Electrocatalytic performance of cobalt/nickel nanoparticles encapsulated by N-doped carbon nanotubes toward the oxygen reduction reaction.

[Display omitted] • The Co@NCNT and Ni@NCNT catalysts were synthesized using the calcination method. • The Co@NCNT and Ni@NCNT catalysts exhibited good electrocatalytic activity for the ORR. • Their electrocatalytic activity of both catalysts was due to the rich N-doped active C sites. • The good catalytic activity was also due to synergistic reaction between Co (Ni) and NCNTs. Electrocatalysts based on nanosized cobalt or nickel particles encapsulated by nitrogen-doped carbon nanotubes (M@NCNTs (M = Co or Ni)) were synthesized using the calcination method. They were served as the catalyst toward an oxygen reduction reaction (ORR). The results implied that the M@NCNT electrocatalysts had ORR catalytic activity in an alkaline electrolyte. The half-wave potential (E 1/2) on the Co@NCNT catalyst reached 0.881 V, which was higher than for commercial Pt/C (0.856 V). The M@NCNT electrocatalysts exhibited good stability in the ORR. After 3000 cycles, the E 1/2 for the Co@NCNTs was almost completely unchanged, whereas for the Ni@NCNTs, shifted negatively to 19 mV, was less than for commercial Pt/C (34 mV). These promising electrochemical properties were due to abundant active carbon sites and the synergistic reaction between Co/Ni and NCNTs. Density functional theory calculations indicated that the OOH had strong absorption on the C atoms (adjacent to pyridinic N) in the Co@NCNT and Ni@NCNT catalysts. [ABSTRACT FROM AUTHOR]