Investigations of carbon-based materials for electrocatalytic carbon dioxide reduction
Abstract/Contents
- Abstract
- There is an urgent need for renewable and sustainable technologies to help abate the consequences of climate change originating from anthropogenic CO2 emissions. Electrochemical CO2 reduction (CO2R) can covert CO2 to useful chemicals like carbon monoxide (CO) or ethanol under ambient conditions and could be a route towards storing renewable electricity and producing carbon-based consumer products. CO2R kinetics are tied to the structure of the catalytic active site and the surrounding chemical environment but precisely describing this interface is challenging which is an impediment for future industrial applications of CO2R. This dissertation describes efforts to determine the effect of carbon-based materials on CO2R rates in two areas: 1) Ni, N co-doped carbon electrocatalysts (Ni-N-C), and 2) Imidazolium-ionomer coatings on Ag. Ni-N-C materials have been shown to have high selectivity for CO but knowledge of the catalytic active site is limited. In this dissertation, the origin of this activity was investigated by a wide variety of techniques including kinetic testing and physiochemical characterization (electron microscopy (STEM), X-ray absorption spectroscopy (XAS), secondary ion mass spectrometry (SIMS), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and 61-Ni Mossbauer spectroscopy). By combining insights from these diverse methods, atomically dispersed, nitrogen-coordinated sites in a distorted square planar geometry were identified as likely CO2R active sites. As these sites are expected to be both thermally and electrochemically stable, the activity of Ni-N-C was extended beyond electrochemical catalysis by demonstrating that the same Ni-N-C catalyst could also selectively facilitate thermal CO2 to CO conversion. This study provides a framework for studying the same active site under very different reaction conditions and driving forces and suggested that the electrochemical environment plays a strong role in reducing transition state barriers relative to the thermal gas-phase environment. Similarly, the effect of ionomers on the intrinsic reaction rates of CO2R catalysts has been hypothesized but rarely quantitatively studied. Here, a series of imidazolium-containing ionomers with different substituents were synthesized and coated on silver foil revealing that imidazolium-ionomers promoted hydrogen evolution and left CO2R rates unchanged. This effect was found to originate from enhanced bicarbonate reduction rates which was dependent on the steric bulk of the imidazolium substituent. This dissertation demonstrates the power of multimodal characterization and kinetic modeling towards identifying atomistic information about CO2R electrocatalytic interfaces. Further work in this area is necessary to expand our understanding of CO2 reduction which can guide materials design efforts to achieve optimized catalytic activity.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2021; ©2021 |
| Publication date | 2021; 2021 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Koshy, David Mathai |
|---|---|
| Degree supervisor | Bao, Zhenan |
| Degree supervisor | Jaramillo, Thomas Francisco |
| Thesis advisor | Bao, Zhenan |
| Thesis advisor | Jaramillo, Thomas Francisco |
| Thesis advisor | Hahn, Christopher |
| Degree committee member | Hahn, Christopher |
| Associated with | Stanford University, Department of Chemical Engineering |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | David Koshy. |
|---|---|
| Note | Submitted to the Department of Chemical Engineering. |
| Thesis | Thesis Ph.D. Stanford University 2021. |
| Location | https://purl.stanford.edu/kg818rg5132 |
Access conditions
- Copyright
- © 2021 by David Mathai Koshy
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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