The electrochemical conversion of Earth abundant resources such as water and CO2 to value-added fuels and chemicals powered by renewable energy is a promising avenue toward a sustainable future. In this thesis, I report a series of studies ranging from more fundamental investigation of bulk metallic surfaces, to reactor engineering/process design, to the synthesis of nanostructured catalysts, and finally to the study of catalytic degradation in efforts to develop highly active, selective, and efficient processes for the H2 evolution and CO2/CO reduction reactions. I will show how various efforts can be utilized in conjunction with one another to solve key challenges faced in the development of these electrochemical systems.
I will first begin by examining bulk Cu-based bimetallic catalysts for the H2 evolution reaction in alkaline conditions to identify key descriptors to guide the design of non-precious catalysts. Through a systematic study using a series of first-row transition metal dopants, I will show that we can enhance the H2 evolution activity by doping Cu with highly oxophilic metals. The enhancement is due to the synergistic effects between the oxophilic dopant and Cu which help absorption and activation of the water molecule to form the first Hads intermediate, thus enhancing activity.
In the second work, I will present a reactor engineering/process design study where we scale up a nanoporous-silver catalyst and design an electrochemical reactor that can continuously convert CO2 to CO with high selectivity and activity. Through engineering design, I will demonstrate how we can take advantage of the solubility of CO2 in aqueous electrolyte to achieve a high single-pass conversion of ~86% with a CO Faradaic efficiency as high as ~96%.
Taking the lessons learned from the previous studies, I will demonstrate CO reduction at high reaction rates (100 mA cm-2) which has not been previously achieved, by utilizing a novel flow-cell electrochemical reactor. In addition, we will study carbon to carbon bond formation in Cu-catalyzed CO2/CO reduction at commercially relevant rates of reaction by designing and integrating nanostructured catalysts that selectively exposed specific surfaces. In particular, Cu nanosheets that selectively expose the (111) facets demonstrate high selectivity toward acetate formation with an acetate Faradaic efficiency as high as ~48% and an acetate partial current density up to 131 mA cm-2 in alkaline conditions. Further analysis suggest that the improved acetate formation is due to the suppression of ethylene and ethanol formation.
Next, I will demonstrate that Cu catalysts are highly susceptive to SO2 impurity in CO2 reduction. Using a combination of electrochemical activity studies, computation predictions, and advanced microscopic efforts, I will show that the formation of surface Cu sulfides is responsible for the irreversible suppression of multi-carbon products.
I conclude by describing emerging directions stemming from these studies in efforts to further push these electrochemical systems toward commercial applications.
|Commitee:||Xu, Bingjun, Lobo, Raul F., Chen, Jingguang G.|
|School:||University of Delaware|
|School Location:||United States -- Delaware|
|Source:||DAI-B 81/2(E), Dissertation Abstracts International|
|Keywords:||Electrochemical conversion, Renewable energy, Bulk metallic surfaces|
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