Highly efficient and low-cost oxygen reduction reaction electrocatalysts play key roles in the development of advanced energy conversion and storage devices, such as fuel cells and metal–air batteries. Herein, a facile strategy of synthesizing cobalt single atoms anchored on an ultrathin N-doped carbon nanosheet electrocatalyst (marked as CoSAs/N-CNS) via an in situ g-C3N4 template strategy was reported. Impressively, benefiting from highly active Co–Nx sites and highly porous and ultrathin nanosheet morphology which has rich edges and more three-phase boundaries, the as-synthesized CoSAs/N-CNS exhibits markedly enhanced ORR activities under alkaline conditions with half-wave potential (E 1/2) as high as 0.91 V vs RHE, as well as durability of ∼67 h. Furthermore, compared with Pt/C, the CoSAs/N-CNS-based Zn–air battery presents outstanding discharge–charge performance, larger power density of 157.7 mW cm–2, and robust durability with a slight decay after 150 h (900 cycles). The experimental and theoretical results fully show the advantages of CoSAs/N-CNS, which also provides a new insight for the design and development of high-performance atomically dispersed metal active site electrocatalysts toward ORR.

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