Molten salt-assisted carbonization and unfolding of Fe, Co-codoped ZIF-8 to engineer ultrathin graphite flakes for bifunctional oxygen electrocatalysis

Zeolitic imidazolate frameworks (ZIFs) are already utilized to synthesis precursors for transition metal and nitrogen co-doped carbon catalysts. However, there are few reports on deliberately tailoring catalyst structure except for the hierarchical pores formed from Zn evaporation during the pyrolysis. Herein, NaCl salt-assisted carbonization and unfolding of Fe, Co-codoped ZIF-8 polyhedron (FeCo/ZIF-8) result in ultrathin Fe, Co, N-codoped graphite flake (FeCo/NG), while FeCo/ZIF-8 pyrolysis without NaCl yields Fe, Co, N-codoped carbon spheres (FeCo/NC). Because of the high specific surface area, porosity, and degree of defects, the active site is further exposed. The synthesized FeCo/NG demonstrates excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties with half-wave potential (E 1/2 ) at 0.88 V and overpotential at 460 mV and good cycling stability, superior to those of FeCo/NC. In addition, the assembled Zn-air batteries with FeCo/NG catalysts deliver high peak power density at 109 mW cm −2 , specific capacity at 783 mAh g −1 and an operating time for 100 h. The study will provide a feasible synthesis method to design high-performance electrocatalysts by deliberate tailoring structures with molten salt-assisted carbonization and unfolding of ZIFs. • Molten salt-assisted pyrolysis tailors ZIF-8 polyhedron into ultrathin graphite flake. • Molten NaCl assists carbonization and unfolding of FeCo/ZIF-8 to form ultrathin FeCo/NG. • Evaporation of Zn in pyrolysis and removal of NaCl result in porous FeCo/NG. • FeCo/NG demonstrates excellent bifunctional oxygen electrocatalytic performances. • Zn-air battery with FeCo/NG delivers high peak power density and specific capacity.