Low-temperature ambient-air synthesis of an efficient and stable axially N-coordinated Fe single-atom catalyst for oxygen reduction

Abstract

Tuning the adsorption of oxygen reduction reaction (ORR) intermediates while suppressing Fe demetallation is essential yet challenging to promote the activity and robustness of single-Fe-atom catalysts. Axial ligation offers a promising electronic/geometric lever, but mild, scalable protocols that precisely construct FeN₅ sites have rarely been realized. Here we report an ambient-air, 180 °C one-step thermal condensation (3 h) that directly generates covalently cross-linked FeN₅ motifs without inert gas or high-temperature pyrolysis. The catalyst exhibits an onset potential and half-wave potential of 1.02 and 0.92 V in alkaline media, together with >98% 4e⁻ selectivity, pronounced methanol tolerance and robustness. DFT calculations attribute the enhancement to the axial N ligand that upshifts Fe valence and lowers the O₂ → OOH* barrier while pyromellitic dianhydride mediated cross-linking anchors the metal centre. A Zn–air battery employing this cathode delivers 209 mW cm⁻² peak power and 810 mAh g_Zn⁻¹ capacity, demonstrating practical viability. This mild, energy-minimized strategy resolves the long-standing synthesis–stability dilemma and provides a general route to high-performance ORR single-atom catalysts.