A metal and nitrogen doped carbon composite with both oxygen reduction and evolution active sites for rechargeable zinc-air batteries

Rechargeable zinc-air batteries (ZABs) are promising renewable energy storage devices due to their high energy density and preeminent safety. However, they still require highly active and stable oxygen reduction/evolution reaction (ORR/OER) bi-functional catalysts to promote their performance. Here, we report the synthesis of Fe,Ni on N doped carbon sheets supported on N doped carbon nanotubes (Fe,Ni-N-C/N-CNT), which shows ORR activity with a half wave potential of 0.879 V and an OER activity of 315 mV overpotential at a current density of 10 mA cm-2. Using Fe,Ni-N-C/N-CNT as the air electrode, the fabricated primary ZAB shows a high peak power density of 271 mW cm-2, and the rechargeable ZAB can stably operate for more than 200 h with a high energy efficiency of 61%, surpassing the conventional ZABs using Pt/C-IrO2. We find that the ORR activity is related to the Fe-N-C species in the catalysts, while the in situ generated NiFe2O4 nanoparticles under the OER conditions are beneficial for the OER activity. Poly(ethylene imine) used in the synthesis was found to be important for obtaining a high performance catalyst and helps the binding of the carbon sheets containing the Fe-N-C sites to carbon nanotubes and also the capture of the in situ generated NiFe2O4 nanoparticles. These results demonstrated the high potential of functionalized carbon composites for application in rechargeable ZABs.