Zirconium-Based Metal-Organic Frameworks for Artificial Electrochemical Photosynthesis
| dc.contributor.author | Thomas, Benjamin David | en |
| dc.contributor.committeechair | Morris, Amanda | en |
| dc.contributor.committeemember | Lin, Feng | en |
| dc.contributor.committeemember | Merola, Joseph S. | en |
| dc.contributor.committeemember | Deck, Paul A. | en |
| dc.contributor.department | Chemistry | en |
| dc.date.accessioned | 2025-02-22T09:00:11Z | en |
| dc.date.available | 2025-02-22T09:00:11Z | en |
| dc.date.issued | 2025-02-21 | en |
| dc.description.abstract | The utilization of porous materials for electrocatalytic applications has been of high interest due to their high surface area and increase in electrode-electrolyte interface. Metal-organic frameworks (MOFs) are an emerging class of 3-D porous materials consisting of inorganic nodes bound by multidentate organic linkers. MOFs have permanently large surface area, high stability, and the tunability of the structure. The metal source or the organic linker can be swapped to create a material with desirable features. MOFs have been explored for applications in electrocatalysis, conductivity and energy storage. The fundamental charge transfer methods of MOF thin films is discussed and the utilization of these conductive materials for the key reactions in artificial photosynthesis is explored to highlight methods to improve the efficiency of these materials for electrocatalysis. The Morris group has previously shown that charge transfer in MOFs can occur through a redox hopping mechanism in which the charge hops from redox center to redox center through space followed by the movement of a charge balancing ions. In Chapter 2, the charge transfer mechanism within the MOF is further investigated by utilization of spectroelectrochemistry. The incorporation of a redox center, Ru(bpy)2(dcbpy), "RuBPY" where bpy = 2,2′-bipyridine; bpy-(COOH)2 = 5,5′-dicarboxylic acid-2,2′-bipyridine into the UiO-67 framework creates a conductive MOF that is also electrochromic. RuBPY is a deep orange color in the standard RuII state and upon oxidation to RuIII it is pale green. The change in absorption profile of the redox center allows for the rate of oxidation to be determined through absorbance measurements. The material showed minimal change in absorbance upon applying an oxidative potential. The incorporation of a sulfonate group into the backbone of the RuBPY-UiO-67-SO3H MOF allowed for a much higher change in absorbance converting the entire MOF into the oxidized state. The change in level of absorbance indicates that the sulfonate groups improve the conductivity within the pores of the MOF allowing for oxidation of previously electrochemically inaccessible redox centers. The sulfonate groups are thought to break ion pairs of the electrolyte and increase effective electrolyte concentration within the pores. The sulfonate groups' ability to improve the conductivity within the MOF can be further investigated to improve charge transfer through porous materials. The sulfonate groups were again incorporated into the UiO-67 MOF framework for use in electrocatalytic applications by also incorporating the known water oxidation catalyst, RuTPY, Ru(tpy)(dcbpy)H2O. A RuTPY-UiO-67 film had previously shown reactivity as a water oxidation catalyst with improved activity over a monolayer of RuTPY on fluorine-doped tin oxide, FTO. The sulfonate groups were added to create a proton transfer chain that shuttled the generated protons away from the catalytic site to improve reactivity. The incorporation of sulfonate groups again showed improved charge transfer from the MOF materials with the RuTPY-UiO-67-SO3H being 100% electrochemically accessible. The water oxidation capabilities improved giving the material increased oxygen generation upon oxidation of water. The improvement of catalytic activity of RuTPY-UiO-67-SO3H was beyond the increased electrochemical accessibility means the proximal sulfonate groups were aiding in catalysis in some manor. This work highlights the use of multivariate approaches to MOFs to improved efficiency in various applications. The fourth chapter discusses the other half of artificial photosynthesis, CO2 reduction. The known CO2 reduction catalyst, Ni(cyclam), is incorporated into a zirconium-based MOF, VPI-100. The VPI-100 powder was electrochemically deposited onto a glassy carbon electrode and the film was used for electrochemical CO2 reduction into carbon dioxide. The film successfully generated CO as a major product with a faradaic efficiency of 56%. The film was stable under electroreduction conditions and was able to be recycled for continuous production of CO. The final chapter is a review that discusses the utilization of MOFs as photocatalysts for CO2 conversion using only abundant earth metals. While most CO2 catalysts are expensive noble metals, the development of cheap abundant catalytic materials is extremely relevant to a clean energy future. | en |
| dc.description.abstractgeneral | The climate crisis has led to a need to develop more efficient renewable energy sources and novel energy storage devices. Electrochemical systems have shown great promise in providing a clean energy future with developments in lithium-ion batteries, fuel cell technologies, and artificial photosynthesis to produce value added chemicals. The basis of all these electrochemical processes is efficient charge transfer to the necessary components. Metal-organic Frameworks (MOFs) which are crystalline, porous materials made up of inorganic metal nodes connected in a discrete pattern by organic linkers. The three-dimensional nature of the MOFs consisting of connected pore networks has shown great promise to be improved conductive materials and electrocatalysts compared to existing materials. Herein, we exploit the modular nature of the MOFs to incorporate functional groups that improve ion transport and allow catalytic activity for artificial photosynthesis. The work here shows that MOF structures can be further modified to provide even more efficient electrocatalytic behavior to aid in a clean energy future. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:42426 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/124681 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | metal-organic framework | en |
| dc.subject | electrocatalysis | en |
| dc.subject | spectroelectrochemistry | en |
| dc.title | Zirconium-Based Metal-Organic Frameworks for Artificial Electrochemical Photosynthesis | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Chemistry | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
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