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• Co-N polymer is pyrolyzed with dicyandiamide to synthesize a Co-N-C catalyst. • Carbon nanosheet/nanotube-interweaved structure favors 3D electrical conduct. • Balanced micro/mesopore distribution facilitates mass diffusion. • Atomic and metal Co separately enable excellent ORR and OER performances. • Promising liquid and flexible rechargeable Zn-air batteries are achieved. Developing active and stable non-precious metal bifunctional electrocatalysts towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) still remains a crucial challenge. Herein, we propose a simple strategy of integrating atomically dispersed and nanoscaled Co species embedded in micro-/mesoporous carbon nanosheet/nanotube architecture. Revealed by control and SCN- poisoning experiments, N species and atomically dispersed Co species are the main active centers for ORR; whereas the metal Co nanocrystals are the chief active species for OER. Additionally, the balanced micro/mesopore distribution offers fast mass diffusion, and carbon nanosheet/nanotube architecture supplies favorable 3D electrical conduct. As a result, the as-prepared CoNC (1:4) exhibits a positive half-wave potential of 0.87 V (vs RHE) for ORR, and a low potential of 1.55 V (vs RHE) at 10 mA cm−2 for the OER. Importantly, the flexible Zn-air battery using the catalyst exhibits a peak power density of 117 mW cm−2, a higher round-trip efficiency of 68% cycling at 2 mA/cm−2, and an excellent cycling stability with 3% decrease after 126 cycles test. This work provides a general strategy to design bifunctional catalysts by integrating atomically dispersed and nanoscaled transitional metal species together with N-doped micro-/mesoporous 3D carbon. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of atomically dispersed Sb-N-C catalysts are prepared via a facile adsorption-pyrolysis strategy. • Atomically dispersed Sb are stabilized by N atoms in terms of Sb-N 5 configuration. • Self-evaporation of Sb during synthesis could create abundant micro/meso-pores. • Sb-N 5 sites enable Sb-N-C catalysts outstanding oxygen reduction reaction activity. • Abundant micro/ meso -pores enable Sb-N-C catalysts enhanced mass transport. Main-group metal based single-atom catalysts are attracting increasing research attention in electrochemical catalysis owing to their partially occupied valence p-orbitals. Herein, we report a series of atomically dispersed Sb-N-C catalysts (including Sb-N-C NP , Sb-N-C NL and Sb-N-C NT) synthesized by a facile adsorption-pyrolysis strategy for oxygen reduction reaction (ORR). Apart from generating atomically dispersed Sb-N 5 sites as active centers, self-evaporation of Sb during pyrolysis process has created abundant micro/meso-pores in Sb-N-C catalysts. Benefitting from these advantageous features, Sb-N-C presents outstanding ORR activity (Sb-N 5 sites) and efficient mass transport (micro/meso-pores). By rotating disk electrode (RDE) test in alkaline media, Sb-N-C exhibits a most positive half-wave potential of 0.90 V vs. RHE and a highest kinetic current density up to 43.8 mA cm−2 at 0.85 V vs. RHE. As gas diffusion electrode (GDE), Sb-N-C NP0.2 demonstrates fast O 2 diffusion and transport that enables smaller mass transport overpotential at high current densities up to 800 mA cm−2. Finally, Zn-air battery that uses the Sb-N-C NP catalyst as air electrode achieves a maximum power density of 180 mW cm−2 and more than 1000 hs of continuous operation. This work further demonstrates the excellent performance of main-group Sb single-atom catalyst toward ORR and applications in practical energy conversion devices. [ABSTRACT FROM AUTHOR]