Confinement synthesis of bimetallic MOF-derived defect-rich nanofiber electrocatalysts for rechargeable Zn-air battery

Zn-air batteries with high energy density and safety have acquired enormous attention, while the practical application is hindered by the sluggish kinetics of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In this work, a three-dimensional (3D) defect-rich bifunctional electrocatalyst (CoFe/N CNFs) comprising irregular hollow CoFe nanospheres in N-doped carbon nanofibers is presented, which is fabricated from CoFe ZIFs-derived (ZIF: zeolitic-imidazolate framework) polymer nanofibers precursor. The CoFe ZIFs with tunable particle size and composition are constructed using a confined synthesis strategy. Moreover, the Kirkendall diffusion process is available for forming the irregular hollow CoFe nanospheres, and the decomposition of polyvinylpyrrolidone (PVP) results in forming the defective carbon nanofibers, which provide more efficient active sites and enhance the electrocatalytic properties toward both OER and ORR. The optimized CoFe/N CNFs exhibit superior bifunctional activities, outperforming that of the benchmark Pt/C + RuO2 catalyst. As a result, the CoFe/N CNFs as an air-cathode endow the rechargeable Zn-air battery with an excellent power density of 149 mW·cm−2, energy density of 875 Wh·kg−1, and cycling stability. This work provides a new strategy to develop bifunctional electrocatalysts with desired nanostructure and regulated performance toward energy applications.