Asymmetric Mn/Fe Dual Single-Atom Catalysts for pH-Universal Oxygen Electroreduction and Sustainable Metal-Air Batteries.

Conquering the sluggish kinetics of the oxygen reduction reaction (ORR) is significantly important for sustainable metal-air batteries. However, the synthesis of advanced Pt-free ORR electrocatalysts still remains challenging owing to the intrinsic activity, site accessibility, and structural stability. Herein, a catalyst of asymmetric N, P-coordinated Mn and Fe dual single atoms supported on hollow carbon polyhedra (MnFe-PNC) is synthesized via a metal-organic framework pyrolysis strategy, which displays excellent pH-universal ORR performance with half-wave potentials of 0.923 V in 0.1 m KOH, 0.803 V in 0.1 m HClO, and 0.774 V in 1 m phosphate buffer solution. Theoretical calculations reveal that the distance-dependent electronic interaction between Mn-NP and Fe-NP structures at the atomic level plays a crucial role in optimizing the adsorption strength of *OH intermediate and consequently boosts ORR performance. Furthermore, the aqueous Zn/Al-air batteries using MnFe-PNC cathode catalyst show ultralong discharge stability and wide-temperature adaptability. Meanwhile, combined with an anti-freezing and zincophilic organohydrogel electrolyte, the MnFe-PNC-based quasi-solid-state Zn-air batteries exhibit robust cycling stability (130 h at 50 mA cm and 70 h at 100 mA cm), an unprecedented discharge capacity of 1.30 Ah at -40 °C, and smooth operation over a broad temperature range of -40 to 60 °C.