Chemistry Department Colloquium

A wide range of chemical processes can be termed proton-coupled electron transfer (PCET), from combustion to water oxidation to the redox dissolution of minerals. This presentation will begin with fundamental studies of single reaction steps that involve transfer of one proton and one electron. Some of these reactions ‘look like’ hydrogen atom transfers, such as oxyl radicals abstracting H• from vitamin C, while in other reactions the electron and proton are quite separated in the reactants or products, as in equation 1. Many of these reactions can typically be using a version Marcus Theory, to good accuracy. The Marcus approach shows the commonality of organic and transition metal H-atom transfer reactions, and the success of this approach raises fundamental issues.
The second portion of the presentation will present initial results on projects extending these ideas to new water-oxidation and oxygen-reduction catalysts. For instance, the iron porphyrin complex at right is a good electrocatalyst for O2 reduction in acidic acetonitrile, with the pendant carboxylic acid ‘proton relays’ enhancing the selectivity for the 4e– reduction to water.
The closing section of the presentation will use PCET concepts to provide new insights into the properties and reactivity of metal oxide nanoparticles, and by implication all metal-oxide/solution interfaces. In one example, reduced ZnO and TiO2 nanoparticles transfer e– and H+ (H•) to a phenoxyl radical: