Highly dispersed iron/nickel dual-sites in hierarchical porous carbon materials as high-performance bifunctional oxygen electrocatalysts for Zn-air batteries

Designing non-precious metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) not only should improve the activity of the catalytic reaction sites, but also need to consider the transport channels of the reactants and electrolyte inside the catalysts to enhance the utilization of active sites. Here, Fe/Ni dual-active sites anchored on the unique honeycomb hierarchical porous carbon materials are successfully prepared by pyrolysis of Fe and Ni bimetal co-doped covalent organic polymer with the assistance of pore-forming agents. The unique honeycomb hierarchical porous structures are favorable for transport and diffusion of oxygen and electrolyte during the electrochemical reaction process, so that the internal active sites can be fully utilized to improve the catalytic activity . The as-synthesized catalyst exhibits excellent ORR (E 1/2  = 874 mV) and OER (overpotential = 352 mV at 10 mA cm −2 ) performance. More importantly, the rechargeable liquid Zn-air battery assembled with the catalyst exhibits a large specific capacity of 781.7 mA h g −1 and a long-term cycle stability with repeatedly charging and discharging for 450 h at 20 mA cm −2 . Additionally, an all-solid-state flexible Zn-air battery based on this catalyst as cathode shows a maximum power density of 83.5 mW cm −2 .