Modeling and Experimental Evaluation of Electrochemical Reactors for Carbon and Nitrogen Circularity
Year: 2026
Type: dissertation
Abstract: This dissertation develops experimental and modeling tools to enable electrochemically based circular use of carbon and nitrogen. A major focus of my dissertation is the development and validation of a novel electrochemical method for carbon dioxide (CO2) removal from ocean water, while functioning as energy storage. Ocean water is a key CO2 sink, absorbing up to 40% of all CO2 emissions, and is adversely affected by ocean acidification. By using redox salt and H2 looping, the method can store electricity for demand-side load shifting, operating continuously despite renewable energy intermittency. Using a cyclic pH-swing process, energy use and operational cost are minimized through modeling and testing a lab-scale reactor. The reactor’s performance is designed to enhance mass transport and reduce electricity costs via design and operational parameters. Results indicate improvements in cost savings and integration with renewable energy systems. Additionally, while mass transport and ohmic limitations are identified as the largest limiters for system performance, mass transport is improved with 3-D printed fins that reduce the diffusion boundary layer up to 41%. Ohmic resistances still dramatically need to be improved for reasonable energy intensities at commercially relevant operating current densities. Precipitation can also be a severe performance limiter for direct ocean capture; however, this work shows that the reversible polarity of the redox/H2 looping process successfully cleans precipitate off electrode surfaces to prevent performance impacts up to 4 cycles. Additionally, precipitation is studied at varied current densities in a specialized H-cell to determine what conditions most effectively remove precipitate. The study on direct ocean capture concludes by determining that the relative length scale of precipitation compared to convection is important for determining precipitation trends with current density. Additionally, this research also develops a reaction-diffusion modeling framework to understand local CO and CO2 concentrations when converting it to methanol in a CO2 electrolyzer. Methanol conversion from CO2 is found to drastically improve at low CO2 flow rates and partial pressures. While some of this improvement can be attributed to larger relative concentrations of CO to CO2 on the surface, more significant improvements are correlated with when the local concentration of OH− is greater than the buffer concentration. Finally, this dissertation also explores nitrate-to-ammonia conversion. Similar to CO2 reduction to methanol, high pH was also found to improve nitrate to ammonia production; however, this was complicated by the electrode surface quality — which presented large variations in performance. This work successfully applied electrochemical impedance spectroscopy as a way to understand trial-to-trial uncertainties. Electrochemical impedance spectroscopy results correlated dramatic shifts in performance with facets of different copper crystal structures. Overall, my thesis introduces an electricity load-shifting architecture for direct ocean capture to reduce operating costs, models and experimentally validates scale-up levers for the presented direct ocean capture process, establishes a relative length scale-based framework for precipitation trends on electrode surfaces, and uses modeling and experimental tools to probe pH and electrode surface effects for nitrate conversion to ammonia and CO2 reduction to methanol. This comprehensive approach combines modeling and lab experiments to accelerate the uptake of carbon removal technologies and safeguard the environment from the impacts of climate change.
DOI: 10.7302/dspace/29701
Author: Silcox, Rachel
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7162464880