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Electrospun interconnected Fe-N/C nanofiber networks as efficient electrocatalysts for oxygen reduction reaction in acidic media.

Wu N, Wang Y, Lei Y, Wang B, Han C, Gou Y, Shi Q, Fang D - Sci Rep (2015)

Bottom Line: One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts.Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions.The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers.

View Article: PubMed Central - PubMed

Affiliation: Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073, P.R. China.

ABSTRACT
One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts. However, contact resistance among the neighbouring nanofibers hinders the electron transport. Here, we report the preparation of interconnected Fe-N/C nanofiber networks (Fe-N/C NNs) with low electrical resistance via electrospinning followed by maturing and pyrolysis. The Fe-N/C NNs show excellent ORR activity with onset and half-wave potential of 55 and 108 mV less than those of Pt/C catalyst in 0.5 M H2SO4. Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions. Additionally, it also displays much better durability and methanol tolerance than Pt/C catalyst. The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers. Thus, our findings provide a novel insight into the design of functional electrospun nanofibers for the application in energy storage and conversion fields.

No MeSH data available.


Related in: MedlinePlus

XPS, TEM and elemental analysis of Fe-N/C NNs.High-resolution XPS spectra of (a) N 1s and (b) Fe 2p. (c) Scanning TEM image and corresponding elemental mapping images of (d) Fe, (e) N, (f) O and (g) C.
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f4: XPS, TEM and elemental analysis of Fe-N/C NNs.High-resolution XPS spectra of (a) N 1s and (b) Fe 2p. (c) Scanning TEM image and corresponding elemental mapping images of (d) Fe, (e) N, (f) O and (g) C.

Mentions: X-ray photoelectron spectroscopy (XPS) analysis was performed to investigate the content and chemical state of nitrogen and iron in the Fe-N/C catalysts. As detected from the survey scans (Fig. S7a and b†), both Fe-N/C NNs and Fe-N/C NMs contain four kinds of elements, carbon, nitrogen, oxygen and iron. In fact, quantum calculations and experimental studies conclude that nitrogen heteroatom may improve the oxygen adsorption and hydrophilicity of the catalyst surface, which can attract electrons readily to enhance the ORR performance3738. Moreover, previous reports also revealed that both pyridinic N coordinated with iron and graphitic N contributed mostly to the increase of the ORR performance3940. The high-resolution N 1s spectrum for Fe-N/C NNs in Fig. 4a is divided into four species at 398.3, 399.7, 400.8 and 402.0 eV, which can be assigned to pyridinic N (31.4%), pyrrolic N (18.0%), graphitic N (36.5%) and pyridinic oxide N (14.1%), respectively. Both samples show high percentage of total nitrogen content and two kinds of active nitrogen groups (Fig. S7c† and Table. S1†). More effective nitrogen species will donate more active sites to boost the catalytic property. Additionally, Xu6 and Sun8et al. have reported that Fe (III) and Fe (II) species as active phase play a major role in the superior ORR activity of Fe-N/C catalysts. It can be clearly noted in Fe 2p spectra (Fig. 4b and Fig. S7d†) that Fe (III) and Fe (II) species co-exist in both as-prepared catalysts. Then, scanning TEM and elemental mapping were acquired to further analyze the distribution of species in Fe-N/C NNs (Fig. 4c–g). Interestingly, the O element signal becomes stronger (Fig. 4f) in the region of intensive distribution of Fe element (Fig. 4d), which is accordant with the presence of Fe3O4 nanoparticles. The homogeneously dispersive N species (Fig. 4e) can bond with the neighbouring C or Fe atoms to provide numerous available active centres for ORR. As can be seen from the Raman spectra (Fig. S8†), the Fe-N/C catalysts display a similar ID/IG value (0.98 for Fe-N/C NNs vs. 0.97 for Fe-N/C NMs), indicating analogous level of defect sites in the obtained carbon4142.


Electrospun interconnected Fe-N/C nanofiber networks as efficient electrocatalysts for oxygen reduction reaction in acidic media.

Wu N, Wang Y, Lei Y, Wang B, Han C, Gou Y, Shi Q, Fang D - Sci Rep (2015)

XPS, TEM and elemental analysis of Fe-N/C NNs.High-resolution XPS spectra of (a) N 1s and (b) Fe 2p. (c) Scanning TEM image and corresponding elemental mapping images of (d) Fe, (e) N, (f) O and (g) C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663764&req=5

f4: XPS, TEM and elemental analysis of Fe-N/C NNs.High-resolution XPS spectra of (a) N 1s and (b) Fe 2p. (c) Scanning TEM image and corresponding elemental mapping images of (d) Fe, (e) N, (f) O and (g) C.
Mentions: X-ray photoelectron spectroscopy (XPS) analysis was performed to investigate the content and chemical state of nitrogen and iron in the Fe-N/C catalysts. As detected from the survey scans (Fig. S7a and b†), both Fe-N/C NNs and Fe-N/C NMs contain four kinds of elements, carbon, nitrogen, oxygen and iron. In fact, quantum calculations and experimental studies conclude that nitrogen heteroatom may improve the oxygen adsorption and hydrophilicity of the catalyst surface, which can attract electrons readily to enhance the ORR performance3738. Moreover, previous reports also revealed that both pyridinic N coordinated with iron and graphitic N contributed mostly to the increase of the ORR performance3940. The high-resolution N 1s spectrum for Fe-N/C NNs in Fig. 4a is divided into four species at 398.3, 399.7, 400.8 and 402.0 eV, which can be assigned to pyridinic N (31.4%), pyrrolic N (18.0%), graphitic N (36.5%) and pyridinic oxide N (14.1%), respectively. Both samples show high percentage of total nitrogen content and two kinds of active nitrogen groups (Fig. S7c† and Table. S1†). More effective nitrogen species will donate more active sites to boost the catalytic property. Additionally, Xu6 and Sun8et al. have reported that Fe (III) and Fe (II) species as active phase play a major role in the superior ORR activity of Fe-N/C catalysts. It can be clearly noted in Fe 2p spectra (Fig. 4b and Fig. S7d†) that Fe (III) and Fe (II) species co-exist in both as-prepared catalysts. Then, scanning TEM and elemental mapping were acquired to further analyze the distribution of species in Fe-N/C NNs (Fig. 4c–g). Interestingly, the O element signal becomes stronger (Fig. 4f) in the region of intensive distribution of Fe element (Fig. 4d), which is accordant with the presence of Fe3O4 nanoparticles. The homogeneously dispersive N species (Fig. 4e) can bond with the neighbouring C or Fe atoms to provide numerous available active centres for ORR. As can be seen from the Raman spectra (Fig. S8†), the Fe-N/C catalysts display a similar ID/IG value (0.98 for Fe-N/C NNs vs. 0.97 for Fe-N/C NMs), indicating analogous level of defect sites in the obtained carbon4142.

Bottom Line: One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts.Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions.The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers.

View Article: PubMed Central - PubMed

Affiliation: Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073, P.R. China.

ABSTRACT
One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts. However, contact resistance among the neighbouring nanofibers hinders the electron transport. Here, we report the preparation of interconnected Fe-N/C nanofiber networks (Fe-N/C NNs) with low electrical resistance via electrospinning followed by maturing and pyrolysis. The Fe-N/C NNs show excellent ORR activity with onset and half-wave potential of 55 and 108 mV less than those of Pt/C catalyst in 0.5 M H2SO4. Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions. Additionally, it also displays much better durability and methanol tolerance than Pt/C catalyst. The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers. Thus, our findings provide a novel insight into the design of functional electrospun nanofibers for the application in energy storage and conversion fields.

No MeSH data available.


Related in: MedlinePlus