(Invited) The Relationship of Morphology and Catalytic Activity: A Case Study of Iron Corrole Incorporated in High Surface Area Carbon Supports

Abstract

In the past several years we have been thoroughly studying the performance of molecular catalysts for oxygen reduction based on metallo-corrole. We studied the effect of the metal center, substituents in their meso and beta positions and ORR mechanism at a wide pH range. The most influential factor was found to be the metal center while the effect of electro-negative substituents seems to diminish once these molecular catalysts were incorporated in porous carbon supports. Moreover, the overall activity and reaction selectivity has increased dramatically after this incorporation, and was found to be dependent on the carbon support. Specifically, metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon: BP2000. The nature of the interaction between carbon surfaces and metallo-corroles was identified in this work. The results suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20-25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction.