Single‐Atomic Co‐N‐C Sites Anchored on Helical Carbonaceous Nanotubes for the Oxygen Reduction Reaction

Metal‐coordinated N‐doped carbon (M‐N‐C) materials with highly curved structures have become a promising class of electrocatalysts for the oxygen reduction reaction (ORR). However, the stability of these electrocatalysts remains a problem due to the traditional post‐metal loading strategy. Herein, single‐atomic Co‐N‐C active sites anchored on helical carbonaceous nanotubes (HCNTs) are prepared (Co‐N‐C@HCNT) by pyrolyzing Co porphyrins and helical polypyrroles (PPys) mixtures at high‐temperature by one‐step method. Aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption fine structure (XAFS) measurements confirm single‐atomic active sites and Co‐N 4 coordination structures of Co‐N‐C@HCNT. The optimized Co‐N‐C@HCNT exhibits excellent catalytic ORR activity with a half‐wave potential ( E 1/2 ) of 0.86 V versus reversible hydrogen electrode (vs RHE) compared to Co‐N‐C@CNT without helical structures ( E 1/2 = 0.81 V vs RHE) measured in 0.1 m KOH. Co‐N‐C@HCNT also displays excellent stability with a slight current decrease (4%) after running for 10 h featuring Co‐N 4 active sites tightly anchored on HCNTs due to electrostatic interactions between metal porphyrins and PPys. Theoretical calculations indicate that the curved structure can increase the charge and decrease d‐band center at Co active site, which enhances electrocatalytic activity. This work provides a simple but effective strategy to construct helical M‐N‐C materials.