Co–VN encapsulated in bamboo-like N-doped carbon nanotubes for ultrahigh-stability of oxygen reduction reaction

Abstract

The electrocatalytic activity of carbon-based non-precious metal composites towards oxygen reduction reaction (ORR) is far from that of the recognized Pt/C catalyst. Thus, it is necessary to exploit novel catalysts based on multicomponent carbon-based composites with both high activity and high stability. Herein, a bottom-up strategy was used for constructing bamboo-like N-doped graphitic CNTs with a few encapsulated Co and VN nanoparticles (namely, NGT-CoV) by adopting melamine as both a nitrogen source and a carbon source. During the synthesis, melamine initially coordinated with cobalt and vanadium ions and then decomposed into carbon nitride nanosheet structures. Simultaneously, cobalt ions/clusters were converted into metal nanocatalysts by the reduced gases that were generated, which further rearranged the carbon nitride nanostructures to form N-doped CNTs. The presence of vanadium species strengthened the electronic structure and increased the contents of Co and N species by enhancing the interactions among Co and N species. The optimized NGT-Co₃₅V₆₅-45-900 exhibited an E_onset of 0.92 V (vs. RHE), an E_1/2 of 0.81 V (vs. RHE), and a Tafel slope of 66.1 mV dec⁻¹ in the ORR. It also displayed much higher durability (a negative shift in E_1/2 of only 11 mV after 10 000 cycles) and methanol tolerance than a commercial Pt/C catalyst. The excellent performance should be attributed to the high exposure level of active sites that originated from Co–N, VN and N-doped bamboo-like graphitic CNTs. Moreover, the skeleton composed of hollow graphitic ultra-long CNTs could not only provide smooth mass transport pathways but also facilitate fast electron transfer.