Design of nanosheet/nanotube composites of Fe, N-doped carbon for enhanced oxygen reduction in zinc-air batteries

Low-density active sites, low-mass transfer rate, and poor stability of carbon-based catalytic materials from the pyrolysis of conventional metal-nitrogen complexes can hamper the oxygen reduction reaction (ORR). Herein, a composite structure of nitrogen-doped carbon nanosheets grafted with carbon nanotubes are synthesized by Zn-ZIF-L breaking and co-functionalized by coupling Fe2O3 nanoparticles with active Fe-Nx species to form an active ORR catalyst (D-FeNC/MOF). Under the synergetic effect of high-density active sites and multi-size pore distribution, the diffusion resistance of oxygen in the pores can be decreased to facilitate the transfer of reactants and products, and the improvement of ORR efficiency. Comparing to the commercial Pt/C catalyst, the d-FeNC/MOF has exhibited a more positive half-wave potential of 0.875 V (vs. RHE) and a higher catalytic stability. Besides, the zinc-air battery assembled with d-FeNC/MOF as a cathode catalyst can also offer a maximum power density of 170 mW cm−2 and a specific energy density of 842 Wh kg−1. This work can provide a new way for designing non-Pt catalysts for various electrochemical energy devices.