Nanoscale Building Blocks for Multi-Electron Electrocatalysi

The goal of this research project is to develop a fundamental understanding of multielectron electrochemical reactions involving coupled electron transfer and atom transfer processes. The design of electrodes to efficiently carry out processes in which atom transfer accompanies electron transfer, such as the 4e- reduction of oxygen to water, is a fundamental problem in electrochemistry. Our approach to electrocatalysis involves the attachment of molecules that are selective for the reaction of interest in homogeneous solution to conducting supports. Redox active electron donors or acceptors that provide the multiple electron oxidizing or reducing equivalents at the required potential for near thermodynamic reversibility mediate electron transfer between the support and the active catalyst site. The attachment of mediating redox couples to the binding site for oxygen reduction will allow greater control over the potential of the electrode. #Electron antennas# such as the cyclopentadienylironcarbonyl tetramer, [(5-C5H5)Fe(�3-CO)]4, or ferrocene are being attached to the periphery of mononuclear and binuclear cobalt porphyrin complexes to provide a site for 4e- reduction of oxygen. The kinetics of the reactivity of these supramolecular assemblies will be studied both experimentally and computationally. We are also conducting in situ X-ray adsorption spectroscopy (XAS)-electrochemistry experiments to determine the local structure(EXAFS) and oxidation state of the electron antenna, metal ion binding site, and porphyrin ligand in the active site (XANES), allowing modeling predictions to be verified. This research program will provide the fundamental basis for the development of electrocatalysts with lower overpotential for oxygen reduction, allowing hydrogen-oxygen fuel cells to operate more efficiently