Regulative Fe-3d Orbitals via Lying-Down Conformation of Metalorganic Molecules-Axially Coordinated MXene for Rechargeable Zn–Air Batteries

Abstract

A bifunctional electrocatalyst is developed, exhibiting high catalytic activity and reversibility for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through a regulative Fe d-orbital engineering strategy. In this strategy, iron phthalocyanine organic molecule (FeOM) crystals are axially coordinated onto multilayer Mo2CTx MXene (FeOM-Mo2CTx), adopting a lying-down conformation. This hybridization fosters unique electronic guest–host interactions, with FeOM donating charge to Mo2CTx via Fe−O bonding, leading to symmetry breaking in electronic distribution and modified delocalization of Fe-3d charge, accompanied by a Fe(II) spin-state transition. These transformations enhance the adsorption and desorption toward oxygenated intermediates, optimizing the *OOH−*O transition to boost the reversibility of ORR and OER kinetics. The FeOM-Mo2CTx exhibits a favorable ORR half-wave potential of 0.961 V and a minimal OER overpotential of 349 mV at 10 mA cm−2 in 1.0 m KOH. The assembled aqueous zinc-air battery (ZAB) achieves a peak power density of 155.3 mW cm−2 and exceptional charge–discharge durability over 1500 h, outperforming a conventional (Pt/C + RuO2) system. Overall, the findings underscore the significance of electronic structural engineering of FeOM with Mo2CTx, paving the way for innovative air cathodes in the development of rechargeable ZABs with enhanced performance and cost-effectiveness.