A hierarchical architecture of Fe/Co/Ni-doped carbon nanotubes/nanospheres grafted on graphene as advanced bifunctional electrocatalyst for Zn-Air batteries

Abstract

Rational design and synthesis of non-precious-metal bifunctional catalysts for oxygen reduction and evolution reactions (ORR and OER) is highly pursued to improve reaction efficiency of Zn-air batteries. Herein, an innovative 0D-1D-2D hierarchical structure material (denoted as FeCoNi-N-rGO) is developed by a facile two-step synthesis strategy to construct N-doped carbon nanotubes (CNTs) and carbon nanospheres (CNSs) for encapsulating ternary Fe/Co/Ni alloy nanoparticles on the surface of reduced graphene oxide (rGO). Specifically, abundant Fe/Co/Ni alloy nanoparticles and M-N-C active sites generated by transition metals (Co, Ni, Fe) coupling with N-doped carbon (CNTs, CNSs, and rGO) can provide the FeCoNi-N-rGO with superior OER and ORR properties; meanwhile, the hierarchical structure endows large specific surface area to expose more active sites and to facilitate mass transfer. Typically, the FeCoNi-N-rGO exhibits a high ORR half-wave potential of 0.836 V and a low OER overpotential of 440 mV at 10 mA cm−2 in 0.1 M KOH. Moreover, the FeCoNi-N-rGO-based rechargeable Zn-air battery can deliver a high peak power density (152.5 mW cm−2), specific capacity (766 mAh g−1) and excellent stability (more than 200 h), surpassing commercial Pt/C-RuO2 catalysts. Therefore, this work will offer an easy fabrication strategy to design bifunctional catalysts with desirable performances for Zn-air batteries.