Bifunctional oxygen electrodes of homogeneous Co₄N nanocrystals@N-doped carbon hybrids for rechargeable Zn-air batteries

The development of transition metal nitrides/carbon hybrids with well-organized morphology, outstanding efficiency and durability for Zn-air batteries are of great urgency. Herein, a morphology-controlled strategy to efficiently fabricate uniform Co₄N nanoparticles anchored on N-doped carbon (Co₄N@NC-m) is reported. The diameters and distribution of Co₄N nanocrystals can be tuned to be homogeneous profited by abundant N sources in melamine. Moreover, thanks to the advantages of higher nitrogen doping content, better electrical conductivity, higher degree of graphitization, and larger electrochemical surface area, Co₄N@NC-m possesses excellent oxygen reduction reaction (half-wave potential of 0.87 V) and oxygen evolution reaction (overpotential of 398 mV at 10 mA cm⁻²) activities in basic solution. The Zn-air battery fabricated with Co₄N@NC-m owns higher open circuit voltage (1.490 V), larger power density, and better rechargeability than those of the commercial IrO₂ + 20% Pt/C catalysts, which proves the potential application in practical energy conversion devices.