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GLO:OKZ/10mar20:adfm202000364-fig-0002.jpg PHOTO (COLOR): S2 a) Low-resolution transmission electron microscopy image of C-CO nanoparticles. The inset is size distribution pattern with an average particle size ~2.0 ± 0.5 nm. b) High-resolution transmission electron microscopy image of C-CO nanoparticles. gl. [Extracted from the article]

Ultrasmall size and abundant defects are two crucial factors for improving the performance of catalysts. However, it is a big challenge to introduce defects into ultrafine catalysts because of the surface tension and self‐purification effect of the nanoparticles. In the present work, physical laser fragmentation with chemical oxidization reaction is combined to synthesize Co3O4 nanoparticles (L‐CO) with ultrasmall size (≈2.1 nm) as well as abundant oxygen vacancies, thus providing an effective solution to the long‐standing contradiction between the size reduction and defect generation. The ultrasmall particle size allows more catalytic sites to be exposed. The surficial oxygen vacancies enhance the intrinsic activity, while the internal oxygen vacancies improve the electron transfer, and all of these benefits make L‐CO an active and durable bifunctional catalyst for oxygen reduction/evolutions. As the air cathode of zinc–air battery, L‐CO displays excellent rechargeable performance with a power density of ≈337 mW cm−2, outperforming the commercial noble metal couple (Pt/C+RuO2). [ABSTRACT FROM AUTHOR]