Iron-based nanostructures represent an emerging class of catalysts with high electroactivity for oxygen reduction reaction (ORR) in energy storage and conversion technologies. However, current practical applications have been limited by insufficient durability in both alkaline and acidic environments. In particular, limited attention has been paid to stabilizing iron-based catalysts by introducing additional metal by the alloying effect. Herein, we report bimetallic Fe₂Mo nanoparticles on N-doped carbon (Fe₂Mo/NC) as an efficient and ultra-stable ORR electrocatalyst for the first time. The Fe₂Mo/NC catalyst shows high selectivity for a four-electron pathway of ORR and remarkable electrocatalytic activity with high kinetics current density and half-wave potential as well as low Tafel slope in both acidic and alkaline medias. It demonstrates excellent long-term durability with no activity loss even after 10,000 potential cycles. Density functional theory (DFT) calculations have confirmed the modulated electronic structure of formed Fe₂Mo, which supports the electron-rich structure for the ORR process. Meanwhile, the mutual protection between Fe and Mo sites guarantees efficient electron transfer and long-term stability, especially under the alkaline environment. This work has supplied an effective strategy to solve the dilemma between high electroactivity and long-term durability for the Fe-based electrocatalysts, which opens a new direction of developing novel electrocatalyst systems for future research.

Efficient, robust and cost-effective bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of vital importance to the widespread utilization of Zn-air batteries. Here we report the fabrication of a bubble-like N,S-codoped porous carbon nanofibers with encapsulated fine Fe/Fe₅C₂ nanocrystals (~ 10 nm) (FeNSCs) by a facile one-pot pyrolysis strategy. The novel FeNSC nanostructures with high Fe content (37.3 wt.%), and synergetic N and S doping demonstrate remarkable ORR and OER catalytic activities in alkaline condition. Particularly for ORR, the optimal FeNSC catalyst exhibits superior performance in terms of current density and durability in both alkaline and acidic media. Moreover, as catalysts on the air electrodes of Zn-air batteries, the optimal FeNSCs show a high peak power density of 59.6 mW/cm² and extraordinary discharge-charge cycling performance for 200 h with negligible voltage gap change of only 8% at current density of 20 mA/cm, surpassing its noble metal counterpart (i.e. Pt). The impressive battery stability can be attributed to favorable electron transfer resulting from appropriate graphitization of the bubble-like carbon nanofibers and thorough protection of Fe/Fe₅C₂ nanoparticles by carbon wrapping to prevent oxidation, agglomeration and dissolution of Fe nanoparticles during battery cycling. The present FeNSC catalyst, which is highly active, robust yet affordable, shows promising prospects in large-scale applications, such as metal-air batteries and fuel cells.