FIRST PRINCIPLES INVESTIGATION OF METALLOCORROLES AS NON-PRECIOUS METAL CATALYSTS FOR OXYGEN REDUCTION REACTION

Among the most appealing options for replacing fossil-fuel technologies, such as internal combustion engines, are proton exchange membrane fuel cells, PEMFCs. However, the commercial viability of these devices is limited by the rate limiting Oxygen Reduction Reaction, ORR, at the cathode and the high price of Pt-based catalysts. Oxygen electrochemistry plays a pivotal role in all modern energy conversion processes and overall understanding of the related processes and mechanisms occurring under the operation conditions is a necessity for the rational design of materials that meet these requirements.

We present a first principles investigation of the ORR catalyzed by first row transition metal metallocorroles, 2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(pentafluorophenyl) corrole [M(tpfcBr8)] M=Mn, Fe, Co, Ni, Cu. In these species, the metal atom is the catalytic site. We show how the electronic structure of these metallocorroles, as well as the stability of the reaction intermediates, dictate the ORR mechanism and activity of these complexes. For example, for the full 4e^- reduction path, for M=Mn, Fe and Co, the formation of the hydroxide intermediate (*OH) is a thermodynamic sink. For M=Cu and Ni, the formation of the peroxide (*OOH) intermediate is a thermodynamic sink. Electronic structure analysis elucidates the reason for the difference in behavior between earlier and later first row transition metal metallocorroles. In agreement with previous studies, the oxygen bound to Cu and Ni, tend to form a single metal-oxygen bond and an oxyl radical, while for M=Mn, Fe and Co the oxygen atom forms a double bond.

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