Abstract:

Carbon capture, utilization, and storage (CCUS) are critical for managing anthropogenic carbon dioxide (CO2) emissions. Great strides have been made in electrification so far, but there are a handful of scenarios that still require hydrocarbon fuels and chemicals, such as aviation, long-haul trucking, and marine shipping. On the one hand, atmospheric CO2 is only 420 ppm, and using alkaline sorbents for direct air capture is energy intensive; and there are issues with carbon utilization during electrochemical CO2 reduction. On the other hand, atmospheric CO2 exchanges with surface seawater constantly, and the concentration of dissolved inorganic carbon (DIC) in the oceans is approximately 140 times higher in carbon molarity than atmospheric CO2. Thus, capturing and converting DIC in seawater represents an alternative approach to CO2 direct air capture. For these new opportunities, our group takes a multi-scale approach: i.e., combining light-driven photocatalysis with reactive transport using engineered photo-reactors, such as utilizing the 2.3-millimolar dissolved bicarbonate in oceanwater under sunlight. Photocatalysis concerns multiple redox reactions located within nanoscale distances: I will first elucidate the chemical physics of coupled processes during photocatalysis essentially to achieve >85% quantum efficiency; and then, I will describe the design and realization of 3D-printed reactors. A flow photoreactor enables realistic ocean operation. This new process achieves one-step conversion to syngas, which directly enables on-site liquid fuel production. Thus, it saves over 50% of the energy that is used for stepwise separation of the 420 ppm CO2 in the air.