Nitrogen-Deficient ORR Active Sites Formation by Iron-Assisted Water Vapor Activation of Electrospun Carbon Nanofibers

Abstract

Fe-and N-modified carbon nanofibers (Fe−CNF) were synthesized via electrospinning and pyrolysis as electrocatalysts for oxygen reduction reaction (ORR). In order to increase the exposed surface area with the active sites buried inside Fe−CNF, we attempted water vapor activation for Fe−CNF and observed a substantial improvement of ORR activity up to the comparable level with Pt/C. Unlike what was expected, however, water vapor activation did not significantly increase the specific surface area of Fe− CNF; instead, it induced a depletion of surface N content, which makes it difficult to explain the improved ORR activity with the increase of surface area with N-based active sites. In water vapor activation, the chemical phase of embedded particles is changed from Fe 3 C to Fe 3 O 4 and nitrogen-free Feand C-based ORR active sites were exposed, which seemed to be related with hierarchical macro/mesopore structure and graphitic edge defects. This study demonstrates a facile activation method for better ORR activity of Fe-modified CNF and suggests a potential relationship of surface carbon structure with the catalytic activity toward ORR rather than the type and concentration of N in Fe−CNF, which should be investigated further.

Tree‐Bark‐Shaped N‐Doped Porous Carbon Anode for Hydrazine Fuel Cells

“…The formation of a mesoporous structure could be explained by the elimination of PMMA from the CNF during the heat treatment leaving hollow vestiges . For Vap‐CNF (Figure c), a smooth surface morphology similar to that of CNF is shown, but it has a small pore structure, which is in agreement with our previous works concluding that the formation of micropores and mesopores is due to the water vapor treatment . Vap‐PM‐CNF, which was treated by both PMMA and water vapor, possesses a fibrous morphology similar to that of PM‐CNF (tree‐bark‐shaped fiber), but the detection of micropores and mesopores is difficult in the TEM image (Figure d).…”

“…In the N 2 ads/des isotherm plot and BJH plot of the pore size distribution (Figure b,c), a rising backward peak indicates that PM‐CNF predominantly has meso /macropores (>10 nm) formed by the elimination of PMMA from the CNF. As our previous work reported, the water vapor treatment substantially increases the BET surface area of Vap‐CNF, measured to be 411.85 m 2 g −1 (Figure a). The N 2 ads/des isotherm plot for Vap‐CNF shows a rising forward peak indicating that the increase in the BET surface area is mostly attributed to a microporous structure (<2 nm) (Figure b).…”

Tree‐Bark‐Shaped N‐Doped Porous Carbon Anode for Hydrazine Fuel Cells

“…On the other hand, PM-CNF shows increased BET and BJH surface areas of 46.85 and 36.81 m 2 g À1 (Figure 2a). In the N 2 ads/des isotherm plot and BJH plot of the pore size distribution (Figure 2b,c), ar ising backward peak indicates that PM-CNF predominantly has meso/macropores (> 10 nm) formed by the elimination of PMMA from the CNF.A so ur previous work reported, [15,18] the water vapor treatment substantially increases the BET surface area of Va p-CNF,m easured to be 411.85 m 2 g À1 (Figure 2a). TheN 2 ads/des isotherm plot for Va p-CNF shows arising forward peak indicating that the increase in the BET surface area is mostly attributed to am icroporous structure (< 2nm) (Figure 2b).…”

“…[6,10,11] We carried out X-ray photoelectron spectroscopy (XPS) measurements of the NDCs and characterized the Nd istributions of the NDCs with deconvolution methods (Figures 3a nd Figure S1 in the Supporting Information). [15,18,19] In particular, graphitic-N and pyridinic-N are enriched in the NDCs,compared with other nitrogen species. 398 eV), pyrrolic-N (ca.…”

In situ self‐template synthesis of cobalt/nitrogen‐doped nanocarbons with controllable shapes for oxygen reduction reaction and supercapacitors

“…Nonprecious metal/nitrogen-doped carbon materials (M/N-C) have been extensively investigated and deemed ideal for the ORR because the reaction performance can be enhanced via the synergism between nitrogen (N) and the metals. 13 It has been reported that metal (M) atoms can facilitate the generation of N-C active sites, while nitrogen plays a nucleation and anchoring role for M sites, which enhances the catalytic activity. [14][15][16] Aside from controlling the chemical composition, a strategy to design and optimize carbon materials with a well-designed porous structure is also required to induce sufficient catalytic activity.…”