(671g) Integrating Direct Air Capture and Ocean Carbon Capture with Photocatalytic CO2 Conversion

One of the grand challenges in the contemporary world is to mitigate greenhouse gas emission that leads to climate change while meeting the increasing demand for energy and chemicals. The ~420 ppm CO₂ in the air also rapidly exchanges dissolved CO₂ in seawater. Therefore, utilizing dissolved inorganic carbon (DIC) is equivalent to coupling direct air capture or indirect ocean carbon capture with the production of value-added materials and chemicals. It not only lowers the net emissions of CO₂ into the atmosphere but also valorizes the captured CO₂ into chemicals and fuels to fulfill a circular carbon economy. When we continuously performed CO2R without bubbling gaseous 1-atm CO₂, the net proton consumption would basify the bicarbonate. Eventually, excess OH- led to near-zero bulk CO₂(aq) concentrations. Therefore, we choose study photocatalytic CO2 reduction (CO2R) in dissolved bicarbonates of ~0 mM CO₂(aq), challenging but relevant to carbon capture utilization.

We take the approach of using the mesoscale long-range chemical transport to modulate the pH and CO₂(aq) local chemical environment for photocatalytic CO2R catalysis at Ag nanoparticle active sites. We achieved record ~0.1 % solar-to-fuel conversion efficiency for CO production using Ag@CrOx nanoparticles that are supported on a coating-protected GaInP photocatalytic panel with proton-coupled redox processes. CO is produced at ~100% selectivity with no detectable H₂, even with copious protons that are co-generated at nanoscale distance. At pH as high as 11, CO₂ flux to the Ag@CrO_x CO2R sites can achieve measurable CO₂ adsorption which was probed by in-situ Raman spectroscopy. We found that light-driven CO2R and CO₂ reactive transport are mutually dependent, which is important for further understanding and manipulating CO2R activity and selectivity. This study enables direct bicarbonate utilization as the source of CO2 thereby achieving CO2 capture and conversion without purifying and feeding gaseous CO2.