The research proposed is directed at the discovery of superior catalysts for the electrochemical reduction of dioxygen and other technologically important molecules. The proposal will also involve work on the development of new catalysts for reactions that require the transfer of multiple electrons. Finally, a new method for determination of the rates of electron transfer across liquid/liquid interfaces will be used for the study of electron transfers in the absence of accompanying ion transfers. Substituted porphyrins will be used as mediators for the reduction of dioxygen. Heteropolyanions will be used as reservoirs of electrons for multiple electron transfer reactions. Applications to improved fuel cells and air batteries are envisioned.