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Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal–organic frameworks (MOFs). These robust, porous materials have garnered significant interest because of their outstanding properties as catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, the synthesis of Co‐ and Ni‐containing ZIF‐67 embedded in carbon nanotubes (CNTs) to be used as a cathode material for rechargeable zinc–air batteries is described. Carbon‐nanotube‐encapsulated metallic Co and Ni form via calcination of the MOF at 700 °C for 4 h and are characterized by X‐ray diffraction and transmission electron microscopy (TEM). Co and Ni graphitization within the CNTs is analyzed by Raman spectroscopy, and morphologies are assessed by scanning electron microscopy (SEM) and TEM. Excellent electrochemical performance of the prepared catalysts during charging and discharging reveals that the catalyst is stable for well over 500 h. Moreover, superior OER performance is observed when CNT@Co or CNT@Ni is used as a bifunctional catalyst in the zinc–air battery. [ABSTRACT FROM AUTHOR]

• Fabrication of efficient bimetallic catalysts for OER. • Nickel decoration was performed on bimetallic CNT/CoNi. • Ni/CNT/CoNi exhibited excellent electrochemical performance and cycling stability. The fabrication of efficient catalysts for the oxygen evolution reactions (OER) that are required to accelerate the sluggish kinetics of metal-air batteries has attracted significant attention for application in energy conversion devices. Metal-organic frameworks (MOFs) have been recognized as potential candidates for the formation of promising catalysts. In this study, we report the formation of Ni/CNT/CoNi using bimetallic-ZIF (CoNi-ZIF) as a precursor. Bimetallic CoNi encapsulated in carbon nanotubes (CNTs) was obtained by calcinating CoNi-ZIF-67 to yield CNT/CoNi. The resulting CNT/CoNi was highly porous with a significant specific surface area of 242 m2/g. After calcination, Ni deposition on the CNT was performed and the surface area was reduced to 168.7 m2/g. Ni/CNT/CoNi was applied as a cathode material in zinc-air batteries, exhibiting excellent electrochemical performance and cycling stability. [ABSTRACT FROM AUTHOR]

• Nickel deposited catalysts using Zeolitic-Imidazolate Frameworks-67 as a precursor were synthesized. • The catalysts exhibited higher catalytic activities for oxygen reduction and evolution reactions. • The catalysts show low overpotential and high stability. Zeolitic imidazolate framework containing cobalt and nickel (Co- and Ni-ZIF-67) were used as a precursor to perform Ni deposition, in order to obtain enhanced catalytic activity and nanocatalysts. Co or Ni embedded in the carbon nanotubes (CNTs) were obtained by the heat treatment of Co- or Ni-ZIF-67. On Co or Ni embedded CNTs, Ni-deposition was performed to obtain the Ni-deposited catalysts, Ni-CNT-(Co or Ni), which have a higher surface area of 136.7 and 259 m2/g, respectively. These catalysts exhibit superior performance, low overpotential, and high stability for both oxygen reduction and evolution reactions. The superior performance is attributed to metal deposition, which creates highly active catalytic sites and has potential application as a catalyst for the rechargeable zinc-air battery. [ABSTRACT FROM AUTHOR]