Low-temperature liquid reflux synthesis of core@shell structured Ni@Fe-doped NiCo nanoparticles decorated on carbon nanotubes as a bifunctional electrocatalyst for Zn–air batteries

Abstract

Exploring high-efficiency electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was a decisive parameter for metal–air batteries, fuel batteries, and water splitting. In this work, core@shell structured Ni@Fe-doped NiCo nanoparticles physically decorated on carbon nanotubes (Fe/Ni@NiCo-CNT) were synthesized through a facile low-temperature liquid reflux strategy. Electron microscope characterization evidenced a unique core@shell structure composed of a metallic Ni core and NiCo alloy shell with Fe element doping. Electrochemical measurements illustrated that the hybrid Fe/Ni@NiCo-CNT electrocatalyst showed superior ORR and OER activities, approaching and even exceeding those of commercial Pt/C and RuO₂ catalysts. The about 4 nm-thick shell of the Fe-doped NiCo alloy combined with the synergetic effects between nanoparticles and carbon nanotubes (CNTs) made dominant contributions to increasing the electrochemically active surface area and accelerating electrocatalytic kinetics. When Fe/Ni@NiCo-CNT was applied in Zn–air batteries (ZABs), the primary ZABs delivered an open circuit potential of 1.427 V and a specific capacity of 796.5 mA h g_Zn⁻¹. Moreover, the rechargeable ZABs surprisingly sustained for more than 1500 cycles with steady voltage polarization at 5 mA cm⁻². This cost-effective strategy shows important guidance for the structural engineering of other metallic alloy materials and further sheds light on developing efficient bifunctional oxygen catalysts for renewable energy conversion devices.