Designing reactors, methods, and catalysts for the understanding of the electrochemical carbon dioxide reduction reaction [electronic resource]
Keywords: Chemical Engineering.

As the worldwide population quickly approaches 8 billion, global energy demands have continued to rise; in order to meet these demands, renewable energy sources need to be developed and implemented. Increases in global concentrations of carbon dioxide due to the consumption of fossil fuels and its negative impact on the climate motivate investigations of the electrochemical carbon dioxide reduction reaction (CO2RR) to fuels and chemicals. The development of a selective, efficient process that converts CO2 into energy stored in chemical bonds using renewable energy would enable a shift to a sustainable energy economy and chemical industry. However, the discovery and development of catalysts that can reduce CO2 to high value products at low overpotentials and high current densities remains a challenge. Furthermore, there remains a lack of fundamental understanding of this reaction, in particular: (1) what dictates the selectivity of various metal electrodes; (2) how the surface of the catalyst changes during electrochemical experiments, and; (3) how variables such as mass transport and temperature affect the activity and selectivity of catalysts. To address these key questions, several investigations on a variety of metal electrodes and electrolytes were conducted. For the first project, the thesis reports a joint experimental and theoretical investigation of the electrochemical reduction of CO2 on polycrystalline Sn surfaces. Scaling relations for Sn and other transition metals are examined using experimental current densities and density functional theory (DFT) binding energies. While *COOH was determined to be the key intermediate for CO production on metal surfaces, *OCHO was determined to be the key intermediate for the CO2RR to HCOO-, with Sn's optimal *OCHO binding energy explaining its high selectivity for HCOO-. The second project focuses on the ability of ionic liquids to suppress HER on Ag, Cu and Fe electrodes in acidic and basic media. In the absence of CO2, HER is suppressed on all three electrodes in acidic media; no such suppression is observed in basic media. 1H NMR spectroscopy was utilized to identify compounds that are formed as the [EMIM] Cl breaks down at both the working and counter electrodes under electrochemical reaction conditions. The third project reports the design and development of several techniques to probe and characterize the catalyst during CO2R. Using eGIXRD and eGIXAS, changes in the surface electronic structure and lattice orientation of thin film Au, Pd, and AuyPd1-y catalysts, including significant expansions in lattice parameter due to hydrogen intercalation, were observed during electrochemical CO2 reduction. These results provide insight into the interesting catalysis of the AuyPd1-y system and why it may differ from the activity of Au and Pd for this reaction. In all, this dissertation presents a variety of experimental work, technique development, and reactor design which directly led to fundamental insights into the activity and selectivity of metal electrodes, and provides key understanding towards the design and development of reactors and catalysts for the electrochemical reduction of CO2.