One-dimensional hierarchical ZnCo-NCNT/Mo2C nanostructure as a high-efficiency bifunctional catalyst for rechargeable Zn-air batteries

Herein, a catalyst precursor is prepared by depositing bimetallic zeolitic imidazolate frameworks (BMZIFs) on a polypyrrole (PPy)-coated MoO3 nanobelt (NB). Next, BMZIFs (ZIF-8/ZIF-67), PPy and MoO3 are calcined into Co nanoparticles (NPs) dotted/Zn, Co doped carbon, nitrogen doped carbon nanotube (NCNT) and Mo2C NPs at 800 degrees C, respectively, to produce a one-dimensional (1D) hierarchical nano-catalyst. The 1D nano-catalyst with porous surface, large specific area and abundant defects maximumly exposes the catalytic active sites. Furthermore, the entire encapsulation of Mo2C NPs by NCNTs effectively restrains their agglomeration during the pyrolysis, and volume change in electrochemical reaction. Moreover, the simultaneous immobilization of bimetallic ZIFs on PPy is more likely to form small-sized Zn/Co NPs on NCNT than single ZIF. Accordingly, the nano-catalyst exhibits a small Delta E value of 0.791 V and the Zn-air battery based on this catalyst achieves an excellent peak power density of 231.6 mW cm-2 at 5 mA cm-2, and a much higher energy round-trip efficiency than Pt/C + RuO2 in the long-term (400 h) cycling experiment. The excellent ORR/OER behaviors of the catalyst is mainly attributed to the synergy between CoN4-graphene and Mo2C, which is verified by both experimental and density function theory (DFT) calculation results.