Stable and efficient bifunctional electrocatalyst for air electrode is still of challenge for rechargeable zinc-air batteries (ZABs). Here, we report an atomic layer oxygen defect cobalt oxides (Co3O4-x) nanosheets (1 nm) as efficient electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Due to the atomic layer nanosheets, more oxygen defects are formed during plasma treatment enabling effective OER catalysis with overpotential of only 309 mV, which is lower compared to bench-marking IrO2 (313 mV). Meanwhile, a Pt-like ORR activity is achieved for Co3O4-x due to the atomic layer nanosheets with highly exposed active sites and loosened binding strength between Co3+ and O-2/OH center dot. The battery performance of Co3O4-x nanosheets is 1.7 times higher than that of Pt/C-IrO2 based ZABs. Besides, Co3O4-x nanosheets exhibit undetectable degradation in battery performance after galvanostatic discharge-charge with 5 mA cm (2) for 150 h implying the superior stability of the atomic layer Co3O4-x nanosheets. All-solid-sate ZABs fabricated from Co3O4-x nanosheets perform an impressive power density of 57 mW cm (2) and stable galvanostatic discharge-charge voltage for 2 h demonstrating that Co3O4-x nanosheets can be utilized as air electrode for practical application. (C) 2019 Elsevier Inc. All rights reserved.