Dioxygen Electrocatalysis: Mechanisms in Relation to the Catalyst Structure

摘要

The overall 4-electron reduction of O2 involves the cleavage of the 0-0 bond. To achieve such requires the strong interaction of the 0-0 species with surface sites of the electrocatalyst, i.e., either Griffiths type lateral interaction with a single site or bridged-type interaction with adjacent surface sites. Such interactions, however, are not sufficient to achieve high catalytic activity unless the various reduction steps required for the overall 4-electron reduction. These macrocycles are capable of forming either intra-molecular -0-0- bridge adducts or in other instances inter-molecular -0-0- adducts. In some instances their electrocatalytic activity is comparable to or even higher than that of platinum. Furthermore, they lend themselves to molecular engineering especially in regard to the formation of -0-0- bridges and their redox potentials. Of significant help in the study of such transition macrocycle electrocatalysts adsorbed on electrode surfaces have been various in-situ spectroscopic methods including laser Raman, UV-visible reflectance and Mossbauer spectroscopies.