Carbonate Electrolysis for Energy Efficient Direct Air Capture of CO2

Abstract

Yearly global energy related CO2 emissions continue to increase, reaching a record breaking 37 billion metric tons in 2022. As a major greenhouse gas, CO2 levels need to be reduced by 10s of gigatons to prevent the worst of climate change, something that is no longer feasible with net-zero emissions alone. Removing atmospheric CO2 is therefore of critical importance for the future of our planet. While major improvements have been made in CO2 capture from large point sources, a significant portion of CO2 emitted each year from the United States comes from distributed sources such as cars and smaller factories. Due to the dilute concentrations of CO2 in ambient air, Direct Air Capture (DAC) needs to be highly selective to preferentially absorb CO2 to collect useable amounts. These challenges have made current DAC systems quite costly, both energetically and economically, and require vastly different strategies than carbon capture from concentrated sources.At Giner, we are developing a novel process for the capture and regeneration of CO2 from air into a purified, concentrated CO2 stream that can be redirected as a feedstock for a wide range 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.Giner has developed a unique 3-compartment carbonate electrolysis flow cell. Using our electrolyzer, we have seen operating voltage as low as 1.2 V at 100 mA/cm2 in a 5 cm2 cell for potassium carbonate conversion to CO2 with H2 assisted electrolysis. Significant improvements in operating voltage have come from optimization of gas-diffusion layers (GDLs), cell geometry, and membrane selection. Furthermore, we have achieved >97% pure CO2 formation in the internal flow-through compartment. Currently, scale-up is in progress to apply these developments to approach comparable conditions in a 50 cm2 multi-cell stack. Further developments will enable pairing with an in-house, carbonate based, air contactor allowing for capture and regeneration of over 1 ton CO2 per year. Acknowledgement: The project is financially supported by the Department of Energy's ARPA-E Office under the Grant DE-AR0001495