cell

TL;DR

This study demonstrates that aqueous bicarbonate solutions can be electrochemically converted into CO in a flow cell with high efficiency, eliminating the need for gaseous CO2 addition and simplifying carbon capture utilization.

Contribution

It introduces a flow cell method using bicarbonate solutions and a bipolar membrane to produce CO efficiently without gaseous CO2 feed, advancing electrochemical CO2 reduction technology.

Findings

Achieved 81% faradaic efficiency for CO at 25 mA/cm²

Comparable CO production efficiency with gaseous CO2 saturation

Bipolar membrane H+ flux facilitates bicarbonate conversion to CO

Abstract

Electrochemical CO2 reduction offers a method to use renewable electricity to convert CO2 into CO and other carbon-based chemical building blocks. While nearly all studies rely on a CO2 feed, we show herein that aqueous bicarbonate solutions can also be electrochemically converted into CO gas at meaningful rates in a flow cell. We achieved this result in a flow cell containing a bipolar membrane (BPM) and a silver nanoparticle catalyst on a porous carbon support. Electrolysis upon a N2-saturated 3.0-M potassium bicarbonate electrolyte solution yields CO with a faradaic efficiency (F.E.CO) of 81% at 25 mA cm-2 and 37% at 100 mA cm-2. This output is comparable to the analogous experiment where the electrolyte is saturated with gaseous CO2 (faradaic efficiency for CO is 78% at 25 mA cm-2 and 35% at 100 mA cm-2). The H+ flux from the BPM is critical to this chemistry in that it reacts with the bicarbonate feed to generate CO2, which is then reduced to CO at the gas diffusion electrode. These results are important in that they show that the addition of gaseous CO2 to bicarbonate electrolytes is not necessary in order to obtain reduced carbon products with a flow cell architecture. This process offers a means of using electrolysis to bypass the thermally-intensive step of extracting CO2 from bicarbonate solutions generated in carbon capture schemes.