Metallocorroles as Non-Precious Metal Electrocatalysts for Highly Efficient Oxygen Reduction in Alkaline Media

A series of non-precious metal complexes, composed of five first-row transition-metal complexes with β-pyrrole-brominated 5,10,15-tris(pentafluorophenyl)corroles [M(tpfcBr₈), M=Mn, Fe, Co, Ni, and Cu], was investigated as catalysts for oxygen reduction in an alkaline solution (0.1 m KOH). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electrochemical measurements to create a unique composite material. The comparison between the different metal complexes revealed a high oxygen reduction reaction (ORR) catalytic performance in the case of the Fe- and Co-corroles. These complexes reduce oxygen at very low overpotentials (with E_1/2=0.79 V and 0.77 V vs. RHE, respectively), which is better than other well-defined molecular catalysts and comparable to that of Pt on carbon (XC-72). The mechanism by which the most active complexes catalyze the ORR in alkaline solutions was also studied, disclosing that the dominant reaction path is a four-electron reduction of molecular oxygen to hydroxide.