(Invited) Hydrogen Assisted Carbonate Electrolysis for Direct Air Capture of CO2

Abstract

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