Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science & Engineering (PhD)

Degree Level

Graduate

Department

Materials Science & Engineering

Advisor/Mentor

Robert H. Coridan

Committee Member

Stefan Kilyanek

Second Committee Member

Jingyi Chen

Third Committee Member

Han Hu

Fourth Committee Member

Matthew B. Leftwich

Keywords

CO2 reduction reaction, Hierarchical structures, Solar fuels, sustainability

Abstract

CO2 released by the combustion of fossil fuels is driving significant changes to the earth’sclimate. The natural cycle for removing CO2 from the atmosphere, namely photosynthesis, cannot keep up with the rate at which it is being added. Developing engineering approaches to remove CO2 from the atmosphere is becoming essential to reduce these effects. Removal leads to further issues of carbon sequestration and favorable CO2 reuse strategies, including the electrochemical transformation of recovered CO2 to useful products such as fuels and materials. Copper is an important electrocatalyst for the CO2 reduction reaction (CO2RR) because of its unique capability for producing a wide range of organic compounds, from carbon monoxide to multi-carbon products such as ethanol, acetate, and ethylene. This research aims to study several aspects of integrated electrochemical CO2 reduction systems, including the effects of catalyst structure and the use of sacrificial oxidative species for converting CO2 to energetic organic molecules. We show that the structure of dendritic copper foam electrocatalysts prepared by high current density electrodeposition can be controlled by the composition of the electrodeposition solution. Multiscale structural characterization shows that simple chemical controls can significantly affect the structure from the nanoscale to the macroscale. Furthermore, we have demonstrated that these structural and morphological differences can affect the product selectivity of the catalyst. In addition, these morphological differences affect the mechanical aspects of electrocatalytic activity, including bubble formation mechanics and detachment, which are important factors in large-scale electrolysis. Towards understanding integrated CO2RR systems, we have also studied electrolysis reactions with reduced overall cell potentials by replacing the water oxidation reaction typically paired with CO2RR and hydrogen evolution with sacrificial glycerol electrooxidation. We have shown that a trimetallic Au-Pt-Bi anode can be used over extended periods to perform two-electron oxidation reactions on glycerol to glyceraldehyde and dihydroxyacetone. We have demonstrated that these reactions reduce the required potential of the electrochemical cell by 1.1 V at practical current densities when compared to a system using the oxygen evolution reaction. Furthermore, by using bipolar membranes to separate the cathode and anode compartments, the advantages of glycerol electrooxidation can be extended to operate opposite a wide range of cathodic reactions. This allows the electrochemical environment for the cathode to be chosen independently from the glycerol electrooxidation environment.

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