This thesis encompasses a suite of coordination-driven self-assembled porphyrin prisms differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. The goal of this work was to apply the facile synthesis methods to rationally design cofacial catalysts and analyze the activity towards the oxygen reduction reaction (ORR). Specifically, we have explored how different molecular clips affected the prisms’ activity, selectivity, overpotential, and kinetics. High selectivity towards H2O and low overpotential are key requirements of an oxygen reduction catalyst for applications in fuel cells.
We have demonstrated the first coordination-driven self-assembled porphyrin catalyst (Benzo-Co) used for small molecule activation, specifically ORR. The first report includes the characterization, along with catalytic chemical and electrochemical reduction studies. The selectivity and rate constants of this catalyst (H2O vs. H2O2) were compared to the mononuclear CoTPyP. After these findings, the goal was to optimize the catalyst using alternative bridging ligands in the molecular clips that held the porphyrin subunits in a cofacial offset and analyze the selectivity towards H2O. We hypothesized that if the metal centers of CoTPyP were held at a shorter distance, the selectivity of the catalyst would improve. The distance of the metals is critical to the O–O bond cleavage step. If there is not a secondary metal to interact with O2, for example mononuclear CoTPyP, O–O cannot be cleaved. If the M–M distance is too large, the secondary metal may not interact with O2 to participate in the bond cleavage step. The catalyst series were immobilized on the electrode surface and the selectivities of Ox-Co, Oxa-Co, and Benzo-Co prisms towards H2O2 as determined by rotating ring-disk electrode studies. Rotating disk electrode studies showed Levich current responses. Koutecký-Levich and Tafel analyses, were used to obtain kinetic information and estimation of rate constants. This thesis highlights how coordination-driven self-assembly can be used to address difficult multi-electron multi-proton transformations, like oxygen reduction, using cofacial polynuclear catalyst.
|Advisor:||Cook, Timothy R.|
|Commitee:||Diver, Stephen T., Keister, Jerome B., Lacy, David C.|
|School:||State University of New York at Buffalo|
|School Location:||United States -- New York|
|Source:||DAI-B 79/10(E), Dissertation Abstracts International|
|Subjects:||Chemistry, Inorganic chemistry|
|Keywords:||Cofacial porphyrin prisms, Coordination-driven self-assembly, Oxygen reduction catalysts|
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