Electro-Polymerized Metallocorroles As Electrocatalysts for Oxygen Reduction

The most active non-precious metal catalysts (NPMCs) for oxygen reduction (ORR) to date are the pyrolyzed catalysts, inspired from Heme-like complexes. These are usually composed of iron and/or cobalt coordinated by nitrogens, claimed to resemble the structure of porphyrins and phthalocynines, on the surface of a carbon support. Unfortunately, the exact structure of the catalytic sites remains a mystery and the solution for this conundrum seems be almost impossible. The advantages of using such catalysts are: (1) their high activity and (2) low price, which is derived from the cost of their precursors. The disadvantages are: (1) low durability compared to precious metal catalysts, and (2) their unknown structure, which limits their further improvement in order to obtain both the activity and durability benchmarks needed to become good alternatives for precious metals.

One of the most promising options to resolve these issues is to find non-pyrolyzed molecular non-precious metal catalysts for ORR that could be tuned to match the necessary requirements. Recently, Metallo-corroles, a relatively new family of molecular catalysts was reported to have very good potential as non-precious metal catalysts for ORR. Inspired from the extensive work on the electropolymerization of metalloporphyrins, and its merits, we electropolymerized of metallocorroles on carbon electrodes to (1) increase their site density in order to overcome their relatively low electrocatalytic turnover frequency (when compared to platinum) and (2) use the proximity of active sites to move from 2- to 4-electroreduction of oxygen. Metallocorroles substituted with anilines were studied and electropolymerized. They show a significant enhancement in the overpotential required for the execution of ORR and tendency for 4-electron reduction to water. The electropolymerization, its characterization and the effect on the electrocatalytic activity of the electropolymerized metallo-corroles vs. the monomers will be presented.