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.