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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]

Exploration high-efficient bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for several renewable energy applications. In this paper, a catalyst composed of Co 9 S 8 and porous carbon (Co 9 S 8 –C) is prepared first via the calcination of Co–S–C based precursor coating on carbon-fibre-paper (CFP) substrate under argon atmosphere. Then, the Co 9 S 8 –C is modified via the decomposition gas of dicyandiamide, thus Co 9 S 8 –N-doped carbon (Co 9 S 8 -NC) catalyst is synthesized. As revealed, the morphology and defect features are effectively modulated by the modification, suggesting the reduced particle sizes of Co 9 S 8 component and obviously improved N proportion and various defects. As a result, Co 9 S 8 -NC represents excellent activities electrocatalytic performances toward OER and ORR, which surpass those of its three counterparts including Co 9 S 8 –C, Co 9 S 8 , and NC. A half-wave potential of 0.86 ​V versus RHE for ORR and a low overpotential of 280 ​mV ​at 10 ​mA ​cm-2 current density for OER are achieved, with the Δ E value of 0.64 ​V. Additionally, the catalyst also demonstrates desirable application prospect for Zn-air battery. The post-treatment method reported here might be utilized widespread to promote the synergistic effects between the Co-contained particles and N-doped carbons in composite catalysts. The DCA post-treatment can produce high amounts of N-doped pore edges, and can simultaneously facilitate the intimate electronic contact between moderately eroded Co 9 S 8 and N-doped carbon matrix thus forming abundant high active coupling Co-N x -C centers. The catalyst demonstrates excellent bifunctional performance for catalyzing OER and ORR. Image 1 • Co 9 S 8 -porous N-doped carbon (NC) catalyst was in-situ synthesized on CFP substrate. • Intimate electronic contact between Co 9 S 8 and NC is achieved through a dicyandiamide post-treatment. • N content is much improved with rich new-formed pyridinic N and interfacial Co–N. • The catalyst exhibits remarkable OER/ORR bifunction and good prospect in flexible Zn-air battery. [ABSTRACT FROM AUTHOR]