Nanoflower-like NiCo₂O₄ Composite Graphene Oxide as a Bifunctional Catalyst for Zinc-Air Battery Cathode

Developing efficient bifunctional catalysts for nonprecious metal-based oxygen reduction (ORR) and oxygen evolution (OER) is crucial to enhance the practical application of zinc-air batteries. The study harnessed electrostatic forces to anchor the nanoflower-like NiCo₂O₄ onto graphene oxide, mitigating the poor inherent conductivity in NiCo₂O₄ as a transition metal oxide and preventing excessive agglomeration of the nanoflower-like structures during catalysis. Consequently, the resulting composite, NiCo₂O₄-GO/C, exhibited notably superior ORR and OER catalytic performance compared to pure nanoflower-like NiCo₂O₄. Notably, it excelled in OER catalytic activity of the OER relative to the precious metal RuO₂. As a bifunctional catalyst for ORR and OER, NiCo₂O₄-GO/C displayed a potential difference of 0.88 V between the ORR half-wave potential and the OER potential at 10 mA·cm^-2, significantly lower than the 1.08 V observed for pure flower-like NiCo₂O₄ and comparable to the 0.88 V exhibited by precious metal catalysts Pt/C + RuO₂. The NiCo₂O₄-GO/C-based zinc-air battery demonstrated a discharge capacity of 817.3 mA h·g^-1, surpassing that of precious metal-based zinc-air batteries. Moreover, charge-discharge cycling tests indicated the superior stability of the NiCo₂O₄-GO/C-based zinc-air battery compared to its precious metal-based counterparts.