Co3C-stabilized-CoFe heterostructure wrapped by bamboo-like N-doped carbon nanotubes for highly-efficient oxygen electrocatalysis

Abstract

Bimetallic alloys have been showing unexpectedly high activity for oxygen reduction reaction (ORR) in alkaline electrolytes. However, many fundamental questions regarding the ORR stability and poor oxygen evolution reaction (OER) performance of bimetallic alloys remain unresolved. Here, we prepare a cobalt carbide-stabilized CoFe alloy wrapped by hollow bamboo-like nitrogen-doped carbon nanotubes (CoFe-Co3C@NCNTs) using bimetallic Prussian-blue-analogue and dicyandiamide as precursors. Interestingly, the spherical CoFe-Co3C heterojunctions are always encapsulated at one end of the tube. The as-marked CoFe-Co3C@NCNTs-20 catalyst exhibits an ultra-high ORR activity (half-wave potential of 0.934 V) and a relatively good OER activity (overpotential of 0.320 V), which are superior to Pt/C and RuO2, respectively. CoFe-Co3C@NCNTs-20 also shows excellent ORR/OER stabilities and potential difference between ORR and OER (0.616 V). Excellent activity and stability benefit from the synergies between CoFe-Co3C and NCNTs, while the hollow structure/conductive skeleton enhances the mass/charge transfers, respectively. The NCNTs coating greatly enhances the stability of the CoFe-Co3C heterojunctions to avoid the corrosion of active sites in alkaline media. Moreover, rechargeable zinc-air battery assembled with CoFe-Co3C@NCNTs-20 cathode shows high power-density (209.15 mW cm−2) and open-circuit voltage (1.505 V). It provides a new reference for promoting the development of bimetallic alloy-coupled transition metal carbide catalysts.