Pyrolysis derived helically nitrogen-doped carbon nanotubes with uniform cobalt for high performance oxygen reduction

Here, CoNx-based helically coiled nitrogen-doped carbon nanotubes (CoNx/HCN-CNTs) are reported based on two-step pyrolysis strategy, in which the helically coiled nitrogen-doped carbon nanotubes (HCN-CNTs) show uniform diameter of approximately 50 nm and CoNx-based nanoparticles are not only distributed either at the tip or inside of HCN-CNTs, but excitingly, they are uniformly dispersed on the surface of HCN-CNTs. When applied for ORR, CoNx/HCN-CNTs show excellent ORR activity, with good onset potential and higher current density, comparable to that of the commercial 20% Pt/C. The half-wave potential is 0.92 V (vs reversible hydrogen electrode, RHE) in 0.1 M KOH, 20 mV higher than that of 20% Pt/C. Most importantly, CoNx/HCN-CNTs display better methanol tolerance and higher stability. After 28,800 s, the current density only decreased by 1.4%. The high ORR performance maybe related with synergistic enhancement effect, in which CoNx-based nanoparticles can induce a host-guest electronic interaction and according improve the local work function of the HCN-CNTs, making carbon layer have higher ORR activity; meanwhile, the ORR activity of embedded CoNx-based nanoparticles can be greatly improved, mainly attributing to the protection of HCN-CNTs and weakness of the Ostwald-ripening-like effect in ORR progress. The features make it one of the best non-noble-metal catalysts for ORR.