Two dimensional ZIF-derived ultra-thin Cu–N/C nanosheets as high performance oxygen reduction electrocatalysts for high-performance Zn–air batteries

Bottom-up construction of transition copper-nitrogen-carbon (Cu-N-C) electrocatalysts with high-performance and long-term durability for the oxygen reduction reaction (ORR) still remains a great challenge. Herein, we propose a temperature-controlled synthesis strategy with confinement effect for fabrication of a novel two-dimensional dual-metal (Cu/Zn) zeolitic imidazolate framework material, which presents an ultrathin nanosheet morphology after high-temperature thermal treatment (denoted as Cu-N-UNS). By controlling the reaction temperature as well as regulating the ratio of metal ions and taking advantages of the confinement effect of surfactants, the rationally designed ultra-thin carbon layer not only prevents aggregation of transition Cu particles and avoids direct contact with reactants and electrolyte solutions to enhance the durability of electrocatalysts, but also shortens the electronic transmission path between the active transition metal species and carbon surface. Therefore, the electrocatalyst exhibits excellent electrocatalytic performance for the ORR (E1/2 ≈ 0.898 V), which is superior to those of state-of-the-art benchmark noble-metal electrocatalysts. Moreover, the even distribution of Cu-N-C and existence of N-Cu2+-Cu0 active sites make a great contribution to the electrocatalyst activity. Notably, the Cu-N-UNS used as air electrodes for Zn-air batteries also exhibits a high peak power density of ≈134.7 mW cm-2 at a current density of ≈231.9 mA cm-2 with remarkable durability.