The structure design and atomic modulation of catalysts are two sides of the same coin, both of which are deemed critical factors to regulate the intrinsic electrocatalytic activity. Herein, cobalt single‐atom anchored on nitrogen‐doped graphene‐sheet@tube (CoSAs‐NGST) is derived from a novel Co, Zn‐coordinated zeolitic imidazolate framework (CoZn‐ZIF) in the presence of dicyandiamide. CoSAs‐NGST exhibited a hybrid structure with a bamboo‐like graphene tube and sheet. The atomic configuration of intrinsic defects is characterized by electron energy loss spectroscopy. The morphology differentiation from cake‐shape structure to low‐dimension hybrid not only enhances the dispersity of single atoms but also induces defect state evolution, which results in the formation of a CoN4‐rich graphene tube. Density functional theory (DFT) modeling revealed that the coupling effect on oxygen reduction reaction and oxygen evolution reaction (ORR/OER) pathways of Co‐N4‐tube and Co‐N4‐sheet is responsible for the enhanced activity of CoSAs‐NGST. In addition to the superb ORR/OER bifunctional catalytic performance, CoSAs‐NGST also demonstrates a notably small charge–discharge voltage drop of 0.93 V when applied in the rechargeable zinc–air battery outperforming Pt/C + RuO2 catalyst. The present study provides an insight into the relationship between the structure design and atomic modulation of the carbon based catalysts.

Cobalt-based, nitrogen-doped porous carbon materials with in situ grown carbon nanotubes (CNTs) were synthesized by the facile carbonization of porous 3D Bio-MOF-11 [Co2(ad)2(CH3COO)2]·2DMF·0.5H2O (ad = adenine). Co-N/PC@CNT-Ts inherit the octahedral shape from the precursor, and have a porous structure with in situ grown CNTs catalyzed by Co particles. Co-N/PC@CNT-T materials have excellent activities as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in 0.1 M KOH electrolyte. Among the Co-N/PC@CNT-Ts, Co-N/PC@CNT-700 has the highest electrocatalytic activity. For ORR, Co-N/PC@CNT-700 has a higher onset potential of 0.92 V vs. reversible hydrogen electrode (RHE), high stability and methanol tolerance, which are even better than that of Pt/C. For OER, it has a low potential of 1.63 V at a current density of 10 mA cm-2. In addition, Co-N/PC@CNT-700 affords a low reversible overvoltage (bifunctional performance parameter) of 0.862 V between ORR and OER compared to the current advancing bifunctional catalysts. The superb bifunctional activity can be attributed to uniform CoNx active sites embedded in graphitized carbon, unique in situ grown CNT structure and ordered mesoporous structure. The synergistic effect enlarged the contact surface, exposed more active centers and provided many pathways, thereby boosting the electrocatalytic performance. In conclusion, this study provides a novel avenue for the application of stable transition metal-based, nitrogen-doped carbon materials as extremely efficient electrocatalysts for ORR and OER.

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