Reduction of greenhouse gases is vital for the long-term environmental health of the planet. While there has been progress in reducing CO₂ emissions at large point sources, a significant portion of the CO₂ emitted each year in the United States is released from distributed sources, like cars, smaller factories, and farms. Direct capture of CO₂ from ambient air is therefore necessary for the ultimate reduction of greenhouse gas emissions in the atmosphere. However, capturing the CO₂ in ambient air presents a much greater challenge due to the dilute nature of the CO₂, requiring different strategies than carbon capture from concentrated CO₂ waste streams.

We are developing a novel process for the capture and containment of CO₂ from air into a purified, concentrated CO₂ stream that can be redirected for use as a feedstock for a wide variety of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO₂ in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO₂ at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO₂. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO₂ capture and electrolysis processes, reducing both overall energy and chemical consumption.

Using a custom designed test stand and traditional electrolysis cell design, we have demonstrated voltage of <1.8 V at 100 mA/cm² for potassium carbonate conversion to carbon dioxide at the anode, with concomitant H₂ and KOH production at the cathode, based on potassium-selective ion exchange across the membrane. Furthermore, using a custom 3-compartment electrolysis flow cell and ion-selective membranes, we successfully demonstrated hydrogen-assisted carbonate electrolysis, with hydrogen consumption at the anode, hydrogen and KOH production at the cathode, and CO₂ formation from potassium carbonate in an internal flow-through compartment, at 1.4 V at 50 mA/cm². Further improvements in operating conditions and cell components and design should decrease the operating voltage significantly, to <1 V at 100 mA/cm².

Acknowledgement: The project is financially supported by the Department of Energy’s ARPA-E Office under the Grant DE-AR0001495