Bifunctional electrocatalysts for rechargeable metal-air batteries often encounter catalyst leaching-resultant performance degradation upon cycling of batteries, which requires stability improvement on catalyst nanoparticles via immobilization onto conductive supports. Herein, we report in-situ growth of Co3O4 nanoparticles onto the concurrently synthesized N-doped Vulcan carbon (NVC) to produce Co3O4/NVC powders with tuneable loading density as scalable, stable and efficient hybrid bifunctional electrocatalysts. With optimized composition the hybrid catalyst exhibited satisfactory ORR and OER activity, giving a voltage difference as small as 0.10 V between the onset potential and half-wave potential at discharge. The good performance of the rechargeable zinc-air batteries constructed using Co3O4/NVC as air-cathodes suggests such hybrid bifunctional electrocatalyst as a practical and cost-effective solution for applications with large quantity materials demand, e.g. in grid-scale energy storage and electric vehicles.