Transition Metals (Co or Ni) Encapsulated in Carbon Nanotubes Derived from Zeolite Imidazolate Frameworks (ZIFs) as Bifunctional Catalysts for the Oxygen Reduction and Evolution Reactions

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.