Structural design of FeCo alloy implanted into N,S co-doped carbon nanotubes via self-catalyzed growth for advanced liquid and flexible all-state-state Zn–air battery

The introduction of transition bimetallic alloys can effectively improve oxygen reduction reaction (ORR) activity. However, the alloy particles are inclined to dissolve under harsher conditions, resulting in a serious decrease in catalytic activity and stability. Herein, an efficient ORR catalyst, FeCo alloy nanoparticles (NPs) encapsulated in N,S co-doped carbon nanotubes (FeCo₁₀-NSCNTs), was developed through a self-catalyzed growth strategy. Due to the delicate structural design, the N,S co-doped structure can effectively improve the ORR performance by modulating the electronic properties and surface polarity of the carbon substrate, and the randomly connected carbon nanotube structure with large specific surface area can further enhance the adsorption and dissociation of gas molecules, accelerating the kinetics of gas participation in the reaction. Carbon-encapsulated FeCo alloys are beneficial for improving catalytic activity and durability. The FeCo₁₀-NSCNTs displayed excellent ORR activity with a half-wave potential of E_1/2 = 0.84 V and robust stability of 13 k cycles. More impressively, the assembled liquid-state Zn-air battery (ZAB) with FeCo₁₀-NSCNTs as the air-electrode delivers an output power density of 146.68 mW cm^-2 along with excellent operation durability. The assembled all-solid ZAB has good cyclic stability under 0-180° bending conditions. The synthesized N,S co-doping, carbon nanotubes and FeCo alloys provide important guidance for the construction of cheap non-noble metal-carbon hybrid nanomaterials.