Oxygen reduction reaction (ORR) electrocatalysts that are stable, highly efficient, and cost-effective play a significant role in the development of energy storage and conversion technologies. Transition metal carbonitrides have been investigated as an alternative to precious metal-based catalysts. Developing noble metal-free two-dimensional (2D) carbon-based materials for efficient ORR electrocatalysts can reduce the consumption of noble metals; more importantly, these materials have the advantages of being highly abundant, having a large active surface area, being easy to functionalize, and being chemical stable. Herein, we exquisitely designed the in situ growth of Co nanoparticles coated with tannin-carbon (CTA) embedded on hierarchical porous two-dimensional ultrathin g-C3N4 nanosheets (Co–CTA@g-C3N4), through the thermal transition of cobalt–polyphenol-networks modified graphitic carbon nitride (Co–TA@g-C3N4) by virtue of the excellent interfacial adhesion ability of an ortho-phenolic hydroxyl group in tannic acid (TA) to metal ions. By carefully tuning the Co/TA molar ratio in the Co–TA@g-C3N4 precursor and the carbonization temperature, an active stable ORR catalyst of the hybrid 2D Co–CTA@g-C3N4 heterostructured nanosheet is obtained. The results reveal that Co2.5–CTA1@g-C3N4-700 °C exhibits outstanding ORR activities, including outperforming the commercial 20 wt% Pt/C with a more positive half-wave potential of −0.864 V versus Ag/AgCl and high selectivity to the four-electron pathway (n ≈ 3.7), as well as outstanding stability and methanol tolerance.
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