Efficient Capture of CO₂ and Its Selective Reduction to Formic Acid Using Tin-Based Nanomaterials

Author

Emmanuel Oluwaseun Abdul, Portland State UniversityFollow

Sponsor

Portland State University. Department of Chemistry

First Advisor

Shankar B. Rananavare

Term of Graduation

Winter 2022

Date of Publication

2-23-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Chemistry

Department

Chemistry

Language

English

Subjects

Carbon dioxide mitigation, Electrochemistry, Nanoscience

DOI

10.15760/etd.7778

Physical Description

1 online resource (xiv, 142 pages)

Abstract

CO₂ emissions from the combustion of fossil fuels and other anthropogenic sources have become the main contributing factors to global warming. Chemical methods of absorbing/capturing CO₂ from combustion flue gases have made it a sought-after approach in engineering emission solutions because of its simplistic and convenient operation and high absorption efficiency. The conversion of CO₂ into renewable fuels and high energy density chemicals by clean and economic processes has drawn scientists' attention over the decades. The electrocatalytic conversion of CO₂ using Sn-based materials has been demonstrated to be a promising method for producing formate, an important industrial chemical. Here, we attempt to capture CO₂ using a simple counter-flow spray-based contactor and convert the dissolved CO₂, using Sn and Cu-based bulk materials and SnO₂-based nanomaterials, to selectively and efficiently produce formic acid by electrolysis. The approach explored in this thesis offers an alternate approach to building stable and efficient electrodes for the electrocatalytic reduction of CO₂ and moving it closer to economic viability.

The analysis of chronoamperometric data using the modified Cottrell equation allowed the fitting data to determine the rate constant, k, of the proton transfer step in the proposed three-step; electron, proton, and electron transfer steps, the so-called ECE model. Periodic sampling of formic acid concentration from the catholyte allowed independent measurement of k, which favorably compared with the one extracted from chronoamperometric data. Observed values of k range from 10^-6 to 10^-3 s^-1 which appear to be several orders less than typical proton transfer reactions on heteroatoms such as oxygen and nitrogen. In light of Marcus' theory, theoretical modelling provided an estimate of the solvent's reorganization energy indicating potential additional contribution from the changes in the bending angle of the CO₂ anion. The k value increased with increasing formate production, suggesting that the proton transfer step is probably the rate-determining step (RDS) in the overall reduction of CO₂ to formate anion. The proton transfer reaction seems to transition from a kinetic to the diffusion-controlled limit at higher electrode potential, which became evident when a rechargeable Li-ion battery was used in place of the potentiostat. Under diffusion control, the electroreduction produced a comparable concentration of formate (about 2000 ppm) over 24 hours.

Rights

© 2022 Emmanuel Oluwaseun Abdul

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Persistent Identifier

https://archives.pdx.edu/ds/psu/37248

Recommended Citation

Abdul, Emmanuel Oluwaseun, "Efficient Capture of CO₂ and Its Selective Reduction to Formic Acid Using Tin-Based Nanomaterials" (2022). Dissertations and Theses. Paper 5907.
https://doi.org/10.15760/etd.7778