NiCo ₂ O ₄ Nanorods Anchored on rGO as a Cathode Material for Flexible Hybrid Zn–Air Batteries

Abstract The growing energy demand calls for storage systems with high energy and power densities. Zn–air batteries (ZABs) offer great potential but are limited by sluggish oxygen reduction (ORR) and evolution (OER) kinetics at the cathode, necessitating efficient bifunctional electrocatalysts. In this study, NiCo ₂ O ₄ nanorods anchored on reduced graphene oxide (rGO) are synthesized via a hydrothermal process and evaluated as cathode materials for ZABs. The NiCo ₂ O ₄ /rGO composite exhibited excellent catalytic performance with an ORR onset potential of 0.90 V and an overpotential (ΔE) of 0.67 V, attributed to the spinel structure and enhanced conductivity from the rGO matrix. The ZAB device showed a hybrid discharge mechanism with two plateaus: one from ORR and another sloping plateau from M─O─OH ↔ M─O redox reactions (M═Ni, Co), contributing to high energy and power densities. The NiCo ₂ O ₄ /rGO‐based battery achieved a peak power density of 108 mW cm ^{− 2} @135 mA cm ^{− 2} , a specific capacity of 722 mAh g _Zn ⁻¹ , and a cycle life of 270 h (810 cycles), outperforming the bare NiCo ₂ O ₄ device. The enhanced performance stems from the synergistic interaction between NiCo ₂ O ₄ and rGO, improving surface area, conductivity, and catalytic sites. These results demonstrate the potential of NiCo ₂ O ₄ /rGO as a bifunctional cathode for high‐performance hybrid Zn–air batteries.