Date of Award

Fall 2023

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Christine A Caputo

Second Advisor

Erik Berda

Third Advisor

Glen Miller

Abstract

Global climate change, induced by increasing anthropogenic emission of heat trapping gases, has drawn great attention from scientists in recent decades. Reducing carbon emissions by decreasing the usage of fossil fuels and applying low/no carbon energy sources is a promising solution for a sustainable future. Electrocatalytic proton reduction to form hydrogen, using green electricity is a practical starting point.

Recent examples of heterogenized molecular catalysts have shown promise but stable anchoring to electrode surfaces is still a challenge. Heterogeneous electrocatalysis shows much more stability, but these systems lack the selectivity provided by a molecular system when more challenging reactions are attempted.

In this thesis, we present the design, synthesis, and fabrication of a unique non-covalent anchoring strategy for molecular catalysts on electrode surfaces. The proof-of-concept tests used here to demonstrate electrocatalytic hydrogen generation, but could be expanded to other catalytic systems in the future.

We hypothesized that this system, which employs a host-modified electrode and a guest-functionalized electrocatalyst, could self-assemble to form a catalytically active supramolecular assembly on the electrode surface. Due to the close proximity between the catalyst and the surface in this assembly, we hope the potential to carry out electrocatalytic hydrogen evolution at low overpotentials and with a prolonged lifetime by replacement of degraded catalyst, would be possible.

Using two synthetic variants of pillar[5]arene as a surface-anchored host molecule, the first bearing hydroxyl- and the second bearing carboxylate-functional groups to act as the anchoring groups, host-functionalized TiO2/FTO electrodes were prepared and characterized. A cobaloxime proton reduction catalyst was synthetically functionalized with a pyridinium cation as an axial ligand due to the predicted high binding constant with pillar[5]arene.

The binding interaction between host and guest was studied in solution using NMR spectroscopy, mass spectrometry and titration monitored by fluorescence spectroscopy. Self-assemblies of the guest@host hybrid electrodes were then tested to determine their catalytic activity for hydrogen evolution.

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