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) have been widely utilized as precursors for the synthesis of 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 the pyrolysis of FeCo/ZIF-8 without NaCl yields Fe, Co, N-codoped carbon spheres (FeCo/NC). Due to large specific surface area, high porosity, great degree defects and further exposure of active sites, the as-synthesized FeCo/NG demonstrates excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances with a half-wave potential (E 1/2 ) of 0.88 V, an overpotential of 460 mV and good cycling stability, superior to those of FeCo/NC. In addition, the assembled Zn-air batteries with FeCo/NG catalysts deliver a peak power density of 109 mW cm 2 , a specific capacity of 783 mAh g -1 and an operation period of 100 h. This 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