Bamboo-like N,S-doped carbon nanotubes with encapsulated Co nanoparticles as high-performance electrocatalyst for liquid and flexible all-solid-state rechargeable Zn-air batteries

• g-C 3 N 4 was converted into Co NPs enclosed bamboo-like N, S-doped CNTs. • Co@bCNTs has excellent bifunctional activity with an ultralow potential gap of 0.72 V. • Deep acid treatment was executed to reveal the roles of functional components. • Peak power densities of liquid and flexible batteries up to 190.3 and 106.2 mW cm -2 . Developing nonprecious-metal carbon-based bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is greatly significant for practical applications of rechargeable Zn-air batteries. Herein, rod-like S-doped g-C 3 N 4 has been used as the nitrogen-rich precursor to synthesize an excellent oxygen electrocatalyst Co@bCNTs by a facile two-step route including cobalt-infiltration and subsequent pyrolysis. In Co@bCNTs, Co nanoparticles are encapsulated within N, S-doped bamboo-like carbon nanotubes (bCNTs), which further are tangled with the doped graphene and hybridized with a small amount of amorphous CoS x . Benefiting from its effective N dopant, highly graphitized carbon and the synergistic effects of its components with different functionalities, the as-prepared catalyst has superior bifunctional ORR/OER electrocatalytic activities with a small potential difference of 0.72 V and outstanding durability. Its assembled liquid and all-solid-state flexible batteries show excellent performance with peak power densities up to 190.3 and 106.2 mW cm -2 , respectively. This work provides a new dimension to design and prepare high-performance bifunctional oxygen eletrocatalysts using nitrogen-rich polymers for developing rechargeable zinc-air batteries.