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 Mo₂CT_x MXene (FeOM-Mo₂CT_x), adopting a lying-down conformation. This hybridization fosters unique electronic guest–host interactions, with FeOM donating charge to Mo₂CT_x 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-Mo₂CT_x 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 Mo₂CT_x, paving the way for innovative air cathodes in the development of rechargeable ZABs with enhanced performance and cost-effectiveness.