© The Royal Society of Chemistry 2015. Bifunctional electrocatalysts for rechargeable metal-air batteries often encounter catalyst leaching-resultant performance degradation upon cycling of the batteries, which requires an improvement in stability of the catalyst nanoparticles via immobilization onto conductive supports. Herein, we report in situ growth of Co 3 O 4 nanoparticles onto concurrently synthesized N-doped Vulcan carbon (NVC) to produce Co 3 O 4 /NVC powders with tuneable loading density as scalable, stable and efficient hybrid bifunctional electrocatalysts. With an 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 Co 3 O 4 /NVC as air-cathodes suggests such a hybrid bifunctional electrocatalyst is a practical and cost-effective solution for applications which demand a large quantity of materials, e.g. in grid-scale energy storage and electric vehicles. ; Link_to_subscribed_fulltext