Nitrogen-Promoted Self-Assembly of N-Doped Carbon Nanotubes and Their Intrinsic Catalysis for Oxygen Reduction in Fuel Cells

Abstract

Nitrogen atoms were found to exhibit a strong ability to promote the self-assembly of nitrogen-doped carbon nanotubes (NCNTs) from gaseous carbons, without an assistance of metal atoms. On the basis of this discovery, pure metal-free CNTs with a nitrogen-doping level as high as 20 atom % can be directly synthesized using melamine as a C/N precursor. This offers a novel pathway for carbon nanotube synthesis. Furthermore, the metal-free and intact characteristics of the NCNT samples facilitate a clear verification of the intrinsic catalytic ability of NCNTs. The results show that the NCNTs intrinsically display excellent catalytic activity for oxygen reduction in fuel cells, comparable to traditional platinum-based catalysts. More notably, they exhibit outstanding stability, selectivity, and resistance to CO poisoning, much superior to the platinum-based catalysts.

Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

“…Generally, they have been synthesized with the help of metal catalysts (e.g Co or Fe), which had raised the concern that the ORR activity was attributable to the metal-nitrogen complexes as in the well-known case of metal-porphyrins [9]. However, synthesis methods that do not use any metal precursors or catalysts have been recently developed and ORR activity of the catalyst has been preserved [15,[18][19][20][21][22].…”

“…graphene [10,[23][24][25][26][27][28][29][30][31][32][33], carbon nanotubes [11,20,21,[34][35][36][37][38][39][40][41][42][43], carbon nanofibers [12,[44][45][46][47], mesoporous carbon [15,22], graphitic carbon [48,49], carbon spheres [19,[50][51][52][53], carbon nanocages 4 [54], flower-like carbon [55], carbon aerogel [56,57], vesicular carbon [58], nanodiamonds [59]) relatively few have been tested in actual fuel cell conditions [58,[60][61][62]…”

Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

“…In in-situ doping methods, usually N atoms are incorporated inside the inner CNT walls, so they are not accessible for the oxygen molecules. For example, in the case of bamboo-like N-CNT structures, N atoms were concentrated at the inner curved joints of the compartments and trapped between the graphitic walls [113]. In some cases, nitrogen gas is trapped in the inner compartments which hinders the conductivity of N-CNT and not rendering any catalytic activity [114].…”

“…We further characterized ORR electrocatalytic activity by RRDE measurements in comparison with a commercial Pt-C. NFW-F-900 showed remarkable ORR electrocatalytic activity even though the nitrogen content (0.57 at.%) was much lower compared to previousely reported values in literature (Table 3 in pub.IV) that usually refer to nitrogen levels higher than 3 at. % [97,110,113,131]. recently highlighted by Tian et al [129].…”

Nitrogen-doped carbon xerogel as high active oxygen reduction catalyst for direct methanol alkaline fuel cell

“…Nitrogen atom is often chosen as the doped atom for its close atom number and unique valence bond structure compared with carbon atom [23]. The introduction of nitrogen atoms into the carbon material breaks the electroneutrality to create positive charge density on the adjacent C atoms [22,24], changes the chemisorptions mode of oxygen, and consequently enhances the ORR activity.…”