UC San Diego

With rising atmospheric CO2 levels and a growing demand for sustainable energy, it is imperative to search for a means of a carbon-neutral fuel source that can replace the current global energy infrastructure. Electrochemical and photoelectrochemical CO2 reduction (CO2R) are promising paths towards producing carbon-neutral fuels like methanol. Recently, immobilized molecular catalysts (CoPc) on carbon nanotubes have been growing in interest as they exhibit extraordinary catalytic properties, such as high current density, high product selectivity, long-term stability, high turnover-frequency, low overpotentials, and the ability to operate in aqueous environments. To improve upon these hybrid CO2R systems, it is crucial to understand how the molecular catalyst interacts with the graphitic support to further tailor the catalyst or the local microenvironment. This dissertation will be focusing on discussing the local microenvironments surrounding the catalysts and multiwalled carbon nanotube (MWCNT) support. First, a broad overview of catalyst types in electrochemistry is discussed, which gives context to the current field of immobilized molecular catalysts on graphitic supports for CO2 reduction. The following chapter discusses how the preparation methods of these hybrid catalyst/MWCNT electrodes can affect the surface morphology, electrochemical behavior, and catalysis. Next, in-situ XAS electrochemical measurements were taken of Re(tBu-bpy)(CO)3Cl on MWCNT to study their electronic coupling and molecular interactions. The next chapter discusses how applied bias and mass transport affect the selectivity of immobilized CoPc on MWCNT for selective methanol generation, and the role of CO as a reactive unbound intermediate. This model catalyst layer preparation was integrated onto a 3-terminal tandem device (3TT) for a photoelectrochemical CO2R cascade scheme to generate methanol using light in a near neutral pH aqueous system. The last chapter is focused on providing ideas and projects for future research.