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 MoO 3 nanobelt (NB). Next, BMZIFs (ZIF-8/ZIF-67), PPy and MoO 3 are calcined into Co nanoparticles (NPs) dotted/Zn, Co doped carbon, nitrogen doped carbon nanotube (NCNT) and Mo 2 C NPs at 800 °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 Mo 2 C 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 Δ 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 + RuO 2 in the long-term (400 h) cycling experiment. The excellent ORR/OER behaviors of the catalyst is mainly attributed to the synergy between CoN 4 -graphene and Mo 2 C, which is verified by both experimental and density function theory (DFT) calculation results. • Bimetallic ZIFs are grown on polypyrrole coated MoO 3 nanobelt to form a precursor. • The precursor is pyrolyzed to produce one-dimensional hierarchical nano-catalyst. • Zn/Co NPs coated NCNTs encapsulate Mo 2 C NPs to form the hierarchical catalyst. • The catalyst has good ORR/OER activity due to large surface area and durability. • The assembled ZAB shows outstanding peak power density and cyclability.