Carbon dioxide (CO₂) emissions account for approximately 80% of anthropogenic contributions to greenhouse gas emissions and there is a growing need for CO₂ utilization strategies. CO₂ at supercritical conditions can be employed as a green solvent for extractions and separations, or can be injected in the subsurface for storage. CO₂ can also be used as a reactant, a raw material to be converted into valuable chemicals via electrocatalysis. It is likely that all such approaches are needed, and more, to substantially reduce greenhouse gas emissions. The study of the physical and chemical properties of CO₂ informs these climate-critical CO₂ mitigation approaches.

Understanding the CO₂ phase behavior of complex fluid mixtures – liquid, gas, supercritical – at different thermodynamic conditions is essential to many industrial and chemical processes. In this work a phase behavior measuring chip was developed that can simultaneously determine the phase behavior of fluids at multiple combinations of temperature and pressure within the application’s scope. This phase chip testing method demonstrated a hundredfold decrease in the processing time comparing to the current industrial testing processes while maintaining experimental resolution and high accuracy (Chapter 3). At the same time, this work provides a platform for exploring CO₂ mixture phase behavior, interface behavior, and mass transport.

Electrochemical reduction of CO₂ to valuable liquid fuels and chemical feedstocks is a sustainable approach to intermittent electricity utilization. Gas diffusion heterogeneous reaction electrodes facilitate effective CO₂ mass transport to the catalyst, enabling electrolyzers to operate at the current densities required for industrial deployment. However, the complex interactions between a solid catalyst, liquid electrolyte, and gas reagents of heterogeneous electrodes significantly influence the CO₂ reduction reaction (CO₂RR) performance. This work focuses on CO₂ local availabilities/pressure (Chapter 4), microstructure wetting capabilities (Chapter 4), pH distribution (Chapter 5), and electromigration (Chapter 5) with the goal of improving the performance of the CO₂ reduction reaction (CO₂RR) in practical systems. Together these efforts improve efficiencies, selectivities, and current densities of CO₂ electrocatalytic systems, and advance the field of CO₂ utilization more generally.