Diatomic Iron with a Pseudo-Phthalocyanine Coordination Environment for Highly Efficient Oxygen Reduction over 150,000 Cycles

Abstract

Atomically dispersed Fe-N-C catalysts emerged as promising alternatives to commercial Pt/C for the oxygen reduction reaction. However, the majority of Fe-N-C catalysts showed unsatisfactory activity and durability due to their inferior O-O bond-breaking capability and rapid Fe demetallization. Herein, we create a pseudo-phthalocyanine environment coordinated diatomic iron (Fe₂-pPc) catalyst by grafting the core domain of iron phthalocyanine (Fe-N_α-C_α-N_β) onto defective carbon. <i>In situ</i> characterizations and theoretical calculation confirm that Fe₂-pPc follows the fast-kinetic dissociative pathway, whereby Fe₂-pPc triggers bridge-mode oxygen adsorption and catalyzes direct O-O radical cleavage. Compared to traditional Fe-N-C and FePc-based catalysts exhibiting superoxo-like oxygen adsorption and an *OOH-involved pathway, Fe₂-pPc delivers a superior half-wave potential of 0.92 V. Furthermore, the ultrastrong N_α-C_α bonds in the pPc environment endow the diatomic iron active center with high tolerance for reaction-induced geometric stress, leading to significantly promoted resistance to demetallization. Upon an unprecedented harsh accelerated degradation test of 150,000 cycles, Fe₂-pPc experiences negligible Fe loss and an extremely small activity decay of 17 mV, being the most robust candidate among previously reported Fe-N-C catalysts. Zinc-air batteries employing Fe₂-pPc exhibit a power density of 255 mW cm^-2 and excellent operation stability beyond 440 h. This work brings new insights into the design of atomically precise metallic catalysts.