Synthesis of nitrogen-rich porous carbon nanotubes coated Co nanomaterials as efficient ORR electrocatalysts via MOFs as precursor

Abstract

Transition metal-based nitrogen-doped carbon materials have been proved to be a promising low-cost electrocatalyst for oxygen reduction reaction (ORR), which is a critical step in systems such as fuel batteries and zinc-air batteries. In this paper, transition metal (cobalt) N-doped carbon nanomaterials derived from metal-organic framework (MOFs) were synthesized by calcination of ZIF-67 precursors at high temperature (Co@NCNTs). Nitrogen atoms were introduced into the carbon matrix by capturing volatile CNx from dicyandiamide, and porous carbon nanotube structures with N-doped and uniformly dispersed active sites were obtained. The effects of different carbonization temperatures and molar ratio of Co/2-MI on the catalytic activity of materials for ORR reaction were studied. It was found that the Co@NCNTs prepared at 700 ℃ with the ratio of cobalt metal to dimethylimidazole of 1: 8 shows excellent ORR activity in both acidic and alkaline electrolytes. In alkaline conditions, the half-wave potential E 1/2 = 0.81 V, initial potential E onset = 0.89 V, and limiting current density even reaching 7.4 mA cm −2 . And in acidic electrolytes, E 1/2 = 0.66 V, while the limiting current density is 6.4 mA cm −2 , which is still better than that of Pt/C. Its excellent ORR performance is due to the synergistic effect of the porous carbon nanotube structure, N-doped carbon and Co-Nx active sites. Meanwhile, the optimum catalyst also shows better stability and methanol resistance than Pt/C in both acidic and alkaline electrolytes. • N-doped porous carbon nanotubes coated Co material was used to enhance ORR activity in alkaline and acidic conditions. • Nanotube structure provides sufficient effective contact area and active sites. • Porous structure is conducive to mass diffusion and reduces electron transmission resistance. • N-doped carbon tube, Co-Nx and pyridine nitrogen jointly promote ORR activity.