Polymeric Porphyrins as Solar Photocatalysts [report]

Nicholas Day
2000 unpublished
Research concentrated on the absorption, transformation, and storage of light energy is useful for the energy challenges faced by humanity. In particular, photocatalysis using solar energy to generate useful fuels has become a primary research goal in the drive to replace fossil fuels for the future. In this dissertation it is shown that poly-tetra(4-aminophenyl)porphyrin (pTAPP) can be oxidatively polymerized using a variety of methods, including electropolymerization, chemical oxidation, and
more » ... nterfacial polymerization and that pTAPP has photocatalytic ability to reduce O 2 to H 2 O 2 for a storable fuel. Organic conductive polymers such as pTAPP are attractive catalysts because of their high surface area and ability to coat electrodes. pTAPP in a mixed oxidation state is shown to have both its minimum charge transfer resistance as well as its minimum impedance to electronic conductivity in the film. The UV-vis-NIR absorption spectra of pTAPP with increased oxidative doping are similar to hyperporphyrin spectra, characteristic of a two-plus charge localized on a single porphyrin unit. This suggests the presence of a bipolaron on the individual porphyrin units, and thus a bipolaron conductivity mechanism has been proposed. pTAPP changes color depending on its oxidation state, and therefore is a promising material for electrochromic devices. A novel Pourbaix diagram was created as a means of illustrating the redox and protonation states of pTAPP as a function of changes in pH, applied potential, electrochromic behavior, and electronic conductivity. ii Both pTAPP and pCoTAPP were shown to be effective catalysts for the reduction of oxygen to hydrogen peroxide, with pCoTAPP a better catalyst than pTAPP. When pCoTAPP is irradiated, oxygen reduction occurs close to the thermodynamic potential, indicating a promising system for storage of solar energy.
doi:10.15760/etd.2621 fatcat:u2zh4oqx5zfd7pswjy7qtwvt2y